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| − | HSRP or Hot Standby Router Protocol is a protocol defined by Cisco and now described in [http://www.ietf.org/rfc/rfc2281.txt rfc2281].
| + | #Redirect [[HSRP]] |
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| − | = Purpose of HSRP =
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| − | The purpose of HSRP is to ensure network connectivity in case of Router or access circuit failure, by having one or more ''standby'' Router(s) waiting to take over from the failing ''active'' Router.
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| − | | |
| − | = Other high availability Router protocols =
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| − | *GLBP [[Gateway Load Balancing Protocol]]
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| − | *VRRP [[Virtual Router Redundancy Protocol]]
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| − | {|
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| − | |-
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| − | |valign="top"|
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| − | | |
| − | = How does HSRP work =
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| − | HSRP works by two or more Routers agreeing upon which Router serves the ''virtual Router''.
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| − | == HSRP Protocol ==
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| − | HSRP runs on top of UDP, and uses port number 1985. Packets are sent to multicast address 224.0.0.2 with TTL 1.
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| − | == The Virtual Router ==
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| − | The Virtual Router is a MAC-address and a IP Address the ''active'' Router serves beside its configured IP address. If the ''active'' Router fails one of the ''standby'' Routers becomes the Virtual Router by serving the virtual MAC-address and IP Address.
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| − | == HSRP example ==
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| − | In picture 1 three Routers R1,R2 and R3 are setup in a HSRP Group. The Virtual IP address 10.0.0.1 and virtual MAC-Address 00-10-0C-07-AC-0A are served by the active Router R1. R1 continuesly transmits hello packets to the standby Routers.<br/>
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| − | If the Active Router fails one of the ''standby'' Routers will become the active Router and start serving the Virtual IP address 10.0.0.1 and the virtual MAC-address 00-10-0C-07-AC-0A.<br/><br/>
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| − | There are no load balancing between the Routers.
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| − | |
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| − | [[Image:HSRP1.png|thumb|500px|float|Picture 1: HSRP group with Router R1 active and Router R2 and R3 as standby Routers]]
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| − | |}
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| − | == Configuration of R1, R2 and R3 ==
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| − |
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| − | {|
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| − | <pre>
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| − | hostname R1
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| − | !
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| − | interface FastEthernet1/0
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| − | ip address 10.0.0.11 255.0.0.0
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| − | standby 10 priority 130
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| − | standby 10 preempt
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| − | standby 10 timers 2 6
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| − | standby 10 ip 10.0.0.1
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| − | </pre>
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| − | |
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| − | <pre>
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| − | hostname R2
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| − | !
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| − | interface FastEthernet1/0
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| − | ip address 10.0.0.12 255.0.0.0
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| − | standby 10 priority 120
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| − | standby 10 preempt
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| − | standby 10 timers 2 6
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| − | standby 10 ip 10.0.0.1
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| − | </pre>
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| − | |
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| − | <pre>
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| − | hostname R3
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| − | !
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| − | interface FastEthernet1/0
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| − | ip address 10.0.0.13 255.0.0.0
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| − | standby 10 priority 110
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| − | standby 10 preempt
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| − | standby 10 timers 2 6
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| − | standby 10 ip 10.0.0.1
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| − | </pre>
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| − | |}
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| − | == HSRP Group number ==
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| − | All the Routers in a HSRP Group must use the same Group number. In the example the Routers uses Group number 10. The group number ranges from 0 - 255. (Default is 0)
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| − | == The virtual MAC-address ==
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| − | The virtual MAC-address is divided into three fields. In the example 00-10-0C-07-AC-0A
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| − | *00-10-0C is the vendor code. (Cisco for example)
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| − | *07-AC is a well-known HSRP code
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| − | *0A is the HSRP group number 10 decimal is 0A hexadecimal
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| − | == Priority ==
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| − | The priority are used to decide which Router should be the active Router and in which order the standby Routers will take over. The priority field can range from 0 - 255. (Default is 100)<br/>
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| − | If more Routers has the same priority the Router with the highest configured IP address will become the active Router.
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| − | == Preempt ==
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| − | If a Router with a higher priority becomes operative in the HSRP group, the active Router will continue to be active regardless of the new Router having a higher priority. To have the new Router with the higher priority to take over operation as the active Router use the ''preempt'' statement.
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| − | == Hello timers ==
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| − | HSRP Routers sends hello packets at regular intervals to each other. | |
| − | *Hello packets are sent default every 3 second (Hello interval)
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| − | *''Holdtime'' is default 10 seconds. (Time should be at least three times hello interval)
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| − | *''Hello interval'' and ''holdtime'' could be learned by a ''standby'' Router from the ''active'' Router.
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| − | [[Category:Cisco]][[Category:CCNP]][[Category:IOS]][[Category:Network]][[Category:CCNP3]]
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