[c-nsp] bgp weird issue

[mm-tech]

Hi guys,

I'm having this weird issue with BGP and I was wondering if you could help.

Topology:
- 2 X cisco 1800 series routers, both connected to 2 different ISPs:
Router1 -> ISPA and RouterB -> ISPB
- Router1 and Router2 are directly connected
- on Router1 receiving only the default route from ISPA
- on Router2 receiving customer routes from ISPB
- announcing a /23 address block through both ISPA and ISPB (91.195.X.X)

The connectivity with ISPA is being done using a /30 subnet
(interconnected subnets): ISPA(172.28.164.17/30) ->
router1(172.28.164.18/30). Also, I have a /29 public address space on
router1 (62.217.X.X) routed through the /30 subnet. The default gw for
Router1 received via eBGP is 62.217.w.w and I have added a static route
for it:
 ip route 62.217.w.w 255.255.255.255 172.28.164.17

That's how ISPA has it's network configured and I cannot change anything.

The connectivity with ISPB is simple: only a /32 ip address on Router2:
89.149.X.X

BGP config Router1:

router bgp myASN
 no synchronization
 bgp router-id 62.217.X.X
 bgp log-neighbor-changes
 network 91.195.X.0 mask 255.255.254.0
 neighbor 62.217.X.X remote-as ASN_ISPA
 neighbor 62.217.X.X ebgp-multihop 8
 neighbor 62.217.X.X soft-reconfiguration inbound
 neighbor 62.217.X.X filter-list 10 out
 neighbor 91.195.y.1 remote-as myASN
 neighbor 91.195.y.1 next-hop-self
 no auto-summary

ip as-path access-list 10 permit ^$

BGP config Router2:

router bgp myASN
 no synchronization
 bgp router-id 89.149.X.X
 bgp log-neighbor-changes
 network 91.195.X.0 mask 255.255.254.0
 neighbor 89.149.X.X remote-as ASN_ISPB
 neighbor 89.149.X.X filter-list 10 out
 neighbor 91.195.z.1 remote-as myASN
 neighbor 91.195.z.1 next-hop-self
 no auto-summary

ip as-path access-list 10 permit ^$

The issue is after I configure the iBGP relationship between Router1 and
Router2: connectivity to the 62.217.X.X/29 subnet on Router1 is lost. It
cannot be pinged anymore from outside. The 91.195.X.X/23 is announced
correctly through both ISPs and any IP in this /23 subnet is pingable from
outside. They only problem is with the 62.217.X.X/29 block that becomes
unreachable after configuring the iBGP relationship and I don't understand
why this is happening.

Sorry for the long post and I hope you'll give me some hints -:)

Thanks,
John