HSRP Question:

[yadavsandip]

1.) There is one layer 2 switch which is connected to one Active & one standby router of hsrp; which is also connected to LAN too...

Active router replies behalf of virtual router but when active router fails how that layer 2 switch knows immediately. Standby router take over n becomes Active n start to communicate with virtual ip n mac....but for layer 2 switch port number is changed...& default arp time out is 4hrs; default mac-add entry time may 5 min....so how L2 switch resolve the same virtual IP & Mac for standby router with diff port immediately...without Interruption...

can ny one provide any nice link for that...

[acampbell]

Hi,

The MAC address will go as soon as inf Fa0/1 goes down.

The R-01 router will uses its own MAC address until its hello

hold timer expires (by default this is 10 seconds)

You can adjust hello & hold timer settings in your config but

you must keep them the same on both routers.

This link here may be old but still very useful:-

http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080094afd.shtml

Regards,
Alex.
Please rate useful posts.

[Jon Marshall · Accepted solution]

If you look at the link Alex posted and look at the HSRP state table you can see that whenever the standby router transitions to the active router (because the active has failed) part of that transition is to send out a gratuitous arp message.

This gratuitous arp message uses the virtual mac address as the source mac address so the switch can update it's mac address table to reflect which port the virtual mac address can now be reached on

Jon

[yadavsandip]

Thanks Jon n Alex...