Which interface should I tell HSRP to track?

[Edil Cajigas]

Hi,

I'm not clear on how to use the HSRP standby track command. All routers in the diagram are really Cisco 3550 layer 2/3 switches. I want Router A to be the primary HSRP router so I set standby priority 100 and standby preempt in the vlan2 interface of Router A. In router B, I set a lower priority and standby preempt as well. On Router A, Fe0/23 and Fe0/24 are switchport and members of vlan2. On RouterB, Fe0/23 is a routed port. On each respective routers Ge0/1 and Ge0/2 are routed ports. I want router B to take over only if Router A is completely down or both interfaces (fe0/23 and fe0/24) are down. If one of the two interfaces are up I want Router A to remain as primary and Router B NOT to take over. Since router B have 3 ways that it can check for router A availability How should I set the standby track command?

Thanks in advanced for your help.

[Vasileios Bouloukos MSc, ITIL, CCIE]

Hi Edil,

It is not clear to me if the fa0/23 and fa0/24 of Router A are aggregated Layer 3 interfaces?Do the clients point as default to an IP assigned to these two interfaces?

If the router A is down,  Router B will be the HSRP Active router, since it will not receive hsrp keepalive packets by Router A.

Regarding HSRP tracking option you need the Router A to not be the ACTIVE if both the Gi0/1 AND Gig0/2 are simultaneously down (to avoid black hole issues). If one of the fa 0.23 or0.24 interfaces is up on Router A, RA remains actives since Router B receives hsrp keepalive packets.

To achieve this you can configure a Tracked List and Boolean Expression in order to monitor (either with an IP sla or interface status) the status of  interface up/down AND reachability for both interfaces.

A tracked list contains one or more objects. The Boolean expression enables two types of calculation by using either "and" or "or" operators.

For example, when tracking two interfaces using the "and" operator, up means that both interfaces are up,

and down means that either interface is down.

You can find detailed examples to the next link:

http://www.cisco.com/en/US/docs/ios/12_2t/12_2t15/feature/guide/fthsrptk.html

Hope that helps!

Vasilis

[siddhartham · Accepted solution]

For scenario 1 -when Router A is down, you don't need to track anything HSRP will failover to Router B

scenarios 2  can be achieved by using decrement command.

Lets say the priority of Router A is  set 130 and priority of Router B is set to 100,

you can configure the below statements on Router A so that Router B will become active when only f0/23 and f0/24 on router A are down.

track 1 interface F0/23 line-protocol

track 2 interface F0/24 line-protocol

UNDER VLAN 2

standby X track 1 decrement 15  (when f0/23 goes down- Router A 's priority decrements by 15 and becomes 115 but stays active )

standby X track 2 decrement 20  (when f0/24 goes down- Router A 's priority decrements by 20 and becoms 95--Now Router B becomes active)

with the above config if either one of f0/23 or f0/24 goes down Router A will stay Active and failover to Router B only when when bother interfaces are down.

[Richard Burts]

I am slightly confused about your network topology. You say that on router B that Fe0/23 is a routed port. If it is a routed port then it does not participate in HSRP for VLAN 2. As a routed port I do not see how it will participate in HSRP.

The drawing does not show it but can I assume that there is some connection from switch 1 to router B in VLAN 2? If there is a layer 2 connection on router B in VLAN 2 then HSRP can work. And the way that HSRP works would accomplish what you describe without needing any special configuration for tracking. HSRP is configured on the VLAN interface and not on the physical interfaces (Fe0/23 or Fe0/24). The HSRP hello packets are transmitted over the VLAN to the HSRP peer. So as long as either Fe0/23 or Fe0/24 is active then HSRP packets will get from router A to router B and router A will continue to be the lead router. router B would only take over if both physical interfaces in VLAN 2 were down.

HTH

Rick

[Edil Cajigas]

Sorry for taking so long to respond.

Well I read all your advise and decided to simulate this with GNS3 (I'm still working with the conection between AP2 and B. Check the new drawing).

Well it was not only that I was confused with how to use the standby track command but also if I need to use it at all specificly for what I originaly asked the status of A's F0/23 (13 with GNS) and F0/24 (14)

Richard, I had to define vlan2 for the 172.18.1.0 segment because vlan1 is already in use with A, B and C. And having B's F0/23 (13) as a routed port and A's F0/23 (13) F0/24 (14) as switchports works fine in GNS. Something that I didn't explain clearly is that devices in the 172.18.1.0 network are connected through a wireless mesh network but all radios are really working as plain hubs, no routing, no vlan taggin, no nothing just forwarding. So I change the drawing and now put AP1 and AP2 instead of SW1 and SW2. So setup everything in GNS and it is working. I can detach any two vlan2 ports in A and A remains as standby active, A goes down B takes over. But now I see Vasileios point and I didn't took that into consideration. If the link between A and C goes down I will like B to take over even if A's F0/23 and F0/24 are up because it doesn't make sense to let A to be standby active when it doesn't have a direct connection to C having to go over B to get to C.

Vasileios F0/23 and F0/24 are switchport access vlan 2 and no Ip address is defined for those interfaces only vlan2 int have the corresponding IP.

I will have to check the document link you gave me but I think that it won't work becasue I'm using old 3550s. Is there any other way to acomplish that?

[Edil Cajigas]

Final configuration using as reference the second diagram (GNS):

Router B

int f0/13

standby 10 ip 172.18.1.1

standby 10 preempt

Router A

int vlan2

standby 10 ip 172.18.1.1

standby 10 priority 115

standby 10 preempt

standby 10 track f0/1 20

standby 10 track f0/13

standby 10 track f0/14

Thanks for all the help.