Tunnel Interface Goes down when enabled IP routing

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Oct 29th, 2007
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Hi Guys,

we have Cisco 3750-12S-E switch and have configures tunnel interfaces on it for point to point connection.

Now the minute i enable IP ROUTING on the switch my tunnel interface goes down and i lose end to end connectivity.

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ssatishh08 Mon, 10/29/2007 - 02:32
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please suggest me some solution for the same, i have also attached my switch config

lgijssel Mon, 10/29/2007 - 02:56
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In your config, you have specified a default gateway. This command will only work when ip routing is not enabled. The solution is that you need to specify a default route,your tunnel goes down because the router has no next hop for the tunnel destination.

Add this to your config: ip route



guruprasadr Mon, 10/29/2007 - 04:30
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The ip default-gateway command is used when IP routing is disabled on the router.

ip route are effective when IP routing is enabled on the router and they are used to route any packets which do not have an exact route match in the routing table.

Refer link below for:

Configuring a Gateway of Last Resort using IP Commands:



Best Regards,

Guru Prasad R

ssatishh08 Tue, 10/30/2007 - 04:44
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thanks for replying guys, just a small clarification i dont want to define default route pointitng to the other end of the tunnel rather i want to define networks something like this

ip route tunnel 1

to be precise specific unicast routing over the tunnel.

but as soon i enable ip routing for defining static route my tunnel interface goes down

Richard Burts Tue, 10/30/2007 - 05:56
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You do not necessarily need to configure a default route. But you do need to configure a route to the tunnel destination. Before you enable ip routing the switch will use the default-gateway definition and will have a route to the tunnel end point ( Once you enable ip routing then the switch no longer uses the default-gateway and it no longer has a route to the tunnel end point. If the switch does not have a route to the tunnel end point then the tunnel will not work.

It is fine to configure routes for specific networks reached through the tunnel. But until the switch has a route to the tunnel end point the tunnel will not work. So you need to configure some kind of route that will provide a forwarding path to address If you do not want a default route (which is essentially what you had before) then you need some other route for




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