Configuring VRRP

This chapter describes how to configure the Virtual Router Redundancy Protocol (VRRP) on Cisco NX-OS switches.

This chapter includes the following sections:

Information About VRRP

VRRP allows for transparent failover at the first-hop IP router, by configuring a group of routers to share a virtual IP address. VRRP selects a master router in that group to handle all packets for the virtual IP address. The remaining routers are in standby and take over if that the master router fails.

VRRP Operation

A LAN client can determine which router should be the first hop to a particular remote destination by using 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 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 disadvantage 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. Although, this approach simplifies client configuration and processing, it 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 by enabling a group of routers (a VRRP group) to share a single virtual IP address. You can then configure the LAN clients with the virtual IP address as their default gateway.

The following figure shows a basic VLAN topology. In this example, Routers A, B, and C form a VRRP group. The IP address of the group is the same address that was configured for the Ethernet interface of Router A (10.0.0.1).

Figure 1. Basic VRRP Topology

Because the virtual IP address uses the IP address of the physical Ethernet interface of Router A, Router A is the master (also known as the IP address owner). As the master, Router A owns the virtual IP address of the VRRP group router and forwards 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 backups. If the master fails, the backup router with the highest priority becomes the master and takes over the virtual IP address to provide uninterrupted service for the LAN hosts. When router A recovers, it becomes the router master again. For more information, see the “VRRP Router Priority and Preemption” section.


Note

Packets received on a routed port destined for the VRRP virtual IP address will terminate on the local router, regardless of whether that router is the master VRRP router or a backup VRRP router. This includes ping and telnet traffic. Packets received on a Layer 2 (VLAN) interface destined for the VRRP virtual IP address will terminate on the master router.

VRRP Benefits

The benefits of VRRP are as follows:

  • Redundance—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—Allows traffic to and from LAN clients to be shared by multiple routers. The traffic load is shared more equitably among available routers.

  • Multiple VRRP groups—Supports up to 255 VRRP groups on a router physical interface if the platform supports multiple MAC addresses. Multiple VRRP groups enable you to implement redundancy and load sharing in your LAN topology.

  • Multiple IP Addresses—Allows you to manage multiple IP addresses, including secondary IP addresses. If you have multiple subnets configured on an Ethernet interface, you can configure VRRP on each subnet.

  • Preemption—Enables you to preempt a backup router that has taken over for a failing master with a higher priority backup router that has become available.

  • Advertisement Protocol—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. IANA has assigned the IP protocol number 112 to VRRP.

  • VRRP Tracking—Ensures that the best VRRP router is the master for the group by altering VRRP priorities based on interface states.

Multiple VRRP Groups

You can configure up to 255 VRRP groups on a physical interface. The actual number of VRRP groups that a router interface can support depends on the following factors:

  • Router processing capability

  • Router memory capability

In a topology where multiple VRRP groups are configured on a router interface, the interface can act as a master for one VRRP group and as a backup for one or more other VRRP groups.

The following figure 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. Routers A and B act as backups to each other if either router fails.

Figure 2. Load Sharing and Redundancy VRRP Topology

This topology contains two virtual IP addresses for two VRRP groups that overlap. For VRRP group 1, Router A is the owner of IP address 10.0.0.1 and is the master. Router B is the backup to router A. Clients 1 and 2 are configured with the default gateway IP address of 10.0.0.1.

For VRRP group 2, Router B is the owner of IP address 10.0.0.2 and is the master. Router A is the backup to router B. Clients 3 and 4 are configured with the default gateway IP address of 10.0.0.2.

VRRP Router Priority and Preemption

An important aspect of the VRRP redundancy scheme is the VRRP router priority because the priority determines the role that each VRRP router plays and what happens if the master router fails.

If a VRRP router owns the virtual IP address and the IP address of the physical interface, this router functions as the master. The priority of the master is 255.

Priority also determines if a VRRP router functions as a backup router and the order of ascendancy to becoming a master if the master fails.

For example, if router A, the master in a LAN topology fails, VRRP must determine if backups B or C should take over. If you configure router B with priority 101 and router C with the default priority of 100, VRRP selects router B to become the master because it has the higher priority. If you configure routers B and C with the default priority of 100, VRRP selects the backup with the higher IP address to become the master.

VRRP uses preemption to determine what happens after a VRRP backup router becomes the master. With preemption enabled by default, VRRP will switch to a backup if that backup comes online with a priority higher than the new master. For example, if Router A is the master and fails, VRRP selects Router B (next in order of priority). If Router C comes online with a higher priority than Router B, VRRP selects Router C as the new master, even though Router B has not failed.

If you disable preemption, VRRP will only switch if the original master recovers or the new master fails.

VRRP Advertisements

The VRRP master sends VRRP advertisements to other VRRP routers in the same group. The advertisements communicate the priority and state of the master. Cisco NX-OS encapsulates the VRRP advertisements in IP packets and sends them to the IP multicast address assigned to the VRRP group. Cisco NX-OS sends the advertisements once every second by default, but you can configure a different advertisement interval.

VRRP Authentication

VRRP supports the following authentication mechanisms:

  • No authentication

  • Plain text authentication

VRRP rejects packets in any of the following cases:

  • The authentication schemes differ on the router and in the incoming packet.

  • Text authentication strings differ on the router and in the incoming packet.

VRRP Tracking

VRRP supports the following two options for tracking:

  • Native interface tracking— Tracks the state of an interface and uses that state to determine the priority of the VRRP router in a VRRP group. The tracked state is down if the interface is down or if the interface does not have a primary IP address.

  • Object tracking—Tracks the state of a configured object and uses that state to determine the priority of the VRRP router in a VRRP group. See Configuring Object Tracking for more information on object tracking.

If the tracked state (interface or object) goes down, VRRP updates the priority based on what you configure the new priority to be for the tracked state. When the tracked state comes up, VRRP restores the original priority for the virtual router group.

For example, you may want to lower the priority of a VRRP group member if its uplink to the network goes down so another group member can take over as master for the VRRP group. See the Configuring VRRP Interface State Tracking section for more information.


Note

VRRP does not support Layer 2 interface tracking.

Virtualization Support

VRRP supports Virtual Routing and Forwarding instances (VRFs). By default, Cisco NX-OS places you in the default VRF unless you specifically configure another VRF.

If you change the VRF membership of an interface, Cisco NX-OS removes all Layer 3 configuration, including VRRP.

For more information, see Configuring Layer 3 Virtualization.

Licensing Requirements for VRRP

The following table shows the licensing requirements for this feature:

Product

License Requirement

Cisco NX-OS

VRRP requires no license. Any feature not included in a license package is bundled with the Cisco NX-OS system images and is provided at no extra charge to you. For a complete explanation of the Cisco NX-OS licensing scheme, see the Cisco NX-OS Licensing Guide.

Note   

Make sure the LAN Base Services license is installed on the switch to enable Layer 3 interfaces.\

Guidelines and Limitations for VRRP

VRRP has the following configuration guidelines and limitations:

  • You cannot configure VRRP on the management interface.

  • When VRRP is enabled, you should replicate the VRRP configuration across switches in your network.

  • We recommend that you do not configure more than one first-hop redundancy protocol on the same interface.

  • You must configure an IP address for the interface that you configure VRRP on and enable that interface before VRRP becomes active.

  • Cisco NX-OS removes all Layer 3 configurations on an interface when you change the interface VRF membership, port channel membership, or when you change the port mode to Layer 2.

  • When you configure VRRP to track a Layer 2 interface, you must shut down the Layer 2 interface and reenable the interface to update the VRRP priority to reflect the state of the Layer 2 interface.

Default Settings for VRRP

Table below lists the default settings for VRRP parameters.

Table 1 Default VRRP Parameters

Parameters

Default

advertisement interval

1 seconds

authentication

no authentication

preemption

enabled

priority

100

VRRP feature

disabled

Configuring VRRP


Note

If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature might differ from the Cisco IOS commands that you would use.

Enabling the VRRP Feature

You must globally enable the VRRP feature before you can configure and enable any VRRP groups.

To enable the VRRP feature, use the following command in global configuration mode:

Command

Purpose

feature vrrp

Example :

switch(config)# feature vrrp

Enables VRRP.

To disable the VRRP feature and remove all associated configuration, use the following command in global configuration mode:

Command

Purpose

no feature vrrp

Example :

switch(config)# no feature vrrp

Disables the VRRP feature.

Configuring VRRP Groups

You can create a VRRP group, assign the virtual IP address, and enable the group.

You can configure one virtual IPv4 address for a VRRP group. By default, the master VRRP router drops the packets addressed directly to the virtual IP address because the VRRP master is only intended as a next-hop router to forward packets. Some applications require that Cisco NX-OS accept packets addressed to the virtual router IP. Use the secondary option to the virtual IP address to accept these packets when the local router is the VRRP master.

Once you have configured the VRRP group, you must explicitly enable the group before it becomes active.

Before You Begin

Ensure that you configure an IP address on the interface (see the Configuring IPv4 Addressing section).

Procedure
     Command or ActionPurpose
    Step 1configure terminal


    Example: 
    switch# configure terminal
switch(config)#
     

    Enters configuration mode.

     
    Step 2interface interface -type slot/port


    Example: 
    switch(config)#
switch(config-if)# interface ethernet 2/1
     

    Enters interface configuration mode.

     
    Step 3no switchport


    Example: 
    switch(config-if)# no switchport
     

    Configures the interface as a Layer 3 routed interface.

     
    Step 4vrrp number


    Example: 
    switch(config-if)# vrrp 250
switch(config-if-vrrp)#
     

    Creates a virtual router group. The range is from 1 to 255.

     
    Step 5address ip-address [ secondary ]


    Example: 
    switch(config-if-vrrp)# address 192.0.2.8
     

    Configures the virtual IPv4 address for the specified VRRP group. This address should be in the same subnet as the IPv4 address of the interface.

    Use the secondary option only if applications require that VRRP routers accept the packets sent to the virtual router’s IP address and deliver to applications.

     
    Step 6no shutdown


    Example: 
    switch(config-if-vrrp)# no shutdown
switch(config-if-vrrp)#
     

    Enables the VRRP group. Disabled by default.

     
    Step 7show vrrp


    Example: 
    switch(config-if-vrrp)# show vrrp
          		(Optional)

    Displays VRRP information.

     
    Step 8copy running-config startup-config


    Example: 
    switch(config-if-vrrp)# copy running-config startup-config
          		(Optional)

    Saves this configuration change.

     

    Configuring VRRP Priority

    The valid priority range for a virtual router is from 1 to 254 (1 is the lowest priority and 254 is the highest). The default priority value for backups is 100. For switches whose interface IP address is the same as the primary virtual IP address (the master), the default value is 255.

    Before You Begin

    Ensure that you have enabled the VRRP feature (see the Configuring VRRP section).

    Ensure that you have configured an IP address on the interface (see the Configuring IPv4 Addressing section.

    Procedure
       Command or ActionPurpose
      Step 1configure terminal


      Example: 
      switch# configure terminal
switch(config)#
       

      Enters configuration mode.

       
      Step 2interface interface -type slot/port


      Example: 
      switch(config)#
switch(config-if)# interface ethernet 2/1
       

      Enters interface configuration mode.

       
      Step 3no switchport


      Example: 
      switch(config-if)# no switchport
       

      Configures the interface as a Layer 3 routed interface.

       
      Step 4vrrp number


      Example: 
      switch(config-if)# vrrp 250
switch(config-if-vrrp)#
       

      Creates a virtual router group. The range is from 1 to 255.

       
      Step 5shutdown


      Example: 
      switch(config-if-vrrp)# shutdown
switch(config-if-vrrp)#
       

      Disables the VRRP group. Disabled by default.

       
      Step 6priority level [ forwarding-threshold lower lower-value upper upper-value ]


      Example: 
      switch(config-if-vrrp)# priority 60 forwarding-threshold lower 40 upper 50
       

      Sets the priority level used to select the active router in an VRRP group. The level range is from 1 to 254. The default is 100 for backups and 255 for a master that has an interface IP address equal to the virtual IP address.

       
      Step 7no shutdown


      Example: 
      switch(config-if-vrrp)# no shutdown
switch(config-if-vrrp)#
       

      Enables the VRRP group. Disabled by default.

       
      Step 8show vrrp


      Example: 
      switch(config-if-vrrp)# show vrrp
              		(Optional)

      Displays VRRP information.

       
      Step 9copy running-config startup-config


      Example: 
      switch(config-if-vrrp)# copy running-config startup-config
              		(Optional)

      Saves this configuration change.

       

      Configuring VRRP Authentication

      You can configure simple text authentication for a VRRP group.

      Before You Begin

      Ensure that the authentication configuration is identical for all VRRP switches in the network.

      Ensure that you have enabled the VRRP feature (see the Configuring VRRP section).

      Ensure that you have configured an IP address on the interface (see the Configuring IPv4 Addressing section.

      Procedure
         Command or ActionPurpose
        Step 1configure terminal


        Example: 
        switch# configure terminal
switch(config)#
         

        Enters configuration mode.

         
        Step 2interface interface -type slot/port


        Example: 
        switch(config)#
switch(config-if)# interface ethernet 2/1
         

        Enters interface configuration mode.

         
        Step 3no switchport


        Example: 
        switch(config-if)# no switchport
         

        Configures the interface as a Layer 3 routed interface.

         
        Step 4vrrp number


        Example: 
        switch(config-if)# vrrp 250
switch(config-if-vrrp)#
         

        Creates a virtual router group. The range is from 1 to 255.

         
        Step 5shutdown


        Example: 
        switch(config-if-vrrp)# shutdown
switch(config-if-vrrp)#
         

        Disables the VRRP group. Disabled by default.

         
        Step 6authentication text password


        Example: 
        switch(config-if-vrrp)# authentication text cisco123
         

        Assigns the simple text authentication option and specifies the keyname password. The keyname range is from 1 to 255 characters. We recommend that you use at least 16 characters. The text password is up to eight alphanumeric characters.

         
        Step 7no shutdown


        Example: 
        switch(config-if-vrrp)# no shutdown
switch(config-if-vrrp)#
         

        Enables the VRRP group. Disabled by default.

         
        Step 8show vrrp


        Example: 
        switch(config-if-vrrp)# show vrrp
                  		(Optional)

        Displays VRRP information.

         
        Step 9copy running-config startup-config


        Example: 
        switch(config-if-vrrp)# copy running-config startup-config
                  		(Optional)

        Saves this configuration change.

         

        Configuring Time Intervals for Advertisement Packets

        You can configure the time intervals for advertisement packets.

        Before You Begin

        Ensure that you have enabled the VRRP feature (see the Configuring VRRP section).

        Ensure that you have configured an IP address on the interface (see the Configuring IPv4 Addressing section.

        Procedure
           Command or ActionPurpose
          Step 1configure terminal


          Example: 
          switch# configure terminal
switch(config)#
           

          Enters configuration mode.

           
          Step 2interface interface -type slot/port


          Example: 
          switch(config)#
switch(config-if)# interface ethernet 2/1
           

          Enters interface configuration mode.

           
          Step 3no switchport


          Example: 
          switch(config-if)# no switchport
           

          Configures the interface as a Layer 3 routed interface.

           
          Step 4vrrp number


          Example: 
          switch(config-if)# vrrp 250
switch(config-if-vrrp)#
           

          Creates a virtual router group. The range is from 1 to 255.

           
          Step 5shutdown


          Example: 
          switch(config-if-vrrp)# shutdown
switch(config-if-vrrp)#
           

          Disables the VRRP group. Disabled by default.

           
          Step 6advertisement-interval seconds


          Example: 
          switch(config-if-vrrp)# advertisement-interval 15
           

          Sets the interval time in seconds between sending advertisement frames. The range is from 1 to 254. The default is 1 second.

           
          Step 7no shutdown


          Example: 
          switch(config-if-vrrp)# no shutdown
switch(config-if-vrrp)#
           

          Enables the VRRP group. Disabled by default.

           
          Step 8show vrrp


          Example: 
          switch(config-if-vrrp)# show vrrp
                      		(Optional)

          Displays VRRP information.

           
          Step 9copy running-config startup-config


          Example: 
          switch(config-if-vrrp)# copy running-config startup-config
                      		(Optional)

          Saves this configuration change.

           

          Disabling Preemption

          You can disable preemption for a VRRP group member. If you disable preemption, a higher-priority backup router will not take over for a lower-priority master router. Preemption is enabled by default.

          Before You Begin

          Ensure that you have enabled the VRRP feature (see the Configuring VRRP section).

          Ensure that you have configured an IP address on the interface (see the Configuring IPv4 Addressing section.

          Procedure
             Command or ActionPurpose
            Step 1configure terminal


            Example: 
            switch# configure terminal
switch(config)#
             

            Enters configuration mode.

             
            Step 2interface interface -type slot/port


            Example: 
            switch(config)#
switch(config-if)# interface ethernet 2/1
             

            Enters interface configuration mode.

             
            Step 3no switchport


            Example: 
            switch(config-if)# no switchport
             

            Configures the interface as a Layer 3 routed interface.

             
            Step 4vrrp number


            Example: 
            switch(config-if)# vrrp 250
switch(config-if-vrrp)#
             

            Creates a virtual router group. The range is from 1 to 255.

             
            Step 5shutdown


            Example: 
            switch(config-if-vrrp)# shutdown
switch(config-if-vrrp)#
             

            Disables the VRRP group. Disabled by default.

             
            Step 6no preempt


            Example: 
            switch(config-if-vrrp)# no preempt
             

            Disables the preempt option and allows the master to remain when a higher-priority backup appears.

             
            Step 7no shutdown


            Example: 
            switch(config-if-vrrp)# no shutdown
switch(config-if-vrrp)#
             

            Enables the VRRP group. Disabled by default.

             
            Step 8show vrrp


            Example: 
            switch(config-if-vrrp)# show vrrp
                          		(Optional)

            Displays VRRP information.

             
            Step 9copy running-config startup-config


            Example: 
            switch(config-if-vrrp)# copy running-config startup-config
                          		(Optional)

            Saves this configuration change.

             

            Configuring VRRP Interface State Tracking

            Interface state tracking changes the priority of the virtual router based on the state of another interface in the switch. When the tracked interface goes down or the IP address is removed, Cisco NX-OS assigns the tracking priority value to the virtual router. When the tracked interface comes up and an IP address is configured on this interface, Cisco NX-OS restores the configured priority to the virtual router (see the Configuring VRRP Priority section).


            Note

            For interface state tracking to function, you must enable preemption on the interface.


            Note

            VRRP does not support Layer 2 interface tracking.

            Before You Begin

            Ensure that you have enabled the VRRP feature (see the Configuring VRRP section).

            Ensure that you have configured an IP address on the interface (see the Configuring IPv4 Addressing section.

            Be sure the virtual router is enabled (see the Configuring VRRP Groups section).

            Procedure
               Command or ActionPurpose
              Step 1configure terminal


              Example: 
              switch# configure terminal
switch(config)#
               

              Enters configuration mode.

               
              Step 2interface interface -type slot/port


              Example: 
              switch(config)#
switch(config-if)# interface ethernet 2/1
               

              Enters interface configuration mode.

               
              Step 3no switchport


              Example: 
              switch(config-if)# no switchport
               

              Configures the interface as a Layer 3 routed interface.

               
              Step 4vrrp number


              Example: 
              switch(config-if)# vrrp 250
switch(config-if-vrrp)#
               

              Creates a virtual router group. The range is from 1 to 255.

               
              Step 5shutdown


              Example: 
              switch(config-if-vrrp)# shutdown
switch(config-if-vrrp)#
               

              Disables the VRRP group. Disabled by default.

               
              Step 6track interface type number priority value


              Example: 
              switch(config-if-vrrp)# track interface ethernet 2/10 priority 254
               

              Enables interface priority tracking for a VRRP group. The priority range is from 1 to 254.

               
              Step 7no shutdown


              Example: 
              switch(config-if-vrrp)# no shutdown
switch(config-if-vrrp)#
               

              Enables the VRRP group. Disabled by default.

               
              Step 8show vrrp


              Example: 
              switch(config-if-vrrp)# show vrrp
                              		(Optional)

              Displays VRRP information.

               
              Step 9copy running-config startup-config


              Example: 
              switch(config-if-vrrp)# copy running-config startup-config
                              		(Optional)

              Saves this configuration change.

               

              Verifying the VRRP Configuration

              To display the VRRP configuration information, perform one of the following tasks:

              Command

              Purpose

              show vrrp

              Displays the VRRP status for all groups.

              show vrrp vr group-number

              Displays the VRRP status for a VRRP group.

              show vrrp interface interface-type port vr number

              Displays the virtual router configuration for an interface.

              Displaying VRRP Statistics

              To display VRRP statistics, use the following commands:

              Command

              Purpose

              show vrrp statistics interface interface-type port vr number

              Displays the virtual router information.

              show vrrp statistics

              Displays the VRRP statistics.

              Use the clear vrrp vr command to clear the IPv4 VRRP statistics for a specified interface.

              Configuration Examples for VRRP

              In this 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

              interface ethernet 1/0
no switchport

ip address 10.1.0.2/16
no shutdown
vrrp 1
priority 120
authentication text cisco
advertisement-interval 3
address 10.1.0.10
no shutdown
vrrp 5
priority 100
advertisement-interval 30
address 10.1.0.50
no shutdown
vrrp 100
no preempt
address 10.1.0.100
no shutdown

              Router B

              interface ethernet 1/0
no switchport

ip address 10.2.0.1/2
no shutdown
vrrp 1
priority 100
authentication text cisco
advertisement-interval 3
address 10.2.0.10
no shutdown
 
vrrp 5
priority 200
advertisement-interval 30
address 10.2.0.50
no shutdown
vrrp 100
no preempt
address 10.2.0.100
no shutdown

              Additional References

              For additional information related to implementing VRRP, see the following sections:

              Related Documents

              Related Topic

              Document Title

              Configuring the Hot Standby Routing Protocol

              Configuring HSRP

              VRRP CLI commands

              Cisco Nexus 3000 Series Command Reference

              Feature History for VRRP

              Table below lists the release history for this feature.

              Table 2 Feature History for VRRP

              Feature Name

              Releases

              Feature Information

              VRRP

              5.0(3)A1(1)

              This feature was introduced.