Virtual Router Redundancy Protocol (VRRP)
Operating Notes
Operating Notes
■ VRRP Advertisements Not Reaching the Backup(s): If a Master
is forwarding traffic properly, but its Backup(s) are prevented from
receiving the Master’s VRRP advertisements, then both routers will
operate in the Master mode for the VR. If this occurs, traffic for the
applicable gateway will continuously alternate between routers
(sometimes termed “flapping”).
■ Deleting an IP Address Used To Support a VR: Refer to “General
Operating Rules” on page 6-11.
■ VR Limits: A VLAN allows up to 32 VRs, and a VR allows up to 32 IP
addresses. This means that one VR can support up to 32 subnets. This
capacity enables use of VRRP on all subnets in a VLAN that has more
than 32 subnets.
■ IPv4: The routers covered by this Guide support IPv4 IP addressing
for VRRP applications.
■ Authentication Type: As per RFC 3768, the authentication type for
VRRP packets inbound on the router is 0 (zero; that is, “no authenti-
cation”). Packets with other authentication types are dropped, and
authentication type is not supported in the VRRP MIB. If you are
coordinating the use of VRRP on the routers covered by this manual
with another vendor’s implementation based on an older RFC, then
you must set the authentication type to 0 (zero) on the other vendor’s
device.
■ Proxy-ARP requests and MAC addresses: The following table
shows which MAC address is returned in response to a proxy-ARP
request.
Configured as: Administratively: Returns:
Owner Enabled VRRP MAC address
Owner Disabled Default VLAN MAC address
Backup Enabled, in Master state VRRP MAC address
Backup Enabled, not in Master VRRP router does not respond to
state proxy-ARP request.
Backup Disabled Default VLAN MAC address
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