This is going to sound like a dumb question, but here goes ...
I am already quite familiar with HSRP, and I am already quite familiar with transparent bridging in switches. I know that when you have an HSRP failover, the new active HSRP router sends out a gratuitous ARP in order to update the MAC forwarding tables in any switches. (I am thinking routers-on-sticks here). So I presume the source MAC address of that gratuitous ARP is 0000.0c07.acnn, where nn is the group number
But does the HSRP active router send out gratuitous ARPs at regular intervals, even outside the failover scenario? If not, then how are the MAC forwarding table entries for 0000.0c07.acnn kept refreshed?
- I think through traffic has the physical BIA of the router as source MAC address
- I think HSRP hellos also use the physical BIA of the router as source MAC address
- Outgoing ARP requests? These are also sourced from the BIA, aren't they? (Otherwise if you had multiple groups, which VMAC would you source from?
So what keeps the 0000.0c07.acnn entry refreshed?
There is a hidden agenda behind this question. I have two data centers joined with OTV, with two routers on each site with the same standby address, and HSRP isolation. I can see that the HSRP isolation is working because I have an active gateway on each site. But there is another element in the HSRP isolation, and that is to make sure that the HSRP MAC address does not get transferred over the OTV. You do that by excluding it from the OTV isis. But somehow I suspect it is getting through anyway. I shall write more about that once someone can confirm to me how HSRP normally keeps switch tables refreshed.
Thanks in advance ...
