Using link congestion to control routing updates

Andy Dills andy at
Thu Dec 19 20:38:00 UTC 2002

On Thu, 19 Dec 2002, David Scott Olverson wrote:

> Hello all,
> 	I was wondering if anyone was aware of a way to use the congestion
> of a network link to control the routing update.  For example if I have a
> very small link that gets congested, I may want the router to withhold a
> routing update until link congestion falls below a certain threshold like
> 60% of bandwidth.  Is anyone aware of anything like this available today
> or a technique that might accomplish something similar?  You can contact
> me off list if this topic isn't germane.

The first thing that comes to my mind would be conditional announcements.
You could have an internal routing server setup on a private ASN, which
monitors the congestion with snmp. When congestion is occuring, inject a
bogus route into BGP (say,, with different IPs to be
injected depending on the link that is experiencing congestion).
Configure your conditional announcements to NOT announce your routes over
the particular link when the bogus route shows up. And of course, to
prevent flapping, advertise your bogus routes for X minimum period of
time after congestion dissapears.

I can't see any reason why this wouldn't work or would be a poor idea...


(dills at HASCS guys hate me, I was a huge pain in the
ass when I was an undergrad...still am, I guess)

Andy Dills                              301-682-9972
Xecunet, LLC                  
Dialup * Webhosting * E-Commerce * High-Speed Access

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