diff options
| author | Ondrej Filip <feela@network.cz> | 2013-08-15 20:20:05 +0200 |
|---|---|---|
| committer | Ondrej Filip <feela@network.cz> | 2013-08-15 20:20:05 +0200 |
| commit | e628cad0ca9eb7d9bf4141e57201169c46faa661 (patch) | |
| tree | 114205a135df8999d3efd9080670e1873651338f | |
| parent | 6d90e57332e102e261d69a1a05dfaa19fb31d933 (diff) | |
BGP option 'route limit' is marked as obsolete. 'import limit' should be used instead.
| -rw-r--r-- | doc/bird-6.html | 1731 |
1 files changed, 1731 insertions, 0 deletions
diff --git a/doc/bird-6.html b/doc/bird-6.html new file mode 100644 index 00000000..d21209ee --- /dev/null +++ b/doc/bird-6.html @@ -0,0 +1,1731 @@ +<!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> |