Cisco Nexus 3000 Series NX-OS Unicast Routing Configuration Guide, Release 5.0(3)U4(1)

Configuring HSRP

This chapter describes how to configure the Hot Standby Router Protocol (HSRP) on the Cisco NX-OS switch.

This chapter includes the following sections:

•Information About HSRP

•Licensing Requirements for HSRP

•Prerequisites for HSRP

•Guidelines and Limitations

•Default Settings

•Configuring HSRP

•Verifying the HSRP Configuration

•Configuration Examples for HSRP

•Additional References

•Feature History for HSRP

Information About HSRP

HSRP is a first-hop redundancy protocol (FHRP) that allows a transparent failover of the first-hop IP router. HSRP provides first-hop routing redundancy for IP hosts on Ethernet networks configured with a default router IP address. You use HSRP in a group of routers for selecting an active router and a standby router. In a group of routers, the active router is the router that routes packets; the standby router is the router that takes over when the active router fails or when preset conditions are met.

Many host implementations do not support any dynamic router discovery mechanisms but can be configured with a default router. Running a dynamic router discovery mechanism on every host is not feasible for a number of reasons, including administrative overhead, processing overhead, and security issues. HSRP provides failover services to these hosts.

This section includes the following topics:

•HSRP Overview

•HSRP for IPv4

•HSRP for IPv6, page 13-4

•HSRP Versions

•HSRP Authentication

•HSRP Messages

•HSRP Load Sharing

•Object Tracking and HSRP

•BFD, page 13-7

•Extended Nonstop Forwarding, page 12-6

•Virtualization Support

HSRP Overview

When you use HSRP, you configure the HSRP virtual IP address as the host's default router (instead of the IP address of the actual router). The virtual IP address is an IPv4 or IPv6 address that is shared among a group of routers that run HSRP.

When you configure HSRP on a network segment, you provide a virtual MAC address and a virtual IP address for the HSRP group. You configure the same virtual address on each HSRP-enabled interface in the group. You also configure a unique IP address and MAC address on each interface that acts as the real address. HSRP selects one of these interfaces to be the active router. The active router receives and routes packets destined for the virtual MAC address of the group.

HSRP detects when the designated active router fails. At that point, a selected standby router assumes control of the virtual MAC and IP addresses of the HSRP group. HSRP also selects a new standby router at that time.

HSRP uses a priority mechanism to determine which HSRP-configured interface becomes the default active router. To configure an interface as the active router, you assign it with a priority that is higher than the priority of all the other HSRP-configured interfaces in the group. The default priority is 100, so if you configure just one interface with a higher priority, that interface becomes the default active router.

Interfaces that run HSRP send and receive multicast User Datagram Protocol (UDP)-based hello messages to detect a failure and to designate active and standby routers. When the active router fails to send a hello message within a configurable period of time, the standby router with the highest priority becomes the active router. The transition of packet forwarding functions between the active and standby router is completely transparent to all hosts on the network.

You can configure multiple HSRP groups on an interface.

Figure 16-1 shows a network configured for HSRP. By sharing a virtual MAC address and a virtual IP address, two or more interfaces can act as a single virtual router.

Figure 16-1 HSRP Topology with Two Enabled Routers

The virtual router does not physically exist but represents the common default router for interfaces that are configured to provide backup to each other. You do not need to configure the hosts on the LAN with the IP address of the active router. Instead, you configure them with the IP address (virtual IP address) of the virtual router as their default router. If the active router fails to send a hello message within the configurable period of time, the standby router takes over, responds to the virtual addresses, and becomes the active router, assuming the active router duties. From the host perspective, the virtual router remains the same.

Note Packets received on a routed port destined for the HSRP virtual IP address will terminate on the local router, regardless of whether that router is the active HSRP router or the standby HSRP router. This includes ping and Telnet traffic. Packets received on a Layer 2 (VLAN) interface destined for the HSRP virtual IP address will terminate on the active router.

HSRP for IPv4

HSRP routers communicate with each other by exchanging HSRP hello packets. These packets are sent to the destination IP multicast address 224.0.0.2 (reserved multicast address used to communicate to all routers) on UDP port 1985. The active router sources hello packets from its configured IP address and the HSRP virtual MAC address while the standby router sources hellos from its configured IP address and the interface MAC address, which may or may not be the burned-in address (BIA). The BIA is the last six bytes of the MAC address that is assigned by the manufacturer of the network interface card (NIC).

Because hosts are configured with their default router as the HSRP virtual IP address, hosts must communicate with the MAC address associated with the HSRP virtual IP address. This MAC address is a virtual MAC address, 0000.0C07.ACxy, where xy is the HSRP group number in hexadecimal based on the respective interface. For example, HSRP group 1 uses the HSRP virtual MAC address of 0000.0C07.AC01. Hosts on the adjoining LAN segment use the normal Address Resolution Protocol (ARP) process to resolve the associated MAC addresses.

HSRP version 2 uses the new IP multicast address 224.0.0.102 to send hello packets instead of the multicast address of 224.0.0.2, which is used by version 1. HSRP version 2 permits an expanded group number range of 0 to 4095 and uses a new MAC address range of 0000.0C9F.F000 to 0000.0C9F.FFFF.

HSRP for IPv6

IPv6 hosts learn of available IPv6 routers through IPv6 neighbor discovery (ND) router advertisement (RA) messages. These messages are multicast periodically, or may be solicited by hosts, but the time delay for detecting when a default route is down may be 30 seconds or more. HSRP for IPv6 provides a much faster switchover to an alternate default router than the IPv6 ND protocol provides, less than a second if the milliseconds timers are used. HSRP for IPv6 provides a virtual first hop for IPv6 hosts.

When you configure an IPv6 interface for HSRP, the periodic RAs for the interface link-local address stop after IPv6 ND sends a final RA with a router lifetime of zero. No restrictions occur for the interface IPv6 link-local address. Other protocols continue to receive and send packets to this address.

IPv6 ND sends periodic RAs for the HSRP virtual IPv6 link-local address when the HSRP group is active. These RAs stop after a final RA is sent with a router lifetime of 0 when the HSRP group leaves the active state. HSRP uses the virtual MAC address for active HSRP group messages only (hello, coup, and redesign).

HSRP for IPv6 uses the following parameters:

•HSRP version 2

•UDP port 2029

•Virtual MAC address range from 0005.73A0.0000 through 0005.73A0.0FFF

•Multicast link-local IP destination address of FF02::66

•Hop limit set to 255

HSRP IPv6 Addresses

An HSRP IPv6 group has a virtual MAC address that is derived from the HSRP group number and a virtual IPv6 link-local address that is derived, by default, from the HSRP virtual MAC address. The default virtual MAC address for an HSRP IPv6 group will always be used to form the virtual Ipv6 link-local address, regardless of the actual virtual MAC address used by the group.

Table 16-1 shows the MAC and IP addresses used for IPv6 neighbor discovery packets and HSRP packets.

HSRP does not add IPv6 link-local addresses to the Unicast Routing Information Base (URIB). There are also no secondary virtual IP addresses for link-local addresses.

For global unicast addresses, HSRP will add the virtual IPv6 address to the URIB and IPv6 but will not register the virtual IPv6 addresses to ICMPv6. ICMPv6 redirects are not supported for HSRP IPv6 groups.

HSRP Versions

Cisco NX-OS supports HSRP version 1 by default. You can configure an interface to use HSRP version 2.

HSRP version 2 has the following enhancements to HSRP version 1:

•Expands the group number range. HSRP version 1 supports group numbers from 0 to 255. HSRP version 2 supports group numbers from 0 to 4095.

•For IPv4, uses the IPv4 multicast address 224.0.0.102 or the IPv6 multicast address FF02::66 to send hello packets instead of the multicast address of 224.0.0.2, which is used by HSRP version 1.

•Uses the MAC address range from 0000.0C9F.F000 to 0000.0C9F.FFFF for IPv4 and 0005.73A0.0000 through 0005.73A0.0FFF for IPv6 addresses. HSRP version 1 uses the MAC address range 0000.0C07.AC00 to 0000.0C07.ACFF.

•Adds support for MD5 authentication.

When you change the HSRP version, Cisco NX-OS reinitializes the group because it now has a new virtual MAC address.

HSRP version 2 has a different packet format than HSRP version 1. The packet format uses a type-length-value (TLV) format. HSRP version 2 packets received by an HSRP version 1 router are ignored.

HSRP Authentication

HSRP message digest 5 (MD5) algorithm authentication protects against HSRP-spoofing software and uses the industry-standard MD5 algorithm for improved reliability and security. HSRP includes the IPv4 or IPv6 address in the authentication TLVs.

HSRP Messages

Routers that are configured with HSRP exchange the following three types of multicast messages:

•Hello—The hello message conveys the HSRP priority and state information of the router to other HSRP routers.

•Coup—When a standby router wants to assume the function of the active router, it sends a coup message.

•Resign—A router that is the active router sends this message when it is about to shut down or when a router that has a higher priority sends a hello or coup message.

HSRP Load Sharing

HSRP allows you to configure multiple groups on an interface. You can configure two overlapping IPv4 HSRP groups to load share traffic from the connected hosts while providing the default router redundancy expected from HSRP. Figure 16-2 shows an example of a load-sharing HSRP IPv4 configuration.

Figure 16-2 HSRP Load Sharing

Figure 16-2 shows two routers (A and B) and two HSRP groups. Router A is the active router for group A but is the standby router for group B. Similarly, router B is the active router for group B and the standby router for group A. If both routers remain active, HSRP load balances the traffic from the hosts across both routers. If either router fails, the remaining router continues to process traffic for both hosts.

Note HSRP for IPv6 load-balances by default. If there are two HSRP IPv6 groups on the subnet, then hosts will learn of both from their router advertisements and choose to use one so that the load is shared between the advertised routers.

Object Tracking and HSRP

You can use object tracking to modify the priority of an HSRP interface based on the operational state of another interface. Object tracking allows you to route to a standby router if the interface to the main network fails.

Two objects that you can track are the line protocol state of an interface or the reachability of an IP route. If the specified object goes down, Cisco NX-OS reduces the HSRP priority by the configured amount. For more information, see the "Configuring HSRP Object Tracking" section.

BFD

This feature supports bidirectional forwarding detection (BFD). BFD is a detection protocol designed to provide fast forwarding-path failure detection times. BFD provides subsecond failure detection between two adjacent devices and can be less CPU-intensive than protocol hello messages because some of the BFD load can be distributed onto the data plane on supported modules. See the Cisco Nexus 7000 Series NX-OS Interfaces Configuration Guide, Release 5.x for more information.

High Availability and Extended Nonstop Forwarding

HSRP supports stateful restarts and stateful switchovers. A stateful restart occurs when the HSRP process fails and is restarted. A stateful switchover occurs when the active supervisor switches to the standby supervisor. Cisco NX-OS applies the run-time configuration after the switchover.

If HSRP hold timers are configured for short time periods, these timers may expire during a controlled switchover or in-service software upgrade (ISSU). HSRP supports extended nonstop forwarding (NSF) to temporarily extend these HSRP hold timers during a controlled switchover or in-service software upgrade (ISSU).

With extended NSF configured, HSRP sends hello messages with the extended timers. HSRP peers update their hold timers with these new values. The extended timers prevent unnecessary HSRP state changes during the switchover or ISSU. After the switchover or ISSU event, HSRP restores the hold timers to their original configured values. If the switchover fails, HSRP restores the hold timers after the extended hold timer values expire.

See the "Configuring Extended Hold Timers for HSRP" section for more information.

Virtualization Support

HSRP supports Virtual Routing and Forwarding instances (VRFs). VRFs exist within virtual device contexts (VDCs). By default, Cisco NX-OS places you in the default VDC and default VRF unless you specifically configure another VDC and VRF.

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

For more information, see the Cisco Nexus 7000 Series NX-OS Virtual Device Context Configuration Guide, Release 5.x, and see Chapter 12 "Configuring Layer 3 Virtualization."

Licensing Requirements for HSRP

The following table shows the licensing requirements for this feature:

Prerequisites for HSRP

HSRP has the following prerequisites:

•You must enable the HSRP feature in a switch before you can configure and enable any HSRP groups.

•If you configure VDCs, install the Advanced Services license and enter the desired VDC (see the Cisco Nexus 7000 Series NX-OS Virtual Device Context Configuration Guide, Release 5.x).

Guidelines and Limitations

HSRP has the following configuration guidelines and limitations:

•The minimum hello timer value is 250 milliseconds.

•The minimum hold timer value is 750 milliseconds.

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

•You must configure HSRP version 2 when you configure an IPv6 interface for HSRP.

•For IPv4, the virtual IP address must be in the same subnet as the interface IP address.

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

•HSRP version 2 does not interoperate with HSRP version 1. An interface cannot operate both version 1 and version 2 because both versions are mutually exclusive. However, the different versions can be run on different physical interfaces of the same router.

•You cannot change from version 2 to version 1 if you have configured groups above the group number range allowed for version 1 (0 to 255).

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

Default Settings

Table 16-2 lists the default settings for HSRP parameters.

Configuring HSRP

This section includes the following topics:

•Enabling the HSRP Feature

•Configuring the HSRP Version

•Configuring an HSRP Group for IPv4

•Configuring an HSRP Group for IPv6, page 13-15

•Configuring the HSRP Virtual MAC Address

•Authenticating HSRP

•Configuring HSRP Object Tracking

•Configuring the HSRP Priority

•Customizing HSRP

•Configuring Extended Hold Timers for HSRP, page 12-17

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 HSRP Feature

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

DETAILED STEPS

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

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

Configuring the HSRP Version

You can configure the HSRP version. If you change the version for existing groups, Cisco NX-OS reinitializes HSRP for those groups because the virtual MAC address changes. The HSRP version applies to all groups on the interface.

Note IPv6 HSRP groups must be configured as HSRP version 2.

To configure the HSRP version, follow these steps:

Step 1 From the Feature Selector pane, choose Routing > Gateway Redundancy > HSRP.

The available devices appear in the Summary pane.

Step 2 From the Summary pane, click the device that you want to configure HSRP on.

The system highlights the HSRP row in the Summary pane, and tabs update in the Details pane.

Step 3 From the highlighted Interface field, select the interface that you want to configure an HSRP group on from the drop-down list.

Step 4 From the Details pane, click the Interface Settings tab.

The Interface Settings tab appears.

Step 5 From the Interface Settings tab, in the HSRP Version field, enter 1 for HSRP version 1 or enter 2 for HSRP version 2.

Step 6 From the menu bar, choose File > Deploy to apply your changes to the device.

To configure the HSRP version, use the following command in interface configuration mode:

Configuring an HSRP Group for IPv4

You can configure an HSRP group on an IPv4 interface and configure the virtual IP address and virtual MAC address for the HSRP group.

BEFORE YOU BEGIN

Ensure that you have enabled the HSRP feature (see the "Enabling the HSRP Feature" section).

Cisco NX-OS enables an HSRP group once you configure the virtual IP address on any member interface in the group. You should configure HSRP attributes such as authentication, timers, and priority before you enable the HSRP group.

SUMMARY STEPS

1. configure terminal

2. interface type number

3. no switchport

4. ip ip-address/length

5. hsrp group-number [ipv4]

6. ip [ip-address [secondary]]

7. exit

8. no shutdown

9. (Optional) show hsrp [group group-number] [ipv4]

10. (Optional) copy running-config startup-config

DETAILED STEPS

To create an IPv4 HSRP group on an interface, follow these steps:

Step 1 From the Feature Selector pane, choose Routing > Gateway Redundancy > HSRP.

The available devices appear in the Summary pane.

Step 2 From the Summary pane, click the device that you want to configure HSRP on.

Step 3 Right-click and choose New IPv4 GroupSetting.

Step 4 From the Interface drop-down list, select the interface or group of interfaces that you want to configure an HSRP group on.

Step 5 From the Group ID field, enter the group number for this group.

The range is from 0 to 255.

Step 6 From the Details pane, click the Group Details tab.

The Group Details tab appears.

Step 7 From the Group Details tab, expand the Group Details section.

The basic group information appears in the Details pane.

Step 8 (Optional) From the Group Name field, enter a name for this HSRP group member.

Step 9 (Optional) From the Virtual IP Address Settings Area, check Learn Virtual IP from Members of Group to learn the virtual IP address from another HSRP group member.

Step 10 (Optional) From the Virtual IP Address Settings Area, in the Virtual IP Address field, enter an IPv4 address.

Step 11 (Optional) From the Virtual IP Address Settings Area, in the Secondary IP Address field, enter an IPv4 address for the secondary IP address.

Step 12 From the menu bar, choose File > Deploy to apply your changes to the device.

Note You should use the no shutdown command to enable the interface after you finish the configuration.

This example shows how to configure an HSRP group on Ethernet 1/2:

switch# configure terminal

switch(config)# interface ethernet 1/2

switch(config-if)# no switchport

switch(config-if)# ip 192.0.2.2/8

switch(config-if)# hsrp 2 

switch(config-if-hsrp)# ip 192.0.2.1

switch(config-if-hsrp)# exit

switch(config-if)# no shutdown

switch(config-if)# copy running-config startup-config

Configuring an HSRP Group for IPv6

You can configure an HSRP group on an IPv6 interface and configure the virtual MAC address for the HSRP group.

When you configure an HSRP group for IPv6, HSRP generates a link-local address from the link-local prefix. HSRP also generates a modified EUI-64 format interface identifier in which the EUI-64 interface identifier is created from the relevant HSRP virtual MAC address.

There are no HSRP IPv6 secondary addresses.

BEFORE YOU BEGIN

Ensure that you have enabled the HSRP feature (see the "Enabling the HSRP Feature" section).

Ensure that you have enabled HSRP version 2 on the interface that you want to configure an IPv6 HSRP group on.

Ensure that you have configured HSRP attributes such as authentication, timers, and priority before you enable the HSRP group.

Ensure that you are in the correct VDC (or use the switchto vdc command).

SUMMARY STEPS

1. configure terminal

2. interface type number

3. ipv6 ipv6-address/length

4. hsrp version 2

5. hsrp group-number ipv6

6. ip ipv6-address
or
ip autoconfig

7. no shutdown

8. show hsrp [group group-number] [ipv6]

9. copy running-config startup-config

DETAILED STEPS

To create an IPv6 HSRP group on an interface, follow these steps:

Step 1 From the Feature Selector pane, choose Routing > Gateway Redundancy > HSRP.

The available devices appear in the Summary pane.

Step 2 From the Summary pane, click the device that you want to configure HSRP on.

Step 3 Right-click and choose New IPv6 GroupSetting.

Step 4 From the Interface drop-down list, select the interface or group of interfaces that you want to configure an HSRP group on.

Step 5 From the Group ID field, enter the group number for this group.

Step 6 From the Details pane, click the Group Details tab.

The Group Details tab appears.

Step 7 From the Group Details tab, expand the Interfaces section.

The HSRP interface information appears in the Details pane.

Step 8 From the HSRP Version field, enter 2 for HSRP version 2.

Step 9 From the Group Details tab, expand the Group Details section.

The basic group information appears in the Details pane.

Step 10 (Optional) From the Group Name field, enter a name for this HSRP group member.

Step 11 (Optional) From the Virtual IP Address Settings Area, check Autoconfigure IP address to configure the virtual IPv6 address from the link-local address and the HSRP virtual MAC address.

Step 12 (Optional) From the Virtual IP Address Settings Area, check Learn Virtual IP from Members of Group to learn the virtual IP address from another HSRP group member.

Step 13 (Optional) From the Virtual IP Address Settings Area, in the Virtual IPv6 Address field, enter an IPv6 address.

Step 14 From the menu bar, choose File > Deploy to apply your changes to the device.

RELATED TOPICS

•Configuring an HSRP Group for IPv4

Note You should use the no shutdown command to enable the interface after you finish the configuration.

The following example shows how to configure an IPv6 HSRP group on Ethernet 3/2:

switch# configure terminal

switch(config)# interface ethernet 3/2

switch(config-if)# ip 12001:0DB8:0001:0001:/64

switch(config-if)# hsrp 2 ipv6

switch(config-if-hsrp)# exit

switch(config-if)# no shutdown

switch(config-if)# copy running-config startup-config

Configuring the HSRP Virtual MAC Address

You can override the default virtual MAC address that HSRP derives from the configured group number.

To manually configure the virtual MAC address for an HSRP group, use the following command in hsrp configuration mode:

To configure HSRP to use the burned-in MAC address of the interface for the virtual MAC address, use the following command in interface configuration mode:

Authenticating HSRP

You can configure HSRP to authenticate the protocol using cleartext or MD5 digest authentication. MD5 authentication uses a key chain (see the Cisco Nexus 7000 Series NX-OS Security Configuration Guide, Release 5.x).

BEFORE YOU BEGIN

Ensure that you have enabled the HSRP feature (see the "Enabling the HSRP Feature" section).

You must configure the same authentication and keys on all members of the HSRP group.

Ensure that you have created the key chain if you are using MD5 authentication.

Ensure that you are in the correct VDC (or use the switchto vdc command).

SUMMARY STEPS

1. configure terminal

2. interface interface-type slot/port

3. no switchport

4. hsrp group-number [ipv4 | ipv6]

5. authentication text string
or
authentication md5 {key-chain key-chain | key-string {0 | 7} text [timeout seconds]}

6. (Optional) show hsrp [group group-number]

7. (Optional) copy running-config startup-config

DETAILED STEPS

This example shows how to configure MD5 authentication for HSRP on Ethernet 1/2 after creating the key chain:

switch# configure terminal

switch(config)# key chain hsrp-keys

switch(config-keychain)# key 0

switch(config-keychain-key)# key-string 7 zqdest

switch(config-keychain-key) accept-lifetime 00:00:00 Jun 01 2008 23:59:59 Sep 12 2008

switch(config-keychain-key) send-lifetime 00:00:00 Jun 01 2008 23:59:59 Aug 12 2008

switch(config-keychain-key) key 1

switch(config-keychain-key) key-string 7 uaeqdyito

switch(config-keychain-key) accept-lifetime 00:00:00 Aug 12 2008 23:59:59 Dec 12 2008

switch(config-keychain-key) send-lifetime 00:00:00 Sep 12 2008 23:59:59 Nov 12 2008

switch(config-keychain-key)# interface ethernet 1/2

switch(config-if)# no switchport

switch(config-if)# hsrp 2 

switch(config-if-hsrp)# authenticate md5 key-chain hsrp-keys

switch(config-if-hsrp)# copy running-config startup-config

Configuring HSRP Object Tracking

You can configure an HSRP group to adjust its priority based on the availability of other interfaces or routes. The priority of a switch can change dynamically if it has been configured for object tracking and the object that is being tracked goes down. The tracking process periodically polls the tracked objects and notes any value change. The value change triggers HSRP to recalculate the priority. The HSRP interface with the higher priority becomes the active router if you configure the HSRP interface for preemption.

HSRP supports tracked objects and track lists. See Chapter 18 "Configuring Object Tracking" for more information on track lists.

BEFORE YOU BEGIN

Ensure that you have enabled the HSRP feature (see the "Enabling the HSRP Feature" section).

Ensure that you are in the correct VDC (or use the switchto vdc command).

SUMMARY STEPS

1. configure terminal

2. track object-id interface interface-type number {{ip | ipv6} routing | line-protocol}
or
track object-id {ip | ipv6} route ip-prefix/length reachability

3. interface interface-type slot/port

4. no switchport

5. hsrp group-number [ipv4 | ipv6]

6. priority [value]

7. track object-number [decrement value]

8. preempt [delay [minimum seconds] [reload seconds] [sync seconds]]

9. (Optional) show hsrp interface interface-type number

10. (Optional) copy running-config startup-config

DETAILED STEPS

This example shows how to configure HSRP object tracking on Ethernet 1/2:

switch# configure terminal

switch(config)# track 1 interface ethernet 2/2 line-protocol

switch(config)# interface ethernet 1/2

switch(config-if)# no switchport

switch(config-if)# hsrp 2 

switch(config-if-hsrp)# track 1 decrement 20

switch(config-if-hsrp)# copy running-config startup-config

Configuring the HSRP Priority

You can configure the HSRP priority on an interface. HSRP uses the priority to determine which HSRP group member acts as the active router.

For IPv6 HSRP groups, if all group members have the same priority, HSRP selects the active router based on the IPv6 link-local address.

To configure the HSRP priority, use the following command in interface configuration mode:

Customizing HSRP

You can optionally customize the behavior of HSRP. Be aware that as soon as you enable an HSRP group by configuring a virtual IP address, that group is now operational. If you first enable an HSRP group before customizing HSRP, the router could take control over the group and become the active router before you finish customizing the feature. If you plan to customize HSRP, you should do so before you enable the HSRP group.

To customize HSRP, use the following commands in hsrp configuration mode:

To customize HSRP, use the following commands in interface configuration mode:

Configuring Extended Hold Timers for HSRP

You can configure HSRP to use extended hold timers to support extended NSF during a controlled (graceful) switchover or ISSU, including software upgrades and supervisor switchovers.You should configure extended hold timers on all HSRP routers (see the "High Availability and Extended Nonstop Forwarding" section).

Note You must configure extended hold timers on all HSRP routers if you configure extended hold timers. If you configure a nondefault hold timer, you should configure the same value on all HSRP routers when you configure HSRP extended hold timers.

Note HSRP extended hold timers are not applied if you configure millisecond HSRP hello and hold timers.

To configure HSRP extended hold timers, use the following command in global configuration mode:

Use the show hsrp command or the show running-config hsrp command to display the extended hold time.

Verifying the HSRP Configuration

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

Configuration Examples for HSRP

This example shows how to enable HSRP on an interface with MD5 authentication and interface tracking:

key chain hsrp-keys

 key 0

   key-string 7 zqdest

   accept-lifetime 00:00:00 Jun 01 2008 23:59:59 Sep 12 2008

   send-lifetime 00:00:00 Jun 01 2008 23:59:59 Aug 12 2008

  key 1

   key-string 7 uaeqdyito

   accept-lifetime 00:00:00 Aug 12 2008 23:59:59 Dec 12 2008

   send-lifetime 00:00:00 Sep 12 2008 23:59:59 Nov 12 2008

feature hsrp

track 2 interface ethernet 2/2 ip

interface ethernet 1/2

 no switchport

 ip address 192.0.2.2/8

 hsrp 1 

  authenticate md5 key-chain hsrp-keys

  priority 90

  track 2 decrement 20

  ip-address 192.0.2.10

 no shutdown

Additional References

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

•Related Documents

•MIBs

Related Documents

MIBs

Feature History for HSRP

Table 16-3 lists the release history for this feature.