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I have iBGP configured between two devices. After the bgp session comes up, the # of routes sent to RouterA from RouterB initially increases to roughly 100k, but then for some reason, it drops down to only 160.

Is there a reason why this would be happening? It's just a simply ibgp configuration on both of the routers.

Example

Starts out:

Neighbor Address  AS#   State   Time     Rt:Accepted Filtered Sent   ToSend
  e.e.e.e         xxxxx ESTAB   1h34m48s    493723   0        1      0     
  i.i.i.i          xxxx ESTAB   0h 0m19s    301708   0        120998 71776 

Ends with:

 Neighbor Address  AS#   State   Time     Rt:Accepted Filtered Sent   ToSend
  e.e.e.e          xxxxx ESTAB   1h35m 4s    493722   0        1      0     
  i.i.i.i           xxxx ESTAB   0h 0m35s    494878   0        150    0  

e.e.e.e are the ebgp neigh and i.i.i.i is the ibgp neighbors. As you can see, once the session comes up, the # of routes sent from this router to routerA initially goes high but then drops to ~150.

If you need specific information, please let me know.

Thank you

  • 1
    I don't know brocade that well, but (494878 - 301708) is rather close to (120998 + 71776); my suspicion is that one side sends less-preferred external prefixes to the iBGP peer. BGP chooses one and only one best path to send via iBGP; thus I suspect the lower Sent number is an artifact of timing and best path selection... without checking a sniff of the iBGP session I'm just speculating... and I'm on vacation, so it's rather challenging to simulate :-) – Mike Pennington Jun 28 '14 at 2:48
  • Can you look at I.I.I.I and see how many routes it learned from this peer? – Avery Abbott Jul 21 '14 at 4:57
  • Is there a max bgp prefix command in your configs? – HAL Mar 4 '15 at 17:47
  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer. – Ron Maupin Aug 9 '17 at 17:13
2

I think this is normal behavoir.

After the reboot you router has to learn the neigbor-routes. The upper and lower left circle in my picture are around the values representing the known active-used routes of your router. The upper right circle shows that there are stimm routes to learn. This is the Reason for the high Send-value. In the end both routers have prety close accepted-Routes-Values and this is fine.

There could be some reasons why router e.e.e.e dont learn all routes, maybe is a configuration thing and he reject some routes or it is misconfiguration in the update timings.

enter image description here

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