Subject: RE: your mail

From: "George Sheng" <[email-masked]>
Date: Tue, 02 Jul 2002 20:35:49 +0000

Hi 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.
>
>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.

understood.

>
>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 ;-)

it does not have to be network of "external" links. an ebgp router
can optionally announce N loopback /32 addresses and use them as
nexthops for their ibgp peers. depends the the network topology,
it usually is needed only on the ebgp routers which have parallel
links.

>
>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?

i think that's overkill, i'd rather hashing on the payload.

thx.
>Giles

-george

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From: Giles Heron <[email-masked]>
Date: 02 Jul 2002 20:39:44 +0000

> it usually is needed only on the ebgp routers which have parallel

agreed.  But this still adds prefixes to your IGP and FECs to LDP :(

> i think that's overkill, i'd rather hashing on the payload.

I hoped you'd say that!

Giles

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