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New Member

Get ip address


I used to have ip address from my ISP through Cisco Switch , and Now When I connect my LAN With a Cisco 3620 Router , I could not get ip address from ISP to my LAN.

I have configures ext. FE with ip address dhcp , I have configured my router to be a Intene DHCP, and my LAN is working propely except my PC`s could connect to the Internet.

I am using cable modem , I am working with 3 ip addresses ,

I hve released ip address from pc`s before connect ing Router.

IOS is 12.2(6)

I wonder how should configure my router to get ip address. ???


Cisco Employee

Re: Get ip address

If I understand correctly, you replaced a switch with a router.

The router is also getting is ip address via dhcp.

The PC behing the router should also get an ip address from the ISP.

If my understanding of the scenario is correct, this is expected behavior.

A switch do packet switching at layer 2 and the router at layer 3.

So the switch was just taking the dhcp request from the pc and forwarding it to the ISP.

The router however will stop the dhcp request because no layer 3 information.

We could configure the router to forward the dhcp request to the ISP but it won't fix the issue because the PC default gateway needs to be the router.

You could use fix ip addresses internally and if they are not public ip addresses, you could configure the router to do nat.

You could also configure the router to act like a switch but then why did you replace the switch for a router ?

In your scenario, a switch seems to be the best choice.

New Member

Re: Get ip address

Hei Gilles Duffor.

Thanks for your reply , it was helpfull , but do you mean with : "You could use fix ip addresses internally " ???

How should we configure a Router to act a Switch ??, I mean that Router is always layer 3 device , and Switch is layer 2 device.

Now my Router is getting one ip address from My ISP , and It acting as DHCP for intern LAN , MY pc`s is configured to get ip address from DHCP ( Router ) , and when I ping with Hostname like :

ping , it `s not translated ,and not reachable.

im my config , I wrote my ISP dns ip address for translation , but It`s not working .

do you have any suggestion about my senario ??



New Member

Re: Get ip address


Can this help you by set the interfaces of the router in to a bridge group? so that the router can act as a bridge. the following is the example config:

bridge 1 protocol ieee

bridge 1 crb

int f0/0

description Interface to ISP

bridge-group 1

int f0/1

description Interface to internal network

bridge-group 1


Hope this can help you

Best Regards

Teru Lei

New Member

Re: Get ip address


Are you using the 'ip address negotiated'-command on the interface which is connected to your ISP?? With this command you should receive an IP-address from your provider

In most cases you need also 3-des-software on your router.

Best regards

Edwin van Wijk

New Member

Re: Get ip address

Hei again.

I am configuring a firewall on my LAN, whaich a combination o

I am connecting a Cisco Router with Firewall ( PIX 515 ).

My Pcs have a static ip addresses ( 172.16.1.x) , and connect to cisco switch.

I can ping to my inside interface , and not to outside interface of PIX , but I can ping to interface of Ext.router that is directly connected to PIX.

I can also ping to the Internet , but I can`t use my browse to go the Internet.

How should configure my Pix in order to access to Internet Web site from My Pc`s .

It seems that My PIX stops Internet traffic from Port 80 ??? Mybe