Cisco 877 Config question

Unanswered Question

Hi All

Would someone be so kind as to check out the diagram attached and see the configuration file (also attached) and tell me if there is a problem with the configuration.

Basically I am trying to have an cisco 877 connect me to the Internet via ADSL, but have a Ubuntu laptop act as a DHCP server rather then have the 877 do DHCP.

The Ubuntu laptop is running DHCP correctly as when I attach a second laptop to the Ubuntu box with a crossover cable I pick up an IP address from the specified range.

However when I connect everything up as per the attached diagram I do not recive an IP address via DHCP.

I suspect I need to assign the Ethernet ports to VLAN1 but I an not sure about this, as when I had the 877 doing DHCP, once I attached something to one of the Ethernet ports it would pick up a IP address with no problem.

I am thinking that I need to create a second VLAN, assign the currnent VLAN1 configuration to this new VLAN and assign the 4 Ethernet ports to this new VLAN. But maybe I am off base or there is another way to achieve this.

Your insight as usual will be much appreciated

Best Regards & TIA


P.S. The Ubuntu laptop has the IP address

I have this problem too.
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Jon Marshall Thu, 05/14/2009 - 06:58


From what i can see you shouldn't need to worry about the 877. Are the DHCP client and the Ubuntu laptop in the same vlan or does your switch not do vlans.

If it doesn't do vlans then the DHCP broadcast from the client should be seen by the Ubuntu laptop. If it does are all the devices in the same vlan ?


Hi Jon

Thank you for taking the time to look that this and respond.

To answer your question, the switch is a small 8 port 10/100 unmanaged switch which does not do VLAN's, so all ports are in the save VLAN.

I had this 877 set up where it was the DHCP server and it was working fine. I connected two unmanaged switches into Eth0 & Eth1 and then everything I plugged into a port on the switches recevied an IP address via DHCP.

However someone wants to set up a demonstration and they require the Ubuntu laptop to be the DHCP server. So I stripped out the DHCP configuration from the Cisco 877.

But now if I connect everything up as per the diagram in my first mail, the DHCP client which is attached to the same switch as the DHCP Server and therefore is in the same VLAN, does not receive an IP address. However if I directly connect the DHCP client to the DHCP server with a crossover cable, then the client will get an IP address. This is why I think that there is an issue with the configuration on the Cisco 877.

Best Regards,


Jon Marshall Fri, 05/15/2009 - 05:19


Could you try a couple of things -

1) connect up as in your diagram but without the 877 and see if your client then gets an IP address

2) run tcpdump on the Ubuntu laptop while doing 1) and also when the 877 is connected and post results.



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