Subject: load balancing

From: "Gao Deyun" <[email-masked]>
Date: 25 Apr 2001 09:58:26 +0800

Dear all,

   We can do load balancing in MPLS networks, but how to distribute load in
several LSP? Who know it, please tell me some papers for reference.
   Thank you in advance,

Deyun Gao

--http://www.eyou.com
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From: Shobhan Lakkapragada <[email-masked]>
Date: Wed, 25 Apr 2001 00:02:29 -0400

Deyun,

There can be two scenarios of load balancing in MPLS.
    (1) load-balance a flow over multiple LSPs and
    (2) load-balance a single LSP over multiple physical paths.

I think your question relates to (1). In this case, you could use
any standard load-balancing algorithm (such as source/destination
IP address hashing).

(2) is a totally different problem and I believe "Optimized
Multipath (OMP)" was meant to address this issue. I am not
sure what happened to MPLS OMP ?

- shobhan

Gao Deyun wrote:

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From: Eric Gray <[email-masked]>
Date: Wed, 25 Apr 2001 09:07:44 -0400

Shobhan,

    You might say that 'sanity' happened to MPLS-OMP.  :-)

    The distinction between your #1 and #2 below is that one
assumes that 'splitting' a load occurs at the ingress to a set
of MPLS LSPs and the other assumes that 'splitting' can be
done anywhere along an LSP.  There were two assumptions
that needed to be true for this latter approach to work:

    1)    you need to be able to plow through to the bottom of
        the MPLS stack (without losing context for all labels
        - meaning you pretty much had to keep all existing
        labels (at least after the first one) and insert (or swap)
        a new label from a set of OMP labels;

    2)    you need to be certain of the format for the header
        that follows the last label (i.e. - is it IPv4, IPv6 or
        something else?).

The first of these is non-trivial at any really interesting
wire rate, but not impossible.  The second would only
work if the last label was an explicit NULL for either
IPv4 or IPv6.  The second assumption must be true
because MPLS-OMP - like other multipathing load-
sharing/balancing approaches - relies on use of some
algorithm (i.e. - a hashing approach you mention) to
ensure that individual streams follow the same path
(avoiding certain problems with packet re-ordering).
If the MPLS payload is opaque, a hashing algorithm
would essentially act to scatter packets from streams
of data across multiple paths.

--
Eric Gray