BGP prefix filter list

Baldur Norddahl baldur.norddahl at
Wed May 15 18:22:42 UTC 2019


On Wed, May 15, 2019 at 3:56 PM Mike Hammett <nanog at> wrote:

> What is the most common platform people are using with such limitations?
> How long ago was it deprecated?
We are a small network with approx 10k customers and two core routers. The
routers are advertised as 2 million FIB and 10 million RIB.

This morning at about 2 AM CET our iBGP session between the two core
routers started flapping every 5 minutes. This is how long it takes to
exchange the full table between the routers. The eBGP sessions to our
transits were stable and never went down.

The iBGP session is a MPLS multiprotocol BGP session that exhanges IPv4,
IPv6 and VRF in a single session.

We are working closely together with another ISP that have the same
routers. His network went down as well.

Nothing would help until I culled the majority of the IPv6 routes by
installing a default IPv6 route together with a filter, that drops every
IPv6 route received on our transits. After that I could not make any more
experimentation. Need to have a maintenance window during the night.

These routers have shared IPv4 and IPv6 memory space. My theory is that the
combined prefix numbers is causing the problem. But it could also be some
IPv6 prefix first seen this night, that triggers a bug. Or something else.


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