HSRP Configuration doubts

[vijay.swaminathan]

I would like to have a basic doubt clarified in the HSRP confiugration.

typically during HSRP configuration we wuld configure the Virtual IP on all the HSRP group members. but while playing wtih the configuration today i figured out that if Virtual IP is configured on one of the HSRP Group member, the other members of the same group would learn this IP by default and there by it produces the desired result.

I;m just trying to understand if configuring virtual IP on only one of the HSRP Group member has any side effects??

ACTIVE:

!

interface Vlan10

ip address 10.10.10.2 255.255.255.0

standby 1 ip 10.10.10.4     >> Configured Virtual IP

standby 1 priority 150

standby 1 preempt

end

Standby:

Current configuration : 99 bytes

!

interface Vlan10

ip address 10.10.10.3 255.255.255.0     >>> Virtual IP not Configured:

standby 1 ip

standby 1 priority 101

end

The standby learns Virtual IP from ACTIVE.

DSW2#sh standby | i Vir

  Virtual IP address is 10.10.10.4 (learnt)

DSW2#

please advice.

-Vijay Swaminathan.

[John Blakley]

Vijay,

It learns the vIP from hello packets. I can't see a drawback to using it like this. Personally, I would set the address on all of them statically rather than allowing it to learn the vIP from the primary:

*Mar  1 00:01:56.583: HSRP: Fa0/1 Grp 1 Redundancy "hsrp-Fa0/1-1" state Init -> Learn

*Mar  1 00:01:56.627: HSRP: Fa0/1 Grp 1 Hello  in  10.10.10.2 Active  pri 105 vIP 10.10.10.1

*Mar  1 00:01:56.627: HSRP: Fa0/1 Grp 1 Active router is 10.10.10.2

*Mar  1 00:01:56.627: HSRP: Fa0/1 Redirect adv out, Passive, active 0 passive 1

*Mar  1 00:01:56.627: HSRP: Fa0/1 API 10.10.10.1 is not an HSRP address

*Mar  1 00:01:56.627: HSRP: Fa0/1 Grp 1 Learn: n/HSRP IP address configured

*Mar  1 00:01:56.627: HSRP: Fa0/1 Grp 1 Learn -> Listen

*Mar  1 00:01:56.627: HSRP: Fa0/1 Grp 1 Redundancy "hsrp-Fa0/1-1" state Learn -> Backup

*Mar  1 00:01:57.247: HSRP: Fa0/1 Grp 1 Hello  in  10.10.10.2 Active  pri 105 vIP 10.10.10.1

HTH,

John

[lgijssel]

Interesting feature! I never used it but it works indeed. Thank you for this.

The most important drawback I can see is that after an outage the backup router will never be able to recover without having seen the primary. Brownouts and similar scenario's can provide interesting results.

The conventional approach where the standby-ip is hardcoded on both routers is definitely more predictable.

regards,

Leo