ospf external type 2 and igp_metric

[Dave Johnson]

Hi,

I'm trying to get igp_metric to work for iBGP based on an OSPF
metric.


Here's my setup:

I'm using OSPF for an IGP, eBGP on border machines for internet
routes, and iBGP within to select the best border for traffic not
covered internally with OSPF.

OSPF is using connected IPs for broadcast and tunnel interfaces and
each machine also includes a static loopback IP for general
communication including iBGP.

iBGP is setup to communicate from/to each machine's loopback IP to be
immune from any connected network or tunnel disruption.  OSPF is
propigating reachability to each loopback just ok.


I would like to make use of the iBGP igp_metric as a tie-breaker if
BGP gets down that far in the route selection process, however I can't
seem to get BGP to pick up the OSPF metric for other machine's
loopbacks.


The loopback is being imported using a proto direct as it's simply
from Linux's lo interface:

  root at archer:~# birdc show route 10.10.10.30/32 all
  BIRD 1.6.6 ready.
  10.10.10.30/32     dev lo [direct1 11:14:34] * (240)
          Type: device unicast univ
  root at archer:~# 

When viewed from another machine via ospf, this route now shows as an
external type 2 route.  The OSPF.metric1 of 26 is correct:

  root at ganges:~# birdc show route 10.10.10.30/32 all
  BIRD 1.6.6 ready.
  10.10.10.30/32     via 10.10.13.1 on tun13 [ospf1 11:14:35] * E2 (150/26/10000) [10.10.10.30]
          Type: OSPF-E2 unicast univ
          OSPF.metric1: 26
          OSPF.metric2: 10000
          OSPF.tag: 0x00000000
          OSPF.router_id: 10.10.10.30
  root at ganges:~# 


So when I'm trying to use iBGP this OSPF.metric1 should be taken into
account as the igp_metric right?

I would expect this to work based on rt_get_igp_metric() however that
function doesn't include pulling an OSPF metric from RTS_OSPF_EXT2
type routes (only type 1).

  #ifdef CONFIG_OSPF
    if ((a->source == RTS_OSPF) ||
        (a->source == RTS_OSPF_IA) ||
        (a->source == RTS_OSPF_EXT1))
      return rt->u.ospf.metric1;
  #endif

Is there some reason RTS_OSPF_EXT2 isn't included here?  Even
RTS_OSPF_EXT2 routes have an OSPF.metric1.


For example, here's an arbitrary internet route that has equal local
preference, equal path lengths, both IGP, no MED, etc..  so igp would
be a deciding factor here.

10.10.10.30 and 10.10.10.31 are border routers, and this command is
run on a interior router:


  root at ganges:~# birdc show route 128.0.128.0/20 table internet all
  BIRD 1.6.6 ready.
  128.0.128.0/20     via 10.10.13.1 on tun13 [bgp_archer 14:50:00 from 10.10.10.30] * (100/?) [AS25513i]
        Type: BGP unicast univ
        BGP.origin: IGP
        BGP.as_path: 64515 65534 20473 8359 25513
        BGP.next_hop: 10.10.10.30
        BGP.local_pref: 100
        BGP.community: (20473,200) (64515,44)
                   via 10.10.13.1 on tun13 [bgp_reliant 14:50:00 from 10.10.10.31] (100/?) [AS25513i]
        Type: BGP unicast univ
        BGP.origin: IGP
        BGP.as_path: 65002 65001 21700 8359 25513
        BGP.next_hop: 10.10.10.31
        BGP.local_pref: 100
        BGP.community: (0,199) (8359,100) (8359,5500) (8359,55277)
        BGP.large_community: (21700, 101, 3) (21700, 102, 840) (21700, 103, 1)
  root at ganges:~# birdc show route 10.10.10.30/32  all
  BIRD 1.6.6 ready.
  10.10.10.30/32     via 10.10.13.1 on tun13 [ospf1 11:14:35] * E2 (150/26/10000) [10.10.10.30]
        Type: OSPF-E2 unicast univ
        OSPF.metric1: 26
        OSPF.metric2: 10000
        OSPF.tag: 0x00000000
        OSPF.router_id: 10.10.10.30
  root at ganges:~# birdc show route 10.10.10.31/32  all
  BIRD 1.6.6 ready.
  10.10.10.31/32     via 10.10.13.1 on tun13 [ospf1 2021-07-26] * E2 (150/15/10000) [10.10.10.31]
        Type: OSPF-E2 unicast univ
        OSPF.metric1: 15
        OSPF.metric2: 10000
        OSPF.tag: 0x00000000
        OSPF.router_id: 10.10.10.31
  root at ganges:~# 

Note that the igp_metric is '?' for both, and the route via
10.10.10.30 is selected even though the OSPF metric is higher for that.


I've tried to work around type by doing 2 things:

1st, trying to get the routes to show up as an external type 1 instead
of type 2, but I dont see how in the config.

2nd, setting igp_metric manually in an import/export filter, however
that doesn't seem to work either.

I'm using debian's bird 1.6.


Thoughts?


-- 
Dave