Lots of prepends - AS20912 case

Mikael Abrahamsson swmike at swm.pp.se
Fri Feb 20 14:05:48 UTC 2009

On Fri, 20 Feb 2009, Dorn Hetzel wrote:

> Replacing what is conventially thought to be a string with an integer
> multiplier seems a massive violation of the principle of least astonishment.

On a Cisco running 12.0S:

route-map test1
set as-path prepend last-as ?
   <1-10>  number of last-AS prepends

Cisco seems to be doing more sensible limits, but I do agree that the 
feature makes sense.

There are two ways of handling when someone puts in a very high number to 
number of prepends:

1. Say "out of limit" and disallow it in the config checker.
2. Actually prepend the number of times specified.

The option done here:

3. Prepend number of times entered modulo 256, is just broken.

Mikael Abrahamsson    email: swmike at swm.pp.se

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