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North American Network Operators Group

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Re: BGP Routing problem

  • From: Bil Herd
  • Date: Thu Jun 05 15:18:50 1997

We have seen upon occasion where a dampened route will not be replaced by
a route of the same specificity for about 20-45 minutes.  While we didn't
care for this behaviour, I guess it was somewhat predictable.  

What had us concerned was we have seen each of our three providers black
hole us on at least one occasion (sometimes more) when their backbone or
core flapped.  It could be described as appearing as if their borders did
not receive the information to withdraw our advertisements. Looking Glass
showed us "history" and "received only" entries, but no active
replacements...  similar to the symptoms that you are describing. 
Sprint's NOC reported hearing active advertisements from our "down"
providerm but I heard this second-hand.  Killing our BGP session with the
offending provider after the problem started would not fix the problem,
our routes continued to be preferred to someone we no longer had a bgp
session with.  This situation would usually fix itself within 45 minutes. 

While this doesn't happen often, it has the affect that having two other 
providers is useless if the third is erronously advertising us.  Is there 
a failure scenerio where borders will continue to advertise AS's due to 
loss of connectivity with their interior routers?

Bil Herd
InterActive

On Thu, 5 Jun 1997, Anthony Walker wrote:
> We are currently multi-homed during the day and tripple homed at
> night. 
> Basicaly we (AS6180) have been announcing all our adresses including
> 196.25.116.0, 196.25.117.0 and 196.25.203.0 via AS 3741 at night,
> and this gets switched of during the day. The problem seems to relate
> to the fact that these addresses are part of AS 5713's CIDR 
> 196.25.0.0/16 and we thought we could get away with announcing them 
> like this. It did work fine for over a week, but now today we have a 
> problem.
> 
> MAE-East (see example at end of message) ,  the Sprintnap and who
> knows who else still have entries for these via AS3741 but they are
> showing as received-only, and no best path. Yet via MAE West they are
> fine. 
> 
> We are going to stop announcing these via AS3741 at night, but its 
> been 9 hours now since they were not announced and these 
> received-only entries are still sitting there blocking these routes 
> from it seems about a third of the internet.
> MAE-East Looking Glass Results
> Query: bgp 
> Addr: 196.25.203.0 
> BGP routing table entry for 196.25.203.0/24, version 5006458
> Paths: (1 available, no best path, advertised over IBGP)
>   1673 1239 4005 3741 6180, (received-only)
>     192.41.177.141 from 192.41.177.141 (140.223.57.217)
>       Origin IGP, external
> 




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