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Thread Index [isp-bgp] iBGP not working properly ?
Hi,
We recently added a second transit link to our network and set up BGP on the link.
The current situation is this :
PC
|
Switch1 -------- Switch2
| |
Router1 -------- Router2
| |
Transit1 Transit2
Router1 has a BGP link to Transit1, Router2 to Transit2, both
get the full routing table.
Router1 and Router2 have an iBGP link.
The 'loop' at Router1-Router2-Switch1-Switch2 uses STP, so no
problems there. The default gateway for PC is Switch2, the
default for Switch2 is Router2.
So far, so good.
When we connected Transit2 to Router2, we noticed that the
routing table in both Router1 and Router2 changed quite a bit,
which was to be expected. Most routes went via Transit2, which
was normal, because the AS path length was shorter.
However, when the path length is the same and we perform a
traceroute on both Router1 and Router2 to the same host, they
both go out via a different link... their own. I don't think
that's normal, right ?
Second problem : when I get a summary of the BGP, this is what
I get :
Router 1 :
Core1# bgp show summary
Neighbor V AS MsgRcvd MsgSent Up/Down Prefixes
Rcvd/Sent
-------- - -- ------- ------- ------- ---------
---------
[Group Id: transit1]
212.23.45.137 4 8928 81494 9792 1d3h11m26s
120248/1
[Group Id: ibgp]
62.213.192.18 4 28707 364891 169743 1d23h32m2s
115210/20896
BGP summary, 2 groups, 2 peers
Core1#
Router 2:
core2# bgp show summary
Neighbor V AS MsgRcvd MsgSent Up/Down Prefixes
Rcvd/Sent
-------- - -- ------- ------- ------- ---------
---------
[Group Id: transit2]
64.212.16.113 4 3549 235153 3328 1d3h42m9s
120464/1
[Group Id: ibgp]
62.213.192.17 4 28707 128012 329835 1d23h34m7s
20898/115223
BGP summary, 2 groups, 2 peers
core2#
If I read this correctly, Router1 only sent 20896 prefixes to
Router2, although it received 120248 from Transit1. On the
other hand, Router2 sent 115223 to Router1 and it received
120464 from Transit2... where does that difference come from ?
Why doesn't Router1 send all of its routes to Router2 ? Is
that the reason why most routes go via Transit2 ?
Any suggestions would be very nice.
Kind greetings,
Wim
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