10-20-2008 04:41 AM - edited 03-03-2019 11:59 PM
I have a neighbor bgp with my mpls provider. In some cases the number of prefixes that I receive is different that the number of prefixes that they advertise.
For example:
In the ISP's router:
sh ip bgp vpnv4 vrf xxxxx neighbors 77.3.220.26 advertised-routes | inc Total
Total number of prefixes 1380
and y my router:
sh ip bgp neighbors 172.56.255.37 received-routes | include T
Total number of prefixes 870
Solved! Go to Solution.
10-21-2008 06:52 AM
Hello Marcelo,
I've noticed you have :
neighbor 172.x.y.129 allowas-in
I think the default-value is 1.
this probably will not allow a prefix were your own AS number appears more then one as a result of AS prepending done on another site and reported to your local router by the PE router because is not using any form of as-override.
Hope to help
Giuseppe
10-20-2008 05:05 AM
Hello Marcelo,
at startup or BGP session it takes some time to load the 1380 prefixes over the BGP/TCP session you can see a partial value during "loading"
Or do you see this in a stable eBGP connection ?
Verify if the eBGP session is stable with sh ip bgp sum.
Hope to help
Giuseppe
10-20-2008 05:13 AM
The session is stable:
172.56.255.37 4 10834 341449 69453 19 0 0 3d16h
10-20-2008 05:39 AM
Do you have the same prefix limit set as your isp?
10-20-2008 05:50 AM
I have de maximum-prefix parameter in default value. I don't know the other peer. Is it possible cause of the problem?
Thanks
Marcelo
10-20-2008 06:07 AM
Depending on what the default maximum prefix is set to it could explain why the you not receiving all the prefixes from you isp. You could try increasing it to say...1400 to see you you will receive the 1380 prefixes your isp is sending to you.
When you do a show ip bgp neighbor xxx.xxx.xx.xxx, what is the max prefix ?
10-20-2008 06:25 AM
I don't find de max prefix in that command output.
On the other hand if I do a clear ip bgp * I start to receive all the prefix. But I want to find out the issue, because there is an usual situation.
Thanks
Marcelo
10-20-2008 07:04 AM
maturo:
Do you have any input route filters pointing to the neighbor in question?
10-20-2008 08:42 AM
Yes, I have a prefix-list filter.
10-20-2008 08:48 AM
OK, so is it possible that the prefix list is filterng routes and this is why there is a disparity between what the ISP is sendin you and what you are viewing with the 'received routes' keyword?
try using the sho ip bgp neighbor x.x.x.x routes command. if you have soft reconfiguration inbound enabled, you will be able to view all routes received by the peer router, not just the ones installed in the bgp table, which typically exclues those that get filtered.
Let me know...
10-20-2008 09:05 AM
The sho ip bgp neighbor x.x.x.x routes command show me the routes after the filters engine.
The sho ip bgp neighbor x.x.x.x received-routes show me all the prefix received before ther are filtered. This last number is different from the advertised routes, so I suppose there is not issue with the filters.
Marcelo
10-20-2008 10:24 AM
What type of router are you using? Please post your config.
10-21-2008 04:04 AM
2801,IOS 12.4(7a)
The bgp config is:
router bgp 65000
no synchronization
bgp log-neighbor-changes
network a.b.c.d mask 255.255.255.255
network a.b.c.d mask 255.255.255.255
neighbor 77.b.c.25 remote-as 65000
neighbor 77.b.c.25 send-community
neighbor 77.b.c.25 distribute-list local in
neighbor 77.b.c.25 prefix-list out out
neighbor 172.x.y.129 remote-as 10xxx
neighbor 172.x.y.129 ebgp-multihop 2
neighbor 172.x.y.129 send-community
neighbor 172.x.y.129 allowas-in
neighbor 172.x.y.129 soft-reconfiguration inbound
neighbor 172.x.y.129 weight 1000
neighbor 172.x.y.129 prefix-list in in
neighbor 172.x.y.129 prefix-list out out
no auto-summary
!
10-21-2008 06:52 AM
Hello Marcelo,
I've noticed you have :
neighbor 172.x.y.129 allowas-in
I think the default-value is 1.
this probably will not allow a prefix were your own AS number appears more then one as a result of AS prepending done on another site and reported to your local router by the PE router because is not using any form of as-override.
Hope to help
Giuseppe
10-21-2008 07:24 AM
Thanks Giuseppe,
I modify to neighbor 172.x.y.129 allowas-in 10 and do a clear soft, so I started to receive the routes.
Marcelo
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