RE: [PWE3] Proposed new 5.4.3 for arch draft

[benjamin.niven-jenkins at bt.com]

> Neil - One of the initial justifications of MPLS was to solve
> the IP equal-cost problem. Of course this could be done
> by only allowing MPLS-TE solutions, and that may be what operators
> like yourself need. 
> 
> But there are a lot of best-effort uses for MPLS as well, 
> and these shouldn't have to suffer from overloaded links
> when there are underloaded ones available. 

I maybe missing something but I don't see how using a best-effort flavour of MPLS (i.e. any non-P2P non-co-ps mode of MPLS) can really solve the IP equal-cost problem when it introduces it's own equal-cost problem (because it tracks the IP IGP).  It's just shifting the problem to somewhere else in the network stack.

Under what circumstances does a cl-ps best-effort flavour of MPLS add value above and beyond what could be achieved using cl-ps best-effort IP (I can't think of any)?

> Admittedly peaking into client layer headers is a hack,
> but it is such a useful one that it may qualify as one of those
> rare exceptions where the rules can be broken

Useful to whom?  I would argue that if you consider its full implications (including OAM, fault finding/diagnosis, SLA tracking and NMS/OSS implications) then it isn't that useful to service providers, it's just a complicated pain in the backside.

IMO it's a case of treating the symptoms and not the cause, this is further compounded by the additional OAM etc. hacks required to fault manage the original ECMP hack.  IMO time would be better spent deprecating the hack and concentrating on how to migrate away from it than producing new hacks that try and fix the old hacks.


Ben

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