# Learn routes

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

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

```toml
[[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](/docs/guides/transit.md#filters) instead of `"all"`.

## Look them up

```sh
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
```

```txt
   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](/docs/concepts/how-it-works.md#best-path).

## 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](/docs/guides/kernel-routes.md). `install = false` on a neighbor keeps its routes
in the RIB but out of the kernel.