v6 subnet size for DSL & leased line customers

Brian Dickson briand at ca.afilias.info
Thu Jan 3 00:29:35 UTC 2008


 >> As to "there must be better knobs" I think it may be a little late 
for that; by design (or as a consequence of it) the set of IPv6 knobs is 
the same as the set of IPv4 knobs.
 > The trouble is that BGP doesn't have a meaningful inter-AS metric. 
(Although there is something that is called that.) If I want to increase 
my path length by 10% through a certain neighboring AS, I don't get to 
do that. I only get to double or triple it. (Unless I was doing very 
heavy prepending to begin with.)

Actually, while it isn't a true metric as such, there *is* just such a knob.

The "origin" attribute, can act as a fractional AS-path-length. It's 
mandatory and transitive.
It gets evaluated after as path length, but before other attributes.

It has three possible values (internal, external, unknown), and as such, 
gives the limited ability to influence path choice at third-party 
locations quite distant.

The only caveat is, that some parties may mess with it on prefixes they 
receive.

I've used it in the past, with considerable success.

Brian Dickson



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