IP Routing Command Issue

[milkboy33]

Hi All,

   We just ran the 'ip routing' command on our 3750x switch stack remotely and .. lost connectivity to the switch. All devices seem to be on and connected so we think the switch is still up, but can anyone tell us what happend? Why can't we ssh/telnet into our switch anymore after running the 'ip routing' 'command?

Thanks a bunch!

-Tom

[paul driver · Accepted solution]

Hello
When you did that the switch stack became a L3 switch and it default-gateway you would have been using to gain access would be rendered useless as it now would require a route in it routing table to provide the remote access.

So instead of ip default-gateway x,x,x.x
you would need to have ip route x.x.x.x y.y.y.y x.x.x.x

Res
Paul

[Bilal Nawaz]

Hello, this is because your switch was purely layer 2 (no routing functionality) and is now layer2/3.

There are differences here in the way gateway's and routing works....

With layer 2 -

Default Gateway is used on a non routing device, meaning if the destination is off the local subnet use the default gateway. If you configure default gateway on a multilayer switch/router, you must do "no ip routing" first. (hence why you enabled ip routing, you want it to be able to do routing)

With layer 3 -

Default route is used as the gateway of last resort meaning if there is no more specific route the default route is used.

Note that the default-gateway is no longer a factor when we change the role to a 'routing role'

In your case, you probably didnt have a default route set. So the switch no longer knows where to go.

In your config you will see: ip default-gateway x.x.x.x

• So you need to add: ip route 0.0.0.0 0.0.0.0 x.x.x.x

Where x.x.x.x was your default-gateway and will now become your gateway of last resort.

• Then enable 'ip routing'
• Then remove the command 'ip default-gateway x.x.x.x'
• Save config changes

Hope this explains well

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