Result from traceing through a HSRP configured router

[admin_2]

Quick question here. When I do a trace that goes through a set of routers configured with HSRP, the first hop come back with a result of:

Tracing the route to 10.185.20.75

1 10.186.99.2 4 msec

10.186.99.3 0 msec

10.186.99.2 0 msec

2 * * *

Now, 10.186.99.1 is the virtual IP address, and .2 & .3 are the physical addresses of the two routers.

Is the 3 entries under the first hop normal, or does it signify some kind of packet loop between the 2 routers as someone is trying to tell me?

Any help would be greatly appreciated.

Gordon

[Richard Burts]

It is not a loop. It is normal behavior (assuming that you are doing the trace from a router). What is happening is that you have two equal cost paths to the destination. You can verify that by doing a show ip route for the destination address. You will see that the destination has been advertised to you by .2 and also by .3 resulting in two entries in the IP routing table for that destination. For packets generated by the router it does per packet load balancing. So the first packet was sent to .2, the second packet was sent to .3, and the third packet was sent to .2.

This is completely normal, not a problem, and certainly not a loop.

[h.parsons]

I have a question about rbutrs response, From what you said packets generated by the router will load balance. If the trace was done from a PC would only one of the routers show up because of the priorities on that routers interfaces.

[Richard Burts]

If the trace were done from a PC, the router would see the packets as transit traffic to be routed. The router knows two paths to the destination. Whether the router will forward all packets over one path or load balance over two paths depends on how the router is configured and which switching path it is using: if the router is process switching the packets will be load balanced on both paths; if the router is fast switching packets will be forwarded to the destination on one path; if CEF is enabled the default is to do destination based forwarding over one path and an option can be configured in CEF to do per packet load balancing over both paths.