Configuring VRRP
The Virtual Router Redundancy Protocol (VRRP) is an election protocol that dynamically assigns responsibility for one or more virtual routers to the VRRP routers on a LAN, allowing several routers on a multiaccess link to utilize the same virtual IP address. A VRRP router is configured to run the VRRP protocol in conjunction with one or more other routers attached to a LAN. In a VRRP configuration, one router is elected as the virtual router master, with the other routers acting as backups in case the virtual router master fails.
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for VRRP" section.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Contents
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Configuration Examples for VRRP
Restrictions for VRRP
VRRP is designed for use over multiaccess, multicast, or broadcast capable LANs. VRRP is not intended as a replacement for existing dynamic protocols.
VRRP is supported on Fast Ethernet, Bridge Group Virtual Interface (BVI), Gigabit Ethernet and TenGigabit interfaces, Multiprotocol Label Switching (MPLS) Virtual Private Networks (VPNs), VRF-aware MPLS VPNs, and VLANs.
The vrrp shutdown commnd should not be used on an interface that is configured to share its interface IP address with the VRRP virtual address. This is a misconfiguration and may result in duplicate IP address errors.
Information About VRRP
•Multiple Virtual Router Support
•VRRP Router Priority and Preemption
•In Service Software Upgrade—VRRP
VRRP Operation
There are several ways a LAN client can determine which router should be the first hop to a particular remote destination. The client can use a dynamic process or static configuration. Examples of dynamic router discovery are as follows:
•Proxy ARP—The client uses Address Resolution Protocol (ARP) to get to the destination it wants to reach, and a router will respond to the ARP request with its own MAC address.
•Routing protocol—The client listens to dynamic routing protocol updates (for example, from Routing Information Protocol [RIP]) and forms its own routing table.
•ICMP Router Discovery Protocol (IRDP) client—The client runs an Internet Control Message Protocol (ICMP) router discovery client.
The drawback to dynamic discovery protocols is that they incur some configuration and processing overhead on the LAN client. Also, in the event of a router failure, the process of switching to another router can be slow.
An alternative to dynamic discovery protocols is to statically configure a default router on the client. This approach simplifies client configuration and processing, but creates a single point of failure. If the default gateway fails, the LAN client is limited to communicating only on the local IP network segment and is cut off from the rest of the network.
VRRP can solve the static configuration problem. VRRP enables a group of routers to form a single virtual router. The LAN clients can then be configured with the virtual router as their default gateway. The virtual router, representing a group of routers, is also known as a VRRP group.
VRRP is supported on Fast Ethernet, BVI, and Gigabit Ethernet interfaces, on MPLS VPNs, VRF-aware MPLS VPNs, and VLANs.
Figure 1 shows a LAN topology in which VRRP is configured. In this example, Routers A, B, and C are VRRP routers (routers running VRRP) that comprise a virtual router. The IP address of the virtual router is the same as that configured for the Gigabit Ethernet interface of Router A (10.0.0.1).
Figure 1 Basic VRRP Topology
Because the virtual router uses the IP address of the physical Gigabit Ethernet interface of Router A, Router A assumes the role of the virtual router master and is also known as the IP address owner. As the virtual router master, Router A controls the IP address of the virtual router and is responsible for forwarding packets sent to this IP address. Clients 1 through 3 are configured with the default gateway IP address of 10.0.0.1.
Routers B and C function as virtual router backups. If the virtual router master fails, the router configured with the higher priority will become the virtual router master and provide uninterrupted service for the LAN hosts. When Router A recovers, it becomes the virtual router master again. For more detail on the roles that VRRP routers play and what happens if the virtual router master fails, see the "VRRP Router Priority and Preemption" section.
Figure 2 shows a LAN topology in which VRRP is configured so that Routers A and B share the traffic to and from clients 1 through 4 and that Routers A and B act as virtual router backups to each other if either router fails.
Figure 2 Load Sharing and Redundancy VRRP Topology
In this topology, two virtual routers are configured. (For more information, see the "Multiple Virtual Router Support" section.) For virtual router 1, Router A is the owner of IP address 10.0.0.1 and virtual router master, and Router B is the virtual router backup to Router A. Clients 1 and 2 are configured with the default gateway IP address of 10.0.0.1.
For virtual router 2, Router B is the owner of IP address 10.0.0.2 and virtual router master, and Router A is the virtual router backup to Router B. Clients 3 and 4 are configured with the default gateway IP address of 10.0.0.2.
VRRP Benefits
Redundancy
VRRP enables you to configure multiple routers as the default gateway router, which reduces the possibility of a single point of failure in a network.
Load Sharing
You can configure VRRP in such a way that traffic to and from LAN clients can be shared by multiple routers, thereby sharing the traffic load more equitably among available routers.
Multiple Virtual Routers
VRRP supports up to 255 virtual routers (VRRP groups) on a router physical interface, subject to the platform supporting multiple MAC addresses. Multiple virtual router support enables you to implement redundancy and load sharing in your LAN topology.
Multiple IP Addresses
The virtual router can manage multiple IP addresses, including secondary IP addresses. Therefore, if you have multiple subnets configured on a GigabitEthernet interface, you can configure VRRP on each subnet.
Preemption
The redundancy scheme of VRRP enables you to preempt a virtual router backup that has taken over for a failing virtual router master with a higher priority virtual router backup that has become available.
Advertisement Protocol
VRRP uses a dedicated Internet Assigned Numbers Authority (IANA) standard multicast address (224.0.0.18) for VRRP advertisements. This addressing scheme minimizes the number of routers that must service the multicasts and allows test equipment to accurately identify VRRP packets on a segment. The IANA assigned VRRP the IP protocol number 112.
Multiple Virtual Router Support
You can configure up to 255 virtual routers on a router physical interface. The actual number of virtual routers that a router interface can support depends on the following factors:
•Router processing capability
•Router memory capability
•Router interface support of multiple MAC addresses
In a topology where multiple virtual routers are configured on a router interface, the interface can act as a master for one virtual router and as a backup for one or more virtual routers.
VRRP Router Priority and Preemption
An important aspect of the VRRP redundancy scheme is VRRP router priority. Priority determines the role that each VRRP router plays and what happens if the virtual router master fails.
If a VRRP router owns the IP address of the virtual router and the IP address of the physical interface, this router will function as a virtual router master.
Priority also determines if a VRRP router functions as a virtual router backup and the order of ascendancy to becoming a virtual router master if the virtual router master fails. You can configure the priority of each virtual router backup with a value of 1 through 254 using the vrrp priority command.
For example, if Router A, the virtual router master in a LAN topology, fails, an election process takes place to determine if virtual router backups B or C should take over. If Routers B and C are configured with the priorities of 101 and 100, respectively, Router B is elected to become virtual router master because it has the higher priority. If Routers B and C are both configured with the priority of 100, the virtual router backup with the higher IP address is elected to become the virtual router master.
By default, a preemptive scheme is enabled whereby a higher priority virtual router backup that becomes available takes over for the virtual router backup that was elected to become virtual router master. You can disable this preemptive scheme using the no vrrp preempt command. If preemption is disabled, the virtual router backup that is elected to become virtual router master remains the master until the original virtual router master recovers and becomes master again.
VRRP Advertisements
The virtual router master sends VRRP advertisements to other VRRP routers in the same group. The advertisements communicate the priority and state of the virtual router master. The VRRP advertisements are encapsulated in IP packets and sent to the IP Version 4 multicast address assigned to the VRRP group. The advertisements are sent every second by default; the interval is configurable.
In Service Software Upgrade—VRRP
VRRP supports In Service Software Upgrade (ISSU). In Service Software Upgrade (ISSU) allows a high-availability (HA) system to run in stateful switchover (SSO) mode even when different versions of Cisco IOS XE software are running on the active and standby Route Processors (RPs) or line cards.
ISSU provides the ability to upgrade or downgrade from one supported Cisco IOS XE release to another while continuing to forward packets and maintain sessions, thereby reducing planned outage time. The ability to upgrade or downgrade is achieved by running different software versions on the active RP and standby RP for a short period of time to maintain state information between RPs. This feature allows the system to switch over to a secondary RP running upgraded (or downgraded) software and continue forwarding packets without session loss and with minimal or no packet loss. This feature is enabled by default.
For detailed information about ISSU, see the Cisco IOS XE In Service Software Upgrade Process document.
Stateful Switchover—VRRP
With the introduction of the SSO—VRRP feature, VRRP is SSO aware. VRRP can detect when a router is failing over to the secondary RP and continue in its current group state.
SSO functions in networking devices (usually edge devices) that support dual RPs. SSO provides RP redundancy by establishing one of the RPs as the active processor and the other RP as the standby processor. SSO also synchronizes critical state information between the RPs so that network state information is dynamically maintained between RPs.
Prior to being SSO aware, if VRRP was deployed on a router with redundant RPs, a switchover of roles between the active RP and the standby RP would result in the router relinquishing its activity as a VRRP group member and then rejoining the group as if it had been reloaded. The SSO—VRRP feature enables VRRP to continue its activities as a group member during a switchover. VRRP state information between redundant RPs is maintained so that the standby RP can continue the router's activities within the VRRP during and after a switchover.
This feature is enabled by default. To disable this feature, use the no vrrp sso command in global configuration mode.
For more information, see the Stateful Switchover document.
How to Configure VRRP
•Customizing VRRP (optional)
•Enabling VRRP (required)
•Disabling a VRRP Group on an Interface (optional)
•Configuring VRRP Text Authentication (optional)
•Enabling VRRP MIB Trap Support (optional)
Customizing VRRP
Perform this task to customize VRRP.
Customizing the behavior of VRRP is optional. Be aware that as soon as you enable a VRRP group, that group is operating. It is possible that if you first enable a VRRP group before customizing VRRP, the router could take over control of the group and become the virtual router master before you have finished customizing the feature. Therefore, if you plan to customize VRRP, it is a good idea to do so before enabling VRRP.
SUMMARY STEPS
1. enable
2. configure terminal
3. interface type number
4. ip address ip-address mask
5. vrrp group description text
6. vrrp group priority level
7. vrrp group preempt [delay minimum seconds]
8. vrrp group timers advertise [msec] interval
9. vrrp group timers learn
10. exit
11. no vrrp sso
DETAILED STEPS
Enabling VRRP
SUMMARY STEPS
1. enable
2. configure terminal
3. interface type number
4. ip address ip-address mask
5. vrrp group ip ip-address [secondary]
6. end
7. show vrrp [brief | group]
8. show vrrp interface type number [brief]
DETAILED STEPS
Disabling a VRRP Group on an Interface
Disabling a VRRP group on an interface allows the protocol to be disabled, but the to be configuration retained. This ability was added with the introduction of the VRRP MIB, RFC 2787, Definitions of Managed Objects for the Virtual Router Redundancy Protocol.
You can use a Simple Network Management Protocol (SNMP) management tool to enable or disable VRRP on an interface. Because of the SNMP management capability, the vrrp shutdown command was introduced to represent a method via the command line interface (CLI) for VRRP to show the state that had been configured using SNMP.
When the show running-config command is entered, you can see immediately if the VRRP group has been configured and set to enabled or disabled. This is the same functionality that is enabled within the MIB.
The no form of the command enables the same operation that is performed within the MIB. If the vrrp shutdown command is specified using the SNMP interface, then entering the no vrrp shutdown command using the Cisco IOS XE CLI will reenable the VRRP group.
SUMMARY STEPS
1. enable
2. configure terminal
3. interface type number
4. ip address ip-address mask
5. vrrp group shutdown
DETAILED STEPS
Configuring VRRP Text Authentication
VRRP ignores unauthenticated VRRP protocol messages. The default authentication type is text authentication.
SUMMARY STEPS
1. enable
2. configure terminal
3. interface type number
4. ip address ip-address mask [secondary]
5. vrrp group authentication text text-string
6. vrrp group ip ip-address
7. Repeat Steps 1 through 6 on each router that will communicate.
8. end
DETAILED STEPS
Enabling VRRP MIB Trap Support
The VRRP MIB supports SNMP Get operations, which allow network devices to get reports about VRRP groups in a network from the network management station.
Enabling VRRP MIB trap support is performed through the CLI, and the MIB is used for getting the reports. A trap notifies the network management station when a router becomes a master or backup router. When an entry is configured from the CLI, the RowStatus for that group in the MIB immediately goes to the active state.
SUMMARY STEPS
1. enable
2. configure terminal
3. snmp-server enable traps vrrp
4. snmp-server host host community-string vrrp
DETAILED STEPS
Configuration Examples for VRRP
•Example: VRRP Text Authentication
•Example: Disable a VRRP Group on an Interface
Example: Configuring VRRP
In the following example, Router A and Router B each belong to three VRRP groups.
In the configuration, each group has the following properties:
•Group 1:
–Virtual IP address is 10.1.0.10.
–Router A will become the master for this group with priority 120.
–Advertising interval is 3 seconds.
–Preemption is enabled.
•Group 5:
–Router B will become the master for this group with priority 200.
–Advertising interval is 30 seconds.
–Preemption is enabled.
•Group 100:
–Router A will become the master for this group first because it has a higher IP address (10.1.0.2).
–Advertising interval is the default 1 second.
–Preemption is disabled.
Router A
Router(config)# interface GigabitEthernet 1/0/0
Router(config-if)# ip address 10.1.0.2 255.0.0.0
Router(config-if)# vrrp 1 priority 120
Router(config-if)# vrrp 1 authentication cisco
Router(config-if)# vrrp 1 timers advertise 3
Router(config-if)# vrrp 1 timers learn
Router(config-if)# vrrp 1 ip 10.1.0.10
Router(config-if)# vrrp 5 priority 100
Router(config-if)# vrrp 5 timers advertise 30
Router(config-if)# vrrp 5 timers learn
Router(config-if)# vrrp 5 ip 10.1.0.50
Router(config-if)# vrrp 100 timers learn
Router(config-if)# no vrrp 100 preempt
Router(config-if)# vrrp 100 ip 10.1.0.100
Router(config-if)# no shutdown
Router B
Router(config)# interface GigabitEthernet 1/0/0
Router(config-if)# ip address 10.1.0.1 255.0.0.0
Router(config-if)# vrrp 1 priority 100
Router(config-if)# vrrp 1 authentication cisco
Router(config-if)# vrrp 1 timers advertise 3
Router(config-if)# vrrp 1 timers learn
Router(config-if)# vrrp 1 ip 10.1.0.10
Router(config-if)# vrrp 5 priority 200
Router(config-if)# vrrp 5 timers advertise 30
Router(config-if)# vrrp 5 timers learn
Router(config-if)# vrrp 5 ip 10.1.0.50
Router(config-if)# vrrp 100 timers learn
Router(config-if)# no vrrp 100 preempt
Router(config-if)# vrrp 100 ip 10.1.0.100
Router(config-if)# no shutdown
Example: VRRP Text Authentication
The following example shows how to configure VRRP text authentication using a text string:
Router(config)# interface GigabitEthernet 0/0/0
Router(config)# ip address 10.21.8.32 255.255.255.0
Router(config-if)# vrrp 10 authentication text stringxyz
Router(config-if)# vrrp 10 ip 10.21.8.10
Example: Disable a VRRP Group on an Interface
The following example shows how to disable one VRRP group on GigabitEthernet interface 0/0/0 while retaining VRRP for group 2 on GigabitEthernet interface 1/0/0:
Router(config)# interface GigabitEthernet 0/0/0
Router(config-if)# ip address 10.24.1.1 255.255.255.0
Router(config-if)# vrrp 1 ip 10.24.1.254
Router(config-if)# vrrp 1 shutdown
Router(config-if)# exit
Router(config)# interface GigabitEthernet 1/0/0
Router(config-if)# ip address 10.168.42.1 255.255.255.0
Router(config-if)# vrrp 2 ip 10.168.42.254
Example: VRRP MIB Trap
Router(config)# snmp-server enable traps vrrp
Router(config)# snmp-server host 10.1.1.0 community abc vrrp
Additional References
Related Documents
Standards
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No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature. |
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MIBs
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VRRP MIB |
To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL: |
RFCs
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RFC 2338 |
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RFC 2787 |
Definitions of Managed Objects for the Virtual Router Redundancy Protocol |
RFC 3768 |
Technical Assistance
Feature Information for VRRP
Table 1 lists the features in this module and provides links to specific configuration information.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Note Table 1 lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
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ISSU—VRRP |
Cisco IOS XE |
VRRP supports In Service Software Upgrade (ISSU). ISSU allows a high-availability (HA) system to run in stateful switchover (SSO) mode even when different versions of Cisco IOS XE software are running on the active and standby Route Processors (RPs) or line cards. This feature provides customers with the same level of HA functionality for planned outages due to software upgrades as is available with SSO for unplanned outages. That is, the system can switch over to a secondary RP and continue forwarding packets without session loss and with minimal or no packet loss. This feature is enabled by default. The following section provides information about this feature: • There are no new or modified commands for this feature. |
SSO—VRRP |
Cisco IOS XE |
VRRP is now SSO aware. VRRP can detect when a router is failing over to the secondary RP and continue in its current VRRP group state. This feature is enabled by default. The following sections provide information about this feature: The following commands were introduced or modified by this feature: debug vrrp ha, show vrrp, vrrp sso. |
Virtual Router Redundancy Protocol |
Cisco IOS XE |
VRRP enables a group of routers to form a single virtual router to provide redundancy. The LAN clients can then be configured with the virtual router as their default gateway. The virtual router, representing a group of routers, is also known as a VRRP group. The following commands were introduced by this feature: debug vrrp all, debug vrrp error, debug vrrp events, debug vrrp packets, debug vrrp state, show vrrp, show vrrp interface, vrrp authentication, vrrp description, vrrp ip, vrrp preempt, vrrp priority, vrrp timers advertise, vrrp timers learn. |
VRRP MIB—RFC 2787 |
Cisco IOS XE |
The VRRP MIB—RFC 2787 feature enables an enhancement to the MIB for use with SNMP-based network management. The feature adds support for configuring, monitoring, and controlling routers that use VRRP. The following sections provide information about this feature: • • The following command was introduced by this feature: vrrp shutdown. The following commands were modified by this feature: snmp-server enable traps and snmp-server host. |
Glossary
virtual IP address owner—The VRRP router that owns the IP address of the virtual router. The owner is the router that has the virtual router address as its physical interface address.
virtual router—One or more VRRP routers that form a group. The virtual router acts as the default gateway router for LAN clients. Also known as a VRRP group.
virtual router backup—One or more VRRP routers that are available to assume the role of forwarding packets if the virtual router master fails.
virtual router master—The VRRP router that is currently responsible for forwarding packets sent to the IP addresses of the virtual router. Usually the virtual router master also functions as the IP address owner.
VRRP router—A router that is running VRRP.
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