HSRP priority vs preempt

StonedHitman

I was watching a video from chris bryant on hsrp and he said that if you don't enable preempt then when your active router goes down and back up it will not take over as active. I wanted to test that so i set up a small hsrp lab with preempt disabled. I gave the active router a higher priority, shut down the router, brought it back up and it took over without problems as expected. I'm assuming when he said that he meant with default priorities the active router will not take over when it's brought back up but im not too sure. Can anyone shed some light on this?


Also, I have one more question. If im using multiple vlans with hsrp and a different hsrp group for each vlan does that mean im also using hsrp load balancing?

10Linefigure

You can check this out > Hot Standby Router Protocol Features and Functionality - Cisco Also CBTnuggets has a free MicroNugget series for the CCNA. Good luck!

Hondabuff

Did the active router have a higher IP address then the standby?

StonedHitman

Hondabuff wrote: »

Did the active router have a higher IP address then the standby?

No, the active router had a lower ip address than the standby

Hondabuff

I would say since you manually set the priority off of the default of 100, As soon as the Standby router sees the neighbor message with a higher priority then it kicked back over to standby. Try them both with priority 100 and see what happens. I really enjoy setting up a IPSLA and Pinging the ISP's GW and using HSRP to track the SLA and if it fails then HSRP kicks over to the Standby Router. Very cool to see it work in production.

tomtom1

StonedHitman wrote: »

I wanted to test that so i set up a small hsrp lab with preempt disabled. I gave the active router a higher priority, shut down the router, brought it back up and it took over without problems as expected. Can anyone shed some light on this?

Preemption is the process of taking over as active router when you have the highest priority for a given group. IP adresses (higher) do not come into account here, for preemption to occur, it needs to be enabled and the priority needs to be explicitly higher.

I labbed out your scenario and it worked as expected, the reloaded router (with higher priority) did not take over, since this is a preemption feature.

StonedHitman wrote: »

Also, I have one more question. If im using multiple vlans with hsrp and a different hsrp group for each vlan does that mean im also using hsrp load balancing?

No, one way you can loadbalance with HSRP is like this:

interface Vlan20
 ip address 20.20.20.2 255.255.255.0
 standby 1 ip 20.20.20.21
 standby 2 ip 20.20.20.22
end

So you have 2 HSRP groups each with a different virtual IP. One router is HSRP active for group 1 and the other for group 2. 50% of your hosts are default gatewayed to 20.20.20.21 and 50% to 20.20.20.22. However, the GLBP protocol is a much better fit for this.

networker050184

Did the other router actually go active before you brought the other back up?

tomtom1

I may have found a scenario in which what you're telling could be the case. Are the routers connected directly? When in my physical lab, I tried this with routed ports, and the (L3) switches were connected directly, R1, with a priority of 110 became the HSRP active router. When I reloaded that device however, the standby state of the other router, R2, became Init, because the interface went down (which was directly connected to R1 - reloading at that time).

SW4#sh standby
FastEthernet0/9 - Group 1
  State is Init (interface down)
  Virtual IP address is 192.168.1.254
  Active virtual MAC address is unknown
    Local virtual MAC address is 0000.0c07.ac01 (v1 default)
  Hello time 3 sec, hold time 10 sec
  Preemption disabled
  Active router is unknown
  Standby router is unknown
  Priority 100 (default 100)
  IP redundancy name is "hsrp-Fa0/9-1" (default)

When the other router came back online, they started the normal HSRP election state of Init -> Learn -> Listen -> Speak -> Active / Standby. In which case R1 had the higher priority and became HSRP active again.

StonedHitman

networker050184 wrote: »

Did the other router actually go active before you brought the other back up?

It did, when i shut down the active router(which has a higher priority) the standby router took over, a sh standby on the second router shows it as active router is local, standby router is unkown

StonedHitman

tomtom1 wrote: »

I may have found a scenario in which what you're telling could be the case. Are the routers connected directly? When in my physical lab, I tried this with routed ports, and the (L3) switches were connected directly, R1, with a priority of 110 became the HSRP active router. When I reloaded that device however, the standby state of the other router, R2, became Init, because the interface went down (which was directly connected to R1 - reloading at that time).



When the other router came back online, they started the normal HSRP election state of Init -> Learn -> Listen -> Speak -> Active / Standby. In which case R1 had the higher priority and became HSRP active again.

no, they each connect to a different switch, which are connected with two other switches for stp

DCD

Can you show the active out put of the HSRP on both routers or the HSRP config.