1111 can't get DHCP for WAN from Comcast - migration from RV325

[fccITAdmin]

We're migrating the office from a Cisco RV325 (which is now End-of-Life) to a new Cisco 1111-4P. I can't get it to receive a WAN DHCP address from Comcast via the cable modem/router which is supplied from Comcast Business. That Comcast supplied modem/router is a Technicolor Model CGA4131COM. The modem/router is in "bridge mode". It has multiple RJ45 ports that can provide several WAN DHCP addresses.

Note that I've left the existing Cisco RV325 plugged into the modem/router (in order to keep the office working for now) and it receives a proper WAN DHCP address. According to Comcast, a couple of WAN DHCP addresses can be pulled from the modem/router simultaneously.

Some tests I did include:
* Plugged in a normal laptop to the Comcast modem/router on the extra RJ45 ports. It was able to receive a new WAN DHCP address.
* Removed the Comcast modem/router from the equation. Used a consumer router which provided DHCP addresses on its LAN ports. I plugged that into the 1111-4P GigabitEthernet0/0/0 port. It was able to receive the DHCP address.

I suspect the problem is a combination of the Comcast equipment/network and the Cisco 1111-4P router.

The problem is similar to @frayedends 
https://community.cisco.com/t5/routing/1111-won-t-pull-dhcp-for-wan-from-comcast-migration-from-891/td-p/4461458

I turned on DHCP debugging on the Cisco 1111-4P via CLI 'debug dhcp'. I've attached the debug output as well the Cisco 1111-4P config.

Any help would be greatly appreciated!

[Georg Pauwen]

Hello,'

try and add the line marked in bold:

interface GigabitEthernet0/0/0
--> ip address dhcp client-id GigabitEthernet0/0/0
ip nat outside
negotiation auto

[paul driver]

Hello

spoof the new router wan interface -

append the mac-address of the old wan rtr interface to the new rtr and test adain just make sure the port you do use on the new rtr is in a routed port

---

[Richard Burts]

The main thing that I notice in the posted output of debug dhcp is that the mac address is shown as 0000.0000.0000. I am not sure why that is. Perhaps the output of show interface G0/0/0 might be helpful? 

I notice that part way through the debug output that G0/0/0 changes state to up. So it was down as the debug started? Perhaps a shut & no shut might be helpful?

[fccITAdmin · Accepted solution]

Thank you for all the suggestions!

I tried all of them but it still wasn't working. Then I decided to just reboot the Comcast modem/router. After doing so, the 1111-4P got a DHCP address on the WAN. And my other router (RV325) also got a DHCP address too.  I only had to have "ip address dhcp" on the g0/0/0 interface.

It turns out that Comcast will provide a few dynamic IP addresses via DHCP for the WAN. But only a couple of them. I think the modem saves the count and then won't issue any more until it power cycles.  During previous testing we connected laptops to the Comcast modem and I think it remembered those MAC addresses as well.

There was a discussion from others on the Comcast forums about Comcast Business issuing multiple dynamic IPs:
Comcast Business issues multiple dynamic IPs in bridge mode 

Thanks again!

[Richard Burts]

Thanks for the update. It is good to know that your issue is resolved and that the solution was a reboot of the Comcast.

[paul driver]

Hello

if in doubt …reboot! - lol

glad you got it working