[c-nsp] Believing iBGP over eBGP?

[Patrick Bohannon]

I'm having an interesting problem with eBGP and iBGP:

I am multihomed and accepting only default route from my eBGP peers.  Both
peers are sending the default route just fine:

BorderA and BorderB do iBGP with each other, and each do eBGP with one of
our upstream providers.  I've indicated in the appropriate places below the
relationship each has to its peer(s).

Total number of prefixes 1 
borderB#sh ip bgp neigh x.x.x.x routes          
BGP table version is 128, local router ID is x.x.x.x
Status codes: s suppressed, d damped, h history, * valid, > best, i -
internal
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
*  0.0.0.0          x.x.x.x (eBGP peer)                    0 4279 4279 4279
7132 i


Total number of prefixes 1 
borderB#

My problem is that on the edge, I am believing the default route from my
other edge router (we'll call it borderA) which is being delivered via iBGP
instead of the eBGP delivered route.

borderB#sh ip route 0.0.0.0
Routing entry for 0.0.0.0/0, supernet
  Known via "bgp 4279", distance 200, metric 0, candidate default path
  Tag 4323, type internal
  Last update from x.x.x.x (borderA's eBGP peer) 00:27:42 ago
  Routing Descriptor Blocks:
  * x.x.x.x (borderA's eBGP peer), from x.x.x.x (borderA), 00:27:42 ago
      Route metric is 0, traffic share count is 1
      AS Hops 1

BorderA is also getting just a default route from its eBGP peer, which is
probably implied here already.  Shouldn't the administrative distance of 20
associated with eBGP-learned routes supercede the administrative distance of
200 associated with iBGP-learned routes?

Here's more:

borderB#sh ip bgp 0.0.0.0 
BGP routing table entry for 0.0.0.0/0, version 128
Paths: (3 available, best #3, table Default-IP-Routing-Table)
  Not advertised to any peer
  4279 4279 4279 7132
    x.x.x.x (borderB's eBGP peer) from x.x.x.x (borderB's eBGP peer)
(x.x.x.x)
      Origin IGP, localpref 100, valid, external
  7132, (received-only)
    x.x.x.x (borderB's eBGP peer) from x.x.x.x (borderB's eBGP peer)
(x.x.x.x)
      Origin IGP, localpref 100, valid, external
  4323
    x.x.x.x (borderA's eBGP peer) (metric 20) from x.x.x.x (borderA)
(x.x.x.x)
      Origin IGP, localpref 100, valid, internal, best
borderB#

Thanks!