[c-nsp] BGP route won't advertise

[Jerry Bacon]

On 2/27/2013 3:48 PM, Jason Lixfeld wrote:
> I presume a.b.c.0/22 is the prefix you are receiving from your customer and AS1xx7 is your customer's AS?

Yes, that is correct. It's actually part of a /19.

> Is there any outbound route policy on R1 facing your transit provider there which might be preventing the re-advertisment?

No, in fact, i have this:

ip prefix-list announce seq 40 deny a.b.48.0/22
ip prefix-list announce seq 41 permit a.b.32.0/19 le 24

The setup on R1 and R4 is virtually the same.

>
> On 2013-02-27, at 6:24 PM, Jerry Bacon <wireless at starbeam.com> wrote:
>
>> I have the following layout:
>>
>> Internet <--> R1 <--> R2 <--> R3 <--> R4 <--> Internet
>>
>> I have a customer attached to R3 for whom I am doing transit.
>>
>> R1, R2, & R4 are GSR 12008 running 12.0(32)S14
>> R3 is a 3825 running 12.3(11)T5
>>
>> At R4 everything is fine:
>>
>> R4#sh ip rou a.b.c.0
>> Routing entry for a.b.c.0/22, supernet
>>   Known via "bgp 1xx77", distance 200, metric 0
>>   Tag 11xx1, type internal
>>   Last update from x.y.z.242 1w5d ago
>>   Routing Descriptor Blocks:
>>   * x.y.z.242, from x.y.z.242, 1w5d ago
>>       Route metric is 0, traffic share count is 1
>>       AS Hops 1, BGP network version 0
>>       Route tag 11xx1
>>
>> R4#sh ip bgp a.b.c.0/22
>> BGP routing table entry for a.b.c.0/22, version 40711009
>> Bestpath Modifiers: always-compare-med, deterministic-med
>> Paths: (1 available, best #1)
>>   Advertised to update-groups:
>>      5
>>   11xx1
>>     x.y.z.242 (metric 143104) from x.y.z.242 (x.y.z.242)
>>       Origin IGP, metric 0, localpref 100, valid, internal, best
>>
>>
>> However, at R1 the same route won't advertise:
>>
>> R1#sh ip rou a.b.c.0
>> Routing entry for a.b.c.0/22, supernet
>>   Known via "bgp 1xx77", distance 200, metric 0
>>   Tag 11xx1, type internal
>>   Last update from x.y.z.242 16:03:41 ago
>>   Routing Descriptor Blocks:
>>   * x.y.z.242, from x.y.z.242, 16:03:41 ago
>>       Route metric is 0, traffic share count is 1
>>       AS Hops 1, BGP network version 0
>>       Route tag 11xx1
>>
>> R1#sh ip bgp a.b.c.0/22
>> BGP routing table entry for a.b.c.0/22, version 406152
>> Bestpath Modifiers: always-compare-med, deterministic-med
>> Paths: (1 available, best #1)
>>   Not advertised to any peer
>>   11xx1
>>     x.y.z.242 (metric 143360) from x.y.z.242 (x.y.z.242)
>>       Origin IGP, metric 0, localpref 100, valid, internal, best
>>
>> None of the issues that I have been able to find that might cause this behaviour seem to apply. Any ideas on what more to look for?
>>

-- 
Jerry Bacon
Senior Network Engineer