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Overview Troubleshooting Virtual Router Redundancy Protocol (VRRP)
page 13-2 OmniSwitch Troubleshooting Guide September 2005
Overview
VRRP specifies an election protocol. All protocol messaging (not user data) is performed using IP multi-
cast datagrams. The Multicast IP address is 224.0.0.18. This allows VRRP to operate over a variety of
LAN technologies supporting IP. There source MAC address for these datagrams is also specified in the
RFC. That is 00-00-5E-00-01-(VRID).
The last pair in the Mac address is the Virtual Router ID (VRID). This is a configurable item. A virtual
router is defined by the VRID and a set of IP addresses. Thus a router may associate a virtual router with a
real address on an interface as well as different addresses for the virtual router and the interface. The
mapping between VRID and addresses must be coordinated among all VRRP routers on a LAN. It is
allowed reuse the same VRID with a different address mapping on a different VLAN. Each Virtual Router
is restricted to a single VLAN.
Only the Master Router for each Virtual Router sends periodic VRRP Advertisements. A back-up router
will not preempt a Master unless it has a higher priority. It is possible to preempt all preempt attempts. The
only exception is when there is a VRRP router that has the virtual router as an interface address. In that
case that router will always preempt.
After election of the Master Router, the Master Router will send VRRP Advertisements.
As long the Backup Router receives the VRRP Advertisements, it will only listen. The moment it’s not
receiving VRRP advertisements for a configured amount of time, the Backup Router will announce itself
as new Master Router in the VLAN.
In case more then one Backup Router exist, the one with the second highest priority will become Master
Router.
It should be noted that while the VRRP router must reply to ARP messages for the IP/MAC address infor-
mation it must not reply to echo request unless the virtual address is a real address on that switch.
VRRP defines three possible types of authentication. Do not mistake this authentication for access to the
network or its resources. This refers to whether or not a VRRP router will accept another VRRP routers
messages. The 3 types are None, Simple Text Password, and IP security.