HSRP Failover

[deeshar]

Hi,

We are experiencing at least one unwanted fail over per day at the peak hours. Sys log showed the messages "master down timer expired" and some of the events related to HSRP. After analyzing the sys logs our vendor recommend to enter the command.

standby use-bia

We tried to find the details of the command but could not located *what* difference it will make. Could anyone please suggest the significance of the command and the difference it will make.

I had referred to TAC documentation and could not find the concrete reason to implement that. As per the Cisco documentation command details are mentioned below.

standby use-bia [scope interface] Configure HSRP to use the burned-in address of an interface as its virtual MAC address instead of the preassigned MAC address (on Ethernet and FDDI) or the functional address (on Token Ring).

Thanks and Regards,

Deepak Sharma

[jolmo]

Hi Deepak

Please read this document: Avoiding HSRP Instability in a Switching Environment with Various Router Platforms

http://www.cisco.com/en/US/tech/tk648/tk362/technologies_configuration_example09186a0080093f93.shtml

and see #4 in "Troubleshooting Procedure".

The "standby use-bia" command can help in avoiding HSRP instability but have a few disadvantages.

Hope this helps

[Giuseppe Larosa]

Hello Deepak,

this is a real issue in complex networks.

In theory HSRP, that isn't a routing protocol because it doesn't interact with the IP routing table, offers a complete emulation of a default gateway over a broadcast domain == VLAN at both L3 and L2 OSI.

In practice it depends from platform to platform.

High end modular routers like C7500 with VIP linecards or Cisco GSR 12000 with Engine 1,2,3 have a low level limit on the NIC like 32 MAC addresses for the capture filter. If the same router is master for 20 HSRP groups defined on subifs of a gigabit ethernet interface 20 items of that MAC table are used.

Using standby use-bia allows to use the interface native MAC address without consuming items on that capture table.

Multilayer switches have opposite needs and is better to use the same HSRP groups on different subifs of the same interface. We noticed that they use the same bia on all ports for the STP protocol needs.

Routing protocols consumes items too.OSPF uses two items / MAC addresses on a LAN, PIM, IGMP counts too.

HTH

giuseppe larosa

senior network engineer

CCIE SP 14802, CCNP, CCNA

[deeshar]

Hi Giuseppe,

Looks like taking about our topology and makes sense too :). I will dig more information in this reagard and if I find any problem or any intresting update I will post in forum.

Thanks once again,

Deepak