Re: [mpls] comments on draft-kompella-mpls-special-purpose-labels-02

[Jeff Wheeler <[e-mail]>]

On Fri, Mar 22, 2013 at 5:25 AM, Loa Andersson <[e-mail]> wrote:
> Specifying is easy, implementing is harder, operating is worse!
> Label stack processing is mostly or at least commonly in HW. You
> would need to do a HW change of your entire network the day you introduce
> the first router with the "grown label space", otherwise
> treatment of labels 15 to X will be non-deterministic

Loa, can you give any example of such hardware?

I believe this draft is a huge mistake, and that mistake is probably based
on the wrong assumption you've posted (quoted above.)

Any feature introduced by extended special-purpose labels is not going to
be supported by routers without at least new software.  If routers exist
that are not capable of taking additional processing steps (such as punt to
CPU, forward as IPv4/IPv6, use entropy label) based on an arbitrary label
value, then these routers simply will not be able to support new features.
 They will not break.

So we're not talking about breaking anyone's deployed hardware.  At worst,
new features might not be able to be supported.  However, I suspect vendors
were not so fantastically stupid as to hard-wire 0..15 special action label
range into their ASICs without making it possible to install a LFIB entry
so arbitrary labels can also take a special action.

If there are such fantastically stupid vendors, it's probably not a good
idea to punish everyone else for their rather obvious mistake.


This adds MTU complexity and wastes bandwidth / wire-time whenever extended
S-P labels are in use.

If you are going to make those sacrifices, I think you should be able to
give at least one example of a router that actually forces you to do it
this way.

-- 
Jeff S Wheeler <[e-mail]>
Sr Network Operator  /  Innovative Network Concepts