Configuring HSRP

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

This chapter includes the following sections:

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.

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 IPv4address 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.

The following figure 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 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 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 224.0.0.102to 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. 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 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—The active router sends this message when it no longer wants to function as the active router.

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 below shows an example of a load-sharing HSRP IPv4 configuration.

Figure 2. HSRP Load Sharing

Figure HSRP Load Sharing 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.

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.

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.

Guidelines and Limitations for HSRP

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.

  • 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.

  • HSRP localization with PACL filtering and 4-way configuration of HSRP is not supported.

Default Settings for HSRP

Table below lists the default settings for HSRP parameters.

Table 1. Default HSRP Parameters

Parameters

Default

HSRP

Disabled

Authentication

Enabled as text for version 1, with cisco as the password

HSRP version

Version 1

Preemption

disabled

Priority

100

virtual MAC address

Derived from HSRP group number

Configuring HSRP


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:

Command

Purpose

feature hsrp

Example : 

switch(config)# feature hsrp

Enables HSRP.

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

Command

Purpose

no feature hsrp

Example : 

switch(config)# no feature hsrp

Disables HSRP.

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.

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

Command

Purpose

hsrp version { 1 | 2 }

Example : 

switch(config-if)# hsrp version 2

Configures the HSRP version. Version 1 is the default.

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 address 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

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters configuration mode.

Step 2

interface type number

Example:

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

Enters interface configuration mode.

Step 3

no switchport

Example:

switch(config-if)# no switchport

Configures the interface as a Layer 3 routed interface.

Step 4

ip address ip-address/length

Example:

switch(config-if)# ip address 192.0.2.2/8

Configures the IPv4 address of the interface.

Step 5

hsrp group-number [ ipv4 ]

Example:

switch(config-if)# hsrp 2
switch(config-if-hsrp)

Creates an HSRP group and enters hsrp configuration mode. The range for HSRP version 1 is from 0 to 255. The range is for HSRP version 2 is from 0 to 4095. The default value is 0.

Step 6

ip [ ip-address [ secondary ]]

Example:

switch(config-if-hsrp)# ip 192.0.2.1

Configures the virtual IP address for the HSRP group and enables the group. This address should be in the same subnet as the IPv4 address of the interface.

Step 7

exit

Example:

switch(config-if-hsrp)# exit

Exits HSRP configuration mode.

Step 8

no shutdown

Example:

switch(config-if)# no shutdown

Enables the interface.

Step 9

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

Example:

switch(config-if)# show hsrp group 2
 (Optional)

Displays HSRP information.

Step 10

(Optional) copy running-config startup-config

Example:

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

Saves this configuration change.

Example


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 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:

Command

Purpose

mac-address string

Example : 

switch(config-if-hsrp)# mac-address 5000.1000.1060

Configures the virtual MAC address for an HSRP group. The string uses the standard MAC address format (xxxx.xxxx.xxxx).

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:

Command

Purpose

hsrp use-bia [ scope interface ]

Example : 

switch(config-if)# hsrp use-bia

Configures HSRP to use the burned-in MAC address of the interface for the HSRP virtual MAC address. You can optionally configure HSRP to use the burned-in MAC address for all groups on this interface by using the scope interface keywords.

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 3548 Switch NX-OS Security Configuration Guide).

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.

SUMMARY STEPS

  1. configure terminal
  2. interface interface type slot/port
  3. no switchport
  4. hsrp group-number [ ipv4 ]
  6. (Optional) show hsrp [ group group-number ]
  7. (Optional) copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters configuration mode.

Step 2

interface interface type slot/port

Example:

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

Enters interface configuration mode..

Step 3

no switchport

Example:

switch(config-if)# no switchport

Configures the interface as a Layer 3 routed interface.

Step 4

hsrp group-number [ ipv4 ]

Example:

switch(config-if)# hsrp 2
switch(config-if-hsrp)

Creates an HSRP group and enters HSRP configuration mode.

Step 5

Option Description

Command

Purpose

authentication text string

Example:

switch(config-if-hsrp)# authentication text mypassword

Configures cleartext authentication for HSRP on this interface.

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

Example:

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

Configures MD5 authentication for HSRP on this interface. You can use a key chain or key string. If you use a key string, you can optionally set the timeout for when HSRP will only accept a new key. The range is from 0 to 32767 seconds.

Step 6

(Optional) show hsrp [ group group-number ]

Example:

switch(config-if-hsrp)# show hsrp group 2
 (Optional)

Displays HSRP information.

Step 7

(Optional) copy running-config startup-config

Example:

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

Saves this configuration change.

Example

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 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).

SUMMARY STEPS

  1. configure terminal
  3. interface interface-type slot/port
  4. no switchport
  5. hsrp group-number [ ipv4 ]
  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

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters configuration mode.

Step 2

Option Description

Command

Purpose

track object-id interface interface-type number { ip routing | line-protocol }

Example:

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

Configures the interface that this HSRP interface tracks. Changes in the state of the interface affect the priority of this HSRP interface as follows:

  • You configure the interface and corresponding object number that you use with the track command in hsrp configuration mode.

  • The line-protocol keyword tracks whether the interface is up. The ip keyword also checks that IP routing is enabled on the interface and an IP address is configured.

track object-id ip route ip-prefix/length reachability

Example:

switch(config)# track 2 ip route 192.0.2.0/8 reachability
switch(config-track#

Creates a tracked object for a route and enters tracking configuration mode. The object-id range is from 1 to 500.

Step 3

interface interface-type slot/port

Example:

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

Enters interface configuration mode.

Step 4

no switchport

Example:

switch(config-if)# no switchport

Configures the interface as a Layer 3 routed interface.

Step 5

hsrp group-number [ ipv4 ]

Example:

switch(config-if)# hsrp 2
switch(config-if-hsrp)#

Creates an HSRP group and enters hsrp configuration mode.

Step 6

priority [ value ]

Example:

switch(config-if-hsrp)# priority 254

Sets the priority level used to select the active router in an HSRP group. The range is from 0 to 255. The default is 100.

Step 7

track object-number [ decrement value ]

Example:

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

Specifies an object to be tracked that affects the weighting of an HSRP interface.

The value argument specifies a reduction in the priority of an HSRP interface when a tracked object fails. The range is from 1 to 255. The default is 10.

Step 8

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

Example:

switch(config-if-hsrp)# preempt delay minimum 60

Configures the router to take over as the active router for an HSRP group if it has a higher priority than the current active router. This command is disabled by default. The range is from 0 to 3600 seconds.

Step 9

(Optional) show hsrp interface interface-type number

Example:

switch(config-if-hsrp)# show hsrp interface ethernet 1/2
 (Optional)

Displays HSRP information for an interface.

Step 10

(Optional) copy running-config startup-config

Example:

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

Saves this configuration change.

Example

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.

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

Command

Purpose

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

Example:

switch(config-if-hsrp)# priority 60 forwarding-threshold lower 40 upper 50

Sets the priority level used to select the active router in an HSRP group. The level range is from 0 to 255. The default is 100.

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:

Command

Purpose

name string

Example:

switch(config-if-hsrp)# name HSRP-1

Specifies the IP redundancy name for an HSRP group. The string is from 1 to 255 characters. The default string has the following format: hsrp-interface-short-name-group-id

For example, 

hsrp-Eth2/1-1

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

Example:

switch(config-if-hsrp)# preempt delay minimum 60

Configures the router to take over as an active router for an HSRP group if it has a higher priority than the current active router. This command is disabled by default. The range is from 0 to 3600 seconds.

timers [ msec ] hellotime [ msec ] holdtime

Example:

switch(config-if-hsrp)# timers 5 18

Configures the hello and hold time for this HSRP member as follows:

The optional msec keyword specifies that the argument is expressed in milliseconds, instead of the default seconds. The timer ranges for milliseconds are as follows:

  • hellotime —The interval between successive hello packets sent. The range is from 255 to 999 milliseconds.

  • holdtime —The interval before the information in the hello packet is considered invalid. The range is from 750 to 3000 milliseconds.

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

Command or Action

Purpose

hsrp delay minimum seconds

Example:

switch(config-if)# hsrp delay minimum 30

Specifies the minimum amount of time that HSRP waits after a group is enabled before participating in the group. The range is from 0 to 10000 seconds. The default is 0.

hsrp delay reload seconds

Example:

switch(config-if)# hsrp delay reload 30

Specifies the minimum amount of time that HSRP waits after reload before participating in the group. The range is from 0 to 10000 seconds. The default is 0.

Verifying the HSRP Configuration

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

Command

Purpose
show hsrp [group group-number]

Displays the HSRP status for all groups or one group.
show hsrp delay [interface interface-type slot/port]

Displays the HSRP delay value for all interfaces or one interface.
show hsrp [interface interface-type slot/port]

Displays the HSRP status for an interface.
show hsrp [group group-number] [interface interface-type slot/port] [active] [all] [init] [learn] [listen] [speak] [standby]

Displays the HSRP status for a group or interface for virtual forwarders in the active, init, learn, listen, or standby state. Use the all keyword to see all states, including disabled.

show hsrp [group group-number] [interface interface-type slot/port] active] [all] [init] [learn] [listen] [speak] [standby] brief

Displays a brief summary of the HSRP status for a group or interface for virtual forwarders in the active, init, learn, listen, or standby state. Use the all keyword to see all states, including disabled.

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