[c-nsp] BGP network stops being advertized

[Deepak Jain]

Justin Shore wrote:
> Jeff Fitzwater wrote:
>> For some unknown reason we stop announcing the 128.112.0.0/16 to all 
>> our ISPs.  This is the second time it has happened in about 2 months.
>>
>> To get things going again I have to remove the BGP "network 
>> 128.112.0.0" statement and just add it again.
> 
> Jeff,
> 
> What did your router think it was advertising when the problem occurred? 
>  sh ip bgp a.b.c.d advertised-routes  will give you what you need.  For 
> example:
> 
> 7206-1.clr#sh ip bgp neighbors aa.bb.cc.dd advertised-routes
> BGP table version is 20975573, local router ID is aa.bb.98.59
> Status codes: s suppressed, d damped, h history, * valid, > best, i - 
> internal,
>               r RIB-failure, S Stale
> Origin codes: i - IGP, e - EGP, ? - incomplete
> 
>    Network          Next Hop            Metric LocPrf Weight Path
> *> aa.bb.96.0/21    0.0.0.0                  0         32768 i
> *> aa.bb.104.0/21   10.64.0.129            200         32768 i
> *> aa.bb.112.0/21   10.64.0.129            200         32768 i
> *> aa.bb.120.0/21   0.0.0.0                  0         32768 i
> *> aa.cc.192.0/21   0.0.0.0                  0         32768 i
> *> aa.cc.200.0/21   10.64.0.129            200         32768 i
> 
> Total number of prefixes 6
> 
> 
> I would be curious to see if there was a RIB-failure at the time of the 
> problem.  Has your SP told you that you aren't advertising the prefix to 
> them?  How are you getting the route that matches your advertisement 
> into the RIB?  Local static or learned via your IGP?
> 
> Justin
> 


Justin hit on most of the right points. The only one I'd add is that you 
probably want to make sure your address blocks are "nailed down" to the 
loopback or another interface (usually a static route of last resort to 
the loopback address/interface). This will ensure that even if the route 
is withdrawn within your network for some reason, your border will still 
announce it to your upstreams.

If you aren't doing any TE and/or aren't prepending announcements, you 
may want to consider having your SPs nail the announcements into their 
BGP mesh for you (with your AS).  This will reduce the potential for 
jitter/flaps/etc. This isn't as commonly done as it used to be, but it 
works.

Deepak Jain
AiNET