RE: OSPF Load Balance

From: Chua, Parry (Parry.Chua@xxxxxxxxxx)
Date: Tue Nov 20 2001 - 21:47:36 GMT-3

   
Hello Brain,

Back yo your example.

> R1--R2---R3--10.1.1.1

Ok, ping from R1 to 10.1.1.1 will be process switch at R1, but could be
different when forward by R2 and R3.

Ping from R2 to 10.1.1.1 will still do per packet destination, right ? (
assume that
R2 has multiple path to reach 10.1.1.1

Parry Chua
-----Original Message-----
From: Brian Hescock [mailto:bhescock@cisco.com]
Sent: Tuesday, November 20, 2001 9:37 PM
To: Chua, Parry
Cc: Hansang Bae; ccielab@groupstudy.com
Subject: Re: OSPF Load Balance

Parry,
     Ping doesn't do per packet load balancing per se, it's a matter of
where you do the ping and how the router that is being traversed is
configured. Example:

R1--R2---R3--10.1.1.1

Ping from R1 to 10.1.1.1. The ping packet is process-switched on R1
since
the packet is originated on the router. But on R2 the packet could be
either process-switch, fast-switched, cef switched, parallel-express
forwarding, etc, depending upon the platform and type of switching
configured on the router / interface. In terms of load balancing, it
reacts different with each switching path and is something that should
be
studied for you day-to-day operations, not just for the lab.

Brian

"Chua, Parry" wrote:

> Hi,
>
> There is two way of load share ? balanceing ? in Cisco router
> implementation, per packet and per destination. With route cache turn
> on, per destination load share/balance is used. I know ping will do
per
> packet load balancing, ie one packet go interface1 and next interface2
> and son on.
>
> Parry Chua
>
> -----Original Message-----
> From: Hansang Bae [mailto:hbae@nyc.rr.com]
> Sent: Tuesday, November 20, 2001 12:03 PM
> To: ccielab@groupstudy.com
> Subject: RE: OSPF Load Balance
>
> >>From: "Chua, Parry" <Parry.Chua@compaq.com>
> >>I thought that when we show IP route, there could be one or more
path
> to
> >>reach a particular destination based on the routing protocol type.
For
> >>OSPF, if we know there could be more than one path to reach that
> >>destination,
>
> Correct.
>
> >>we can then manuiplate the COST to get a equal cost
> >>for load balanceing, right ?
>
> Perhaps. Load Balancing is not as easy as people think.
>
> >>Other protocolos such as (E)IGRP support
> >>unequal cost load balancing. As for RIP, I belive we can use offset
to
> >>change the hop count from unequal to
> >>equal and vice versa, right ?
>
> But keep in mind that fast processing's job is to limit the lookup of
> the
> routing table (forwarding table I guess). So even if you have two
equal
>
> cost routes to a destination, by default, it will use one and only one
> link. If it didn't, it kinda defeats the purpose of fast-processing.
> If
> you do a "sho ip cache" you'll see what I mean.
>
> hsb

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