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Guides / Learn routes

Learn routes

Keep the routes neighbors send, limit how many, and look them up.

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By default ansage stores nothing a neighbor sends (import = "none", RFC 8212). Learned routes are useful to look at with ansage show rib, and with [kernel] they go into the Linux routing table, e.g. to send a server's outgoing traffic the way BGP says.

Keep a neighbor's routes

[[neighbor]]
address = "10.0.0.1"
asn = 64501
import = "all"
max_prefixes_ipv4 = 1000     # optional limits, see below
max_prefixes_ipv6 = 1000

Apply with ansage reload; the session stays up and ansage asks the neighbor to send its routes again (route refresh). To keep only some routes, import names a filter instead of "all".

Look them up

ansage show rib                    # best routes, at most 1000 per family
ansage show rib --family ipv6 --limit 50
ansage show rib 198.51.100.0/24    # every candidate for this exact prefix
ansage show rib 198.51.100.7       # the longest prefix containing this address
   PREFIX              SOURCE     NEXT HOP     AS PATH  ORIGIN  LOCAL PREF  MED  COMMUNITIES
*  192.0.2.0/24        local      -            (empty)  igp     -           -    -
*  198.51.100.0/24     127.0.0.1  127.0.0.1    64501    igp     -           -    -
*  2001:db8:1::/48     local      -            (empty)  igp     -           -    -
*  2001:db8:ffff::/48  127.0.0.1  2001:db8::2  64501    igp     -           -    -

* marks the best route, local our own prefixes. How ansage picks the best route is in How ansage works.

Limit what a neighbor may send

max_prefixes_ipv4 / max_prefixes_ipv6 protect ansage from a neighbor that suddenly sends a full table:

  • At 90 % of the limit ansage logs a warning (once per session).
  • Above the limit ansage closes the session with Cease / Maximum Number of Prefixes Reached (RFC 4486) and connects again after max_prefix_restart seconds (default 300).

Routes ansage does not keep

  • Routes whose AS path contains our own AS (a loop).
  • Routes with broken attributes: treated as a withdraw or the attribute is discarded (RFC 7606); counted in ansage show peer under Problems and in ansage_peer_malformed_updates_total.

Into the kernel

Add a [kernel] section to install the best learned routes, see Kernel routes. install = false on a neighbor keeps its routes in the RIB but out of the kernel.

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