Silly question: Can't get the second IP on a router through DHCP

[Difan Zhao]

I can't believe I can't make it work!

I am using a Cisco 1721 router with two Ethernet ports and one FastEthernet ports. Here is my config:

interface Ethernet0

ip address dhcp client-id Ethernet0 hostname E0

half-duplex

!

interface Ethernet1

ip address dhcp client-id Ethernet1 hostname E1

half-duplex

!

interface FastEthernet0

no ip address

shutdown

speed auto

E0 and E1 are connecting with ISP's ADSL modem. However only one can get an IP address! ISP is fine because if I plug one cable to my laptop my laptop gets the second IP address without problems. Somebody please HELP!! Thanks a lot!

[sirdudesly]

Also, why are you running e0 and e1 in half duplex?

[Difan Zhao]

I just keep the default settings. I didn't do too much on the interface settings as you can see. Didn't go that far yet... Thank you for reminding me!

[Richard Burts]

Difan

My memory of the 1721 is that one restriction of the Ethernet interfaces (as compared to the FastEthernet) is that they only support half duplex.

HTH

Rick

[Difan Zhao]

You are right!! The 1721 supports either half duplex or full duplex but not auto-duplex. However most modems are not compatible if you set the router as full duplex. However if you set it as half duplex even it will sacrifice some performance however it won't bring you some very VERY wierd problems as in full duplex!! I was really pissed off by those modems but for testing purpose I don't have newer models available... However I don't think it will be the reason for our problem here. I think getting a second ISP would still be the solution.