border routers

  > epg at merit.edu writes:
  > 3 "- border router level - this should not go in the as-out attributes but
  > rather be a separate set of attributes line 'link-out' 'link-in' with
  > a requirement to have the as-in and as-out as well.  this way you get
  > an optional level of complexity."
  > 
  > The border router extension solves the problem of an autonomous
  > system that has two border routers that have different routing
  > policies 

Understood.  But the differences cannot be that big. 
Otherwise we'd talk about different ASes.

  > - Barrnet does this all the time. So it seemed logical
  > to associate 'border route', 'neighbor', and 'cost' in the same
  > attribute.  In the RIPE-81 as-in attribute this added one optional
  > value; in the RIPE-81 as-out attribute it would require making
  > as-out syntactically consistent with as-in. The value of adding
  > this (even if rarely used) is the ability to generate router
  > configurations and for prtraceroute (as Tony says).

I agree with adding the possibility for this.  It is actually a long
standing action on PeterL to come up with a proposal.  There is no
dispute about this. 

What I object to is to putting this added complexity into as-in/as-out
because it is another level of the ASes routing policy altogether.  This
is something entirely between the neighbors in a peering and not visible
beyond that, right?  It should be documented as such *in addition* to
the generally valid routing policy. 

Advantages: no confusion of current users; no added complexity to worry
about in as-in/as-out for ASes with homogeneous policy in border routers
- the majority; clarity what the ASes common policy is and what is exit
dependent; existing tools still work. 

Disadvatages: none that I can see

Syntactic consistency -while appealing and seemingly simpler to use- is
not a goal in itself in a design like this.  It can actually make things
more difficult to understand by adding too many "null" or "unused"
options.  as-in and as-out as they stand are not syntactically
consistent.  as-out does not have a cost.  This has a reason as
explained in my last message. 

Daniel



-------- Logged at  Thu Apr 28 22:22:25 MET DST 1994  ---------