Subject: RE: your mail

From: "George Sheng" <[email-masked]>
Date: Tue, 02 Jul 2002 19:53:30 +0000

>
>If there is only one label at the core then it is pretty much a given
>that you are doing IP over MPLS (the only exception I know to this only
>works with RSVP-TE assigned labels).  In this case you can use standard
>IP load balancing techniques.
>
>Giles

You could have hashed on this top label, which basically give you
the loadsharing granularity of ebgp peering nexthops in the case
of LDP(prefix label scheme). This sounds more natural for a LSR.

-george

_________________________________________________________________
Join the world’s largest e-mail service with MSN Hotmail. 
http://www.hotmail.com

---

From: Giles Heron <[email-masked]>
Date: 02 Jul 2002 21:15:49 +0000

> of LDP(prefix label scheme). This sounds more natural for a LSR.

Hi George,

my mail was explaining why "one layer higher" wasn't a problem for load
balancing in MPLS - I wasn't suggesting that IP load balancing was
necessarily a better choice for IP/MPLS than load balancing on the top
label.

However, whilst hashing on the top label will work in the core, it
doesn't give you anything at the penultimate hop (or at least not in the
usual case where you advertise one /32 address prefix FEC for each PE,
and have "next-hop self" turned on for your iBGP peering sessions).  I
suspect many SPs will not wish to inject external links into their IGPs,
and advertise a FEC for each such link - even if this gives them better
architectural purity for their load balancing than using IP load
balancing in MPLS ;-)

For SPs who don't want to inject external links into their IGP one other
valid option would presumably be to use MP-iBGP so that there is a label
for every route - this label could map to the egress interface for
example.  However that would add 4 bytes to every packet in your network
for seemingly marginal benefit?

Giles

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