OSPF per destination

Unanswered Question
Feb 11th, 2007

Hi Expert,

I have few questions on my lab test.

(1) Load balance can be classifield as per destination and per packet method, but under what situation will choose per destination and what situation will choose per packet.

(2) With the Attach configure and diagram, it is the per destination method, I try to ping 192.168.170.254 by using PC machine. The result come out that use 2620 serial 0/0 for the first session but there is 6000 bits/sec go through 2620 serial 0/1. To my view, I expect there is no traffic in 2620 serial 0/1. It seems there is echo reply packet travel back to 10.1.1.1 via 2620. It it right ? As it is a per destination method, why it will use another path for echo reply ? Can I adjust the echo reply

back to 2620 serial 0/0 link ?

I have this problem too.
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Jon Marshall Mon, 02/12/2007 - 10:38

Hi

1) The router will by default do per-destination load-balancing unless you tell it not to.

If you are not running CEF on your router then to turn on per-packet load balancing under the interface configuration enter "no ip route-cache"

If you are running CEF under the interface configuration enter "ip load-sharing per-packet".

Again with both CEF and non-CEF it is important to remember that the router will load balance by destination by default.

2) Are you sure that the bits you are seeing on your s0/1 interface is the ping. Remember you are running OSPF between these routers so there will be some routing protocol traffic.

As for the echo reply. Load balancing per-destination is done on the destination address only so the return traffic is an independent traffic flow ie. there is nothing to stop it being routed over the other link.

HTH

Jon

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