How to force LAN interface down if WAN link drops.

[jay_finley]

Is there a way to have a Cisco router monitor the Line Protocol of a WAN interface and subsequently shutdown or otherwise disable another (specified) interface should the WAN interface LP goes down?

[Jon Marshall]

Jay

There are a number of things that spring to mind but we would need to know more about your topology. At one extreme you could use EEM which is a scripting engine that allows you to add additional programming logic to the router. There is an expert in this in the Network Management forum.

However there are other less complicated options eg. HSRP tracking, IP SLA.

But without more detail on your topology it's difficult to give you a precise answer.

Jon

[jay_finley]

Jon, thanks for the quick reply.

We have a 3 facility LAN campus - each facility with it's own subnets - that has 2 WAN routers available into the corporate network. The routers have HSRP defined on their LAN interfaces. R1 is the DG for two of the facilities with R2 the HSRP backup. Vise Versa for the 3rd facility. If a WAN interface dies on one of the routers, it's LAN interface will stay active and remain the DG when in fact we want the other router to become the HSRP primary. I was hoping for a simpler approach rather than getting into manipulating dynamic routing.

[Jon Marshall · Accepted solution]

Jay

HSRP track should achieve what you want. It won't shut an interface down but what it does is if the active HSRP routers WAN interface goes down then the HSRP priority is changed so the other router with the functioning WAN interface takes over the HSRP VIP. See this link for more details -

http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080094e8c.shtml

Jon