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VRRP MAC address

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.

1 REPLY

Re: VRRP MAC address

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.

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