diff options
Diffstat (limited to 'doc/bird.sgml')
| -rw-r--r-- | doc/bird.sgml | 53 |
1 files changed, 45 insertions, 8 deletions
diff --git a/doc/bird.sgml b/doc/bird.sgml index 3f2e46e7..86ae5b0d 100644 --- a/doc/bird.sgml +++ b/doc/bird.sgml @@ -215,7 +215,27 @@ an <it/import/ filter checks routes in the opposite direction. When the routing table gets a route from a protocol, it recalculates the selected route and broadcasts it to all protocols connected to the table. The protocols typically send the update to other routers -in the network. +in the network. Note that although most protocols are interested +in receiving just selected routes, some protocols (e.g. the <cf/Pipe/ +protocol) receive and process all entries in routing tables (accepted +by filters). + +<p><label id="dsc-sorted">Usually, a routing table just chooses a +selected route from a list of entries for one network. But if the +<cf/sorted/ option is activated, these lists of entries are kept +completely sorted (according to preference or some protocol-dependent +metric). + +This is needed for some features of some protocols +(e.g. <cf/secondary/ option of BGP protocol, which allows to accept +not just a selected route, but the first route (in the sorted list) +that is accepted by filters), but it is incompatible with some other +features (e.g. <cf/deterministic med/ option of BGP protocol, which +activates a way of choosing selected route that cannot be described +using comparison and ordering). Minor advantage is that routes are +shown sorted in <cf/show route/, minor disadvantage is that it is +slightly more computationally expensive. + <chapt>Configuration @@ -354,11 +374,14 @@ protocol rip { defaults are here for a compatibility with older versions and might change in the future. - <tag>table <m/name/</tag> Create a new routing table. The default - routing table is created implicitly, other routing tables have - to be added by this command. + <tag>table <m/name/ [sorted]</tag> + Create a new routing table. The default routing table is + created implicitly, other routing tables have to be added by + this command. Option <cf/sorted/ can be used to enable + sorting of routes, see <ref id="dsc-sorted" name="sorted table"> + description for details. - <tag>roa table [ { roa table options ... } ] <m/name/</tag> + <tag>roa table <m/name/ [ { roa table options ... } ]</tag> Create a new ROA (Route Origin Authorization) table. ROA tables can be used to validate route origination of BGP routes. A ROA table contains ROA entries, each consist of a @@ -1270,8 +1293,10 @@ for each neighbor using the following configuration parameters: 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. Default: - <cf/direct/ for singlehop eBGP, <cf/recursive/ otherwise. + handle well nontrivial iBGP setups and multihop. Recursive + mode is incompatible with <ref id="dsc-sorted" name="sorted + tables">. Default: <cf/direct/ for singlehop eBGP, + <cf/recursive/ otherwise. <tag>igp table <m/name/</tag> Specifies a table that is used as an IGP routing table. Default: the same as the table BGP is @@ -1317,6 +1342,16 @@ for each neighbor using the following configuration parameters: attributes to be transparent (for example does not prepend its AS number to AS PATH attribute and keeps MED attribute). Default: disabled. + <tag>secondary <m/switch/</tag> 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 + <ref id="dsc-sorted" name="sorted">. Default: off. + <tag>enable route refresh <m/switch/</tag> When BGP speaker changes its import filter, it has to re-examine all routes received from its neighbor against the new filter. As these @@ -1422,7 +1457,9 @@ for each neighbor using the following configuration parameters: 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 <cf/med metric/ option. Default: off. + behavior is to use <cf/med metric/ option. This option is + incompatible with <ref id="dsc-sorted" name="sorted tables">. + Default: off. <tag>igp metric <m/switch/</tag> Enable comparison of internal distances to boundary routers during best route selection. Default: on. |