Configuring router for cable modem

[drae73]

Hello all here's the deal. I have a cable modem from my provider, this one as with most give an ip address via dhcp. When I configured my router with the ip, subnet mask, and gw that my laptop obtained I was still unable to ping the outside world. The interface shows up and up but no luck on the ping.

1) Is there any way to configure a router int to obtain an ip address etc.. automatically, like a vpn or cable router?

2) If not, are there any ideas?

Thanks in advance,

 

[andrew4728]

heya Drae73, What router are you trying to configure?
Seeing as you posted in the cisco routers forum, I'm taking a guess it is a cisco router

You will need to make sure you have an IOS version that supports DHCP, my router did not when I purchased it, so I had to update it to 12.2.

to set an interface to obtain ip address via DHCP, you will need to configure the interface similar to this :


Router#conf t
Router(config)#int e0
Router(config-if)#ip address dhcp client-id Ethernet0

The above command will set Ethernet0 to obtain IP address via DHCP. If you get a message stating "Invalid input", you most likely have an IOS that doesn't do DHCP.



Also, don't forget you will need to setup NAT before your PCs will be able to communicate with the internet. To do this, you need to specify which interface is the OUTSIDE and INSIDE nat.

You can do that like this :

Router#conf t
Router(config)#int e0
Router(config-if)#ip nat outside

and

Router#conf t
Router(config)#int e1
Router(config-if)#ip nat inside

in the case above, you will want to plug your cable modem into E0, and your comp or switch into e1.

Last, but not least, you will need to specify the ip range to NAT. It will take 2 steps to do this :

A:
Router#conf t
Router(config)#access-list 100 permit ip 192.168.1.0 0.0.0.255 any

This is an access list that permits any IP between 192.168.1.0 - 192.168.1.255

B:
Now you need to set the router to use that range for NAT :

Router#conf t
Router(config)#ip nat inside source list 100 interface Ethernet0 overload


Hope this info helps out, if you need any help with your cisco router, you should post the TYPE of router, what interfaces you will be using and what you are plugging into each, and copy your running config (make sure to remove any sensitive info such as external IPS and passwords before posting it)