VRRP MAC address

[cisco2003]

Please tell me what MAC address VRRP uses for the virtual IP. Do all cisco IOS use only one unique MAC for one VRRP group? What about the virtual MAC address in case master failure, does new master(previously backup) still use same virtual MAC after previous master fails?

Also I want to know if it is possible that IOS answer ARP request for the virtual IP with master's real physical MAC address in some cases.

For example, R1 e0 is configed with VRRP, its physical MAC address is MAC-PHY, virtual MAC for that virtual ip is MAC-VIR. When ping the virtual IP, master R1 answer ARP with MAC-PHY, or other MAC than MAC-VIR. Is that possible in some cases?

I used 2610 and 3610 IOS 12.3 test it. And I found it always use same virtual MAC. But I am not sure different platform/IOS has different beheavior.

Thanks in advance.

[Roberto Salazar]

Please tell me what MAC address VRRP uses for the virtual IP. Do all cisco IOS use only one unique MAC for one VRRP group?

>>>The virtual router MAC address associated with a virtual router is an IEEE 802 MAC Address in the following format:

00-00-5E-00-01-{VRID} (in hex in internet standard bit-order)

The first three octets are derived from the IANA's OUI. The next two octets (00-01) indicate the address block assigned to the VRRP protocol. {VRID} is the VRRP Virtual Router Identifier. This

mapping provides for up to 255 VRRP routers on a network.

What about the virtual MAC address in case master failure, does new master(previously backup) still use same virtual MAC after previous master fails?

>>> Yes, per above that mac-address is associated to Virtual Router.

Also I want to know if it is possible that IOS answer ARP request for the virtual IP with master's real physical MAC address in some cases.

For example, R1 e0 is configed with VRRP, its physical MAC address is MAC-PHY, virtual MAC for that virtual ip is MAC-VIR. When ping the virtual IP, master R1 answer ARP with MAC-PHY, or other MAC than MAC-VIR. Is that possible in some cases?

>>> I don;t think so since there is no interface command to tell router to use BIA for VRRP much like the HSRP.

I used 2610 and 3610 IOS 12.3 test it. And I found it always use same virtual MAC. But I am not sure different platform/IOS has different beheavior.

>>> It's not platform dependent it's how it operate per RFC 2338.

Please rate helpful posts.

[russell.hughes]

"

Also I want to know if it is possible that IOS answer ARP request for the virtual IP with master's real physical MAC address in some cases.

For example, R1 e0 is configed with VRRP, its physical MAC address is MAC-PHY, virtual MAC for that virtual ip is MAC-VIR. When ping the virtual IP, master R1 answer ARP with MAC-PHY, or other MAC than MAC-VIR. Is that possible in some cases?"

Well I'm no expert but, can't you use a unique ip address on the physical interfaces of each router(say 10.1.1.2 for R1 and 10.1.1.3 for R2)and have a unique Virtual Router address in the same subnet( 10.1.1.1). If you arp to the VIP(10.1.1.1) you get the virtual mac. If you arp for 10.1.1.2 you get R1's BIA mac. If you arp for 10.1.1.3 you get R2's BIA mac. Now the only one that is redundant is the VIP(10.1.1.1).

[russell.hughes]

But the real question is what are you trying to get done?

[paul driver]

Hello

Very old post however regards first hop redundency servcies such as VRRP devices use by default as you have stated a virtual mac-address and a virtual ip address, When VRRP failover occurs the end hosts will have no need to change their own cam/arp entries becasue they will have the same vip and vmac however any switchports interconnecting the FHRP devcies will change because the active master will broadcast a GARP so say its now the active member servicing the FHRP group and the switchs will then update their own cam table to show the vmac is now via a different switchport.

IF you use the BIA mac address of each specific FHRP device instead of the the groups vmac so that the FHRP devcies only share the same vip address and NOT the vmac then when failover initates the master will again broadcast an GARP but this time the swithes and end hosts will both change their cam/arp tables to acommodate the failover change.