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From: ferriby@perot.com (John Ferriby)
Newsgroups: comp.dcom.sys.cisco
Subject: Re: Load Balancing
Message-ID: <4144@perot.com>
Date: 29 May 91 21:56:46 GMT
References: <35406@boulder.Colorado.EDU> <10613@labtam.labtam.oz>
Organization: Perot Systems Corporation, Detroit, Michigan, USA
Lines: 47

In article <10613@labtam.labtam.oz>, timr@labtam.labtam.oz (Tim Roper) writes:
> In article <35406@boulder.Colorado.EDU>, HANK@VM.BIU.AC.IL (Hank Nussbacher) writes:
>> >Subject: Load Balancing between Equal Cost Routes
>> >
>> >If two serial links terminate at a the same cisco router at one end and to
>> >the same node at the other end, will a cisco router recognise that there
>> >are multiple equal cost routes to that node, and places beyond?
>> >...
>> 
>> It all depends what you are routing and also whether you are bridging.
>> If you are routing TCPIP traffic it depends on what routing protocol
>> is being used.  RIP will not load balance, but IGRP will do a reasonable
>> job of balancing the load on the two lines.  If you are routing
>> DECNET via Phase IV you will not be using one line at all and it will
>> ...

Just to clear up a common misconception...

Unlike what the cisco documentation suggests, (by calling it Phase IV) the
gateway software [8.2(3)] does in fact support path splitting.  (This function
falls under the DEC afterthought, Phase IV+, which among other things supports
path splitting.)  The configuration commands are 'decnet path-split-mode' and
'decnet max-paths'.  I've found that the 'max-paths' tends to get folks who are
experimenting with this -- it is defaulted to a value of 1 in both the DEC and
cisco implementations.  Intuitively, a value of 1 turns path splitting off. 
Also make sure that all routers involved are "symetrically configured" or your
load will split in one direction but not the other or do some even weirder
stuff if you have a mesh topology or more than 3 paths. Also of note, the the
'path-split-mode' value 'interim' supports those cases where a Phase IV router
needs to talk to a Phase IV+ router, but I expect that is a relatively rare
condition.


> 
> We are routing TCP/IP only and not bridging.
> 
> Can anyone recommend sources of the specification of IGRP and/or sample
> implementations?
> 
> Thanks,
> -Tim.
--                             
John Ferriby

Perot Systems Corporation    Telephone: +1-313-641-3660
4555 Corporate Drive         Internet: ferriby@perot.com
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