Wednesday, March 21, 2018

HSRP and return traffic

Lets see if I can explain this w/out resorting to picture...

OSPF network.

Switch A is connected (L2) to Router1 and Router2 (which have no links between them). Router1 and 2 are in an hsrp pair with Router1 active. From there, Router1 and Router2 have separate paths (wan links) out, before converging back into the enterprise network at different points.

So my traffic from my switch is going to use the hsrp active link. From there it's going to make it's way to the enterprise on it's wan link.

However, lets say on the return link, from some point in the network, it's actually faster to use Router2's path. I'm correct in that traffic will use that path (router2), even though router2 is the hsrp standby, right? The network knows that my fastest path back is via that router, and traffic will go that way and use the (standby) L2 link to get back to switch A.

So in this configuration/scenario, I will wind up getting circular/asymmetrical traffic from/to switch A.



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