hot standby router protocol

8/3/2019 Hot Standby Router Protocol

1/5

Hot Standby Router Protocol 1

Hot Standby Router Protocol

Hot Standby Router Protocol (HSRP) is a Cisco proprietary redundancy protocol for establishing a fault-tolerant

default gateway, and has been described in detail in RFC 2281.

The protocol establishes a framework between network routers in order to achieve default gateway failover if the

primary gateway should become inaccessible,[1] in close association with a rapid-converging routing protocol like

EIGRP or OSPF. By multicasting packets, HSRP sends its hello messages to the multicast address 224.0.0.2 (all

routers) for version 1, or 224.0.0.102 for version 2[2]

, using UDP port 1985, to other HSRP-enabled routers, defining

priority between the routers. The primary router with the highest configured priority will act as a virtual router with a

pre-defined gateway IP address and will respond to the ARP request from machines connected to the LAN with the

MAC address 0000.0c07.acXX where XX is the group ID in hex. If the primary router should fail, the router with

the next-highest priority would take over the gateway IP address and answer ARP requests with the same mac

address, thus achieving transparent default gateway fail-over. A HSRP Basics Simulation[3]

visualizes

Active/Standby election and link failover with Hello, Coup, ARP Reply packets and timers.

HSRP is not a routing protocol as it does not advertise IP routes or affect the routing table in any way.HSRP has the ability to trigger a failover if one or more interfaces on the router go down. This can be useful for dual

branch routers each with a single serial link back to the head end. If the serial link of the primary router goes down,

the backup router would take over the primary functionality and thus retain connectivity to the head end.

Examples

Load Sharing

Router 1:

track 1 interface Serial0/0/0.1 ip routing ! Points at the interface that needs to be Prioritized

interface FastEthernet0/0

description interface to LAN

ip address 10.10.10.1 255.255.255.0 ! Make sure this IP is in the same subnet as your Virtual Gateway1 IP

ip address 192.168.1.1 255.255.255.0 Secondary ! Make sure this IP is in the same subnet as your Virtual Gateway2 IP

standby 1 ip 10.10.10.25 ! Virtual IP 1 (10.10.10.0 Network Takes Priority)

standby 1 priority 105 ! The Higher the # The Higher the Priority

standby 1 preempt ! Enables the router with the highest priority to immediately become the active router

standby 1 track 1 ! WAN SUBINTERFACE

standby 2 ip 192.168.1.25 ! Virtual IP 2

standby 2 priority 100 ! Lower Priority = Backup Route



!

Router bgp

network 10.10.10.0 mask 255.255.255.0 ! Broadcasts Gateway1 out the WAN through BGP


Router 2:



http://en.wikipedia.org/w/index.php?title=Head_endhttp://en.wikipedia.org/w/index.php?title=Routinghttp://en.wikipedia.org/w/index.php?title=Internet_Protocolhttp://en.wikipedia.org/w/index.php?title=Routing_protocolshttp://pre.visualland.net/view.php?cid=846&protocol=HSRP&title=1.%20HSRP%20basichttp://en.wikipedia.org/w/index.php?title=Hexidecimalhttp://en.wikipedia.org/w/index.php?title=User_Datagram_Protocolhttp://en.wikipedia.org/w/index.php?title=Multicast_addresshttp://en.wikipedia.org/w/index.php?title=OSPFhttp://en.wikipedia.org/w/index.php?title=EIGRPhttp://en.wikipedia.org/w/index.php?title=Default_gatewayhttp://en.wikipedia.org/w/index.php?title=Default_gatewayhttp://en.wikipedia.org/w/index.php?title=Proprietary_protocolhttp://en.wikipedia.org/w/index.php?title=Cisco_Systems%2C_Inc.


2/5


ip address 192.168.1.2 255.255.255.0 ! Make sure this IP is in the same subnet as your Virtual Gateway2 IP

ip address 10.10.10.2 255.255.255.0 Secondary ! Make sure this IP is in the same subnet as your Virtual Gateway1 IP

standby 1 ip 10.10.10.25 ! Virtual IP 1

standby 1 priority 100 ! Lower Priority = Backup Router



standby 2 ip 192.168.1.25 ! Virtual IP 2 (192.168.1.0 Network Takes Priority)

standby 2 priority 105 ! The Higher the # The Higher the Priority



!

Router bgp



Primary and BackupRouter 1:




ip address x.x.x.x 255.255.255.0

standby 1 ip ! Virtual IP

standby 1 priority 105 ! Higher Priority = Primary Router



!

Router bgp

network mask 255.255.255.0 ! Broadcasts Gateway out the WAN through BGP

Router 2:




ip address x.x.x.x 255.255.255.0

standby 1 ip ! Virtual IP

standby 1 priority 100 ! Lower Priority = Backup Router



!

Router bgp

network mask 255.255.255.0 ! Broadcasts Gateway out the WAN through BGP

This is what you should see in a Primary/Backup situation (notice how Router 1 is active):

Router1# show standby

Ethernet0 - Group 1

Local state is Active, priority 105, may preempt

Hellotime 3 sec, holdtime 10 sec


3/5


Next hello sent in 1.458

Virtual IP address is 171.16.6.100 configured

Active router is local

Standby router is 171.16.6.6 expires in 8.428

Virtual mac address is 0000.0c07.ac01

2 state changes, last state change 02:09:49

IP redundancy name is "hsrp-Et0-1" (default)

Priority tracking 1 interface, 1 up:

Interface Decrement State

Serial0 10 Up

Router2# show standby

Ethernet0 - Group 1

Local state is Standby, priority 100, may preempt


Next hello sent in 1.814Virtual IP address is 171.16.6.100

Active router is 171.16.6.5, priority 105 expires in 9.896

Standby router is local





Serial1 10 Up

This is what it will look like during a successful fail-over (notice how the Router 2 is active and HSRP Priority was

lowered on Router 1 to 95):

R1# show standby

Ethernet0 - Group 1

Local state is Standby, priority 95 (confgd 105), may preempt



Virtual IP address is 171.16.6.100 configured

Active router is 171.16.6.6, priority 100 expires in 8.596

Standby router is local

4 state changes, last state change 00:01:45IP redundancy name is "hsrp-Et0-1" (default)



Serial0 10 Down

R2# show standby

Ethernet0 - Group 1

Local state is Active, priority 100, may preempt



Virtual IP address is 171.16.6.100


4/5


Active router is local

Standby router is 171.16.6.5 expires in 9.028

Virtual mac address is 0000.0c07.ac01





Serial1 10 Up

Load Sharing will be similar except both routers will have an active and a standby. Just make sure the correct group

is active.

References

[1] Avoiding HSRP Configuration Errors (http://www.netcordia.com/resources/tech-tips/avoiding-hsrp-configuration-errors.asp)

[2] HSRP Version 2 Feature Design (http://www.cisco.com/en/US/docs/ios/12_3t/12_3t4/feature/guide/gthsrpv2. html#wp1027184)

[3] http://pre.visualland.net/view. php?cid=846&protocol=HSRP&title=1. %20HSRP%20basic

External links

Cisco: HSRP Features (http://www.cisco.com/en/US/tech/tk648/tk362/

technologies_tech_note09186a0080094a91.shtml)

Netcraftsmen: HSRP by Peter J. Welcher (http://www.netcraftsmen.net/welcher/papers/hsrp. htm)

HSRP Protocol Configuration by Szukala K. (http://www.szukalak.ovh.org:)

RFC2281 State Table Simulation. (http://pre.visualland.net/view. php?cid=847&protocol=HSRP&title=2.

RFC2281 state table)

HSRP Link Fail-over Lab Animation. (http://pre.visualland.net/view.php?cid=882&protocol=HSRP&title=4.

Link down lab)
http://pre.visualland.net/view.php?cid=882&protocol=HSRP&title=4.%20Link%20down%20labhttp://pre.visualland.net/view.php?cid=882&protocol=HSRP&title=4.%20Link%20down%20labhttp://pre.visualland.net/view.php?cid=847&protocol=HSRP&title=2.%20RFC2281%20state%20tablehttp://pre.visualland.net/view.php?cid=847&protocol=HSRP&title=2.%20RFC2281%20state%20tablehttp://www.szukalak.ovh.org/http://www.netcraftsmen.net/welcher/papers/hsrp.htmhttp://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080094a91.shtmlhttp://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080094a91.shtmlhttp://pre.visualland.net/view.php?cid=846&protocol=HSRP&title=1.%20HSRP%20basichttp://www.cisco.com/en/US/docs/ios/12_3t/12_3t4/feature/guide/gthsrpv2.html#wp1027184http://www.netcordia.com/resources/tech-tips/avoiding-hsrp-configuration-errors.asp


5/5

Article Sources and Contributors 5

Article Sources and ContributorsHot Standby Router Protocol Source: http://en.wikipedia.org/w/index.php?oldid=459082444 Contributors: Biot, Cheque some, Cwolfsheep, DavidDouthitt, Draftpass, Echoray, Fb12,

Fudoreaper, F, Gz33, Hessi, JLD, JTN, Jeffreyahaines, Johnuniq, Klykken, Lentoyip, MessiFCB, Mgrif, Mincebert, Missy Prissy, Mr Tanner, Nitefood, Nityanandparab, Pap3rinik, Pgr94,

Philippe.amiot, RainbowOfLight, Rich Farmbrough, Romanc19s, Sfisher, Sietse Snel, Smecherel, Stefan Kgl, Tinucherian, Wk muriithi, 59 anonymous edits

LicenseCreative Commons Attribution-Share Alike 3.0 Unported

//creativecommons.org/licenses/by-sa/3.0/

hot standby router protocol

Documents