Subject: RE: your mail

From: Shahram Davari <[email-masked]>
Date: Mon, 1 Jul 2002 19:12:58 -0700

> -----Original Message-----
> From: Eric Rosen [mailto:[email-masked]]
> Sent: Friday, June 28, 2002 11:10 AM
> To: Eric Osborne
> Cc: Shahram Davari; George Sheng; [email-masked]; [email-masked]
> Subject: Re: your mail 
> 
> 
> 
> Shahram> ECMP is a kludge to overcome LDP's inability to TE. 
> 
> EricO> That seems to be an Extremely Silly statement
> 
> Yes, indeed.  That's  a bit like saying that dynamic routing  
> is a kludge to
> overcome IP's inability to set up end-to-end circuits for 
> individual flows.

I don't think this is a good analogy.

> 
> The ability to do load  balancing without creating extra 
> states is generally
> construed as  a good  thing,

Sure, but LDP ECMP requires hashing states to be created in the LSRs.

 but I  guess not  by the "CO  
> networking rules"
> crowd.  Next  we'll be  hearing  that  equal  cost load  
> balancing  couldn't
> possibly work; violates some ITU architecture, no doubt.  ;

---

From: Eric Osborne <[email-masked]>
Date: Mon, 1 Jul 2002 22:32:13 -0400

> I don't think this is a good analogy.

Why not?  Given that LDP (not CR-LDP) simply follows the IGP routing,
shouldn't you have said something like "...to overcome {ISIS|OSPF}'s
ability to TE..."?  At the very least, that's spitting into the wind;
what we have with IP now has made a lot of people happy for a very
long time.  

> Sure, but LDP ECMP requires hashing states to be created in the LSRs.

Not sure what "hash states" are, but at least in one implementation
I'm familiar with, there's no state kept for any sort of load
balancing, be it IP ECMP, MPLS ECMP, or MPLS unequal-cost balancing.
No per-flow state, no per-packet state, nothing.  It's true that the
forwarding path involves a hash lookup during forwarding to a
load-balanced prefix, but to inherently declare that unacceptable
doesn't seem right.  And for what it's worth, the same forwarding
implementation handles MPLS-TE loadsharing as well, which I think
we've agreed so far is pretty useful.

Maybe you and I are just on different planes.  In simple words, so
folks like me who actually deploy the stuff can understand, what is
the fundamental problem with LDP's load-sharing that doesn't also
exist in IP, and how is this fundamental problem different from
whatever it is that MPLS-TE (CR-LDP or RSVP) does?

eric