[c-nsp] RIB failure : Higher admin distance

[Andy Ashley]

Hi all,

We have two routers at site A and one at site B, both routers at site A 
have an uplink each to a transit provider. There are two Layer 3 core 
switches below the two routers.
The router at site B has an uplink to another transit provider and there 
is also a private link between the routers at site A and B.

We run OSPF between all the routers/switches, also over the private link 
between site A and B and use "redistribute static subnets"
There is iBGP running between the routers/switches and an iBGP session 
runs over a GRE tunnel between site A and B so that if the private link 
breaks,
the traffic will go out over the transit providers and they will still 
talk to each other, etc (same AS in path)

There is an issue:
We have a /20 that is announced from site A and we split this up into 3 
longer prefixes (/21, /22 and /24). We want to use the /24 for site B 
and announce the /21 and /23 from site A.
However, when we remove the aggregate /20 route at site A and put a 
static in for the /24, it is not announced to our transit providers at 
site B due to rib failure.

(Site A Router)#sh ip bgp rib-failure
Network            Next Hop                      
RIB-failure                              RIB-NH Matches
X.X.X.X/20       (Layer 3 Core Switch)   Higher admin 
distance              n/a

etc etc (there is a list of all of our static routes here)

(Site A Router)#show ip bgp (Slash /24 in question)
BGP routing table entry for (Slash /24 in question)/24, version 4317116
Paths: (1 available, best #1, table default, not advertised to EBGP 
peer, RIB-failure(17))
  Not advertised to any peer
  (65003)
    (Site B Router Tunnel IP) (metric 1002) from (Site A Router IP) 
(X.X.X.X)
      Origin IGP, metric 0, localpref 100, valid,  confed-internal, best
      Community: ASN:200 no-export

(Site A Router)#show ip route (Slash /24 in question)
Routing entry for (Slash /24 in question)/24
  Known via "ospf 100", distance 110, metric 20, type extern 2, forward 
metric 2
  Last update from (Site A Router Private Link Interface) on 
GigabitEthernet0/1.8, 5w5d ago
  Routing Descriptor Blocks:
  * (Site A Router Private Link Interface), from (Site B Router), 5w5d 
ago, via GigabitEthernet0/1.8
      Route metric is 20, traffic share count is 1

The rib failure condition seems to be persistent.

Any ideas how to overcome this issue?

Thanks.
Andy.


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