What happens when I configure more than 16 HSRP Standby Groups in Sup2/PFC2?

If you configure more than 16 HSRP Standby Groups you see a message similar to this:

%MLS-3-FIB_MAXHSRP:Maximum number of supported HSRP addresses (16) exceeded

This message indicates that the number of Hot Standby Router Protocol (HSRP) groups sent from the MSRP exceeds the number of HSRP groups supported by NMP.

You must configure a maximum of 16 HSRP groups in hardware in order for hardware switching to take place. If there are more than 16, those flows are not hardware switched, but are switched in software by the MSFC.

Verify the MAC address usage for each VLAN with the show mls cef maccommand.

Caution: Identically numbered HSRP groups use the same virtual MAC address, which can cause errors if you configure bridging on the MSFC.

Note: Because of the restriction to 16 unique HSRP group numbers, CEF for PFC2 cannot support the standby use-biaHSRP command.