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| author | Ondrej Filip <feela@network.cz> | 2013-08-15 20:26:50 +0200 |
|---|---|---|
| committer | Ondrej Filip <feela@network.cz> | 2013-08-15 20:26:50 +0200 |
| commit | b0a8c7fc8547eef21ede33887580b5e867ee742c (patch) | |
| tree | e52c49397f845d834f074d1de7e3c2fe58742e96 /doc/bird-6.html | |
| parent | e628cad0ca9eb7d9bf4141e57201169c46faa661 (diff) | |
Wrong change commited - 'route limit' marked as obsolete.
Diffstat (limited to 'doc/bird-6.html')
| -rw-r--r-- | doc/bird-6.html | 1731 |
1 files changed, 0 insertions, 1731 deletions
diff --git a/doc/bird-6.html b/doc/bird-6.html deleted file mode 100644 index d21209ee..00000000 --- a/doc/bird-6.html +++ /dev/null @@ -1,1731 +0,0 @@ -<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> -<HTML> -<HEAD> - <META NAME="GENERATOR" CONTENT="LinuxDoc-Tools 1.0.9"> - <TITLE>BIRD User's Guide: Protocols</TITLE> - <LINK HREF="bird-7.html" REL=next> - <LINK HREF="bird-5.html" REL=previous> - <LINK HREF="bird.html#toc6" REL=contents> -</HEAD> -<BODY> -<A HREF="bird-7.html">Next</A> -<A HREF="bird-5.html">Previous</A> -<A HREF="bird.html#toc6">Contents</A> -<HR> -<H2><A NAME="s6">6.</A> <A HREF="bird.html#toc6">Protocols</A></H2> - -<H2><A NAME="ss6.1">6.1</A> <A HREF="bird.html#toc6.1">BGP</A> -</H2> - -<P>The Border Gateway Protocol is the routing protocol used for backbone -level routing in the today's Internet. Contrary to the other protocols, its convergence -doesn't rely on all routers following the same rules for route selection, -making it possible to implement any routing policy at any router in the -network, the only restriction being that if a router advertises a route, -it must accept and forward packets according to it. -<P> -<P>BGP works in terms of autonomous systems (often abbreviated as -AS). Each AS is a part of the network with common management and -common routing policy. It is identified by a unique 16-bit number -(ASN). Routers within each AS usually exchange AS-internal routing -information with each other using an interior gateway protocol (IGP, -such as OSPF or RIP). Boundary routers at the border of -the AS communicate global (inter-AS) network reachability information with -their neighbors in the neighboring AS'es via exterior BGP (eBGP) and -redistribute received information to other routers in the AS via -interior BGP (iBGP). -<P> -<P>Each BGP router sends to its neighbors updates of the parts of its -routing table it wishes to export along with complete path information -(a list of AS'es the packet will travel through if it uses the particular -route) in order to avoid routing loops. -<P> -<P>BIRD supports all requirements of the BGP4 standard as defined in -RFC 4271 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc4271.txt">ftp://ftp.rfc-editor.org/in-notes/rfc4271.txt</A> -It also supports the community attributes -(RFC 1997 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc1997.txt">ftp://ftp.rfc-editor.org/in-notes/rfc1997.txt</A>), -capability negotiation -(RFC 3392 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc3392.txt">ftp://ftp.rfc-editor.org/in-notes/rfc3392.txt</A>), -MD5 password authentication -(RFC 2385 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc2385.txt">ftp://ftp.rfc-editor.org/in-notes/rfc2385.txt</A>), -extended communities -(RFC 4360 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc4360.txt">ftp://ftp.rfc-editor.org/in-notes/rfc4360.txt</A>), -route reflectors -(RFC 4456 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc4456.txt">ftp://ftp.rfc-editor.org/in-notes/rfc4456.txt</A>), -multiprotocol extensions -(RFC 4760 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc4760.txt">ftp://ftp.rfc-editor.org/in-notes/rfc4760.txt</A>), -4B AS numbers -(RFC 4893 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc4893.txt">ftp://ftp.rfc-editor.org/in-notes/rfc4893.txt</A>), -and 4B AS numbers in extended communities -(RFC 5668 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc5668.txt">ftp://ftp.rfc-editor.org/in-notes/rfc5668.txt</A>). -<P> -<P>For IPv6, it uses the standard multiprotocol extensions defined in -RFC 2283 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc2283.txt">ftp://ftp.rfc-editor.org/in-notes/rfc2283.txt</A> -including changes described in the -latest draft -<A HREF="ftp://ftp.rfc-editor.org/internet-drafts/draft-ietf-idr-bgp4-multiprotocol-v2-05.txt">ftp://ftp.rfc-editor.org/internet-drafts/draft-ietf-idr-bgp4-multiprotocol-v2-05.txt</A> -and applied to IPv6 according to -RFC 2545 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc2545.txt">ftp://ftp.rfc-editor.org/in-notes/rfc2545.txt</A>. -<P> -<H3>Route selection rules</H3> - -<P>BGP doesn't have any simple metric, so the rules for selection of an optimal -route among multiple BGP routes with the same preference are a bit more complex -and they are implemented according to the following algorithm. It starts the first -rule, if there are more "best" routes, then it uses the second rule to choose -among them and so on. -<P> -<UL> -<LI>Prefer route with the highest Local Preference attribute.</LI> -<LI>Prefer route with the shortest AS path.</LI> -<LI>Prefer IGP origin over EGP and EGP origin over incomplete.</LI> -<LI>Prefer the lowest value of the Multiple Exit Discriminator.</LI> -<LI>Prefer routes received via eBGP over ones received via iBGP.</LI> -<LI>Prefer routes with lower internal distance to a boundary router.</LI> -<LI>Prefer the route with the lowest value of router ID of the -advertising router.</LI> -</UL> -<P> -<H3>IGP routing table</H3> - -<P>BGP is mainly concerned with global network reachability and with -routes to other autonomous systems. When such routes are redistributed -to routers in the AS via BGP, they contain IP addresses of a boundary -routers (in route attribute NEXT_HOP). BGP depends on existing IGP -routing table with AS-internal routes to determine immediate next hops -for routes and to know their internal distances to boundary routers -for the purpose of BGP route selection. In BIRD, there is usually -one routing table used for both IGP routes and BGP routes. -<P> -<H3>Configuration</H3> - -<P>Each instance of the BGP corresponds to one neighboring router. -This allows to set routing policy and all the other parameters differently -for each neighbor using the following configuration parameters: -<P> -<DL> -<DT><CODE>local [<I>ip</I>] as <I>number</I></CODE><DD><P>Define which AS we -are part of. (Note that contrary to other IP routers, BIRD is -able to act as a router located in multiple AS'es -simultaneously, but in such cases you need to tweak the BGP -paths manually in the filters to get consistent behavior.) -Optional <CODE>ip</CODE> argument specifies a source address, -equivalent to the <CODE>source address</CODE> option (see below). -This parameter is mandatory. -<P> -<DT><CODE>neighbor <I>ip</I> as <I>number</I></CODE><DD><P>Define neighboring router -this instance will be talking to and what AS it's located in. Unless -you use the <CODE>multihop</CODE> clause, it must be directly connected to one -of your router's interfaces. In case the neighbor is in the same AS -as we are, we automatically switch to iBGP. This parameter is mandatory. -<P> -<DT><CODE>multihop [<I>number</I>]</CODE><DD><P>Configure multihop BGP -session to a neighbor that isn't directly connected. -Accurately, this option should be used if the configured -neighbor IP address does not match with any local network -subnets. Such IP address have to be reachable through system -routing table. For multihop BGP it is recommended to -explicitly configure <CODE>source address</CODE> to have it -stable. Optional <CODE>number</CODE> argument can be used to specify -the number of hops (used for TTL). Note that the number of -networks (edges) in a path is counted, i.e. if two BGP -speakers are separated by one router, the number of hops is -2. Default: switched off. -<P> -<DT><CODE>source address <I>ip</I></CODE><DD><P>Define local address we -should use for next hop calculation and as a source address -for the BGP session. Default: the address of the local -end of the interface our neighbor is connected to. -<P> -<DT><CODE>next hop self</CODE><DD><P>Avoid calculation of the Next Hop -attribute and always advertise our own source address as a -next hop. This needs to be used only occasionally to -circumvent misconfigurations of other routers. Default: -disabled. -<P> -<DT><CODE>next hop keep</CODE><DD><P>Forward the received Next Hop -attribute even in situations where the local address should be -used instead, like when the route is sent to an interface with -a different subnet. Default: disabled. -<P> -<DT><CODE>missing lladdr self|drop|ignore</CODE><DD><P>Next Hop attribute -in BGP-IPv6 sometimes contains just the global IPv6 address, -but sometimes it has to contain both global and link-local -IPv6 addresses. This option specifies what to do if BIRD have -to send both addresses but does not know link-local address. -This situation might happen when routes from other protocols -are exported to BGP, or when improper updates are received -from BGP peers. <CODE>self</CODE> means that BIRD advertises its own -local address instead. <CODE>drop</CODE> means that BIRD skips that -prefixes and logs error. <CODE>ignore</CODE> means that BIRD ignores -the problem and sends just the global address (and therefore -forms improper BGP update). Default: <CODE>self</CODE>, unless BIRD -is configured as a route server (option <CODE>rs client</CODE>), in -that case default is <CODE>ignore</CODE>, because route servers usually -do not forward packets themselves. -<P> -<DT><CODE>gateway direct|recursive</CODE><DD><P>For received routes, their -<CODE>gw</CODE> (immediate next hop) attribute is computed from -received <CODE>bgp_next_hop</CODE> attribute. This option specifies -how it is computed. Direct mode means that the IP address from -<CODE>bgp_next_hop</CODE> is used if it is directly reachable, -otherwise the neighbor IP address is used. Recursive mode -means that the gateway is computed by an IGP routing table -lookup for the IP address from <CODE>bgp_next_hop</CODE>. Recursive -mode is the behavior specified by the BGP standard. Direct -mode is simpler, does not require any routes in a routing -table, and was used in older versions of BIRD, but does not -handle well nontrivial iBGP setups and multihop. Recursive -mode is incompatible with -<A HREF="bird-2.html#dsc-sorted">sorted tables</A>. Default: <CODE>direct</CODE> for singlehop eBGP, -<CODE>recursive</CODE> otherwise. -<P> -<DT><CODE>igp table <I>name</I></CODE><DD><P>Specifies a table that is used -as an IGP routing table. Default: the same as the table BGP is -connected to. -<P> -<DT><CODE>ttl security <I>switch</I></CODE><DD><P>Use GTSM (RFC 5082 - the -generalized TTL security mechanism). GTSM protects against -spoofed packets by ignoring received packets with a smaller -than expected TTL. To work properly, GTSM have to be enabled -on both sides of a BGP session. If both <CODE>ttl security</CODE> and -<CODE>multihop</CODE> options are enabled, <CODE>multihop</CODE> option should -specify proper hop value to compute expected TTL. Kernel -support required: Linux: 2.6.34+ (IPv4), 2.6.35+ (IPv6), BSD: -since long ago, IPv4 only. Note that full (ICMP protection, -for example) RFC 5082 support is provided by Linux -only. Default: disabled. -<P> -<DT><CODE>password <I>string</I></CODE><DD><P>Use this password for MD5 authentication -of BGP sessions. Default: no authentication. Password has to be set by -external utility (e.g. setkey(8)) on BSD systems. -<P> -<DT><CODE>passive <I>switch</I></CODE><DD><P>Standard BGP behavior is both -initiating outgoing connections and accepting incoming -connections. In passive mode, outgoing connections are not -initiated. Default: off. -<P> -<DT><CODE>rr client</CODE><DD><P>Be a route reflector and treat the neighbor as -a route reflection client. Default: disabled. -<P> -<DT><CODE>rr cluster id <I>IPv4 address</I></CODE><DD><P>Route reflectors use cluster id -to avoid route reflection loops. When there is one route reflector in a cluster -it usually uses its router id as a cluster id, but when there are more route -reflectors in a cluster, these need to be configured (using this option) to -use a common cluster id. Clients in a cluster need not know their cluster -id and this option is not allowed for them. Default: the same as router id. -<P> -<DT><CODE>rs client</CODE><DD><P>Be a route server and treat the neighbor -as a route server client. A route server is used as a -replacement for full mesh EBGP routing in Internet exchange -points in a similar way to route reflectors used in IBGP routing. -BIRD does not implement obsoleted RFC 1863, but uses ad-hoc implementation, -which behaves like plain EBGP but reduces modifications to advertised route -attributes to be transparent (for example does not prepend its AS number to -AS PATH attribute and keeps MED attribute). Default: disabled. -<P> -<DT><CODE>secondary <I>switch</I></CODE><DD><P>Usually, if an import filter -rejects a selected route, no other route is propagated for -that network. This option allows to try the next route in -order until one that is accepted is found or all routes for -that network are rejected. This can be used for route servers -that need to propagate different tables to each client but do -not want to have these tables explicitly (to conserve memory). -This option requires that the connected routing table is -<A HREF="bird-2.html#dsc-sorted">sorted</A>. Default: off. -<P> -<DT><CODE>enable route refresh <I>switch</I></CODE><DD><P>When BGP speaker -changes its import filter, it has to re-examine all routes -received from its neighbor against the new filter. As these -routes might not be available, there is a BGP protocol -extension Route Refresh (specified in RFC 2918) that allows -BGP speaker to request re-advertisement of all routes from its -neighbor. This option specifies whether BIRD advertises this -capability and accepts such requests. Even when disabled, BIRD -can send route refresh requests. Default: on. -<P> -<DT><CODE>interpret communities <I>switch</I></CODE><DD><P>RFC 1997 demands -that BGP speaker should process well-known communities like -no-export (65535, 65281) or no-advertise (65535, 65282). For -example, received route carrying a no-adverise community -should not be advertised to any of its neighbors. If this -option is enabled (which is by default), BIRD has such -behavior automatically (it is evaluated when a route is -exported to the BGP protocol just before the export filter). -Otherwise, this integrated processing of well-known -communities is disabled. In that case, similar behavior can be -implemented in the export filter. Default: on. -<P> -<DT><CODE>enable as4 <I>switch</I></CODE><DD><P>BGP protocol was designed to use 2B AS numbers -and was extended later to allow 4B AS number. BIRD supports 4B AS extension, -but by disabling this option it can be persuaded not to advertise it and -to maintain old-style sessions with its neighbors. This might be useful for -circumventing bugs in neighbor's implementation of 4B AS extension. -Even when disabled (off), BIRD behaves internally as AS4-aware BGP router. -Default: on. -<P> -<DT><CODE>capabilities <I>switch</I></CODE><DD><P>Use capability advertisement -to advertise optional capabilities. This is standard behavior -for newer BGP implementations, but there might be some older -BGP implementations that reject such connection attempts. -When disabled (off), features that request it (4B AS support) -are also disabled. Default: on, with automatic fallback to -off when received capability-related error. -<P> -<DT><CODE>advertise ipv4 <I>switch</I></CODE><DD><P>Advertise IPv4 multiprotocol capability. -This is not a correct behavior according to the strict interpretation -of RFC 4760, but it is widespread and required by some BGP -implementations (Cisco and Quagga). This option is relevant -to IPv4 mode with enabled capability advertisement only. Default: on. -<P> -<DT><CODE>route limit <I>number</I></CODE><DD><P>The maximal number of routes -that may be imported from the protocol. If the route limit is -exceeded, the connection is closed with an error. Limit is currently implemented as -<CODE>import limit <I>number</I> action restart</CODE>. This option is obsolete and it is -replaced by -<A HREF="bird-3.html#import-limit">import limit option</A>. Default: no limit. -<P> -<DT><CODE>disable after error <I>switch</I></CODE><DD><P>When an error is encountered (either -locally or by the other side), disable the instance automatically -and wait for an administrator to fix the problem manually. Default: off. -<P> -<DT><CODE>hold time <I>number</I></CODE><DD><P>Time in seconds to wait for a Keepalive -message from the other side before considering the connection stale. -Default: depends on agreement with the neighboring router, we prefer -240 seconds if the other side is willing to accept it. -<P> -<DT><CODE>startup hold time <I>number</I></CODE><DD><P>Value of the hold timer used -before the routers have a chance to exchange open messages and agree -on the real value. Default: 240 seconds. -<P> -<DT><CODE>keepalive time <I>number</I></CODE><DD><P>Delay in seconds between sending -of two consecutive Keepalive messages. Default: One third of the hold time. -<P> -<DT><CODE>connect retry time <I>number</I></CODE><DD><P>Time in seconds to wait before -retrying a failed attempt to connect. Default: 120 seconds. -<P> -<DT><CODE>start delay time <I>number</I></CODE><DD><P>Delay in seconds between protocol -startup and the first attempt to connect. Default: 5 seconds. -<P> -<DT><CODE>error wait time <I>number</I>,<I>number</I></CODE><DD><P>Minimum and maximum delay in seconds between a protocol -failure (either local or reported by the peer) and automatic restart. -Doesn't apply when <CODE>disable after error</CODE> is configured. If consecutive -errors happen, the delay is increased exponentially until it reaches the maximum. Default: 60, 300. -<P> -<DT><CODE>error forget time <I>number</I></CODE><DD><P>Maximum time in seconds between two protocol -failures to treat them as a error sequence which makes the <CODE>error wait time</CODE> -increase exponentially. Default: 300 seconds. -<P> -<DT><CODE>path metric <I>switch</I></CODE><DD><P>Enable comparison of path lengths -when deciding which BGP route is the best one. Default: on. -<P> -<DT><CODE>med metric <I>switch</I></CODE><DD><P>Enable comparison of MED -attributes (during best route selection) even between routes -received from different ASes. This may be useful if all MED -attributes contain some consistent metric, perhaps enforced in -import filters of AS boundary routers. If this option is -disabled, MED attributes are compared only if routes are -received from the same AS (which is the standard behavior). -Default: off. -<P> -<DT><CODE>deterministic med <I>switch</I></CODE><DD><P>BGP route selection -algorithm is often viewed as a comparison between individual -routes (e.g. if a new route appears and is better than the -current best one, it is chosen as the new best one). But the -proper route selection, as specified by RFC 4271, cannot be -fully implemented in that way. The problem is mainly in -handling the MED attribute. BIRD, by default, uses an -simplification based on individual route comparison, which in -some cases may lead to temporally dependent behavior (i.e. the -selection is dependent on the order in which routes appeared). -This option enables a different (and slower) algorithm -implementing proper RFC 4271 route selection, which is -deterministic. Alternative way how to get deterministic -behavior is to use <CODE>med metric</CODE> option. This option is -incompatible with -<A HREF="bird-2.html#dsc-sorted">sorted tables</A>. -Default: off. -<P> -<DT><CODE>igp metric <I>switch</I></CODE><DD><P>Enable comparison of internal -distances to boundary routers during best route selection. Default: on. -<P> -<DT><CODE>prefer older <I>switch</I></CODE><DD><P>Standard route selection algorithm -breaks ties by comparing router IDs. This changes the behavior -to prefer older routes (when both are external and from different -peer). For details, see RFC 5004. Default: off. -<P> -<DT><CODE>default bgp_med <I>number</I></CODE><DD><P>Value of the Multiple Exit -Discriminator to be used during route selection when the MED attribute -is missing. Default: 0. -<P> -<DT><CODE>default bgp_local_pref <I>number</I></CODE><DD><P>A default value -for the Local Preference attribute. It is used when a new -Local Preference attribute is attached to a route by the BGP -protocol itself (for example, if a route is received through -eBGP and therefore does not have such attribute). Default: 100 -(0 in pre-1.2.0 versions of BIRD). -</DL> -<P> -<H3>Attributes</H3> - -<P>BGP defines several route attributes. Some of them (those marked with `<CODE>I</CODE>' in the -table below) are available on internal BGP connections only, some of them (marked -with `<CODE>O</CODE>') are optional. -<P> -<DL> -<DT><CODE>bgppath <CODE>bgp_path</CODE></CODE><DD><P>Sequence of AS numbers describing the AS path -the packet will travel through when forwarded according to the particular route. -In case of internal BGP it doesn't contain the number of the local AS. -<P> -<DT><CODE>int <CODE>bgp_local_pref</CODE> [I]</CODE><DD><P>Local preference value used for -selection among multiple BGP routes (see the selection rules above). It's -used as an additional metric which is propagated through the whole local AS. -<P> -<DT><CODE>int <CODE>bgp_med</CODE> [O]</CODE><DD><P>The Multiple Exit Discriminator of the route -is an optional attribute which is used on external (inter-AS) links to -convey to an adjacent AS the optimal entry point into the local AS. -The received attribute is also propagated over internal BGP links. -The attribute value is zeroed when a route is exported to an external BGP -instance to ensure that the attribute received from a neighboring AS is -not propagated to other neighboring ASes. A new value might be set in -the export filter of an external BGP instance. -See RFC 4451 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc4451.txt">ftp://ftp.rfc-editor.org/in-notes/rfc4451.txt</A> -for further discussion of BGP MED attribute. -<P> -<DT><CODE>enum <CODE>bgp_origin</CODE></CODE><DD><P>Origin of the route: either <CODE>ORIGIN_IGP</CODE> -if the route has originated in an interior routing protocol or -<CODE>ORIGIN_EGP</CODE> if it's been imported from the <CODE>EGP</CODE> protocol -(nowadays it seems to be obsolete) or <CODE>ORIGIN_INCOMPLETE</CODE> if the origin -is unknown. -<P> -<DT><CODE>ip <CODE>bgp_next_hop</CODE></CODE><DD><P>Next hop to be used for forwarding of packets -to this destination. On internal BGP connections, it's an address of the -originating router if it's inside the local AS or a boundary router the -packet will leave the AS through if it's an exterior route, so each BGP -speaker within the AS has a chance to use the shortest interior path -possible to this point. -<P> -<DT><CODE>void <CODE>bgp_atomic_aggr</CODE> [O]</CODE><DD><P>This is an optional attribute -which carries no value, but the sole presence of which indicates that the route -has been aggregated from multiple routes by some router on the path from -the originator. -<P> -<DT><CODE>clist <CODE>bgp_community</CODE> [O]</CODE><DD><P>List of community values associated -with the route. Each such value is a pair (represented as a <CODE>pair</CODE> data -type inside the filters) of 16-bit integers, the first of them containing the number of the AS which defines -the community and the second one being a per-AS identifier. There are lots -of uses of the community mechanism, but generally they are used to carry -policy information like "don't export to USA peers". As each AS can define -its own routing policy, it also has a complete freedom about which community -attributes it defines and what will their semantics be. -<P> -<DT><CODE>eclist <CODE>bgp_ext_community</CODE> [O]</CODE><DD><P>List of extended community -values associated with the route. Extended communities have similar usage -as plain communities, but they have an extended range (to allow 4B ASNs) -and a nontrivial structure with a type field. Individual community values are -represented using an <CODE>ec</CODE> data type inside the filters. -<P> -<DT><CODE>quad <CODE>bgp_originator_id</CODE> [I, O]</CODE><DD><P>This attribute is created by the -route reflector when reflecting the route and contains the router ID of the -originator of the route in the local AS. -<P> -<DT><CODE>clist <CODE>bgp_cluster_list</CODE> [I, O]</CODE><DD><P>This attribute contains a list -of cluster IDs of route reflectors. Each route reflector prepends its -cluster ID when reflecting the route. -</DL> -<P> -<H3>Example</H3> - -<P> -<HR> -<PRE> -protocol bgp { - local as 65000; # Use a private AS number - neighbor 198.51.100.130 as 64496; # Our neighbor ... - multihop; # ... which is connected indirectly - export filter { # We use non-trivial export rules - if source = RTS_STATIC then { # Export only static routes - # Assign our community - bgp_community.add((65000,64501)); - # Artificially increase path length - # by advertising local AS number twice - if bgp_path ~ [= 65000 =] then - bgp_path.prepend(65000); - accept; - } - reject; - }; - import all; - source address 198.51.100.14; # Use a non-standard source address -} -</PRE> -<HR> -<P> -<H2><A NAME="ss6.2">6.2</A> <A HREF="bird.html#toc6.2">Device</A> -</H2> - -<P>The Device protocol is not a real routing protocol. It doesn't generate -any routes and it only serves as a module for getting information about network -interfaces from the kernel. -<P> -<P>Except for very unusual circumstances, you probably should include -this protocol in the configuration since almost all other protocols -require network interfaces to be defined for them to work with. -<P> -<H3>Configuration</H3> - -<P> -<DL> -<DT><CODE>scan time <I>number</I></CODE><DD><P>Time in seconds between two scans -of the network interface list. On systems where we are notified about -interface status changes asynchronously (such as newer versions of -Linux), we need to scan the list only in order to avoid confusion by lost -notification messages, so the default time is set to a large value. -<P> -<DT><CODE>primary [ "<I>mask</I>" ] <I>prefix</I></CODE><DD><P>If a network interface has more than one network address, BIRD -has to choose one of them as a primary one. By default, BIRD -chooses the lexicographically smallest address as the primary -one. -<P>This option allows to specify which network address should be -chosen as a primary one. Network addresses that match -<I>prefix</I> are preferred to non-matching addresses. If more -<CODE>primary</CODE> options are used, the first one has the highest -preference. If "<I>mask</I>" is specified, then such -<CODE>primary</CODE> option is relevant only to matching network -interfaces. -<P>In all cases, an address marked by operating system as -secondary cannot be chosen as the primary one. -</DL> -<P> -<P>As the Device protocol doesn't generate any routes, it cannot have -any attributes. Example configuration looks like this: -<P> -<P> -<HR> -<PRE> -protocol device { - scan time 10; # Scan the interfaces often - primary "eth0" 192.168.1.1; - primary 192.168.0.0/16; -} -</PRE> -<HR> -<P> -<H2><A NAME="ss6.3">6.3</A> <A HREF="bird.html#toc6.3">Direct</A> -</H2> - -<P>The Direct protocol is a simple generator of device routes for all the -directly connected networks according to the list of interfaces provided -by the kernel via the Device protocol. -<P> -<P>The question is whether it is a good idea to have such device -routes in BIRD routing table. OS kernel usually handles device routes -for directly connected networks by itself so we don't need (and don't -want) to export these routes to the kernel protocol. OSPF protocol -creates device routes for its interfaces itself and BGP protocol is -usually used for exporting aggregate routes. Although there are some -use cases that use the direct protocol (like abusing eBGP as an IGP -routing protocol), in most cases it is not needed to have these device -routes in BIRD routing table and to use the direct protocol. -<P> -<P>There is one notable case when you definitely want to use the -direct protocol -- running BIRD on BSD systems. Having high priority -device routes for directly connected networks from the direct protocol -protects kernel device routes from being overwritten or removed by IGP -routes during some transient network conditions, because a lower -priority IGP route for the same network is not exported to the kernel -routing table. This is an issue on BSD systems only, as on Linux -systems BIRD cannot change non-BIRD route in the kernel routing table. -<P> -<P>The only configurable thing about direct is what interfaces it watches: -<P> -<P> -<DL> -<DT><CODE>interface <I>pattern [, ...]</I></CODE><DD><P>By default, the Direct -protocol will generate device routes for all the interfaces -available. If you want to restrict it to some subset of interfaces -(for example if you're using multiple routing tables for policy -routing and some of the policy domains don't contain all interfaces), -just use this clause. -</DL> -<P> -<P>Direct device routes don't contain any specific attributes. -<P> -<P>Example config might look like this: -<P> -<P> -<HR> -<PRE> -protocol direct { - interface "-arc*", "*"; # Exclude the ARCnets -} -</PRE> -<HR> -<P> -<H2><A NAME="ss6.4">6.4</A> <A HREF="bird.html#toc6.4">Kernel</A> -</H2> - -<P>The Kernel protocol is not a real routing protocol. Instead of communicating -with other routers in the network, it performs synchronization of BIRD's routing -tables with the OS kernel. Basically, it sends all routing table updates to the kernel -and from time to time it scans the kernel tables to see whether some routes have -disappeared (for example due to unnoticed up/down transition of an interface) -or whether an `alien' route has been added by someone else (depending on the -<CODE>learn</CODE> switch, such routes are either ignored or accepted to our -table). -<P> -<P>Unfortunately, there is one thing that makes the routing table -synchronization a bit more complicated. In the kernel routing table -there are also device routes for directly connected networks. These -routes are usually managed by OS itself (as a part of IP address -configuration) and we don't want to touch that. They are completely -ignored during the scan of the kernel tables and also the export of -device routes from BIRD tables to kernel routing tables is restricted -to prevent accidental interference. This restriction can be disabled using -<CODE>device routes</CODE> switch. -<P> -<P>If your OS supports only a single routing table, you can configure -only one instance of the Kernel protocol. If it supports multiple -tables (in order to allow policy routing; such an OS is for example -Linux), you can run as many instances as you want, but each of them -must be connected to a different BIRD routing table and to a different -kernel table. -<P> -<P>Because the kernel protocol is partially integrated with the -connected routing table, there are two limitations - it is not -possible to connect more kernel protocols to the same routing table -and changing route destination/gateway in an export -filter of a kernel protocol does not work. Both limitations can be -overcome using another routing table and the pipe protocol. -<P> -<H3>Configuration</H3> - -<P> -<DL> -<DT><CODE>persist <I>switch</I></CODE><DD><P>Tell BIRD to leave all its routes in the -routing tables when it exits (instead of cleaning them up). -<DT><CODE>scan time <I>number</I></CODE><DD><P>Time in seconds between two consecutive scans of the -kernel routing table. -<DT><CODE>learn <I>switch</I></CODE><DD><P>Enable learning of routes added to the kernel -routing tables by other routing daemons or by the system administrator. -This is possible only on systems which support identification of route -authorship. -<P> -<DT><CODE>device routes <I>switch</I></CODE><DD><P>Enable export of device -routes to the kernel routing table. By default, such routes -are rejected (with the exception of explicitly configured -device routes from the static protocol) regardless of the -export filter to protect device routes in kernel routing table -(managed by OS itself) from accidental overwriting or erasing. -<P> -<DT><CODE>kernel table <I>number</I></CODE><DD><P>Select which kernel table should -this particular instance of the Kernel protocol work with. Available -only on systems supporting multiple routing tables. -</DL> -<P> -<H3>Attributes</H3> - -<P>The Kernel protocol defines several attributes. These attributes -are translated to appropriate system (and OS-specific) route attributes. -We support these attributes: -<P> -<DL> -<DT><CODE>int <CODE>krt_source</CODE></CODE><DD><P>The original source of the imported -kernel route. The value is system-dependent. On Linux, it is -a value of the protocol field of the route. See -/etc/iproute2/rt_protos for common values. On BSD, it is -based on STATIC and PROTOx flags. The attribute is read-only. -<P> -<DT><CODE>int <CODE>krt_metric</CODE></CODE><DD><P>The kernel metric of -the route. When multiple same routes are in a kernel routing -table, the Linux kernel chooses one with lower metric. -<P> -<DT><CODE>ip <CODE>krt_prefsrc</CODE></CODE><DD><P>(Linux) The preferred source address. -Used in source address selection for outgoing packets. Have to -be one of IP addresses of the router. -<P> -<DT><CODE>int <CODE>krt_realm</CODE></CODE><DD><P>(Linux) The realm of the route. Can be -used for traffic classification. -</DL> -<P> -<H3>Example</H3> - -<P>A simple configuration can look this way: -<P> -<P> -<HR> -<PRE> -protocol kernel { - export all; -} -</PRE> -<HR> -<P> -<P>Or for a system with two routing tables: -<P> -<P> -<HR> -<PRE> -protocol kernel { # Primary routing table - learn; # Learn alien routes from the kernel - persist; # Don't remove routes on bird shutdown - scan time 10; # Scan kernel routing table every 10 seconds - import all; - export all; -} - -protocol kernel { # Secondary routing table - table auxtable; - kernel table 100; - export all; -} -</PRE> -<HR> -<P> -<H2><A NAME="ss6.5">6.5</A> <A HREF="bird.html#toc6.5">OSPF</A> -</H2> - -<H3>Introduction</H3> - -<P>Open Shortest Path First (OSPF) is a quite complex interior gateway -protocol. The current IPv4 version (OSPFv2) is defined in RFC -2328 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt">ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt</A> and -the current IPv6 version (OSPFv3) is defined in RFC 5340 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc5340.txt">ftp://ftp.rfc-editor.org/in-notes/rfc5340.txt</A> It's a link state -(a.k.a. shortest path first) protocol -- each router maintains a -database describing the autonomous system's topology. Each participating -router has an identical copy of the database and all routers run the -same algorithm calculating a shortest path tree with themselves as a -root. OSPF chooses the least cost path as the best path. -<P> -<P>In OSPF, the autonomous system can be split to several areas in order -to reduce the amount of resources consumed for exchanging the routing -information and to protect the other areas from incorrect routing data. -Topology of the area is hidden to the rest of the autonomous system. -<P> -<P>Another very important feature of OSPF is that -it can keep routing information from other protocols (like Static or BGP) -in its link state database as external routes. Each external route can -be tagged by the advertising router, making it possible to pass additional -information between routers on the boundary of the autonomous system. -<P> -<P>OSPF quickly detects topological changes in the autonomous system (such -as router interface failures) and calculates new loop-free routes after a short -period of convergence. Only a minimal amount of -routing traffic is involved. -<P> -<P>Each router participating in OSPF routing periodically sends Hello messages -to all its interfaces. This allows neighbors to be discovered dynamically. -Then the neighbors exchange theirs parts of the link state database and keep it -identical by flooding updates. The flooding process is reliable and ensures -that each router detects all changes. -<P> -<H3>Configuration</H3> - -<P>In the main part of configuration, there can be multiple definitions of -OSPF areas, each with a different id. These definitions includes many other -switches and multiple definitions of interfaces. Definition of interface -may contain many switches and constant definitions and list of neighbors -on nonbroadcast networks. -<P> -<HR> -<PRE> -protocol ospf <name> { - rfc1583compat <switch>; - stub router <switch>; - tick <num>; - ecmp <switch> [limit <num>]; - area <id> { - stub; - nssa; - summary <switch>; - default nssa <switch>; - default cost <num>; - default cost2 <num>; - translator <switch>; - translator stability <num>; - - networks { - <prefix>; - <prefix> hidden; - } - external { - <prefix>; - <prefix> hidden; - <prefix> tag <num>; - } - stubnet <prefix>; - stubnet <prefix> { - hidden <switch>; - summary <switch>; - cost <num>; - } - interface <interface pattern> [instance <num>] { - cost <num>; - stub <switch>; - hello <num>; - poll <num>; - retransmit <num>; - priority <num>; - wait <num>; - dead count <num>; - dead <num>; - rx buffer [normal|large|<num>]; - type [broadcast|bcast|pointopoint|ptp| - nonbroadcast|nbma|pointomultipoint|ptmp]; - strict nonbroadcast <switch>; - real broadcast <switch>; - ptp netmask <switch>; - check link <switch>; - ecmp weight <num>; - ttl security [<switch>; | tx only] - tx class|dscp <num>; - tx priority <num>; - authentication [none|simple|cryptographic]; - password "<text>"; - password "<text>" { - id <num>; - generate from "<date>"; - generate to "<date>"; - accept from "<date>"; - accept to "<date>"; - }; - neighbors { - <ip>; - <ip> eligible; - }; - }; - virtual link <id> [instance <num>] { - hello <num>; - retransmit <num>; - wait <num>; - dead count <num>; - dead <num>; - authentication [none|simple|cryptographic]; - password "<text>"; - }; - }; -} -</PRE> -<HR> -<P> -<DL> -<DT><CODE>rfc1583compat <I>switch</I></CODE><DD><P>This option controls compatibility of routing table -calculation with RFC 1583 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc1583.txt">ftp://ftp.rfc-editor.org/in-notes/rfc1583.txt</A>. Default -value is no. -<P> -<DT><CODE>stub router <I>switch</I></CODE><DD><P>This option configures the router to be a stub router, i.e., -a router that participates in the OSPF topology but does not -allow transit traffic. In OSPFv2, this is implemented by -advertising maximum metric for outgoing links, as suggested -by RFC 3137 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc3137.txt">ftp://ftp.rfc-editor.org/in-notes/rfc3137.txt</A>. -In OSPFv3, the stub router behavior is announced by clearing -the R-bit in the router LSA. Default value is no. -<P> -<DT><CODE>tick <I>num</I></CODE><DD><P>The routing table calculation and clean-up of areas' databases -is not performed when a single link state -change arrives. To lower the CPU utilization, it's processed later -at periodical intervals of <I>num</I> seconds. The default value is 1. -<P> -<DT><CODE>ecmp <I>switch</I> [limit <I>number</I>]</CODE><DD><P>This option specifies whether OSPF is allowed to generate -ECMP (equal-cost multipath) routes. Such routes are used when -there are several directions to the destination, each with -the same (computed) cost. This option also allows to specify -a limit on maximal number of nexthops in one route. By -default, ECMP is disabled. If enabled, default value of the -limit is 16. -<P> -<DT><CODE>area <I>id</I></CODE><DD><P>This defines an OSPF area with given area ID (an integer or an IPv4 -address, similarly to a router ID). The most important area is -the backbone (ID 0) to which every other area must be connected. -<P> -<DT><CODE>stub</CODE><DD><P>This option configures the area to be a stub area. External -routes are not flooded into stub areas. Also summary LSAs can be -limited in stub areas (see option <CODE>summary</CODE>). -By default, the area is not a stub area. -<P> -<DT><CODE>nssa</CODE><DD><P>This option configures the area to be a NSSA (Not-So-Stubby -Area). NSSA is a variant of a stub area which allows a -limited way of external route propagation. Global external -routes are not propagated into a NSSA, but an external route -can be imported into NSSA as a (area-wide) NSSA-LSA (and -possibly translated and/or aggregated on area boundary). -By default, the area is not NSSA. -<P> -<DT><CODE>summary <I>switch</I></CODE><DD><P>This option controls propagation of summary LSAs into stub or -NSSA areas. If enabled, summary LSAs are propagated as usual, -otherwise just the default summary route (0.0.0.0/0) is -propagated (this is sometimes called totally stubby area). If -a stub area has more area boundary routers, propagating -summary LSAs could lead to more efficient routing at the cost -of larger link state database. Default value is no. -<P> -<DT><CODE>default nssa <I>switch</I></CODE><DD><P>When <CODE>summary</CODE> option is enabled, default summary route is -no longer propagated to the NSSA. In that case, this option -allows to originate default route as NSSA-LSA to the NSSA. -Default value is no. -<P> -<DT><CODE>default cost <I>num</I></CODE><DD><P>This option controls the cost of a default route propagated to -stub and NSSA areas. Default value is 1000. -<P> -<DT><CODE>default cost2 <I>num</I></CODE><DD><P>When a default route is originated as NSSA-LSA, its cost -can use either type 1 or type 2 metric. This option allows -to specify the cost of a default route in type 2 metric. -By default, type 1 metric (option <CODE>default cost</CODE>) is used. -<P> -<DT><CODE>translator <I>switch</I></CODE><DD><P>This option controls translation of NSSA-LSAs into external -LSAs. By default, one translator per NSSA is automatically -elected from area boundary routers. If enabled, this area -boundary router would unconditionally translate all NSSA-LSAs -regardless of translator election. Default value is no. -<P> -<DT><CODE>translator stability <I>num</I></CODE><DD><P>This option controls the translator stability interval (in -seconds). When the new translator is elected, the old one -keeps translating until the interval is over. Default value -is 40. -<P> -<DT><CODE>networks { <I>set</I> }</CODE><DD><P>Definition of area IP ranges. This is used in summary LSA origination. -Hidden networks are not propagated into other areas. -<P> -<DT><CODE>external { <I>set</I> }</CODE><DD><P>Definition of external area IP ranges for NSSAs. This is used -for NSSA-LSA translation. Hidden networks are not translated -into external LSAs. Networks can have configured route tag. -<P> -<DT><CODE>stubnet <I>prefix</I> { <I>options</I> }</CODE><DD><P>Stub networks are networks that are not transit networks -between OSPF routers. They are also propagated through an -OSPF area as a part of a link state database. By default, -BIRD generates a stub network record for each primary network -address on each OSPF interface that does not have any OSPF -neighbors, and also for each non-primary network address on -each OSPF interface. This option allows to alter a set of -stub networks propagated by this router. -<P>Each instance of this option adds a stub network with given -network prefix to the set of propagated stub network, unless -option <CODE>hidden</CODE> is used. It also suppresses default stub -networks for given network prefix. When option -<CODE>summary</CODE> is used, also default stub networks that are -subnetworks of given stub network are suppressed. This might -be used, for example, to aggregate generated stub networks. -<P> -<DT><CODE>interface <I>pattern</I> [instance <I>num</I>]</CODE><DD><P>Defines that the specified interfaces belong to the area being defined. -See -<A HREF="bird-3.html#dsc-iface">interface</A> common option for detailed description. -In OSPFv3, you can specify instance ID for that interface -description, so it is possible to have several instances of -that interface with different options or even in different areas. -<P> -<DT><CODE>virtual link <I>id</I> [instance <I>num</I>]</CODE><DD><P>Virtual link to router with the router id. Virtual link acts -as a point-to-point interface belonging to backbone. The -actual area is used as transport area. This item cannot be in -the backbone. In OSPFv3, you could also use several virtual -links to one destination with different instance IDs. -<P> -<DT><CODE>cost <I>num</I></CODE><DD><P>Specifies output cost (metric) of an interface. Default value is 10. -<P> -<DT><CODE>stub <I>switch</I></CODE><DD><P>If set to interface it does not listen to any packet and does not send -any hello. Default value is no. -<P> -<DT><CODE>hello <I>num</I></CODE><DD><P>Specifies interval in seconds between sending of Hello messages. Beware, all -routers on the same network need to have the same hello interval. -Default value is 10. -<P> -<DT><CODE>poll <I>num</I></CODE><DD><P>Specifies interval in seconds between sending of Hello messages for -some neighbors on NBMA network. Default value is 20. -<P> -<DT><CODE>retransmit <I>num</I></CODE><DD><P>Specifies interval in seconds between retransmissions of unacknowledged updates. -Default value is 5. -<P> -<DT><CODE>priority <I>num</I></CODE><DD><P>On every multiple access network (e.g., the Ethernet) Designed Router -and Backup Designed router are elected. These routers have some -special functions in the flooding process. Higher priority increases -preferences in this election. Routers with priority 0 are not -eligible. Default value is 1. -<P> -<DT><CODE>wait <I>num</I></CODE><DD><P>After start, router waits for the specified number of seconds between starting -election and building adjacency. Default value is 40. -<P> -<DT><CODE>dead count <I>num</I></CODE><DD><P>When the router does not receive any messages from a neighbor in -<I>dead count</I>*<I>hello</I> seconds, it will consider the neighbor down. -<P> -<DT><CODE>dead <I>num</I></CODE><DD><P>When the router does not receive any messages from a neighbor in -<I>dead</I> seconds, it will consider the neighbor down. If both directives -<I>dead count</I> and <I>dead</I> are used, <I>dead</I> has precendence. -<P> -<DT><CODE>rx buffer <I>num</I></CODE><DD><P>This sets the size of buffer used for receiving packets. The buffer should -be bigger than maximal size of any packets. Value NORMAL (default) -means 2*MTU, value LARGE means maximal allowed packet - 65535. -<P> -<DT><CODE>type broadcast|bcast</CODE><DD><P>BIRD detects a type of a connected network automatically, but -sometimes it's convenient to force use of a different type -manually. On broadcast networks (like ethernet), flooding -and Hello messages are sent using multicasts (a single packet -for all the neighbors). A designated router is elected and it -is responsible for synchronizing the link-state databases and -originating network LSAs. This network type cannot be used on -physically NBMA networks and on unnumbered networks (networks -without proper IP prefix). -<P> -<DT><CODE>type pointopoint|ptp</CODE><DD><P>Point-to-point networks connect just 2 routers together. No -election is performed and no network LSA is originated, which -makes it simpler and faster to establish. This network type -is useful not only for physically PtP ifaces (like PPP or -tunnels), but also for broadcast networks used as PtP links. -This network type cannot be used on physically NBMA networks. -<P> -<DT><CODE>type nonbroadcast|nbma</CODE><DD><P>On NBMA networks, the packets are sent to each neighbor -separately because of lack of multicast capabilities. -Like on broadcast networks, a designated router is elected, -which plays a central role in propagation of LSAs. -This network type cannot be used on unnumbered networks. -<P> -<DT><CODE>type pointomultipoint|ptmp</CODE><DD><P>This is another network type designed to handle NBMA -networks. In this case the NBMA network is treated as a -collection of PtP links. This is useful if not every pair of -routers on the NBMA network has direct communication, or if -the NBMA network is used as an (possibly unnumbered) PtP -link. -<P> -<DT><CODE>strict nonbroadcast <I>switch</I></CODE><DD><P>If set, don't send hello to any undefined neighbor. This switch -is ignored on other than NBMA or PtMP networks. Default value is no. -<P> -<DT><CODE>real broadcast <I>switch</I></CODE><DD><P>In <CODE>type broadcast</CODE> or <CODE>type ptp</CODE> network -configuration, OSPF packets are sent as IP multicast -packets. This option changes the behavior to using -old-fashioned IP broadcast packets. This may be useful as a -workaround if IP multicast for some reason does not work or -does not work reliably. This is a non-standard option and -probably is not interoperable with other OSPF -implementations. Default value is no. -<P> -<DT><CODE>ptp netmask <I>switch</I></CODE><DD><P>In <CODE>type ptp</CODE> network configurations, OSPFv2 -implementations should ignore received netmask field in hello -packets and should send hello packets with zero netmask field -on unnumbered PtP links. But some OSPFv2 implementations -perform netmask checking even for PtP links. This option -specifies whether real netmask will be used in hello packets -on <CODE>type ptp</CODE> interfaces. You should ignore this option -unless you meet some compatibility problems related to this -issue. Default value is no for unnumbered PtP links, yes -otherwise. -<P> -<DT><CODE>check link <I>switch</I></CODE><DD><P>If set, a hardware link state (reported by OS) is taken into -consideration. When a link disappears (e.g. an ethernet cable is -unplugged), neighbors are immediately considered unreachable -and only the address of the iface (instead of whole network -prefix) is propagated. It is possible that some hardware -drivers or platforms do not implement this feature. Default value is no. -<P> -<DT><CODE>ttl security [<I>switch</I> | tx only]</CODE><DD><P>TTL security is a feature that protects routing protocols -from remote spoofed packets by using TTL 255 instead of TTL 1 -for protocol packets destined to neighbors. Because TTL is -decremented when packets are forwarded, it is non-trivial to -spoof packets with TTL 255 from remote locations. Note that -this option would interfere with OSPF virtual links. -<P>If this option is enabled, the router will send OSPF packets -with TTL 255 and drop received packets with TTL less than -255. If this option si set to <CODE>tx only</CODE>, TTL 255 is used -for sent packets, but is not checked for received -packets. Default value is no. -<P> -<DT><CODE>tx class|dscp|priority <I>num</I></CODE><DD><P>These options specify the ToS/DiffServ/Traffic class/Priority -of the outgoing OSPF packets. See -<A HREF="bird-3.html#dsc-prio">tx class</A> common option for detailed description. -<P> -<DT><CODE>ecmp weight <I>num</I></CODE><DD><P>When ECMP (multipath) routes are allowed, this value specifies -a relative weight used for nexthops going through the iface. -Allowed values are 1-256. Default value is 1. -<P> -<DT><CODE>authentication none</CODE><DD><P>No passwords are sent in OSPF packets. This is the default value. -<P> -<DT><CODE>authentication simple</CODE><DD><P>Every packet carries 8 bytes of password. Received packets -lacking this password are ignored. This authentication mechanism is -very weak. -<P> -<DT><CODE>authentication cryptographic</CODE><DD><P>16-byte long MD5 digest is appended to every packet. For the digest -generation 16-byte long passwords are used. Those passwords are -not sent via network, so this mechanism is quite secure. -Packets can still be read by an attacker. -<P> -<DT><CODE>password "<I>text</I>"</CODE><DD><P>An 8-byte or 16-byte password used for authentication. -See -<A HREF="bird-3.html#dsc-pass">password</A> common option for detailed description. -<P> -<DT><CODE>neighbors { <I>set</I> } </CODE><DD><P>A set of neighbors to which Hello messages on NBMA or PtMP -networks are to be sent. For NBMA networks, some of them -could be marked as eligible. In OSPFv3, link-local addresses -should be used, using global ones is possible, but it is -nonstandard and might be problematic. And definitely, -link-local and global addresses should not be mixed. -<P> -</DL> -<P> -<H3>Attributes</H3> - -<P>OSPF defines four route attributes. Each internal route has a <CODE>metric</CODE>. -Metric is ranging from 1 to infinity (65535). -External routes use <CODE>metric type 1</CODE> or <CODE>metric type 2</CODE>. -A <CODE>metric of type 1</CODE> is comparable with internal <CODE>metric</CODE>, a -<CODE>metric of type 2</CODE> is always longer -than any <CODE>metric of type 1</CODE> or any <CODE>internal metric</CODE>. -<CODE>Internal metric</CODE> or <CODE>metric of type 1</CODE> is stored in attribute -<CODE>ospf_metric1</CODE>, <CODE>metric type 2</CODE> is stored in attribute <CODE>ospf_metric2</CODE>. -If you specify both metrics only metric1 is used. -<P>Each external route can also carry attribute <CODE>ospf_tag</CODE> which is a -32-bit integer which is used when exporting routes to other protocols; -otherwise, it doesn't affect routing inside the OSPF domain at all. -The fourth attribute <CODE>ospf_router_id</CODE> is a router ID of the router -advertising that route/network. This attribute is read-only. Default -is <CODE>ospf_metric2 = 10000</CODE> and <CODE>ospf_tag = 0</CODE>. -<P> -<H3>Example</H3> - -<P> -<P> -<HR> -<PRE> -protocol ospf MyOSPF { - rfc1583compat yes; - tick 2; - export filter { - if source = RTS_BGP then { - ospf_metric1 = 100; - accept; - } - reject; - }; - area 0.0.0.0 { - interface "eth*" { - cost 11; - hello 15; - priority 100; - retransmit 7; - authentication simple; - password "aaa"; - }; - interface "ppp*" { - cost 100; - authentication cryptographic; - password "abc" { - id 1; - generate to "22-04-2003 11:00:06"; - accept from "17-01-2001 12:01:05"; - }; - password "def" { - id 2; - generate to "22-07-2005 17:03:21"; - accept from "22-02-2001 11:34:06"; - }; - }; - interface "arc0" { - cost 10; - stub yes; - }; - interface "arc1"; - }; - area 120 { - stub yes; - networks { - 172.16.1.0/24; - 172.16.2.0/24 hidden; - } - interface "-arc0" , "arc*" { - type nonbroadcast; - authentication none; - strict nonbroadcast yes; - wait 120; - poll 40; - dead count 8; - neighbors { - 192.168.120.1 eligible; - 192.168.120.2; - 192.168.120.10; - }; - }; - }; -} -</PRE> -<HR> -<P> -<H2><A NAME="ss6.6">6.6</A> <A HREF="bird.html#toc6.6">Pipe</A> -</H2> - -<H3>Introduction</H3> - -<P>The Pipe protocol serves as a link between two routing tables, allowing routes to be -passed from a table declared as primary (i.e., the one the pipe is connected to using the -<CODE>table</CODE> configuration keyword) to the secondary one (declared using <CODE>peer table</CODE>) -and vice versa, depending on what's allowed by the filters. Export filters control export -of routes from the primary table to the secondary one, import filters control the opposite -direction. -<P> -<P>The Pipe protocol may work in the transparent mode mode or in the opaque mode. -In the transparent mode, the Pipe protocol retransmits all routes from -one table to the other table, retaining their original source and -attributes. If import and export filters are set to accept, then both -tables would have the same content. The transparent mode is the default mode. -<P> -<P>In the opaque mode, the Pipe protocol retransmits optimal route -from one table to the other table in a similar way like other -protocols send and receive routes. Retransmitted route will have the -source set to the Pipe protocol, which may limit access to protocol -specific route attributes. This mode is mainly for compatibility, it -is not suggested for new configs. The mode can be changed by -<CODE>mode</CODE> option. -<P> -<P>The primary use of multiple routing tables and the Pipe protocol is for policy routing, -where handling of a single packet doesn't depend only on its destination address, but also -on its source address, source interface, protocol type and other similar parameters. -In many systems (Linux being a good example), the kernel allows to enforce routing policies -by defining routing rules which choose one of several routing tables to be used for a packet -according to its parameters. Setting of these rules is outside the scope of BIRD's work -(on Linux, you can use the <CODE>ip</CODE> command), but you can create several routing tables in BIRD, -connect them to the kernel ones, use filters to control which routes appear in which tables -and also you can employ the Pipe protocol for exporting a selected subset of one table to -another one. -<P> -<H3>Configuration</H3> - -<P> -<DL> -<DT><CODE>peer table <I>table</I></CODE><DD><P>Defines secondary routing table to connect to. The -primary one is selected by the <CODE>table</CODE> keyword. -<P> -<DT><CODE>mode opaque|transparent</CODE><DD><P>Specifies the mode for the pipe to work in. Default is transparent. -</DL> -<P> -<H3>Attributes</H3> - -<P>The Pipe protocol doesn't define any route attributes. -<P> -<H3>Example</H3> - -<P>Let's consider a router which serves as a boundary router of two different autonomous -systems, each of them connected to a subset of interfaces of the router, having its own -exterior connectivity and wishing to use the other AS as a backup connectivity in case -of outage of its own exterior line. -<P> -<P>Probably the simplest solution to this situation is to use two routing tables (we'll -call them <CODE>as1</CODE> and <CODE>as2</CODE>) and set up kernel routing rules, so that packets having -arrived from interfaces belonging to the first AS will be routed according to <CODE>as1</CODE> -and similarly for the second AS. Thus we have split our router to two logical routers, -each one acting on its own routing table, having its own routing protocols on its own -interfaces. In order to use the other AS's routes for backup purposes, we can pass -the routes between the tables through a Pipe protocol while decreasing their preferences -and correcting their BGP paths to reflect the AS boundary crossing. -<P> -<HR> -<PRE> -table as1; # Define the tables -table as2; - -protocol kernel kern1 { # Synchronize them with the kernel - table as1; - kernel table 1; -} - -protocol kernel kern2 { - table as2; - kernel table 2; -} - -protocol bgp bgp1 { # The outside connections - table as1; - local as 1; - neighbor 192.168.0.1 as 1001; - export all; - import all; -} - -protocol bgp bgp2 { - table as2; - local as 2; - neighbor 10.0.0.1 as 1002; - export all; - import all; -} - -protocol pipe { # The Pipe - table as1; - peer table as2; - export filter { - if net ~ [ 1.0.0.0/8+] then { # Only AS1 networks - if preference>10 then preference = preference-10; - if source=RTS_BGP then bgp_path.prepend(1); - accept; - } - reject; - }; - import filter { - if net ~ [ 2.0.0.0/8+] then { # Only AS2 networks - if preference>10 then preference = preference-10; - if source=RTS_BGP then bgp_path.prepend(2); - accept; - } - reject; - }; -} -</PRE> -<HR> -<P> -<H2><A NAME="ss6.7">6.7</A> <A HREF="bird.html#toc6.7">RAdv</A> -</H2> - -<H3>Introduction</H3> - -<P>The RAdv protocol is an implementation of Router Advertisements, -which are used in the IPv6 stateless autoconfiguration. IPv6 routers -send (in irregular time intervals or as an answer to a request) -advertisement packets to connected networks. These packets contain -basic information about a local network (e.g. a list of network -prefixes), which allows network hosts to autoconfigure network -addresses and choose a default route. BIRD implements router behavior -as defined in -RFC 4861 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc4861.txt">ftp://ftp.rfc-editor.org/in-notes/rfc4861.txt</A> -and also the DNS extensions from -RFC 6106 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc6106.txt">ftp://ftp.rfc-editor.org/in-notes/rfc6106.txt</A>. -<P> -<H3>Configuration</H3> - -<P>There are several classes of definitions in RAdv configuration -- -interface definitions, prefix definitions and DNS definitions: -<P> -<DL> -<DT><CODE>interface <I>pattern [, ...]</I> { <I>options</I> }</CODE><DD><P>Interface definitions specify a set of interfaces on which the -protocol is activated and contain interface specific options. -See -<A HREF="bird-3.html#dsc-iface">interface</A> common options for -detailed description. -<P> -<DT><CODE>prefix <I>prefix</I> { <I>options</I> }</CODE><DD><P>Prefix definitions allow to modify a list of advertised -prefixes. By default, the advertised prefixes are the same as -the network prefixes assigned to the interface. For each -network prefix, the matching prefix definition is found and -its options are used. If no matching prefix definition is -found, the prefix is used with default options. -<P>Prefix definitions can be either global or interface-specific. -The second ones are part of interface options. The prefix -definition matching is done in the first-match style, when -interface-specific definitions are processed before global -definitions. As expected, the prefix definition is matching if -the network prefix is a subnet of the prefix in prefix -definition. -<P> -<DT><CODE>rdnss { <I>options</I> }</CODE><DD><P>RDNSS definitions allow to specify a list of advertised -recursive DNS servers together with their options. As options -are seldom necessary, there is also a short variant <CODE>rdnss -<I>address</I></CODE> that just specifies one DNS server. Multiple -definitions are cumulative. RDNSS definitions may also be -interface-specific when used inside interface options. By -default, interface uses both global and interface-specific -options, but that can be changed by <CODE>rdnss local</CODE> option. -<P> -<DT><CODE>dnssl { <I>options</I> }</CODE><DD><P>DNSSL definitions allow to specify a list of advertised DNS -search domains together with their options. Like <CODE>rdnss</CODE> -above, multiple definitions are cumulative, they can be used -also as interface-specific options and there is a short -variant <CODE>dnssl <I>domain</I></CODE> that just specifies one DNS -search domain. -<P> -<A NAME="dsc-trigger"></A> -<DT><CODE>trigger <I>prefix</I></CODE><DD><P>RAdv protocol could be configured to change its behavior based -on availability of routes. When this option is used, the -protocol waits in suppressed state until a <I>trigger route</I> -(for the specified network) is exported to the protocol, the -protocol also returnsd to suppressed state if the -<I>trigger route</I> disappears. Note that route export depends -on specified export filter, as usual. This option could be -used, e.g., for handling failover in multihoming scenarios. -<P>During suppressed state, router advertisements are generated, -but with some fields zeroed. Exact behavior depends on which -fields are zeroed, this can be configured by -<CODE>sensitive</CODE> option for appropriate fields. By default, just -<CODE>default lifetime</CODE> (also called <CODE>router lifetime</CODE>) is -zeroed, which means hosts cannot use the router as a default -router. <CODE>preferred lifetime</CODE> and <CODE>valid lifetime</CODE> could -also be configured as <CODE>sensitive</CODE> for a prefix, which would -cause autoconfigured IPs to be deprecated or even removed. -</DL> -<P> -<P>Interface specific options: -<P> -<DL> -<DT><CODE>max ra interval <I>expr</I></CODE><DD><P>Unsolicited router advertisements are sent in irregular time -intervals. This option specifies the maximum length of these -intervals, in seconds. Valid values are 4-1800. Default: 600 -<P> -<DT><CODE>min ra interval <I>expr</I></CODE><DD><P>This option specifies the minimum length of that intervals, in -seconds. Must be at least 3 and at most 3/4 * <CODE>max ra interval</CODE>. -Default: about 1/3 * <CODE>max ra interval</CODE>. -<P> -<DT><CODE>min delay <I>expr</I></CODE><DD><P>The minimum delay between two consecutive router advertisements, -in seconds. Default: 3 -<P> -<DT><CODE>managed <I>switch</I></CODE><DD><P>This option specifies whether hosts should use DHCPv6 for -IP address configuration. Default: no -<P> -<DT><CODE>other config <I>switch</I></CODE><DD><P>This option specifies whether hosts should use DHCPv6 to -receive other configuration information. Default: no -<P> -<DT><CODE>link mtu <I>expr</I></CODE><DD><P>This option specifies which value of MTU should be used by -hosts. 0 means unspecified. Default: 0 -<P> -<DT><CODE>reachable time <I>expr</I></CODE><DD><P>This option specifies the time (in milliseconds) how long -hosts should assume a neighbor is reachable (from the last -confirmation). Maximum is 3600000, 0 means unspecified. -Default 0. -<P> -<DT><CODE>retrans timer <I>expr</I></CODE><DD><P>This option specifies the time (in milliseconds) how long -hosts should wait before retransmitting Neighbor Solicitation -messages. 0 means unspecified. Default 0. -<P> -<DT><CODE>current hop limit <I>expr</I></CODE><DD><P>This option specifies which value of Hop Limit should be used -by hosts. Valid values are 0-255, 0 means unspecified. Default: 64 -<P> -<DT><CODE>default lifetime <I>expr</I> [sensitive <I>switch</I>]</CODE><DD><P>This option specifies the time (in seconds) how long (after -the receipt of RA) hosts may use the router as a default -router. 0 means do not use as a default router. For -<CODE>sensitive</CODE> option, see -<A HREF="#dsc-trigger">trigger</A>. -Default: 3 * <CODE>max ra interval</CODE>, <CODE>sensitive</CODE> yes. -<P> -<DT><CODE>rdnss local <I>switch</I></CODE><DD><P>Use only local (interface-specific) RDNSS definitions for this -interface. Otherwise, both global and local definitions are -used. Could also be used to disable RDNSS for given interface -if no local definitons are specified. Default: no. -<P> -<DT><CODE>dnssl local <I>switch</I></CODE><DD><P>Use only local DNSSL definitions for this interface. See -<CODE>rdnss local</CODE> option above. Default: no. -</DL> -<P> -<P> -<P>Prefix specific options: -<P> -<DL> -<DT><CODE>skip <I>switch</I></CODE><DD><P>This option allows to specify that given prefix should not be -advertised. This is useful for making exceptions from a -default policy of advertising all prefixes. Note that for -withdrawing an already advertised prefix it is more useful to -advertise it with zero valid lifetime. Default: no -<P> -<DT><CODE>onlink <I>switch</I></CODE><DD><P>This option specifies whether hosts may use the advertised -prefix for onlink determination. Default: yes -<P> -<DT><CODE>autonomous <I>switch</I></CODE><DD><P>This option specifies whether hosts may use the advertised -prefix for stateless autoconfiguration. Default: yes -<P> -<DT><CODE>valid lifetime <I>expr</I> [sensitive <I>switch</I>]</CODE><DD><P>This option specifies the time (in seconds) how long (after -the receipt of RA) the prefix information is valid, i.e., -autoconfigured IP addresses can be assigned and hosts with -that IP addresses are considered directly reachable. 0 means -the prefix is no longer valid. For <CODE>sensitive</CODE> option, see -<A HREF="#dsc-trigger">trigger</A>. Default: 86400 (1 day), <CODE>sensitive</CODE> no. -<P> -<DT><CODE>preferred lifetime <I>expr</I> [sensitive <I>switch</I>]</CODE><DD><P>This option specifies the time (in seconds) how long (after -the receipt of RA) IP addresses generated from the prefix -using stateless autoconfiguration remain preferred. For -<CODE>sensitive</CODE> option, see -<A HREF="#dsc-trigger">trigger</A>. -Default: 14400 (4 hours), <CODE>sensitive</CODE> no. -</DL> -<P> -<P> -<P>RDNSS specific options: -<P> -<DL> -<DT><CODE>ns <I>address</I></CODE><DD><P>This option specifies one recursive DNS server. Can be used -multiple times for multiple servers. It is mandatory to have -at least one <CODE>ns</CODE> option in <CODE>rdnss</CODE> definition. -<P> -<DT><CODE>lifetime [mult] <I>expr</I></CODE><DD><P>This option specifies the time how long the RDNSS information -may be used by clients after the receipt of RA. It is -expressed either in seconds or (when <CODE>mult</CODE> is used) in -multiples of <CODE>max ra interval</CODE>. Note that RDNSS information -is also invalidated when <CODE>default lifetime</CODE> expires. 0 -means these addresses are no longer valid DNS servers. -Default: 3 * <CODE>max ra interval</CODE>. -</DL> -<P> -<P> -<P>DNSSL specific options: -<P> -<DL> -<DT><CODE>domain <I>address</I></CODE><DD><P>This option specifies one DNS search domain. Can be used -multiple times for multiple domains. It is mandatory to have -at least one <CODE>domain</CODE> option in <CODE>dnssl</CODE> definition. -<P> -<DT><CODE>lifetime [mult] <I>expr</I></CODE><DD><P>This option specifies the time how long the DNSSL information -may be used by clients after the receipt of RA. Details are -the same as for RDNSS <CODE>lifetime</CODE> option above. -Default: 3 * <CODE>max ra interval</CODE>. -</DL> -<P> -<P> -<H3>Example</H3> - -<P> -<HR> -<PRE> -protocol radv { - interface "eth2" { - max ra interval 5; # Fast failover with more routers - managed yes; # Using DHCPv6 on eth2 - prefix ::/0 { - autonomous off; # So do not autoconfigure any IP - }; - }; - - interface "eth*"; # No need for any other options - - prefix 2001:0DB8:1234::/48 { - preferred lifetime 0; # Deprecated address range - }; - - prefix 2001:0DB8:2000::/48 { - autonomous off; # Do not autoconfigure - }; - - rdnss 2001:0DB8:1234::10; # Short form of RDNSS - - rdnss { - lifetime mult 10; - ns 2001:0DB8:1234::11; - ns 2001:0DB8:1234::12; - }; - - dnssl { - lifetime 3600; - domain "abc.com"; - domain "xyz.com"; - }; -} -</PRE> -<HR> -<P> -<H2><A NAME="ss6.8">6.8</A> <A HREF="bird.html#toc6.8">RIP</A> -</H2> - -<H3>Introduction</H3> - -<P>The RIP protocol (also sometimes called Rest In Pieces) is a simple protocol, where each router broadcasts (to all its neighbors) -distances to all networks it can reach. When a router hears distance to another network, it increments -it and broadcasts it back. Broadcasts are done in regular intervals. Therefore, if some network goes -unreachable, routers keep telling each other that its distance is the original distance plus 1 (actually, plus -interface metric, which is usually one). After some time, the distance reaches infinity (that's 15 in -RIP) and all routers know that network is unreachable. RIP tries to minimize situations where -counting to infinity is necessary, because it is slow. Due to infinity being 16, you can't use -RIP on networks where maximal distance is higher than 15 hosts. You can read more about RIP at -<A HREF="http://www.ietf.org/html.charters/rip-charter.html">http://www.ietf.org/html.charters/rip-charter.html</A>. Both IPv4 -(RFC 1723 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc1723.txt">ftp://ftp.rfc-editor.org/in-notes/rfc1723.txt</A>) -and IPv6 (RFC 2080 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc2080.txt">ftp://ftp.rfc-editor.org/in-notes/rfc2080.txt</A>) versions of RIP are supported by BIRD, historical RIPv1 (RFC 1058 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc1058.txt">ftp://ftp.rfc-editor.org/in-notes/rfc1058.txt</A>)is -not currently supported. RIPv4 MD5 authentication (RFC 2082 -<A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc2082.txt">ftp://ftp.rfc-editor.org/in-notes/rfc2082.txt</A>) is supported. -<P> -<P>RIP is a very simple protocol, and it has a lot of shortcomings. Slow -convergence, big network load and inability to handle larger networks -makes it pretty much obsolete. (It is still usable on very small networks.) -<P> -<H3>Configuration</H3> - -<P>In addition to options common for all to other protocols, RIP supports the following ones: -<P> -<DL> -<DT><CODE>authentication none|plaintext|md5</CODE><DD><P>selects authentication method to be used. <CODE>none</CODE> means that -packets are not authenticated at all, <CODE>plaintext</CODE> means that a plaintext password is embedded -into each packet, and <CODE>md5</CODE> means that packets are authenticated using a MD5 cryptographic -hash. If you set authentication to not-none, it is a good idea to add <CODE>password</CODE> -section. Default: none. -<P> -<DT><CODE>honor always|neighbor|never </CODE><DD><P>specifies when should requests for dumping routing table -be honored. (Always, when sent from a host on a directly connected -network or never.) Routing table updates are honored only from -neighbors, that is not configurable. Default: never. -</DL> -<P> -<P>There are some options that can be specified per-interface: -<P> -<DL> -<DT><CODE>metric <I>num</I></CODE><DD><P>This option specifies the metric of the interface. Valid -<P> -<DT><CODE>mode multicast|broadcast|quiet|nolisten|version1</CODE><DD><P>This option selects the mode for RIP to work in. If nothing is -specified, RIP runs in multicast mode. <CODE>version1</CODE> is -currently equivalent to <CODE>broadcast</CODE>, and it makes RIP talk -to a broadcast address even through multicast mode is -possible. <CODE>quiet</CODE> option means that RIP will not transmit -any periodic messages to this interface and <CODE>nolisten</CODE> -means that RIP will send to this interface butnot listen to it. -<P> -<DT><CODE>ttl security [<I>switch</I> | tx only]</CODE><DD><P>TTL security is a feature that protects routing protocols -from remote spoofed packets by using TTL 255 instead of TTL 1 -for protocol packets destined to neighbors. Because TTL is -decremented when packets are forwarded, it is non-trivial to -spoof packets with TTL 255 from remote locations. -<P>If this option is enabled, the router will send RIP packets -with TTL 255 and drop received packets with TTL less than -255. If this option si set to <CODE>tx only</CODE>, TTL 255 is used -for sent packets, but is not checked for received -packets. Such setting does not offer protection, but offers -compatibility with neighbors regardless of whether they use -ttl security. -<P>Note that for RIPng, TTL security is a standard behavior -(required by RFC 2080), but BIRD uses <CODE>tx only</CODE> by -default, for compatibility with older versions. For IPv4 RIP, -default value is no. -<P> -<DT><CODE>tx class|dscp|priority <I>num</I></CODE><DD><P>These options specify the ToS/DiffServ/Traffic class/Priority -of the outgoing RIP packets. See -<A HREF="bird-3.html#dsc-prio">tx class</A> common option for detailed description. -</DL> -<P> -<P>The following options generally override behavior specified in RFC. If you use any of these -options, BIRD will no longer be RFC-compliant, which means it will not be able to talk to anything -other than equally configured BIRD. I have warned you. -<P> -<DL> -<DT><CODE>port <I>number</I></CODE><DD><P>selects IP port to operate on, default 520. (This is useful when testing BIRD, if you -set this to an address >1024, you will not need to run bird with UID==0). -<P> -<DT><CODE>infinity <I>number</I></CODE><DD><P>selects the value of infinity, default is 16. Bigger values will make protocol convergence -even slower. -<P> -<DT><CODE>period <I>number</I></CODE><DD><P>specifies the number of seconds between periodic updates. Default is 30 seconds. A lower -number will mean faster convergence but bigger network -load. Do not use values lower than 12. -<P> -<DT><CODE>timeout time <I>number</I></CODE><DD><P>specifies how old route has to be to be considered unreachable. Default is 4*<CODE>period</CODE>. -<P> -<DT><CODE>garbage time <I>number</I></CODE><DD><P>specifies how old route has to be to be discarded. Default is 10*<CODE>period</CODE>. -</DL> -<P> -<H3>Attributes</H3> - -<P>RIP defines two route attributes: -<P> -<DL> -<DT><CODE>int <CODE>rip_metric</CODE></CODE><DD><P>RIP metric of the route (ranging from 0 to <CODE>infinity</CODE>). -When routes from different RIP instances are available and all of them have the same -preference, BIRD prefers the route with lowest <CODE>rip_metric</CODE>. -When importing a non-RIP route, the metric defaults to 5. -<P> -<DT><CODE>int <CODE>rip_tag</CODE></CODE><DD><P>RIP route tag: a 16-bit number which can be used -to carry additional information with the route (for example, an originating AS number -in case of external routes). When importing a non-RIP route, the tag defaults to 0. -</DL> -<P> -<H3>Example</H3> - -<P> -<HR> -<PRE> -protocol rip MyRIP_test { - debug all; - port 1520; - period 12; - garbage time 60; - interface "eth0" { metric 3; mode multicast; }; - interface "eth*" { metric 2; mode broadcast; }; - honor neighbor; - authentication none; - import filter { print "importing"; accept; }; - export filter { print "exporting"; accept; }; -} -</PRE> -<HR> -<P> -<H2><A NAME="ss6.9">6.9</A> <A HREF="bird.html#toc6.9">Static</A> -</H2> - -<P>The Static protocol doesn't communicate with other routers in the network, -but instead it allows you to define routes manually. This is often used for -specifying how to forward packets to parts of the network which don't use -dynamic routing at all and also for defining sink routes (i.e., those -telling to return packets as undeliverable if they are in your IP block, -you don't have any specific destination for them and you don't want to send -them out through the default route to prevent routing loops). -<P> -<P>There are five types of static routes: `classical' routes telling -to forward packets to a neighboring router, multipath routes -specifying several (possibly weighted) neighboring routers, device -routes specifying forwarding to hosts on a directly connected network, -recursive routes computing their nexthops by doing route table lookups -for a given IP and special routes (sink, blackhole etc.) which specify -a special action to be done instead of forwarding the packet. -<P> -<P>When the particular destination is not available (the interface is down or -the next hop of the route is not a neighbor at the moment), Static just -uninstalls the route from the table it is connected to and adds it again as soon -as the destination becomes adjacent again. -<P> -<P>The Static protocol does not have many configuration options. The -definition of the protocol contains mainly a list of static routes: -<P> -<DL> -<DT><CODE>route <I>prefix</I> via <I>ip</I></CODE><DD><P>Static route through -a neighboring router. -<DT><CODE>route <I>prefix</I> multipath via <I>ip</I> [weight <I>num</I>] [via ...]</CODE><DD><P>Static multipath route. Contains several nexthops (gateways), possibly -with their weights. -<DT><CODE>route <I>prefix</I> via <I>"interface"</I></CODE><DD><P>Static device -route through an interface to hosts on a directly connected network. -<DT><CODE>route <I>prefix</I> recursive <I>ip</I></CODE><DD><P>Static recursive route, -its nexthop depends on a route table lookup for given IP address. -<DT><CODE>route <I>prefix</I> blackhole|unreachable|prohibit</CODE><DD><P>Special routes -specifying to silently drop the packet, return it as unreachable or return -it as administratively prohibited. First two targets are also known -as <CODE>drop</CODE> and <CODE>reject</CODE>. -<P> -<DT><CODE>check link <I>switch</I></CODE><DD><P>If set, hardware link states of network interfaces are taken -into consideration. When link disappears (e.g. ethernet cable -is unplugged), static routes directing to that interface are -removed. It is possible that some hardware drivers or -platforms do not implement this feature. Default: off. -<P> -<DT><CODE>igp table <I>name</I></CODE><DD><P>Specifies a table that is used -for route table lookups of recursive routes. Default: the -same table as the protocol is connected to. -</DL> -<P> -<P>Static routes have no specific attributes. -<P> -<P>Example static config might look like this: -<P> -<P> -<HR> -<PRE> -protocol static { - table testable; # Connect to a non-default routing table - route 0.0.0.0/0 via 198.51.100.130; # Default route - route 10.0.0.0/8 multipath # Multipath route - via 198.51.100.10 weight 2 - via 198.51.100.20 - via 192.0.2.1; - route 203.0.113.0/24 unreachable; # Sink route - route 10.2.0.0/24 via "arc0"; # Secondary network -} -</PRE> -<HR> -<P> -<HR> -<A HREF="bird-7.html">Next</A> -<A HREF="bird-5.html">Previous</A> -<A HREF="bird.html#toc6">Contents</A> -</BODY> -</HTML> |