- Cisco IOS IP Application Services Configuration Guide, Release 12.4T
Table Of Contents
HSRP Groups and Group Attributes
HSRP Support for ICMP Redirects
ICMP Redirects to Active HSRP Routers
ICMP Redirects to Passive HSRP Routers
ICMP Redirects to Non-HSRP Routers
Passive HSRP Router Advertisements
HSRP Multiple Group Optimization
Delaying the Initialization of HSRP on an Interface
Configuring HSRP Priority and Preemption
How Object Tracking Affects the Priority of an HSRP Router
Configuring HSRP Object Tracking
Configuring HSRP MD5 Authentication Using a Key String
Configuring HSRP MD5 Authentication Using a Key Chain
Troubleshooting HSRP MD5 Authentication
Configuring HSRP Text Authentication
Configuring Multiple HSRP Groups for Load Balancing
Improving CPU and Network Performance with HSRP Multiple Group Optimization
Enabling HSRP Support for ICMP Redirects
Configuring HSRP Virtual MAC Addresses or BIA MAC Addresses
Linking IP Redundancy Clients to HSRP Groups
SSO Dual-Route Processors and Cisco Nonstop Forwarding
Configuring BFD Session Parameters on the Interface
Configuring HSRP Gratuitous ARP
Configuration Examples for HSRP
HSRP Priority and Preemption: Example
HSRP MD5 Authentication Using Key Strings: Example
HSRP MD5 Authentication Using Key Chains: Example
HSRP MD5 Authentication Using Key Strings and Key Chains: Example
HSRP Text Authentication: Example
Multiple HSRP for Load Balancing: Example
Improving CPU and Network Performance with HSRP Multiple Group Optimization: Example
HSRP Support for ICMP Redirect Messages: Example
HSRP Virtual MAC Addresses and BIA MAC Address: Example
Linking IP Redundancy Clients to HSRP Groups: Example
SSO HSRP (Cisco IOS Release 12.2(25)S): Example
Configuring HSRP
First Published: May 2, 2005Last Updated: November 20, 2009The Hot Standby Router Protocol (HSRP) is a First Hop Redundancy Protocol (FHRP) designed to allow for transparent fail-over of the first-hop IP router. HSRP provides high network availability by providing first-hop routing redundancy for IP hosts on Ethernet, Fiber Distributed Data Interface (FDDI), Bridge-Group Virtual Interface (BVI), LAN Emulation (LANE), or Token Ring networks configured with a default gateway IP address. HSRP is used in a group of routers for selecting an active router and a standby router. In a group of router interfaces, the active router is the router of choice for routing packets; the standby router is the router that takes over when the active router fails or when preset conditions are met.
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 HSRP" section.
Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS 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 HSRP
Restrictions for HSRP
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Note
Information About HSRP
To configure HSRP, you should understand the following concepts:
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HSRP Operation
Most IP hosts have an IP address of a single router configured as the default gateway. When HSRP is used, the HSRP virtual IP address is configured as the host's default gateway instead of the IP address of the router.
HSRP is useful for hosts that do not support a router discovery protocol (such as ICMP Router Discovery Protocol [IRDP]) and cannot switch to a new router when their selected router reloads or loses power. Because existing TCP sessions can survive the failover, this protocol also provides a more transparent recovery for hosts that dynamically choose a next hop for routing IP traffic.
When HSRP is configured on a network segment, it provides a virtual MAC address and an IP address that is shared among a group of routers running HSRP. The address of this HSRP group is referred to as the virtual IP address. One of these devices is selected by the protocol to be the active router. The active router receives and routes packets destined for the MAC address of the group. For n routers running HSRP, n + 1 IP and MAC addresses are assigned.
HSRP detects when the designated active router fails, at which point a selected standby router assumes control of the MAC and IP addresses of the Hot Standby group. A new standby router is also selected at that time.
HSRP uses a priority mechanism to determine which HSRP configured router is to be the default active router. To configure a router as the active router, you assign it a priority that is higher than the priority of all the other HSRP-configured routers. The default priority is 100, so if you configure just one router to have a higher priority, that router will be the default active router.
Devices that are running HSRP send and receive multicast User Datagram Protocol (UDP)-based hello messages to detect router 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 routers is completely transparent to all hosts on the network.
You can configure multiple Hot Standby groups on an interface, thereby making fuller use of redundant routers and load sharing.
Figure 1 shows a network configured for HSRP. By sharing a virtual MAC address and IP address, two or more routers can act as a single virtual router. The virtual router does not physically exist but represents the common default gateway for routers 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 gateway. If the active router fails to send a hello message within the configurable period of time, the standby router takes over and responds to the virtual addresses and becomes the active router, assuming the active router duties.
Figure 1 HSRP Topology
HSRP is supported over Inter-Switch Link (ISL) encapsulation. See the "Virtual LANs" section of the "Configuring Routing Between VLANs" chapter in the Cisco IOS LAN Switching Configuration Guide, Release 12.4.
HSRP Configuration Changes
In Cisco IOS Release 12.2(33)SXI, 12.4(24)T, 12.2(33)SRE and later releases, an HSRP group may be configured with a virtual IP address that matches the subnet of an IP address of a secondary interface.
When the virtual IP address of an HSRP group is configured with the same network ID as a secondary interface IP address, the source address of HSRP messages is automatically set to the most appropriate
interface address. This configuration change allows the following configuration:interface Ethernet1/0ip address 192.168.1.1 255.255.255.0ip address 192.168.2.1 255.255.255.0 secondarystandby 1 ip 192.168.1.254standby 1 priority 105standby 1 preemptstandby 2 ip 192.168.2.254 !Same network ID as secondary interfacePrior to Cisco IOS Release 12.2(33)SXI, 12.4(24)T, or 12.2(33)SRE, an HSRP group remained in INIT state unless the HSRP virtual IP address had the same network ID as the primary interface address.
In addition, the following warning message is displayed if an HSRP group address is configured when there are no interface addresses configured:
% Warning: address is not within a subnet on this interfaceHSRP Benefits
Redundancy
HSRP employs a redundancy scheme that is time proven and deployed extensively in large networks.
Fast Failover
HSRP provides transparent fast failover of the first-hop router.
Preemption
Preemption allows a standby router to delay becoming active for a configurable amount of time.
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 Groups and Group Attributes
By using the command-line interface (CLI), group attributes can be applied to:
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HSRP Preemption
When a newly reloaded router becomes HSRP active, and there is already an HSRP active router on the network, it may appear that HSRP preemption is not functioning. This can occur because the new HSRP active router did not receive any hello packets from the current HSRP active router, and the preemption configuration never factored into the new routers decision making.
This can occur on some larger platforms such as the Cisco 7600 series routers where there can be a delay in an interface receiving packets.
In general, we recommend that all HSRP routers have the following configuration:
standby delay minimum 30 reload 60
The standby delay minimum reload interface configuration command delays HSRP groups from initializing for the specified time after the interface comes up.
This command is separate from the standby preempt delay interface configuration command, which enables HSRP preemption delay.
HSRP Addressing
HSRP routers communicate between 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 MAC address (BIA).
Because hosts are configured with their default gateway as the HSRP virtual IP address, hosts must communicate with the MAC address associated with the HSRP virtual IP address. This MAC address will be a virtual MAC address composed of 0000.0C07.ACxy, where xy is the HSRP group number in hexadecimal based on the respective interface. For example, HSRP group one will use 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.
Token Ring interfaces use functional addresses for the HSRP MAC address. Functional addresses are the only general multicast mechanism available. There are a limited number of Token Ring functional addresses available, and many of them are reserved for other functions. The following are the only three addresses available for use with HSRP:
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Thus, only three HSRP groups may be configured on Token Ring interfaces unless the standby use-bia interface configuration command is configured.
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. This new multicast address allows Cisco Group Management Protocol (CGMP) leave processing to be enabled at the same time as HSRP.
HSRP version 2 permits an expanded group number range, 0 to 4095, and consequently uses a new MAC address range 0000.0C9F.F000 to 0000.0C9F.FFFF.
HSRP Text Authentication
HSRP ignores unauthenticated HSRP protocol messages. The default authentication type is text authentication.
HSRP authentication protects against false HSRP hello packets causing a denial-of-service attack. For example, Router A has a priority of 120 and is the active router. If a host sends spoof HSRP hello packets with a priority of 130, then Router A stops being the active router. If Router A has authentication configured such that the spoof HSRP hello packets are ignored, Router A will remain the active router.
HSRP packets will be rejected in any of the following cases:
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HSRP MD5 Authentication
Before the introduction of HSRP MD5 authentication, HSRP authenticated protocol packets with a simple plain text string. HSRP MD5 authentication is an enhancement to generate an MD5 digest for the HSRP portion of the multicast HSRP protocol packet. This functionality provides added security and protects against the threat from HSRP-spoofing software.
MD5 authentication provides greater security than the alternative plain text authentication scheme. MD5 authentication allows each HSRP group member to use a secret key to generate a keyed MD5 hash that is part of the outgoing packet. A keyed hash of an incoming packet is generated and if the hash within the incoming packet does not match the generated hash, the packet is ignored.
The key for the MD5 hash can be either given directly in the configuration using a key string or supplied indirectly through a key chain.
HSRP has two authentication schemes:
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HSRP authentication protects against false HSRP hello packets causing a denial-of-service attack. For example, Router A has a priority of 120 and is the active router. If a host sends spoof HSRP hello packets with a priority of 130, then Router A stops being the active router. If Router A has authentication configured such that the spoof HSRP hello packets are ignored, Router A will remain the active router.
HSRP packets will be rejected in any of the following cases:
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HSRP Support for IPv6
Most IPv4 hosts have a single router's IP address configured as the default gateway. When HSRP is used, then the HSRP virtual IP address is configured as the host's default gateway instead of the router's IP address. Simple load sharing may be achieved by using two HSRP groups and configuring half the hosts with one virtual IP address and half the hosts with the other virtual IP address.
In contrast, IPv6 hosts learn of available IPv6 routers through IPv6 neighbor discovery Router Advertisement (RA) messages. These are multicast periodically, or may be solicited by hosts. HSRP is designed to provide only a virtual first hop for IPv6 hosts.
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, by default, derived from the HSRP virtual MAC address. HSRP IPv6 uses the MAC address range 0005.73A0.0000 to 0005.73A0.0FFF. Periodic RAs are sent for the HSRP virtual IPv6 link-local address when the HSRP group is active. These RAs stop after a final RA is sent when the group leaves the active state.
Periodic RAs for the interface link-local address stop after a final RA is sent while at least one virtual IPv6 link-local address is configured on the interface. No restrictions occur for the interface IPv6 link-local address other than that mentioned for the RAs. Other protocols continue to receive and send packets to this address.
HSRP uses a priority mechanism to determine which HSRP configured router is to be the default active router. To configure a router as the active router, you assign it a priority that is higher than the priority of all the other HSRP-configured routers. The default priority is 100, so if you configure just one router to have a higher priority, that router will be the default active router.
For more information see the "Configuring First Hop Redundancy Protocols in IPv6" chapter of the Cisco IOS IPv6 Configuration Guide.
HSRP Messages and States
Routers configured with HSRP exchange three types of multicast messages:
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At any time, a router configured with HSRP is in one of the following states:
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In Cisco IOS Release 12.2(33)SXH and later Cisco IOS 12.2SX releases, Cisco IOS Release 12.2(33)SRB and later Cisco IOS 12.2SR releases, and Cisco IOS Release 12.4(8) and later Cisco IOS 12.4 releases, HSRP uses logging Level 5 for syslog messages related to HSRP state changes to allow logging of an event without filling up the syslog buffer on the router with low-priority Level 6 messaging.
Cisco IOS software prior to these releases uses logging Level 6 for syslog messages related to HSRP state changes.
HSRP and ARP
HSRP also works when the hosts are configured for proxy ARP. When the active HSRP router receives an ARP request for a host that is not on the local LAN, the router replies with the MAC address of the virtual router. If the active router becomes unavailable or its connection to the remote LAN goes down, the router that becomes the active router receives packets addressed to the virtual router and transfers them accordingly. If the Hot Standby state of the interface is not active, proxy ARP responses are suppressed.
HSRP Gratuitous ARP
The HSRP Gratuitous ARP feature configures HSRP to check that the entries in the ARP cache are correct and to send periodic gratuitous ARP packets from one or more HSRP active groups. By default, HSRP sends out three gratuitous ARP packets from an HSRP group when the group state changes to Active. HSRP sends the first gratuitous ARP packet when the group becomes active. The second two gratuitous ARP packets are sent 2 and 4 seconds later.
The HSRP Gratuitous ARP feature enhances the capability of HSRP so that the number and frequency of gratuitous ARP packets sent by an active HSRP group are configurable. Use the standby arp gratuitous command in interface configuration mode to configure a specific number of gratuitous ARP packets to be sent at a specified interval.
Use the standby send arp command in EXEC mode to configure HSRP to send a single gratuitous ARP packet for each active group. When the standby send arp command is configured, HSRP checks that the entries in the ARP cache are correct prior to sending a gratuitous ARP packet. If an ARP entry is incorrect, HSRP will try to re-add it. Static or alias ARP entries cannot be overwritten by HSRP.
Configuring the standby send arp command ensures that a host ARP cache is updated prior to heavy CPU-usage processes or configurations are started.
When CPU usage is above 50% due to heavy ARP traffic combined with moderate software switched IP traffic, ARP refresh requests could fail, causing some application servers to lose their default gateway ARP entries and fail to communicate with the rest of the network. In some scenarios, operations such as enabling a large access list, can cause ARP requests from hosts to be delayed, causing the host to have no default gateway for a short time. A periodic gratuitous ARP packet sent from the HSRP active router refreshes the host ARP cache before it expires.
HSRP Object Tracking
Object tracking separates the tracking mechanism from HSRP and creates a separate standalone tracking process that can be used by any other process as well as HSRP. The priority of a device can change dynamically when it has been configured for object tracking and the object that is being tracked goes down. Examples of objects that can be tracked are the line protocol state of an interface or the reachability of an IP route. If the specified object goes down, the HSRP priority is reduced.
A client process, such as HSRP, Virtual Router Redundancy Protocol (VRRP), or Gateway Load Balancing Protocol (GLBP), can now register its interest in tracking objects and then be notified when the tracked object changes state.
For more information about Object Tracking, see the Configuring Enhanced Object Tracking document.
HSRP Support for ICMP Redirects
ICMP is a network layer Internet protocol that provides message packets to report errors and other information relevant to IP processing. ICMP can send error packets to a host and can send redirect packets to a host.
When running HSRP, it is important to prevent hosts from discovering the interface (or real) IP addresses of routers in the HSRP group. If a host is redirected by ICMP to the real IP address of a router, and that router later fails, then packets from the host will be lost.
ICMP redirect messages are automatically enabled on interfaces configured with HSRP. This functionality works by filtering outgoing ICMP redirect messages through HSRP, where the next hop IP address may be changed to an HSRP virtual IP address.
ICMP Redirects to Active HSRP Routers
The next-hop IP address is compared to the list of active HSRP routers on that network; if a match is found, then the real next-hop IP address is replaced with a corresponding virtual IP address and the redirect message is allowed to continue.
If no match is found, then the ICMP redirect message is sent only if the router corresponding to the new next hop IP address is not running HSRP. Redirects to passive HSRP routers are not allowed (a passive HSRP router is a router running HSRP, but which contains no active HSRP groups on the interface).
For optimal operation, every router in a network that is running HSRP should contain at least one active HSRP group on an interface to that network. Every HSRP router need not be a member of the same group. Each HSRP router will snoop on all HSRP packets on the network to maintain a list of active routers (virtual IP addresses versus real IP addresses).
Consider the network shown in Figure 2, which supports the HSRP ICMP redirection filter.
Figure 2 Network Supporting the HSRP ICMP Redirection Filter
If the host wants to send a packet to another host on Net D, then it first sends it to its default gateway, the virtual IP address of HSRP group 1.
The following is the packet received from the host:
dest MAC = HSRP group 1 virtual MACsource MAC = Host MACdest IP = host-on-netD IPsource IP = Host IPRouter R1 receives this packet and determines that router R4 can provide a better path to Net D, so it prepares to send a redirect message that will redirect the host to the real IP address of router R4 (because only real IP addresses are in its routing table).
The following is the initial ICMP redirect message sent by router R1:
dest MAC = Host MACsource MAC = router R1 MACdest IP = Host IPsource IP = router R1 IPgateway to use = router R4 IPBefore this redirect occurs, the HSRP process of router R1 determines that router R4 is the active HSRP router for group 3, so it changes the next hop in the redirect message from the real IP address of router R4 to the virtual IP address of group 3. Furthermore, it determines from the destination MAC address of the packet that triggered the redirect message that the host used the virtual IP address of group 1 as its gateway, so it changes the source IP address of the redirect message to the virtual IP address of group 1.
The modified ICMP redirect message showing the two modified fields (*) is as follows:
dest MAC = Host MACsource MAC = router R1 MACdest IP = Host IPsource IP* = HSRP group 1 virtual IPgateway to use* = HSRP group 3 virtual IPThis second modification is necessary because hosts compare the source IP address of the ICMP redirect message with their default gateway. If these addresses do not match, the ICMP redirect message is ignored. The routing table of the host now consists of the default gateway, virtual IP address of group 1, and a route to Net D through the virtual IP address of group 3.
ICMP Redirects to Passive HSRP Routers
Redirects to passive HSRP routers are not permitted. Redundancy may be lost if hosts learn the real IP addresses of HSRP routers.
In Figure 2, redirection to router R8 is not allowed because R8 is a passive HSRP router. In this case, packets from the host to Net D will first go to router R1 and then be forwarded to router R4; that is, they will traverse the network twice.
A network configuration with passive HSRP routers is considered a misconfiguration. For HSRP ICMP redirection to operate optimally, every router on the network that is running HSRP should contain at least one active HSRP group.
ICMP Redirects to Non-HSRP Routers
Redirects to routers not running HSRP on their local interface are permitted. No redundancy is lost if hosts learn the real IP address of non-HSRP routers.
In Figure 2, redirection to router R7 is allowed because R7 is not running HSRP. In this case, the next hop IP address is unchanged. The source IP address is changed dependent upon the destination MAC address of the original packet. You can specify the no standby redirect unknown command to stop these redirects from being sent.
Passive HSRP Router Advertisements
Passive HSRP routers send out HSRP advertisement messages both periodically and when entering or leaving the passive state. Thus, all HSRP routers can determine the HSRP group state of any HSRP router on the network. These advertisements inform other HSRP routers on the network of the HSRP interface state, as follows:
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You can adjust the advertisement interval and holddown time using the standby redirect timers command.
ICMP Redirects Not Sent
If the HSRP router cannot uniquely determine the IP address used by the host when it sends the packet that caused the redirect, the redirect message will not be sent. The router uses the destination MAC address in the original packet to make this determination. In certain configurations, such as the use of the standby use-bia interface configuration command specified on an interface, redirects cannot be sent. In this case, the HSRP groups use the interface MAC address as their virtual MAC address. The router now cannot determine if the default gateway of the host is the real IP address or one of the HSRP virtual IP addresses that are active on the interface.
Using HSRP with ICMP redirects is not possible in the Cisco 800 series, Cisco 1000 series, Cisco 1600 series, Cisco 2500 series, Cisco 3000 series, and Cisco 4500 series routers because the Ethernet controller can only support one MAC address.
The IP source address of an ICMP packet must match the gateway address used by the host in the packet that triggered the ICMP packet, otherwise the host will reject the ICMP redirect packet. An HSRP router uses the destination MAC address to determine the gateway IP address of the host. If the HSRP router is using the same MAC address for multiple IP addresses then it is not possible to uniquely determine the gateway IP address of the host and the redirect message is not sent.
The following is sample output from the debug standby events icmp EXEC command if HSRP could not uniquely determine the gateway used by the host:
10:43:08: HSRP: ICMP redirect not sent to 20.0.0.4 for dest 30.0.0.210:43:08: HSRP: could not uniquely determine IP address for mac 00d0.bbd3.bc22
HSRP Group Shutdown
The FHRP—HSRP Group Shutdown feature enables you to configure an HSRP group to become disabled (its state changed to Init) instead of having its priority decremented when a tracked object goes down. Use the standby track command with the shutdown keyword to configure HSRP group shutdown.
If an object is already being tracked by an HSRP group, you cannot change the configuration to use the HSRP Group Shutdown feature. You must first remove the tracking configuration using the no standby track command and then reconfigure it using the standby track command with the shutdown keyword.
The following example shows how to change the configuration of a tracked object to include the HSRP Group Shutdown feature:
no standby 1 track 101 decrement 10standby 1 track 101 shutdownHSRP Support for MPLS VPNs
HSRP support for a Multiprotocol Label Switching (MPLS) Virtual Private Network (VPN) interface is useful when an Ethernet LAN is connected between two provider edge (PE) routers with either of the following conditions:
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Each VPN is associated with one or more VPN routing/forwarding (VRF) instances. A VRF consists of the following elements:
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VPN routing information is stored in the IP routing table and the CEF table for each VRF. A separate set of routing and CEF tables is maintained for each VRF. These tables prevent information from being forwarded outside a VPN and also prevent packets that are outside a VPN from being forwarded to a router within the VPN.
HSRP adds ARP entries and IP hash table entries (aliases) using the default routing table instance. However, a different routing table instance is used when VRF forwarding is configured on an interface, causing ARP and ICMP echo requests for the HSRP virtual IP address to fail.
HSRP support for MPLS VPNs ensures that the HSRP virtual IP address is added to the correct IP routing table and not to the default routing table.
HSRP Multiple Group Optimization
Increasingly, many hundreds of subinterfaces are being configured on the same physical interface, with each subinterface having its own HSRP group. The negotiation and maintenance of multiple HSRP groups can have a detrimental impact on network traffic and CPU utilization.
Only one HSRP group is required on a physical interface for the purposes of electing active and standby routers. This group is known as the master group. Other HSRP groups may be created on each subinterface and linked to the master group via the group name. These linked HSRP groups are known as client or slave groups.
The HSRP group state of the client groups follows that of the master group. Client groups do not participate in any sort of router election mechanism.
Client groups send periodic messages in order to refresh their virtual MAC addresses in switches and learning bridges. The refresh message may be sent at a much lower frequency compared with the protocol election messages sent by the master group.
HSRP—ISSU
The In Service Software Upgrade (ISSU) process allows Cisco IOS software to be updated or otherwise modified while packet forwarding continues. In most networks, planned software upgrades are a significant cause of downtime. ISSU allows Cisco IOS software to be modified while packet forwarding continues, which increases network availability and reduces downtime caused by planned software upgrades. This document provides information about ISSU concepts and describes the steps taken to perform ISSU in a system.
For detailed information about ISSU, see the Cisco IOS In Service Software Upgrade Process document at the following URL:
http://www.cisco.com/en/US/docs/ios/ha/configuration/guide/ha-inserv_updg.html
For detailed information about ISSU on the 7600 series routers, see the ISSU and eFSU on Cisco 7600 Series Routers document at the following URL:
http://www.cisco.com/en/US/docs/routers/7600/ios/12.2SR/configuration/guide/efsuovrw.html
For detailed information about ISSU on Cisco Catalyst 4500 series switches, see the "Configuring the Cisco IOS In Service Software Upgrade Process" chapter of the Catalyst 4500 Series Switch Cisco IOS Software Configuration Guide, Release 12.2(31)SGA at the following URL:
http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/12.2/31sga/configuration/guide/issu.html
HSRP BFD Peering
The HSRP BFD Peering feature introduces BFD in the HSRP group member health monitoring system. HSRP supports BFD as a part of the HSRP group member health monitoring system. Without BFD, HSRP runs as a process in a multiprocess system and cannot be guaranteed to be scheduled in time to service large numbers of groups with millisecond hello and hold timers. BFD runs as a pseudo-preemptive process and can therefore be guaranteed to run when required. Only one BFD session between two routers can provide early failover notification for multiple HSRP groups.
This feature is enabled by default. The HSRP standby router learns the real IP address of the HSRP active router from the HSRP Hello messages. The standby router will register as a BFD client and ask to be notified if the active router becomes unavailable.
BFD provides a low-overhead, short-duration method of detecting failures in the forwarding path between two adjacent routers, including the interfaces, data links, and forwarding planes. BFD is a detection protocol that you enable at the interface and routing protocol levels. Cisco supports the BFD asynchronous mode, which depends on the sending of BFD control packets between two systems to activate and maintain BFD neighbor sessions between routers. Therefore, in order for a BFD session to be created, you must configure BFD on both systems (or BFD peers). When BFD has been enabled on the interfaces and at the router level for HSRP, a BFD session is created, BFD timers are negotiated, and the BFD peers will begin to send BFD control packets to each other at the negotiated interval.
BFD provides fast BFD peer failure detection times independently of all media types, encapsulations, topologies, and routing protocols BGP, EIGRP, HSRP, IS-IS, and OSPF. By sending rapid failure detection notices to the routing protocols in the local router to initiate the routing table recalculation process, BFD contributes to greatly reduce overall network convergence time. Figure 3 shows a simple network with two routers running HSRP and BFD.
Figure 3 HSRP BFD Peering
For more information on BFD, see the "Bidirectional Forwarding Detection" chapter in the Cisco IOS IP Routing Configuration Guide at the following URL:
http://www.cisco.com/en/US/docs/ios/iproute/configuration/guide/irp_bfd.html
How to Configure HSRP
This section contains the following procedures:
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Enabling HSRP
Perform this task to enable HSRP.
The standby ip interface configuration command activates HSRP on the configured interface. If an IP address is specified, that address is used as the virtual IP address for the Hot Standby group. For HSRP to elect a designated router, you must configure the virtual IP address for at least one of the routers in the group; it can be learned on the other routers in the group.
Prerequisites
You can configure many attributes in HSRP such as authentication, timers, priority, and preemption. It is best practice to configure the attributes first before enabling the HSRP group.
This practice avoids authentication error messages and unexpected state changes in other routers that can occur if the group is enabled first and then there is a long enough delay (one or two hold times) before the other configuration is entered.
We recommend that you always specify an HSRP IP address.
SUMMARY STEPS
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Delaying the Initialization of HSRP on an Interface
Perform this task to delay the initialization of HSRP on an interface.
The standby delay command is used to delay HSRP initialization either after a reload and/or after an interface comes up. This configuration allows the interface and router time to settle down after the interface up event and helps prevent HSRP state flapping.
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Troubleshooting Tips
We recommend that you use the standby delay minimum reload command if the standby timers command is configured in milliseconds or if HSRP is configured on a VLAN interface of a switch.
Configuring HSRP Priority and Preemption
Perform this task to configure HSRP priority and preemption.
HSRP Priority and Preemption
Preemption enables the HSRP router with the highest priority to immediately become the active router. Priority is determined first by the configured priority value, and then by the IP address. In case of ties, the primary IP addresses are compared, and the higher IP address has priority. In each case, a higher value is of greater priority. If you do not use the standby preempt interface configuration command in the configuration for a router, that router will not become the active router, even if its priority is higher than all other routers.
A standby router with equal priority but a higher IP address will not preempt the active router.
When a router first comes up, it does not have a complete routing table. You can set a preemption delay that allows preemption to be delayed for a configurable time period. This delay period allows the router to populate its routing table before becoming the active router.
If preemption is not enabled, then a router may appear to preempt the active router if it does not receive any Hello messages from the active router.
How Object Tracking Affects the Priority of an HSRP Router
The priority of a device 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 change of value. The changes in the tracked object are communicated to HSRP, either immediately or after a specified delay. The object values are reported as either up or down. Examples of objects that can be tracked are the line protocol state of an interface or the reachability of an IP route. If the specified object goes down, the HSRP priority is reduced. The HSRP router with the higher priority can now become the active router if it has the standby preempt command configured. See the "Configuring HSRP Object Tracking" section for more information on object tracking.
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Configuring HSRP Object Tracking
Perform this task to configure HSRP to track an object and change the HSRP priority based on the state of the object.
Each tracked object is identified by a unique number that is specified on the tracking CLI. Client processes use this number to track a specific object.
For more information on object tracking, see the "Configuring Enhanced Object Tracking" document.
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Configuring HSRP MD5 Authentication Using a Key String
Perform this task to configure HSRP MD5 authentication using a key string.
Restrictions
Text authentication cannot be combined with MD5 authentication for an HSRP group at any one time. When MD5 authentication is configured, the text authentication field in HSRP hello messages is set to all zeroes on transmit and ignored on receipt, provided the receiving router also has MD5 authentication enabled.
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Troubleshooting Tips
If you are changing a key string in a group of routers, change the active router last to prevent any HSRP state change. The active router should have its key string changed no later than one holdtime period, specified by the standby timers interface configuration command, after the non-active routers. This procedure ensures that the non-active routers do not time out the active router.
Configuring HSRP MD5 Authentication Using a Key Chain
Perform this task to configure HSRP MD5 authentication using a key chain. Key chains allow a different key string to be used at different times according to the key chain configuration. HSRP will query the appropriate key chain to obtain the current live key and key ID for the specified key chain.
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Troubleshooting HSRP MD5 Authentication
Perform this task if HSRP MD5 authentication is not operating correctly.
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enable
Example:Router> enable
Enables privileged EXEC mode.
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debug standby errors
Example:Router# debug standby errorsDisplays error messages related to HSRP.
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Examples
In the following example, Router A has MD5 text string authentication configured, but Router B has the default text authentication:
Router# debug standby errorsA:Jun 16 12:14:50.337:HSRP:Et0/1 Grp 0 Auth failed for Hello pkt from 10.21.0.5, MD5 confgd but no tlvB:Jun 16 12:16:34.287:HSRP:Et0/1 Grp 0 Auth failed for Hello pkt from 10.21.0.4, Text auth failedIn the following example, both Router A and Router B have different MD5 authentication strings:
Router# debug standby errorsA:Jun 16 12:19:26.335:HSRP:Et0/1 Grp 0 Auth failed for Hello pkt from 10.21.0.5, MD5 auth failedB:Jun 16 12:18:46.280:HSRP:Et0/1 Grp 0 Auth failed for Hello pkt from 10.21.0.4, MD5 auth failedConfiguring HSRP Text Authentication
Perform this task to configure HSRP text authentication.
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Customizing HSRP Parameters
Perform this task to customize HSRP parameters.
HSRP Timers
Each HSRP router maintains three timers that are used for timing hello messages: an active timer, a standby timer, and a hello timer. When a timer expires, the router changes to a new HSRP state. Routers or access servers for which timer values are not configured can learn timer values from the active or standby router. The timers configured on the active router always override any other timer settings. All routers in a Hot Standby group should use the same timer values.
For HSRP version 1, nonactive routers learn timer values from the active router, unless millisecond timer values are being used. If millisecond timer values are being used, all routers must be configured with the millisecond timer values. This rule applies if either the hello time or the hold time is specified in milliseconds. This configuration is necessary because the HSRP hello packets advertise the timer values in seconds. HSRP version 2 does not have this limitation; it advertises the timer values in milliseconds.
HSRP MAC Refresh Interval
When HSRP runs over FDDI, you can change the interval at which a packet is sent to refresh the MAC cache on learning bridges and switches. HSRP hello packets on FDDI interfaces use the burned-in address (BIA) instead of the MAC virtual address. Refresh packets keep the MAC cache on switches and learning bridges current. Refresh packets are also used for HSRP groups configured as multigroup slaves because these do not send regular Hello messages.
You can change the refresh interval on FDDI rings to a longer or shorter interval, thereby using bandwidth more efficiently. You can prevent the sending of any MAC refresh packets if you do not need them (if you have FDDI but do not have a learning bridge or switch).
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Step 1
enable
Example:Router> enable
Enables privileged EXEC mode.
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configure terminal
Example:Router# configure terminal
Enters global configuration mode.
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interface type number
Example:Router(config)# interface Ethernet0/1
Configures an interface type and enters interface configuration mode.
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ip address ip-address mask [secondary]
Example:Router(config-if)# ip address 10.0.0.1 255.255.255.0
Specifies a primary or secondary IP address for an interface.
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standby [group-number] timers [msec] hellotime [msec] holdtime
Example:Router(config-if)# standby 1 timers 5 15
Configures the time between hello packets and the time before other routers declare the active Hot Standby router to be down.
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standby mac-refresh seconds
Example:Router(config-if)# standby mac-refresh 100
Changes the interval at which packets are sent to refresh the MAC cache when HSRP is running over FDDI.
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standby [group-number] ip [ip-address [secondary]]
Example:Router(config-if)# standby 1 ip 10.0.0.3
Activates HSRP.
Troubleshooting Tips
We recommend configuring a minimum hellotime value of 250 milliseconds and a minimum holdtime value of 800 milliseconds.
You can use the standby delay command to allow the interface to come up completely before HSRP initializes.
Configuring Multiple HSRP Groups for Load Balancing
Perform this task to configure multiple HSRP groups for load balancing.
Multiple HSRP groups enable redundancy and load-sharing within networks and allow redundant routers to be more fully utilized. While a router is actively forwarding traffic for one HSRP group, it can be in standby or in the listen state for another group.
If two routers are used, then Router A would be configured as active for group 1 and standby for group 2. Router B would be standby for group 1 and active for group 2. Fifty percent of the hosts on the LAN would be configured with the virtual IP address of group 1 and the remaining hosts would be configured with the virtual IP address of group 2. See the "Multiple HSRP for Load Balancing: Example" section for a diagram and configuration example.
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Improving CPU and Network Performance with HSRP Multiple Group Optimization
Configure the HSRP master group using the steps in the previous section, "Configuring Multiple HSRP Groups for Load Balancing."
Perform this task to configure multiple HSRP client groups.
The standby follow command configures an HSRP group to become a slave of another HSRP group.
HSRP client groups follow the master HSRP with a slight, random delay so that all client groups do not change at the same time.
Active client groups use the existing FDDI MAC refresh mechanism to send hello packets at less frequent intervals than the master group. The default interval is 10 seconds and can be configured to as much as 255 seconds.
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Router(config-if)# standby 1 priority 110%Warning: This setting has no effect while following another group.Router(config-if)# standby 1 timers 5 15% Warning: This setting has no effect while following another group.Router(config-if)# standby 1 preempt delay minimum 300% Warning: This setting has no effect while following another group.SUMMARY STEPS
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Enabling HSRP Support for ICMP Redirects
By default, HSRP filtering of ICMP redirect messages is enabled on routers running HSRP. Perform this task to reenable this feature on your router if it is disabled.
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Configuring HSRP Virtual MAC Addresses or BIA MAC Addresses
Perform this task to configure an HSRP virtual MAC address or a burned-in address (BIA) MAC address.
A router automatically generates a virtual MAC address for each HSRP router. However, some network implementations, such as Advanced Peer-to-Peer Networking (APPN), use the MAC address to identify the first hop for routing purposes. In this case, it is often necessary to be able to specify the virtual MAC address by using the standby mac-address command in the group; the virtual IP address is unimportant for these protocols.
The standby use-bia command was implemented to overcome the limitations of using a functional address for the HSRP MAC address on Token Ring interfaces. This command allows HSRP groups to use the BIA MAC address of an interface instead of the HSRP virtual MAC address. When HSRP runs on a multiple-ring, source-routed bridging environment and the HSRP routers reside on different rings, configuring the standby use-bia command can prevent confusion about the routing information field (RFI).
The standby use-bia command applies to an interface and the standby mac-address command applies to an HSRP group.
Restrictions
You cannot use the standby use-bia and standby mac-address commands in the same configuration; they are mutually exclusive.
The standby use-bia command has the following disadvantages:
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standby use-bia [scope interface]6.
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Linking IP Redundancy Clients to HSRP Groups
Perform this task to link IP redundancy clients to HSRP groups.
HSRP provides stateless redundancy for IP routing. HSRP by itself is limited to maintaining its own state. Linking an IP redundancy client to an HSRP group provides a mechanism that allows HSRP to provide a service to client applications so they can implement stateful failover.
IP redundancy clients are other Cisco IOS processes or applications that use HSRP to provide or withhold a service or resource dependent upon the state of the group.
HSRP groups have a default name of hsrp-interface-group so specifying a group name is optional. For example, Group 1 on Ethernet0/0 has a default group name of `hsrp-Et0/0-1.'
Prerequisites
Within the client application, you must first specify the same name as configured in the standby name command.
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Changing to HSRP Version 2
HSRP version 2 was introduced to prepare for further enhancements and to expand the capabilities beyond what is possible with HSRP version 1. HSRP version 2 has a different packet format than HSRP version 1.
HSRP Version 2 Design
HSRP version 2 is designed to address the following issues relative to HSRP version 1:
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Version 1 is the default version of HSRP.
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. This new multicast address allows CGMP leave processing to be enabled at the same time as HSRP.
HSRP version 2 permits an expanded group number range, 0 to 4095, and consequently uses a new MAC address range 0000.0C9F.F000 to 0000.0C9F.FFFF. The increased group number range does not imply that an interface can, or should, support that many HSRP groups. The expanded group number range was changed to allow the group number to match the VLAN number on subinterfaces.
When the HSRP version is changed, each group will reinitialize 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 will have the type field mapped to the version field by HSRP version 1 and subsequently ignored.
The Gateway Load Balancing Protocol (GLBP) also addresses the same issues relative to HSRP version 1 that HSRP version 2 does. See the Configuring GLBP document for more information on GLBP.
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Configuring SSO HSRP
This section contains the following tasks:
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SSO HSRP alters the behavior of HSRP when a router with redundant Route Processors (RPs) is configured for Stateful Switchover (SSO) redundancy mode. When an RP is active and the other RP is standby, SSO enables the standby RP to take over if the active RP fails.
With this functionality, HSRP SSO information is synchronized to the standby RP, allowing traffic that is sent using the HSRP virtual IP address to be continuously forwarded during a switchover without a loss of data or a path change. Additionally, if both RPs fail on the active HSRP router, then the standby HSRP router takes over as the active HSRP router.
The feature is enabled by default when the redundancy mode of operation is set to SSO.
SSO Dual-Route Processors and Cisco Nonstop Forwarding
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.
SSO is generally used with Cisco Nonstop Forwarding (NSF). Cisco NSF enables forwarding of data packets to continue along known routes while the routing protocol information is being restored following a switchover. With NSF, users are less likely to experience service outages.
HSRP and SSO Working Together
SSO HSRP enables the Cisco IOS HSRP subsystem software to detect that a standby RP is installed and the system is configured in SSO redundancy mode. Further, if the active RP fails, no change occurs to the HSRP group itself and traffic continues to be forwarded through the current active gateway router.
Prior to this feature, when the primary RP of the active router failed, it would stop participating in the HSRP group and trigger another router in the group to take over as the active HSRP router.
SSO HSRP is required to preserve the forwarding path for traffic destined to the HSRP virtual IP address through an RP switchover.
Configuring SSO on the edge router enables the traffic on the Ethernet links to continue during an RP failover without the Ethernet traffic switching over to an HSRP standby router (and then back, if preemption is enabled).
Enabling SSO Aware HSRP
The functionality is enabled by default when the redundancy mode is set to SSO. Perform this task to reenable HSRP to be SSO aware if it has been disabled.
Note
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Verifying SSO Aware HSRP
To verify or debug HSRP SSO operation, perform the following steps from the active RP console.
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Step 1
Use the show standby command to display the state of the standby RP, for example:
Router# show standbyGigabitEthernet3/25 - Group 1State is Init (standby RP, peer state is Active)Virtual IP address is 10.0.0.1Active virtual MAC address is unknownLocal virtual MAC address is 0000.0c07.ac01 (v1 default)Hello time 3 sec, hold time 10 secPreemption disabledActive router is unknownStandby router is unknownPriority 100 (default 100)Group name is "hsrp-Gi3/25-1" (default)Step 2
Use the debug standby events ha command to display the active and standby RPs, for example:
Router# debug standby events ha!Active RP*Sep 1 09:46:19.788 UTC: HSRP: Gi3/25 Grp 1 HA send sync state Listen *Sep 1 09:46:31.435 UTC: HSRP: Gi3/25 Grp 1 HA send sync state Speak *Sep 1 09:46:40.940 UTC: HSRP: Gi3/25 Grp 1 HA send sync state Standby *Sep 1 09:46:41.724 UTC: HSRP: Gi3/25 Grp 1 HA send sync state Active Standby RP *Sep 1 09:46:19.143 UTC: STBY: HSRP: Gi3/25 Grp 1 RF sync state Unknown -> Init *Sep 1 09:46:20.167 UTC: STBY: HSRP: Gi3/25 Grp 1 RF sync state Init -> Listen *Sep 1 09:46:30.812 UTC: STBY: HSRP: Gi3/25 Grp 1 RF sync state Listen -> Speak *Sep 1 09:46:41.315 UTC: STBY: HSRP: Gi3/25 Grp 1 RF sync state Speak -> Standby *Sep 1 09:46:42.103 UTC: STBY: HSRP: Gi3/25 Grp 1 RF sync state Standby -> Active
Enabling HSRP MIB Traps
HSRP MIB supports Simple Network Management Protocol (SNMP) Get operations, to allow network devices to get reports about HSRP groups in a network from the network management station.
Enabling HSRP 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 leaves or enters the active or standby state. When an entry is configured from the CLI, the RowStatus for that group in the MIB immediately goes to the active state.
The Cisco IOS software supports a read-only version of the MIB, and set operations are not supported.
This functionality supports four MIB tables, as follows:
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The cHsrpGrpEntry table consists of all HSRP group information; the other tables consist of the Cisco extensions to HSRP, which are defined in CISCO-HSRP-EXT-MIB.my.
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Configuring HSRP BFD Peering
In Cisco IOS Release 12.4(11)T and later releases, the HSRP BFD Peering feature introduces BFD in the HSRP group member health monitoring system. Previously, group member monitoring relied exclusively on HSRP multicast messages, which are relatively large and consume CPU memory to produce and check. In architectures where a single interface hosts a large number of groups, there is a need for a protocol with low CPU memory consumption and processing overhead. BFD addresses this issue and offers sub-second health monitoring (failure detection in milliseconds) at a relatively low CPU impact. HSRP BFD peering is enabled by default.
This section contains the following procedures:
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Configuring BFD Session Parameters on the Interface
Perform this task to configure BFD on the interface by setting the baseline BFD session parameters on an interface. Repeat the steps in this procedure for each interface over which you want to run BFD sessions to BFD neighbors.
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Configuring HSRP BFD Peering
Perform this task to enable HSRP BFD peering. Repeat the steps in this procedure for each interface over which you want to run BFD sessions to HSRP peers.
HSRP supports BFD peering by default. If HSRP BFD peering has been manually disabled, you can reenable it at the router level to enable BFD support globally for all interfaces or you can reenable it on a per-interface basis at the interface level.
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Verifying HSRP BFD Peering
To verify HSRP BFD Peering, use any of the following optional commands.
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Step 1
Use the show standby command to display HSRP information.
Router# show standbyFastEthernet2/0 - Group 1State is Active2 state changes, last state change 00:08:06Virtual IP address is 10.0.0.11Active virtual MAC address is 0000.0c07.ac01Local virtual MAC address is 0000.0c07.ac01 (v1 default)Hello time 3 sec, hold time 10 secNext hello sent in 2.772 secsPreemption enabledActive router is localStandby router is 10.0.0.2, priority 90 (expires in 8.268 sec)BFD enabled !Priority 110 (configured 110)Group name is "hsrp-Fa2/0-1" (default)Step 2
Use the show standby neighbors command to display information about HSRP peer routers on an interface.
Router1# show standby neighborsHSRP neighbors on FastEthernet2/010.1.0.22No active groupsStandby groups: 1BFD enabled !Router2# show standby neighborsHSRP neighbors on FastEthernet2/010.0.0.2Active groups: 1No standby groupsBFD enabled !Step 3
Use the show bfd neighbors command to display a line-by-line listing of existing Bidirectional Forwarding Detection (BFD) adjacencies. The details keyword displays BFD protocol parameters and timers for each neighbor.
Router# show bfd neighbors detailsOurAddr NeighAddr LD/RD RH/RS Holdown(mult) State Int10.0.0.2 10.0.0.1 5/0 Down 0 (0 ) Down Fa2/0Local Diag: 0, Demand mode: 0, Poll bit: 0MinTxInt: 1000000, MinRxInt: 1000000, Multiplier: 3Received MinRxInt: 0, Received Multiplier: 0Holdown (hits): 0(0), Hello (hits): 1000(55)Rx Count: 0, Rx Interval (ms) min/max/avg: 0/0/0 last: 3314120 ms agoTx Count: 55, Tx Interval (ms) min/max/avg: 760/1000/872 last: 412 ms agoRegistered protocols: HSRP !Last packet: Version: 1 - Diagnostic: 0State bit: AdminDown - Demand bit: 0Poll bit: 0 - Final bit: 0Multiplier: 0 - Length: 0My Discr.: 0 - Your Discr.: 0Min tx interval: 0 - Min rx interval: 0Min Echo interval: 0What to Do Next
For more information about configuring BFD, see the "Bidirectional Forwarding Detection" document in the Cisco IOS IP Routing Configuration Guide at the following URL:
http://www.cisco.com/en/US/docs/ios/iproute/configuration/guide/irp_bfd.html
Configuring HSRP Gratuitous ARP
Perform this task to configure HSRP to check that the entries in the ARP cache are correct and to send periodic gratuitous ARP packets from one or more HSRP active groups. By default, HSRP sends out three gratuitous ARP packets from an HSRP group when the group state changes to Active. HSRP sends the first gratuitous ARP packet when the group becomes active. The second two gratuitous ARP packets are sent 2 and 4 seconds later.
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Example
The following is sample output from the show standby arp gratuitous command:
Router# show standby arp gratuitous ethernet1/1HSRP Gratuitous ARPInterface Interval CountEthernet1/1 4 3Configuration Examples for HSRP
This section provides the following configuration examples:
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HSRP Priority and Preemption: Example
In the following example, Router A is configured to be the active router for group 1 because it has the higher priority and standby router for group 2. Router B is configured to be the active router for group 2 and standby router for group 1.
Router A Configuration
interface Ethernet0/0ip address 10.1.0.21 255.255.0.0standby 1 priority 110standby 1 preemptstandby 1 ip 10.1.0.1standby 2 priority 95standby 2 preemptstandby 2 ip 10.1.0.2Router B Configuration
interface Ethernet0/0ip address 10.1.0.22 255.255.0.0standby 1 preemptstandby 1 priority 105standby 1 ip 10.1.0.1standby 2 priority 110standby 2 preemptstandby 2 ip 10.1.0.2HSRP Object Tracking: Example
In the following example, the tracking process is configured to track the IP-routing capability of serial interface 1/0. HSRP on Ethernet interface 0/0 then registers with the tracking process to be informed of any changes to the IP-routing state of serial interface 1/0. If the IP state on serial interface 1/0 goes down, the priority of the HSRP group is reduced by 10.
If both serial interfaces are operational, Router A will be the HSRP active router because it has the higher priority. However, if IP routing on serial interface 1/0 in Router A fails, the HSRP group priority will be reduced and Router B will take over as the active router, thus maintaining a default virtual gateway service to hosts on the 10.1.0.0 subnet.
Router A Configuration
track 100 interface serial1/0 ip routing!interface Ethernet0/0ip address 10.1.0.21 255.255.0.0standby 1 preemptstandby 1 priority 110standby 1 track 100 decrement 10standby 1 ip 10.1.0.1Router B Configuration
track 100 interface serial1/0 ip routing!interface Ethernet0/0ip address 10.1.0.22 255.255.0.0standby 1 preemptstandby 1 priority 105standby 1 track 100 decrement 10standby 1 ip 10.1.0.1HSRP Group Shutdown: Example
In the following example, the tracking process is configured to track the IP-routing capability of serial interface 1/0. HSRP on Ethernet interface 0/0 then registers with the tracking process to be informed of any changes to the IP-routing state of serial interface 1/0. If the IP state on serial interface 1/0 goes down, the HSRP group is disabled.
If both serial interfaces are operational, Router A will be the HSRP active router because it has the higher priority. However, if IP routing on serial interface 1/0 in Router A fails, the HSRP group will be disabled and Router B will take over as the active router, thus maintaining a default virtual gateway service to hosts on the 10.1.0.0 subnet.
Router A Configuration
track 100 interface serial1/0 ip routing!interface Ethernet0/0ip address 10.1.0.21 255.255.0.0standby 1 ip 10.1.0.1standby 1 preemptstandby 1 priority 110standby 1 track 100 shutdownRouter B Configuration
track 100 interface serial1/0 ip routing!interface Ethernet0/0ip address 10.1.0.22 255.255.0.0standby 1 ip 10.1.0.1standby 1 preemptstandby 1 priority 105standby 1 track 100 shutdownIf an object is already being tracked by an HSRP group, you cannot change the configuration to use the HSRP Group Shutdown feature. You must first remove the tracking configuration using the no standby track command and then reconfigure it using the standby track command with the shutdown keyword.
The following example shows how to change the configuration of a tracked object to include the HSRP Group Shutdown feature:
no standby 1 track 101 decrement 10standby 1 track 101 shutdownHSRP MD5 Authentication Using Key Strings: Example
The following example shows how to configure HSRP MD5 authentication using a key string:
interface Ethernet0/1standby 1 priority 110standby 1 preemptstandby 1 authentication md5 key-string 54321098452103ab timeout 30standby 1 ip 10.21.0.10HSRP MD5 Authentication Using Key Chains: Example
In the following example, HSRP queries the key chain "hsrp1" to obtain the current live key and key ID for the specified key chain:
key chain hsrp1key 1key-string 54321098452103abinterface Ethernet0/1standby 1 priority 110standby 1 preemptstandby 1 authentication md5 key-chain hsrp1standby 1 ip 10.21.0.10HSRP MD5 Authentication Using Key Strings and Key Chains: Example
The key ID for key-string authentication is always zero. If a key chain is configured with a key ID of zero, then the following configuration will work:
Router 1
key chain hsrp1key 0key-string 54321098452103abinterface Ethernet0/1standby 1 authentication md5 key-chain hsrp1standby 1 ip 10.21.0.10Router 2
interface Ethernet0/1standby 1 authentication md5 key-string 54321098452103abstandby 1 ip 10.21.0.10HSRP Text Authentication: Example
The following example shows how to configure HSRP text authentication using a text string:
interface Ethernet0/1standby 1 priority 110standby 1 preemptstandby 1 authentication text company2standby 1 ip 10.21.0.10Multiple HSRP for Load Balancing: Example
You can use HSRP or multiple HSRP groups when you configure load sharing. In Figure 4, half of the clients are configured for Router A, and half of the clients are configured for Router B. Together, the configuration for Routers A and B establish two Hot Standby groups. For group 1, Router A is the default active router because it has the assigned highest priority, and Router B is the standby router. For group 2, Router B is the default active router because it has the assigned highest priority, and Router A is the standby router. During normal operation, the two routers share the IP traffic load. When either router becomes unavailable, the other router becomes active and assumes the packet-transfer functions of the router that is unavailable. The standby preempt interface configuration command is necessary so that if a router goes down and then comes back up, preemption occurs and restores load sharing.
Figure 4 HSRP Load Sharing Example
The following example shows Router A configured as the active router for group 1 with a priority of 110 and Router B configured as the active router for group 2 with a priority of 110. The default priority level is 100. Group 1 uses a virtual IP address of 10.0.0.3 and Group 2 uses a virtual IP address of 10.0.0.4.
Router A Configuration
hostname RouterA!interface ethernet 0ip address 10.0.0.1 255.255.255.0standby 1 ip 10.0.0.3standby 1 priority 110standby 1 preemptstandby 2 preemptstandby 2 ip 10.0.0.4Router B Configuration
hostname RouterB!interface ethernet 0ip address 10.0.0.2 255.255.255.0standby 1 ip 10.0.0.3standby 1 preemptstandby 2 priority 110standby 2 preemptstandby 2 ip 10.0.0.4Improving CPU and Network Performance with HSRP Multiple Group Optimization: Example
The following example shows how to configure an HSRP client and master group:
interface Ethernet1/0no shutdownstandby mac-refresh 30! Client Hello message interval!interface Ethernet1/0.2no shutdownencapsulation dot1Q 2ip vrf forwarding VRF2ip address 10.0.0.100 255.255.0.0standby 1 ip 10.0.0.254standby 1 priority 110standby 1 preemptstandby 1 name HSRP1!Server group!interface Ethernet1/0.3no shutdownencapsulation dot1Q 3ip vrf forwarding VRF3ip address 10.0.0.100 255.255.0.0standby 2 ip 10.0.0.254standby 2 follow HSRP1! Client group!interface Ethernet1/0.4no shutdownencapsulation dot1Q 4ip vrf forwarding VRF4ip address 10.0.0.100 255.255.0.0standby 2 ip 10.0.0.254standby 2 follow HSRP1! Client groupHSRP Support for ICMP Redirect Messages: Example
The following is a configuration example for two HSRP groups that allow the filtering of ICMP redirect messages:
Router A Configuration—Active for Group 1 and Standby for Group 2
interface Ethernet1ip address 10.0.0.10 255.0.0.0standby redirectstandby 1 priority 120standby 1 preempt delay minimum 20standby 1 ip 10.0.0.1standby 2 priority 105standby 2 preempt delay minimum 20standby 2 ip 10.0.0.2Router B Configuration—Standby for Group 1 and Active for Group 2
interface Ethernet1ip address 10.0.0.11 255.0.0.0standby redirectstandby 1 priority 105standby 1 preempt delay minimum 20standby 1 ip 10.0.0.1standby 2 priority 120standby 2 preempt delay minimum 20standby 2 ip 10.0.0.2HSRP Virtual MAC Addresses and BIA MAC Address: Example
In an APPN network, an end node is typically configured with the MAC address of the adjacent network node. In the following example, if the end nodes are configured to use 4000.1000.1060, HSRP group 1 is configured to use the same MAC address:
interface Ethernet0/2ip address 10.0.0.1standby 1 mac-address 4000.1000.1060standby 1 ip 10.0.0.11In the following example, the burned-in address of Token Ring interface 3/0 will be the virtual MAC address mapped to the virtual IP address:
interface token3/0standby use-bia
Note
Linking IP Redundancy Clients to HSRP Groups: Example
The following example shows HSRP support for a static NAT configuration. The NAT client application is linked to HSRP via the correlation between the name specified by the standby name command. Two routers are acting as HSRP active and standby, and the NAT inside interfaces are HSRP enabled and configured to belong to the group named "group1."
Active Router Configuration
interface BVI10ip address 192.168.5.54 255.255.255.255.0no ip redirectsip nat insidestandby 10 ip 192.168.5.30standby 10 priority 110standby 10 preemptstandby 10 name group1standby 10 track Ethernet2/1!!ip default-gateway 10.0.18.126ip nat inside source static 192.168.5.33 10.10.10.5 redundancy group1ip classlessip route 10.10.10.0 255.255.255.0 Ethernet2/1ip route 172.22.33.0 255.255.255.0 Ethernet2/1no ip http serverStandby Router Configuration
interface BVI10ip address 192.168.5.56 255.255.255.255.0no ip redirectsip nat insidestandby 10 priority 95standby 10 preemptstandby 10 name group1standby 10 ip 192.168.5.30standby 10 track Ethernet3/1!ip default-gateway 10.0.18.126ip nat inside source static 192.168.5.33 3.3.3.5 redundancy group1ip classlessip route 10.0.32.231 255.255.255 Ethernet3/1ip route 10.10.10.0 255.255.255.0 Ethernet3/1no ip http serverHSRP Version 2: Example
The following example shows how to configure HSRP version 2 on an interface with a group number of 350:
interface vlan350standby version 2standby 350 priority 110standby 350 preemptstandby 350 timers 5 15standby 350 ip 172.20.100.10SSO HSRP (Cisco IOS Release 12.2(25)S): Example
The following example shows how to set the redundancy mode to SSO. HSRP is automatically SSO-aware when this mode is enabled.
redundancymode ssoIf SSO HSRP is disabled using the no standby sso command, you can reenable using the standby sso command in global configuration mode.
HSRP MIB Traps: Example
The following examples show how to configure HSRP on two routers and enable the HSRP MIB trap support functionality. As in many environments, one router is preferred as the active one. Configuring a router's preference as the active router is realized by configuring it at a higher priority level and enabling preemption. In the following example, the active router is referred to as the primary router. The second router is referred to as the backup router:
Router A
interface Ethernet1ip address 10.1.1.1 255.255.0.0standby priority 200standby preemptstandby ip 10.1.1.3snmp-server enable traps hsrpsnmp-server host yourhost.cisco.com public hsrpRouter B
interface Ethernet1ip address 10.1.1.2 255.255.0.0standby priority 101standby ip 10.1.1.3snmp-server enable traps hsrpsnmp-server host myhost.cisco.com public hsrpHSRP BFD Peering: Example
HSRP supports BFD as a part of the HSRP group member health monitoring system. Without BFD, HSRP runs as a process in a multiprocess system and cannot be guaranteed to be scheduled in time to service large numbers of groups with millisecond hello and hold timers. BFD runs as a pseudo-preemptive process and can therefore be guaranteed to run when required. Only one BFD session between two routers can provide early failover notification for multiple HSRP groups.
In the following example, the standby bfd and the standby bfd all-interfaces commands are not displayed. HSRP support for BFD is enabled by default when BFD is configured on the router or interface using the bfd interval command. The standby bfd and standby bfd all-interfaces commands are needed only if BFD has been manually disabled on a router or interface.
Router A
ip cefinterface FastEthernet2/0no shutdownip address 10.0.0.2 255.0.0.0ip router-cache cefbfd interval 200 min_rx 200 multiplier 3standby 1 ip 10.0.0.11standby 1 preemptstandby 1 priority 110standby 2 ip 10.0.0.12standby 2 preemptstandby 2 priority 110Router B
interface FastEthernet2/0ip address 10.1.0.22 255.255.0.0no shutdownbfd interval 200 min_rx 200 multiplier 3standby 1 ip 10.0.0.11standby 1 preemptstandby 1 priority 90standby 2 ip 10.0.0.12standby 2 preemptstandby 2 priority 80HSRP Gratuitous ARP: Example
The following example shows how to configure HSRP to check that the entries in the ARP cache are correct and to send three gratuitous ARP packets at 4-second intervals when an HSRP group on the interface changes to active state:
Router> enableRouter# standby send arp Ethernet1/1 1Router# configure terminalRouter(config)# interface Ethernet1/1Router(config-if)# standby arp gratuitous count 3 interval 4Router(config-if)# endRouter# show standby arp gratuitous ethernet1/1HSRP Gratuitous ARPInterface Interval CountEthernet1/1 4 3Additional References
The following sections provide references related to HSRP.
Related Documents
Cisco IOS commands
BFD
GLBP
"Configuring GLBP" module
HSRP commands: complete command syntax, command mode, command history, defaults, usage guidelines, and examples
ISSU
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Object tracking
Troubleshooting HSRP
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VRRP
"Configuring VRRP" module
Standards
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
CISCO-HSRP-MIB
CISCO-HSRP-EXT-MIBTo locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:
RFCs
RFC 792
Internet Control Message Protocol
RFC 1828
IP Authentication Using Keyed MD5
RFC 2281
Cisco Hot Standby Router Protocol
Technical Assistance
Feature Information for HSRP
Table 1 lists the features in this module and provides links to specific configuration information.
Not all commands may be available in your Cisco IOS software release. For details on when support for specific commands was introduced, see the command reference documents.
For information on a feature in this technology that is not documented here, see the "Cisco IOS IP Application Services Features Roadmap" or the "FHRP Features Roadmap."
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS and Catalyst OS 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.
Table 1 Feature Information for HSRP
FHRP—HSRP BFD Peering
12.4(11)T
The FHRP—HSRP BFD Peering feature introduces BFD in the HSRP group member health monitoring system. Previously, group member monitoring relied exclusively on HSRP multicast messages, which are relatively large and consume CPU memory to produce and check. In architectures where a single interface hosts a large number of groups, there is a need for a protocol with low CPU memory consumption and processing overhead. BFD addresses this issue and offers sub second health monitoring (failure detection in milliseconds) at a relatively low CPU impact.
The following sections provide information about this feature:
The following commands were introduced or modified by this feature: debug standby events neighbor, show standby, show standby neighbors, standby bfd, standby bfd all-interfaces.
FHRP—HSRP Group Shutdown
12.4(9)T
12.2(33)SRC
12.2(33)SXIThe FHRP—HSRP Group Shutdown feature enables you to configure an HSRP group to become disabled (its state changed to Init) instead of having its priority decremented when a tracked object goes down.
The following sections provide information about this feature:
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The following commands were modified by this feature: standby track, show standby.
FHRP—HSRP-MIB
12.0(3)T
12.0(12)SThe FHRP—HSRP-MIB feature introduces support for the CISCO-HRSP-MIB.
FHRP—HSRP Multiple Group Optimization
12.4(6)T
12.2(33)SRB
12.2(33)SXIFHRP—HSRP Multiple Group Optimization feature improves the negotiation and maintenance of multiple HSRP groups configured on a subinterface. Only one HSRP group is required on a physical interface for the purposes of electing active and standby routers. This group is known as the master group. Other HSRP groups may be created on each subinterface and linked to the master group via the group name. These linked HSRP groups are known as client or slave groups.
The following sections provide information about this feature:
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The following commands were introduced or modified by this feature: standby follow, show standby.
FHRP—HSRP Support for IPv6
12.4(4)T
12.2(33)SRB
12.2(33)SXISupport for IPv6 was added.
For more information see the "Configuring First Hop Redundancy Protocols in IPv6" module of the Cisco IOS IPv6 Configuration Guide.
HSRP Gratuitous ARP
12.2(33)SXI
The HSRP Gratuitous ARP feature configures HSRP to check that the entries in the ARP cache are correct and to send periodic gratuitous ARP packets from one or more HSRP active groups.
The following sections provide information about this feature:
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The following commands were introduced by this feature: show standby arp gratuitous, standby arp gratuitous, standby send arp.
The following commands were modified by this feature: show standby, debug standby events.
HSRP—ISSU
12.2(31)SGA
12.2(33)SRB1The HSRP—ISSU feature enables support for ISSU in HSRP.
The In Service Software Upgrade (ISSU) process allows Cisco IOS software to be updated or otherwise modified while packet forwarding continues. In most networks, planned software upgrades are a significant cause of downtime. ISSU allows Cisco IOS software to be modified while packet forwarding continues, which increases network availability and reduces downtime caused by planned software upgrades. This document provides information about ISSU concepts and describes the steps taken to perform ISSU in a system.
The following section provides information about this feature:
For more information about this feature, see the Cisco IOS In Service Software Upgrade Process document.
There are no new or modified commands for this feature.
HSRP MD5 Authentication
12.3(2)T
12.2(25)S
12.2(33)SRA
12.2(33)SXHPrior to the introduction of the HSRP MD5 Authentication feature, HSRP authenticated protocol packets with a simple plain text string. The HSRP MD5 Authentication feature is an enhancement to generate an MD5 digest for the HSRP portion of the multicast HSRP protocol packet. This feature provides added security and protects against the threat from HSRP-spoofing software.
The following sections provide information about this feature:
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•
•
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The following commands were introduced or modified by this feature: show standby, standby authentication.
HSRP Support for ICMP Redirects
12.1(3)T
The HSRP support for ICMP Redirects feature enables ICMP redirection on interfaces configured with HSRP.
The following sections provide information about this feature:
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•
•
The following commands were introduced or modified by this feature:
debug standby event, debug standby events icmp, show standby, standby redirects
HSRP Support for MPLS VPNs
12.0(23)S, 12.0(17)ST, 12.2(28)SB, 12.2(17b)SXA, 12.2(8)T
HSRP support for a Multiprotocol Label Switching (MPLS) Virtual Private Network (VPN) interface is useful when an Ethernet LAN is connected between two provider edge (PE) routers with either of the following conditions:
The following section provides information about this feature:
There are no new or modified commands for this feature.
HSRP Version 2
12.3(4)T
12.2(25)SHSRP Version 2 feature was introduced to prepare for further enhancements and to expand the capabilities beyond what is possible with HSRP version 1. HSRP version 2 has a different packet format than HSRP version 1.
The following sections provide information about this feature:
The following commands were introduced or modified by this feature: show standby, standby ip, standby version.
SSO—HSRP
12.2(25)S
12.2(33)SRA
12.2(33)SXHThe SSO—HSRP feature alters the behavior of HSRP when a router with redundant RPs is configured for SSO. When an RP is active and the other RP is standby, SSO enables the standby RP to take over if the active RP fails.
The following sections provide information about this feature:
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The following commands were introduced or modified by this feature: debug standby events, standby sso.
Glossary
ARP—Address Resolution Protocol (ARP). ARP performs a required function in IP routing. ARP finds the hardware address, also known as Media Access Control (MAC) address, of a host from its known IP address. ARP maintains a cache (table) in which MAC addresses are mapped to IP addresses. ARP is part of all Cisco IOS systems running IP.
active router—The primary router in an HSRP group that is currently forwarding packets for the virtual router.
active RP—The active RP that controls the system, provides network services, runs the routing protocols, and presents the system management interface.
BFD—Bidirectional Forwarding Detection. A detection protocol designed to provide fast forwarding path failure detection encapsulations, topologies, and routing protocols. In addition to fast forwarding, BFD provides a consistent failure detection method for network administrators.
client group—An HSRP group that is created on a subinterface and linked to the master group via the group name.
HSRP—Hot Standby Router Protocol. Protocol that provides high network availability and transparent network-topology changes. HSRP creates a router group with a lead router that services all packets sent to the HSRP address. The lead router is monitored by other routers in the group, and if it fails, one of these standby HSRP routers inherits the lead position and the HSRP group address.
ISSU—In Service Software Upgrade. A process that allows Cisco IOS software to be updated or otherwise modified while packet forwarding continues. In most networks, planned software upgrades are a significant cause of downtime. ISSU allows Cisco IOS software to be modified while packet forwarding continues, which increases network availability and reduces downtime caused by planned software upgrades.
master group—An HSRP group that is required on a physical interface for the purposes of electing active and standby routers.
NSF—Nonstop Forwarding. The ability of a router to continue to forward traffic to a router that may be recovering from a failure. Also, the ability of a router recovering from a failure to continue to correctly forward traffic sent to it by a peer.
RF—Redundancy Facility. A structured, functional interface used to notify its clients of active and standby state progressions and events.
RP—Route Processor. A generic term for the centralized control unit in a chassis. Platforms usually use a platform-specific term, such as RSP on the Cisco 7500, the PRE on the Cisco 10000, or the SUP+MSFC on the Cisco 7600.
RPR—Route Processor Redundancy. RPR provides an alternative to the High System Availability (HSA) feature. HSA enables a system to reset and use a standby Route Processor (RP) if the active RP fails. Using RPR, you can reduce unplanned downtime because RPR enables a quicker switchover between an active and standby RP if the active RP experiences a fatal error.
RPR+—An enhancement to RPR in which the standby RP is fully initialized.
SSO—Stateful Switchover. SSO refers to the implementation of Cisco IOS software that allows applications and features to maintain a defined state between an active and standby RP. When a switchover occurs, forwarding and sessions are maintained. Along with NSF, SSO makes an RP failure undetectable to the network.
standby group—The set of routers participating in HSRP that jointly emulate a virtual router.
standby router—The backup router in an HSRP group.
standby RP—The backup RP.
switchover—An event in which system control and routing protocol execution are transferred from the active RP to the standby RP. Switchover may be a manual operation or may be induced by a hardware or software fault. Switchover may include transfer of the packet forwarding function in systems that combine system control and packet forwarding in an indivisible unit.
virtual IP address—The default gateway IP address configured for an HSRP group.
virtual MAC address—For Ethernet and FDDI, the automatically generated MAC address when HSRP is configured. The standard virtual MAC address used is: 0000.0C07.ACxy, where xy is the group number in hexadecimal. The functional address is used for Token Ring. The virtual MAC address is different for HSRP version 2.
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