subnetting an exsiting class c

radfojc used Ask the Experts™
I'm a administrator of an isp who has a full class c.

We want to break it in half (  Currently the cisco router connecting the class to the internet is configured for the full range (it's sitting on .254).

I have a linux box configured to route from the network, with the default gateway set to .254 (the cisco router) and eth0 and eth1, this seems to route between the 2 networks fine.

My question is we dont seem to be able to get out through the cisco now from the .0 network, does it need to be told that the class c has been broken up now?


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Sr. Systems Engineer
Top Expert 2008
Yes, you need to change the mask on the local interface of the router and put in a static route entry:

interface ethernet 0/0
 ip address
ip route



Thanks, worked great!


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