Configuring Standby + an SLA

[charles.e.davis]

I configured standby on my 2 Cisco 3750 Switches to migrate a default gateway address in the event of loss of communications.  I tied the Stand By to a sla ping that is hitting an outside gateway.  The issue that I'm running into is that both switches seem to be working but in the event that I turn off the path out of the primary path, the failover doesn't seem to happen but once.  If I try to get it to fail back over or repeat the same process the IP address stays with the primary switch.  Could someone please look at these configurations and tell me what I'm doing wrong?  Also, is there a way software test the fail over instead of having to actually turn off a port within the path out?  Thanks again.

Charles Davis

Primary Configutions

interface Vlan30
description Access Control VLAN
ip address 10.1.0.9 255.255.0.0
ip access-group net0987 in
ip access-group net0988 out
no ip redirects
no ip unreachables
no ip proxy-arp
ipv6 traffic-filter ipv6 in
standby 30 ip 10.1.0.1
standby 30 priority 110
standby 30 preempt
standby 30 track GigabitEthernet1/0/1
standby 30 track 30 decrement 10

!
ip sla 30
icmp-echo 198.253.57.242 source-ip 10.0.0.2
timeout 1000
frequency 5
ip sla schedule 30 life forever start-time now
ip sla enable reaction-alerts

Secondary configurations

interface Vlan30
description Access Control VLAN
ip address 10.1.0.5 255.255.0.0
ip access-group net0987 in
ip access-group net0988 out
no ip redirects
no ip unreachables
no ip proxy-arp
ipv6 traffic-filter ipv6 in
standby 30 ip 10.1.0.1
standby 30 preempt

ip sla enable reaction-alerts

[Amit Singh]

This is not the correct configuration to use IP SLA with HSRP tracking. You have to track the object rather than the interface in the "standby " track command.

Please use the configuration option below.

http://www.cisco.com/en/US/docs/ios/12_2t/12_2t15/feature/guide/fthsrptk.html#wp1146585

Please test the config after changing the configuration and let us know it it is working.

Cheers,

-amit singh

[Amit Singh]

I overlooked your config. Please take the " standby" interface tracking out from the interface vlan.Also try the decrement value to  be greater than 20 or so. The default HSRP priority is 100 , if you are decrementing the interface track value by 10, both the HSRP peers will become the 100 and HSRP active router with the same priority might stay active.

Cheers,

-amit singh

[charles.e.davis]

Amit,

Could you be a little more precise.  Maybe it is because I've been looking at these configs for several hours but what do you mean by changing the decrement to 20 or more?  I can see that by tracking 2 different things, the ping to the ip address and the port that I was getting myself into issues if the port didn't go down.  Also, do you have a way to test this via software commands instead of actually turning off ports?  Plus, if I change the decrement will it come back to the primary once connectivity is resumed?  Thanks

Charles

[Amit Singh]

Charles,

With the command " standby 30 track GigabitEthernet1/0/1" under the interface, you wont acheive much. As you are just tracking the interface without any decrement value so it will just generate a log but wont take any actions. The whole idea of the "interface tracking " is to track a particular interface and if that interface us down, bring the HSRP priority (which is 100 bydefault) down by a certain value so that the other router takes over the active duties.

With the command "standby 30 track 30 decrement  10", if the tracked object goes down, HSRP will decrement the HSRP riority by 10 and will bring down the overall priority to 100, which the default HSRP priority. Even after the tracked object going down and reducing the priority, both the active and standby router will have the same priority. If HSRP election takes place the active router will continue to assume the active role as there is no way to force this router to go in standby mode and make the other router active. If you have decrement value > 20, when the tracked object goes down, it will bring the HSRP priority to 90 or less which is lower than the HSRP default priority and this will bring the active to go into a stanby state.

Hope this clarifies the doubt.

Cheers,

-amit singh

[charles.e.davis]

Amit,

I just followed your instructions and it worked perfectly.  thank you for the help and also the explanation.  This is pretty new to me and the understanding really helps when troubleshooting.  The only other thing is there anyway to test it or because it is tied to an interface, you just have to shut something down downstream?  Thanks again.    

Charles

[Amit Singh · Accepted solution]

Hi Charles,

Glad that it helped you. You have to manually force the links up/down to test it. There is no software as such to test this.

Please rate all helpful posts.

Cheers,

-amit singh

[charles.e.davis]

Thanks, you were very helpful.

Charles