Strange BGP phantom announce remaining

Chrisy Luke chrisy at
Mon Nov 12 16:03:00 UTC 2001

Stephane Bortzmeyer wrote (on Nov 12):
> Does you have any idea why routers at Colt still see the old announce?
> People at Colt have no idea. Abovenet checked on its side and sees
> only the good prefix.

Dodgy Cisco-ism probably. Use looking glasses and NOC's to find the one
router where the phantom prefix appears in a BGP table and (have someone)
drop the BGP session associated with it.

Failing that, re-advertise the prefix for a period of time (minutes
not seconds) and then withdraw it.

I have found IOS sometimes unable to "keep up" when it is faced with
a prefix that is withdrawn too quickly. Because "soft" configuration
maintains the same state the BGP engine sees, a soft clear doesn't solve
the problem. You have top dump all state for that session, ergo, drop
the BGP session or renew the phantom prefix.

Just my experience, and it's always been with other networks routers,
not mine.

== chris at                                    T: +44 845 333 0122
== Global IP Network Engineering, Easynet Group PLC     F: +44 845 333 0122

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