VRRP, Virtual Router Redundancy Protocol

Description Glossary RFCs Publications Obsolete RFCs


Protocol suite: TCP/IP.
Protocol type:Transport layer election protocol.
Multicast addresses:
IP Protocol:112.
MIME subtype:
SNMP MIBs: iso.org.dod.internet.mgmt.mib-2.vrrpMIB (
Working groups: vrrp, Virtual Router Redundancy Protocol.

This protocol is intended for use with IPv4 routers only.

VRRP packets are sent encapsulated in IP packets. They are sent to the IPv4 multicast address assigned to VRRP.

RFC 2338:

VRRP is designed to eliminate the single point of failure inherent in the static default routed environment. VRRP specifies an election protocol that dynamically assigns responsibility for a virtual router to one of the VRRP routers on a LAN. The VRRP router controlling the IP address(es) associated with a virtual router is called the Master, and forwards packets sent to these IP addresses. The election process provides dynamic fail-over in the forwarding responsibility should the Master become unavailable. Any of the virtual router's IP addresses on a LAN can then be used as the default first hop router by end-hosts. The advantage gained from using VRRP is a higher availability default path without requiring configuration of dynamic routing or router discovery protocols on every end-host.

VRRP provides a function similar to the HSRP protocol and to a Digital Equipment Corporation, Inc. proprietary protocol named IP Standby Protocol.

MAC header IP header VRRP message

VRRP version 2 message:

0001020304050607 0809101112131415 1617181920212223 2425262728293031
Version Type VRID Priority IP address count
Authentication type Advertisement interval Checksum
IP Addresses [] :::
Authentication data :::

Version. 4 bits. Must be set to 2.
VRRP protocol version number.

Type. 4 bits.


VRID, Virtual Router ID. 8 bits.
Identifies the virtual router this packet is reporting status for.

Priority. 8 bits, unsigned.
(RFC 2338) Specifies the sending VRRP router's priority for the virtual router. Higher values equal higher priority. The priority value for the VRRP router that owns the IP address(es) associated with the virtual router MUST be 255. VRRP routers backing up a virtual router MUST use priority values between 1 and 254. The default priority value for VRRP routers backing up a virtual router is 100. The priority value zero (0) has special meaning indicating that the current Master has stopped participating in VRRP. This is used to trigger Backup routers to quickly transition to Master without having to wait for the current Master to timeout.

IP address count. 8 bits.
The number of IP addresses contained in this VRRP advertisement.

Authentication type. 8 bits.
Identifies the authentication method being utilized. Authentication type is unique on a per interface basis. The authentication type field is an 8 bit unsigned integer. A packet with unknown authentication type or that does not match the locally configured authentication method MUST be discarded.

0No authentication.
1Simple text password.
2 AH, IP Authentication Header.

Advertisement interval. 8 bits. Default 1 second.
Indicates the time interval in seconds between ADVERTISEMENTS. This field is used for troubleshooting misconfigured routers.

Checksum. 16 bits.
16-bit one's complement of the one's complement sum of the entire VRRP message starting with the version field. For computing the checksum, the checksum field is cleared to zero.

IP addresses. Variable length.
One or more IP addresses that are associated with the virtual router. The number of addresses included is specified by IP address count. These fields are used for troubleshooting misconfigured routers.

Authentication data. Variable length, 0 to 8 bytes.
Currently only utilized for simple text authentication, similar to the simple text authentication found in OSPF. It may contain up to 8 characters of plain text. If the configured authentication string is shorter than 8 bytes, the remaining space MUST be cleared to zero. Any VRRP packet received with an authentication string that does not match the locally configured authentication string MUST be discarded. The authentication string is unique on a per interface basis.


IP address owner.
The VRRP router that has the virtual router's IP address(es) as real interface address(es). This is the router that, when up, will respond to packets addressed to one of these IP addresses for ICMP pings, TCP connections, etc.

Primary IP address.
An IP address selected from the set of real interface addresses. One possible selection algorithm is to always select the first address. VRRP advertisements are always sent using the primary IP address as the source of the IP packet.

Virtual router.
An abstract object managed by VRRP that acts as a default router for hosts on a shared LAN. It consists of a Virtual Router Identifier and a set of associated IP address(es) across a common LAN. A VRRP Router may backup one or more virtual routers.

Virtual router backup.
The set of VRRP routers available to assume forwarding responsibility for a virtual router should the current Master fail.

Virtual router master.
The VRRP router that is assuming the responsibility of forwarding packets sent to the IP address(es) associated with the virtual router, and answering ARP requests for these IP addresses. Note that if the IP address owner is available, then it will always become the Master.

VRRP router.
A router running VRRP. It may participate in one or more virtual routers.


[RFC 2787] Definitions of Managed Objects for the Virtual Router Redundancy Protocol.

[RFC 3768] Virtual Router Redundancy Protocol (VRRP).


Obsolete RFCs:

[RFC 2338] Virtual Router Redundancy Protocol.

Description Glossary RFCs Publications Obsolete RFCs