[quagga-dev 11541] Re: [PATCH 1/1] bgpd: implement route-map set as-path prepend last-as

Timo Teras timo.teras at iki.fi
Wed Oct 1 06:28:41 BST 2014

On Tue, 30 Sep 2014 16:30:59 -0400
Michael H Lambert <lambert at psc.edu> wrote:

> On 30 Sep 2014, at 15:55, Nick Hilliard <nick at inex.ie> wrote:
> > On 30/09/2014 20:46, Michael H Lambert wrote:
> >> RFC violating per 1771 and 4271?
> > 
> > there are many useful features in BGP which are strictly forbidden
> > in the rfcs.  E.g. route-server-client.
> Agreed (and ignoring 1863 like the whole world has).  But IMHO
> extensions should be clearly documented as such (just so the next
> developer doesn't spend much head scratching trying to map code to
> [non-existent] RFC).

Could describe what is the exact place this violates? Yes, I know the
RFC explicitly allows only prepending one's own AS (one or multiple
times). But that does not work with iBGP. After quick look prepending
other AS numbers does not seem to be explicitly forbidden.

In any case, this patch does not strictly add new functionality. The
existing 'set as-path prepend' can be used to prepend an arbitrary list
of ASNs. This patch adds syntax that makes it less harmful (though it is
still doing non-RFC things). But given the way some build networks and
ignore, or rewrite MED, hacks like this are needed.

In other words, this is syntactic "sugar" to simplify configurations
(use one route-map for all neighbors instead of making one route-map
per each unique remote-as). And the syntax originates from Cisco boxes.

If documenting something as non-compliance or violation of RFCs, it is
the whole 'prepend' stanza. Not just the 'last-as' part of it that this
patch adds.

But thanks for the clarification.


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