BGP Updates

[fabio.marino]

Hi to all. I have the following topology:

After creating neighbor relationship between all routers, i was debugging the updates packet sent by the ISP router.

Following a snapshot of my debug:

How you can see, ISP sends updates for network 192.168.100.1 only to the neighbor 192.168.1.2 (SanJose2).

Why ISP does not send an update relate to the same network (192.168.100.1) also to the neighbor 192.168.100.6 (SanJose1)?

I checked the neighbor states and is "established" for both.

Sure, i'm missing some basic concept here, but i'm studying BGP right now and is not so simple or natural to understand.

Thanks for your time.

[cadet alain]

hi,

does 192.168.1.6 have the route in his bgp table? The answer should be yes because in the debug output the last line is talking about 192.168.1.6 neighbour and if there is a peering with both neighbours and there is no outbound filtering why this prefix shouldn't be advertised to all his eBGP neighbours?

Regards.

Alain.

[fabio.marino]

Thanks Alain for your time.

Now i'm reading the output of router ISP and i read

"*Mar  1 00:04:36.787: BGP(0): updgrp 1 - 192.168.1.2 updates replicated for neighbors: 192.168.1.6"

so i thing (but i don't know why) for this reason ISP does not send more update about 192.168.100.1 also to the router SanJose1.

However, based on my book, i did not expect this type of behaviour.

However all works, i mean SanJose1 reach the 192.168.100.1 with next hop 192.168.1.5 and SanJose2 using as next hop the 192.168.1.1.

Thanks Alain for your attention...may be my question is not so vital to understand the BGP...

[Giuseppe Larosa · Accepted solution]

Hello Fabio,

your tests shows update-groups feature in effect:

the set of updates prepared for first eBGP neighbor is also sent to the other neighbor 192.168.1.6

This is a feature that was introduced some years ago: you can think of update-groups as implicit peer-groups that the router manages without explicit configuration.

Before of the introduction of update-groups the use of peer-groups was also an help to improve performance in addition to making complex configurations easier to be read

what neighbors can be in an update-group? all those that share the same outbound policy

I did perfomance tests on this using agilent router test

Edit:

I mean with 80 BGP neighbors emulated with the instrument I tried to see what if those 80 are in the sameupdate group, what if there are 10,20,40 or 80 update groups.

see

http://www.cisco.com/en/US/docs/ios/12_3t/12_3t4/feature/guide/gtbgpdpg.html

Hope to help

Giuseppe

[fabio.marino]

Ok Giuseppe,

i knew about peer-group but i had no idea about update-groups feature.

So far is enough for me to know it, i'll go in deep as soon as completed to study the ccnp route module.

Thanks for your time,

Fabio.