Subject: RE: your mail

From: "George Sheng" <[email-masked]>
Date: Mon, 01 Jul 2002 08:18:56 +0000

> >SD: Silly or not, I am afraid it is the reality. LDP is inherently unable 
>to
> >SD:do load ballancing, that is why this kludge is there.
>
>Shahram,
>
>What are we comparing this against? IP? Please explain how in the IP world 
>one
>achieved IP vs non-IP load balancing and how it is different when you run 
>LDP?

well, for example, take a topology below:

       R2
     /    \
  R1        R3 -- R5 -- R6
     \    /
       R4

assume the IGP cost is the same for all the links above. In the
"native" IP mode, traffic from R6 to R1, they will be(normally)
load shared using the links to both R2 and R4, R3 is the router
performs this ECMP loadsharing(IP flow based usually).

now, if R1 through R6 are running LDP, please tell me how does
R3 perform the same flow based ECMP loadsharing(without looking
into the IP packets)?

-george

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From: Giles Heron <[email-masked]>
Date: 01 Jul 2002 11:11:51 +0000

> R3 perform the same flow based ECMP loadsharing(without looking

you can't.

however there is, of course, nothing to stop you looking into the IP
packets (using the "first nibble hack".)

What you *do* get with LDP is the ability to load-balance *without*
looking into the IP packets.

For example for traffic flowing from R1 to R3, R5, R6 it would be
possible to hash this across the links to R2 and R4 just by looking at
the LDP-assigned label.

In addition if you are doing L2 over MPLS then you can hash different L2
tunnels over the different links by "walking the stack".  Similar
techniques are possible for RFC2547.

With IP you wouldn't have either of these options (both are technically
possible but are AFAIK unimplemented today...)

Giles

-- 
=================================================================
Giles Heron    Principal Network Architect    PacketExchange Ltd.
ph: +44 7880 506185              "if you build it they will yawn"
=================================================================

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From: Richard Stephens <[email-masked]>
Date: Mon, 1 Jul 2002 10:37:26 -0700 (PDT)

wouldn't it be possible to solve the problem by having
the ingress node create multiple explicit path lsp's
based on it's igp ecmp information?  All that should
take is initiative by the vendor.

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From: Eric Osborne <[email-masked]>
Date: Mon, 1 Jul 2002 17:24:19 -0400

> take is initiative by the vendor.

What does that buy you that LDP+IGP doesn't?  traffic ends up taking
the same path, and you have the advantage of p2mp at each hop.

eric