8.2. VRRP

VRRP (Virtual Router Redundancy Protocol) is a computer network protocol designed to increase the availability of routers acting as a default gateway. This is achieved by combining a group of routers into one virtual router and assigning them a common IP address which will be used in the same L2 network. vCGNAT implements VRRP v3 (RFC 5798).

8.2.1. Definitions

VRRP Router	A router on which the VRRP is run. It can participate in one or more virtual routers
Virtual Router	An abstract object managed by VRRP acts as the host’s default router. In fact, a virtual router is a group of router interfaces on the same network that share a Virtual Router Identifier (VRID) and a virtual IP address
Virtual IP address	It is an IP address is selected from the set of real interface addresses. VRRP advertisements are always sent using the primary IP address as the source of the IP packet
IP Address Owner	It is a VRRP router that uses the IP address assigned to the virtual router as the real IP address
Virtual Router Master	It is a VRRP router responsible for forwarding packets sent to the IP address associated with the virtual router and responding to ARP requests sent to that address. If the IP address owner is available, then it always becomes the Master
Virtual Router Backup	It is a group of idle routers that are ready to take over the role of Virtual Router Master as soon as the current VRRP Master router becomes unavailable
Virtual MAC	The virtual MAC address 0000:5E00:01xx, where xx is the VRRP group number

8.2.2. Configuring

To configure VRRP, enter the data interface configuration mode and use the command:

vrrp (1-255)

where (1-255) is a VRID.

The following keys are available:

Key	Argument	Description
ip	A.B.C.D	Set Virtual Router IPv4 address
ipv6	X:X::X:X	Set Virtual Router IPv6 address
preempt		Preempt mode controls whether the Backup router with a higher priority will try to take over the Master role from the current Master router with a lower priority. The exception is that a VRRP router will always become Master if it is an IP Address Owner. By default, this mode is disabled. Enter this command to enable it
preempt delay minimum	1-65535)	Delay in seconds between Backup router with higher priority goes to backup state and starts to sent VRRP advertisements to become Master
priority	(1-254)	Set the priority for this VRRP router that will be used to select a VRRP Master. Higher values equal higher priority. The value 255 is reserved for the router that owns the IP address associated with the virtual router. The value 0 is used when the current Master router should be stopped from participating in VRRP. Backup routers will then begin selecting the Master without waiting for the current Master to timeout. The default value is 100
timers advertise	(1-4095)	The interval (in seconds) between sending VRRP advertisements. The default setting is 1 second

8.2.3. Show Commands

show vrrp (1-255) counters [ip|ipv6]

Display VRRP counters for IPv4 or IPv6 protocol. The output will be as follows:

Router1# show vrrp 1 counters
------------------------------------------------------------
Counter                                 Value
------------------------------------------------------------
VRRP advertisement packets sent         14336
VRRP advertisement packets received     0
Transitions to INIT state               1
Transitions to BACKUP state             1
Transitions to MASTER state             1
VRRP priority 0 adv packets sent        0
Allocation packet buffer drops          0
Sending nd announce packet drops        0
------------------------------------------------------------

Note: if you have several VRRP Routers and do not point out the VRID, then the counters will be summarized.

clear vrrp (1-255) counters [ip|ipv6]

Clear VRRP counters for IPv4 or IPv6 protocol.

show vrrp (1-255)

Display various information about VRRP Router:

if1 - Group 1 - Address-Family IPv4
State is MASTER
State duration 28 mins 34.826 secs
Virtual IP address is 192.168.3.14
Virtual MAC address is 00:00:5E:00:01:01
Advertisement interval is 100 csec
Preemption enabled
Priority is 100
Master Router is 192.168.3.4, priority is 100
Master Advertisement interval is 100 csec (expires in 67 csec)