Subject: RE: inter-as and reflection (was option-d consensus)

From: "Martin Halstead" <[email-masked]>
Date: Fri, 28 Apr 2006 10:28:26 +0100

Pedro

You make some valid points about the need for regionalized RRs and the
need to scale the control plane. As you know, SPs do load balance
traffic to multi-homed sites within their domains. They do that via
configuring different RD values per PE VRF pairs. All the option'd'
draft says is that the same thing can be achieved using option'd' (just
like option 'a'). That however is also not solved via distributed RRs
within a region. Your statement in a previous email on load balancing:

'That is not true. Naive network designs on the receiver that use 
centralized route reflectors (a solution that will not scale) cause 
problems such as lack of required path information. This is just a 
question of network design on the receiver... a problem for the receiver

to solve for sure.'

therefore does not stack up. As you now describe:

' The information one actually desires is to have on a per region basis 
the best exit point for a given "reachability" point. This is what you 
get by default by doing path selection on an NLRI using metrics as tie 
breaker. The logical conclusion, imho, would be that for large scale 
deployments a SP needs to have RRs per region that perform this local 
selection decision so that PEs are not bothered w/ it.'

Load balancing is not solved via regional route reflectors in option 'b'
environments. I know I am being pedantic here, but you cannot therefore
argue that option 'b' achieves the same end as option'd' for load
balancing (and for that matter 'optimal' path selection across ASes).

BTW: The phrase 'infernal' is definitely intentional :-)

Regards

Martin

---

From: Pedro Roque Marques <[email-masked]>
Date: Fri, 28 Apr 2006 11:28:14 -0700

Martin Halstead wrote:
> need to scale the control plane.

> As you know, SPs do load balance
> like option 'a').

Does this document imply or recommend that different inter-as peering 
points rewrite the same "reachability information" with different RDs ? 
if so this practice can have very negative scaling implications and i 
would recommend the WG to think very carefully before putting its stamp 
of approval on such proposal.

> That however is also not solved via distributed RRs
> within a region.

My claim is that using a reflection cluster per region makes it 
unnecessary to have different RD values. And is a more scalable 
approach. You have not refuted that, i believe.

> Your statement in a previous email on load balancing:
> [...]
> there fore does not stack up.

Please explain.

> environments.

Can you please provide some data to substantiate that claim.

My data point: standard internet RR design of a pair of reflectors per 
"POP"/Region. Seems to work fine w/ locally optimal best exist point 
choices. Been deployed for a while.

Inter-as mpls-vpn routing is equivalent to internet inter-as peering 
exchanges. Same prefix advertised via multiple exit points.

> I know I am being pedantic here, but you cannot therefore

My claim is:
  - that "local best route selection" is best solved using per region RRs;
  - centralized RRs will not scale.
  - option "d" has no magic properties.

The entire argument for rewriting RDs stems from the concept of a 
centralized RR with per ingress PE decision. Which means each PE needs 
to do path selection between M different paths (number of inter-as 
exchange points... i.e. one per city). This is not the best way to scale 
a network.

   Pedro.