[c-nsp] MAC addresses unlearned with HSRP

[Vincent De Keyzer]

Hello,

 

in the classical HSRP scenario, with two routers (R1 and R2) and two "core"
switches (S1 and S2), a host (H) connected to an access switch (that is
dual-homed to the two core switches S1 & S2) will always send traffic
towards S1 and R1 (R1 being the HSRP active router).

 

Problem with this set-up is that R2 might very well send out packets for the
H via S2, which at some point will have timed out the MAC address of H, and
will hence have to flood all of its ports (like a good switch is supposed to
do). This will result in increased and useless traffic on the ports of S2.

 

One solution to this would be that R2 would not see that "connected" IP
route anymore, because it is HSRP standby. This idea has been discussed
often on this list but it does not seem that Cisco has any plans to
implement that.

 

It seems that GLBP is not a solution either - as far as I understand it,
each host will use one of the routers as a default gateway, while what we
want is that H uses both (so that S2 does not forget about H's MAC address).

 

So, is there a solution to this problem with HSRP asymmetrical routing and
MAC addresses not being known?

 

Vincent