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# Configuring VRRP

Configuring VRRP requires that you first configure an IP interface over which you can configure VRRP and any VRID instances in which you want the VRRP routers to participate. The following sections contain information for configuring the IP interface for VRRP, any VRID instances for the VRRP routers, and steps for creating a basic VRRP configuration.

## Configuring the IP Interface

Before you configure VRRP, you must configure an IP interface and assign a primary IP address and subnet mask. When the IP address belongs to the owner of the VRID, you must associate the IP address with the VRID that you create.

To configure the IP interface for VRRP:

1. Configure an IP interface.
   `
   host1(config)#interface fastEthernet 4/0
   `
2. Assign an IP address and a subnet mask.
   `
   host1(config-if)#ip address 194.50.1.42 255.255.255.0
   `

   | Note: We recommend that you complete all IP address configurations before you configure VRRP. If for any reason the IP address information changes after you configure VRRP, you must revise the associated IP addresses configured on the related VRRP entries. If you specify auto addresses in the ip vrrp virtual-address command along with using priority 255, you must disable and reenable the VRRP entry to update the association list.

## Creating VRIDs

A master or backup router running the VRRP protocol can participate in one or more VRID instances. You can create a VRID instance in several ways:

- We recommend that you create and configure a VRID instance first, and enable it last. For example:
  `
  host1(config-if)#ip vrrp 198
  host1(config-if)#ip vrrp 198 priority 255
  `
- You can create and enable a VRID instance by using the ip vrrp vrid enable command. For example:
  `
  host1(config-if)#ip vrrp 25 enable
  `
- You continue to configure the VRID by identifying the VRID each time you use a VRRP command. For example:
  `
  host1(config-if)#ip vrrp 175 authentication-type none
  `
- Alternatively, you can create a new VRID when you use any VRRP command, provided that you are using the VRID instance for the first time. For example, if you execute the ip vrrp vrid preempt command and it is the first time that you use the VRID, the command creates a new VRID.
  `
  host1(config-if)#ip vrrp 16 preempt
  `
- Use the ip vrrp vrid enable command last. The new VRID is not enabled until you execute this command.
  `
  host1(config-if)#ip vrrp 198 enable
  host1(config-if)#ip vrrp 16 enable
  host1(config-if)#ip vrrp 175 enable
  `

## Configuration Steps

Before you configure VRRP, we recommend that you review the configuration examples in the earlier section How VRRP Works.

To configure VRRP parameters:

1. (Optional) Create a VRID instance.
   `
   host1(config-if)#ip vrrp 25
   `
2. (Optional) Set a VRRP advertisement interval for the same VRID.
   `
   host1(config-if)#ip vrrp 25 advertise-interval 50
   `
3. Set the VRRP router priority for owner or backup routers.

   This step is mandatory to configure priority for the owner VRID (255). This step is optional to configure priority for a backup VRID (1–254). The default value is 100.

   `
   host1(config-if)#ip vrrp 25 priority 255
   host1(config-if)#ip vrrp 22 priority 254
   `
4. (Optional) Specify that the backup router can process packets with an IP destination address of the virtual address.
   `
   host1(config-if)#ip vrrp 22 accept-data
   `
5. (Optional) Set the preempt option. This example creates a new VRID.
   `
   host1(config-if)#ip vrrp 10 preempt
   `
6. Associate an IP address with a VRID.
   `
   host1(config-if)#ip vrrp 25 virtual-address 194.2.1.63
   `
7. (Optional) Set the VRRP authentication type to either text or none.
   `
   host1(config-if)#ip vrrp 25 authentication-type none
   `
8. (Optional) Configure the VRRP authentication key.
   `
   host1(config-if)#ip vrrp 25 authentication-key dublin
   `
9. Enable the VRID instance.
   `
   host1(config-if)#ip vrrp 25 enable
   `

ip vrrp

- Use to create a VRID instance.
- The VRID range is 1–255.
- Example
  `
  host1(config-if)#ip vrrp 25
  `
- Use the no version to remove a VRID instance.
- See ip vrrp.

ip vrrp accept-data

- Use to enable the backup router to process packets with an IP destination address equivalent to the virtual addresses while the backup router is in the master state.
- Use the default state (disabled) for full compliance with RFC 2338.
- The configuration ignores this attribute if the VRRP entry uses a priority of 255 (owner).

  | Note: When using this attribute and also restricting incoming packets to ICMP only, you must use policy filters to accept only ICMP packets with the virtual address as the destination address.

- Example
  `
  host1(config-if)#ip vrrp 22 accept-data
  `
- Use the no version to disable processing of data packets by the backup router while the router is in the master state. When disabled, the master router drops any packets with an IP destination address equivalent to the virtual addresses.
- See ip vrrp accept-data.

ip vrrp advertise-interval

- Use to configure the amount of time the VRRP router waits between advertisements.
- Specify the interval time in seconds or milliseconds.
- Use seconds to be in compliance with RFC 2338.
- If your VRID environment consists of only E Series routers, you can optionally use milliseconds.
- Example
  `
  host1(config-if)#ip vrrp 25 advertise-interval 50
  `
- Use the no version to restore the default value, 1 second.
- See ip vrrp advertise-interval.

ip vrrp authentication-key

- Use to specify the authentication key.
- Use the key keyword only when the authentication type is text. See the ip vrrp authentication-type command.
- Example
  `
  host1(config-if)#ip vrrp 25 authentication-key dublin
  `
- Use the no version to set the authentication key to its default, an empty string.
- See ip vrrp authentication-key.

ip vrrp authentication-type

- Use to specify the authentication type; text or none.
- Example
  `
  host1(config-if)#ip vrrp 175 authentication-type none
  `
- Use the no version to set the authentication type to its default, none.
- See ip vrrp authentication-type.

ip vrrp enable

- Use to enable an existing VRID instance.
- Specify a VRID in the range 1–255.
- The default is that VRRP is disabled.
- Example
  `
  host1(config-if)#ip vrrp 175 enable
  `
- Use the no version to disable an existing VRID instance.
- See ip vrrp enable.

ip vrrp preempt

- Use to enable preemption. When preemption is enabled, a backup router always takes over the responsibility of the master router. When preemption is disabled, the lower-priority backup router is left in the backup state.
- Example
  `
  host1(config-if)#ip vrrp 10 preempt
  `
- The default is that VRRP preemption is enabled.
- Use the no version to disable preemption.
- See ip vrrp preempt.

ip vrrp priority

- Use to configure the priority of VRRP routers.
- Use a value of 255 to imply master router priority.
- Use a value in the range 1–254 to imply backup router priority.
- Example
  `
  host1(config-if)#ip vrrp 25 priority 255
  `
- Use the no version to set the priority to the default value, 100.
- See ip vrrp priority.

ip vrrp virtual-address

- Use to associate an IP address with a VRID.
- Use the auto keyword to automatically learn or configure associated addresses, depending on the priority attribute.
- There is no default.
- Example
  `
  host1(config-if)#ip vrrp 25 virtual-address 194.2.1.63
  `
- Use the no version to remove an IP address association with a VRID. If you use auto addressing, the no version clears the auto flag.
- See ip vrrp virtual-address.

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