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iBGP Peering Issue

when issuing sh ip bgp neigh <IP> i am getting header sync problems and the peering stays IDLE - see below for output

Any help is appreciated before logging a TAC case :-)

RP/0/RP1/CPU0:ND-NEO-RCRS1-ISP-DMZ-R1C11#sh ip bgp neig

Tue Jun 22 17:10:03.580 GMT

BGP neighbor is

Remote AS 37168, local AS 37168, internal link

Description: IBGP_Esher_Neotel

Remote router ID

Cluster ID 10

  BGP state = Connect

  Last read 00:00:03, hold time is 180, keepalive interval is 60 seconds

  Configured hold time: 180, keepalive: 60, min acceptable hold time: 3

  Last write 00:01:26, Last write before reset 00:01:43

  Last write pulse rcvd  Jun 22 17:09:47.913 last full not set pulse count 4

  Socket not armed for io, armed for read, armed for write

  Precedence: internet

  Received 0 messages, 0 notifications, 0 in queue

  Sent 3 messages, 2 notifications, 0 in queue

  Minimum time between advertisement runs is 0 secs

For Address Family: IPv4 Unicast

  BGP neighbor version 0

  Update group: 0.2

  Route-Reflector Client

  Inbound soft reconfiguration allowed

  Route refresh request: received 0, sent 0

  0 accepted prefixes, 0 are bestpaths

  Prefix advertised 0, suppressed 0, withdrawn 0, maximum limit 524288

  Threshold for warning message 75%

  An EoR was not received during read-only mode

  Last ack version 1, Last synced ack version 0

  Outstanding version objects: current 0, max 0

  Connections established 0; dropped 0

  Last reset 00:01:26, due to BGP Notification sent: header synchronization problems

  Time since last notification sent to neighbor: 00:01:26

New Member

Re: iBGP Peering Issue


What IGP are you using? This is generally related to ISIS.

If its is ISIS, have you made any adjustments to ISIS packet headers (turning off hello padding, changing hello-interval, etc)? Try removing any tweaks you have made.

Also try clearing the TCP session with the TCB address.

Also, what hardware are you using? Please attach configs so we can see the full picture.



Hall of Fame Super Silver

Re: iBGP Peering Issue

Hello S-Vanjaarsveld,

what IOS XR version is running  on this CRS-1 router?

the session is not established since 1h and 26 minutes and peer BGP router-id is

All this points to a problem at the TCP or BGP level.

>> Route-Reflector Client

the other device is configured as route-reflector-client may you check if the other device is not considering this CRS-1 node a route-reflector client too?

>> Last reset 00:01:26, due to BGP Notification sent: header synchronization problems

this looks like it had received a TCP segment with unexpected sequence number or Ack number.

follow Joe's suggestions you can also start by  resetting  the BGP neighbor with clear ip bgp neigh OR clear bgp neigh (being this IOS XR)

Hope to help