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21. Juli 2006

HSRP => Hot Standby Router Protocol

Filed under: IP and IOS Features — ocsic @ 10:25

HSRP = HOT Standby Router Protocol

This protocol provides redundancy in case a router is not more available, by emulating a virtual router. This virtual router can consist of many other routers depending on how many are setup for redundancy. At least there have to be two routers configured for redundancy.

MHSRP is Multi Group Hot Standby Router Protocol. It can be used for load sharing.

This configuration is an example for MHSRP.

R1 config:

interface e0

ip add
standby 1 preempt
standby 1 priority 110
standby 1 ip
standby 1 track serial0 120
standby 2 preempt
standby 2 ip

R2 config:

interface e0

ip address
standby 1 ip
standby 1 preempt
standby 2 ip
standby 2 priority 110
standby 2 preempt
standby 2 track serial0 120


The default prio for an interface is 110. So for 1.100 R1 has by default active state. For 1.200 it’s router 2. The track parameter change the prio, so if an serial interface goes down, the prio is changed, the means decremented by the value configured. So then the other interface with the higher value goes into active state.

You can watch state change from „Standby -> Active“ if a serial0 interface comes back again. And the other side reactes with:

02:21:09: %HSRP-6-STATECHANGE: Ethernet0/0 Grp 1 state Active -> Speak
02:21:19: %HSRP-6-STATECHANGE: Ethernet0/0 Grp 1 state Speak -> Standby

And goes to standby again.

If a serial0 interface goes down, the other side imediately goes into active state:

06:50:01: %HSRP-6-STATECHANGE: Ethernet0/0 Grp 2 state Standby -> Active

and the other router reacts with:

02:22:41: %HSRP-6-STATECHANGE: Ethernet0/0 Grp 2 state Active -> Speak
02:22:51: %HSRP-6-STATECHANGE: Ethernet0/0 Grp 2 state Speak -> Standby

Pay attention. A really pitfall i have meet, was that with my old 2500’er router and the AUI – ethernet Transiver/Adapter, it was not possbile to configure MHSRP. There seems to be a problem with the mac address handling. Although i could set it up, it does not work and there are no error messages and it works partly. But if you try to have more than one group active on the 2500’er, that does not work. Took me three hours, after that i changed the 2500’er with a 2600’er and i worked like a charm.

HSRP Load sharing

HSRP Technology:

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