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AT-WR4500 Series - IEEE 802.11abgh Outdoor Wireless Routers 249
RouterOS v3 Configuration and User Guide
11 High Availability protocols and techniques
11.1 VRRP
Document revisi on: 1.5 (Mon Jul 10 16:51:20 GMT 2006)
Applies to: V2.9
11.1.1 General Information
Summary
Virtual Router Redundancy Protocol (VRRP) implementation in the RouterOS is RFC2338 compliant.
VRRP protocol is used to ensure constant access to some resources. Two or more routers (referred as
VRRP Routers in this context) create a highly available cluster (also referred as Virtual routers) with
dynamic fail over. Each router can participate in not more than 255 virtual routers per interface. Many
modern routers support this protocol.
Network setups with VRRP clusters provide high availability for routers without using clumsy ping-based
scripts.
Specifications
Packages required: system
License required: Level1
Submenu level: /ip vrrp
Standards and Technologies: VRRP, AH, HMAC-MD5-96 within ESP and AH
Hardware usage: Not significant
Related Topics
IP Addresses and ARP
Description
Virtual Router Redundancy Protocol is an election protocol that provides high availability for routers. A
number of routers may participate in one or more virtual routers. One or more IP addresses may be
assigned to a virtual router.
A node of a virtual router can be in one of the following states:
• MASTER state, when the node answers all the requests to the instance's IP addresses. There may
only be one MASTER node in a virtual router. This node sends VRRP advertisement packets to all the
backup routers (using multicast address) every once in a while (set in interval property).
• BACKUP state, when the VRRP router monitors the availability and state of the Master Router. It
does not answer any requests to the instance's IP addresses. Should master become unavailable (if at
least three sequential VRRP packets are lost), election process happens, and new master is
proclaimed based on its priority. For more details on virtual routers, see RFC2338.
VRRP does not currently work on VLAN interfaces, as it is impossible to have the MAC address of a
VLAN interface different from the MAC address of the physical interface it is put on.
11.1.2 VRRP Routers
Submenu level: /ip vrrp
Description
A number of VRRP routers may form a virtual router. The maximal number of clusters on one network is
255 each having a unique VRID (Virtual Router ID). Each router participating in a VRRP cluster must have
it priority set to a valid value. Each VRRP instance is configured like a virtual interface that bound to a real
interface (in a similar manner VLAN is). VRRP addresses are then put on the virtual VRRP interface
normally. The VRRP master has running flag enabled, making the address (and the associated routes and