Failed trying to get DHCP from WAN



  • This has happened a couple of times now and I'm not sure why it's happening. I'm a Comcast subscriber with my cable modem in bridged mode. If the cable modem dies, I have issues trying to renew the lease on the WAN side. Sometimes the cable modem will die in the middle of the night due to maintenance. I can fiddle around with things and usually get it back up and running, but it takes manual intervention.

    Unfortunately, I haven't been able to grab a full packet capture, so all I have are the logs. What happens in the DHCP logs are as follows...

    Oct 5 04:47:23	dhclient	19144	DHCPDISCOVER on em0 to 255.255.255.255 port 67 interval 5
    Oct 5 04:47:28	dhclient	19144	No DHCPOFFERS received.
    Oct 5 04:47:28	dhclient	19144	Trying recorded lease x.x.x.103
    Oct 5 04:47:28	dhclient		TIMEOUT
    Oct 5 04:47:28	dhclient		Starting add_new_address()
    Oct 5 04:47:28	dhclient		ifconfig em0 inet x.x.x.103 netmask 255.255.254.0 broadcast 255.255.255.255
    Oct 5 04:47:28	dhclient		New IP Address (em0): x.x.x.103
    Oct 5 04:47:28	dhclient		New Subnet Mask (em0): 255.255.254.0
    Oct 5 04:47:28	dhclient		New Broadcast Address (em0): 255.255.255.255
    Oct 5 04:47:28	dhclient		New Routers (em0): 73.209.78.1
    Oct 5 04:47:29	dhclient		New Routers (em0): 73.209.78.1
    Oct 5 04:47:30	dhclient		Deleting old routes
    Oct 5 04:47:30	dhclient	19144	No working leases in persistent database - sleeping.
    Oct 5 04:47:30	dhclient		FAIL
    Oct 5 04:47:43	dhclient	19144	DHCPDISCOVER on em0 to 255.255.255.255 port 67 interval 2
    Oct 5 04:47:45	dhclient	19144	DHCPDISCOVER on em0 to 255.255.255.255 port 67 interval 5
    

    I see this happening at about every minute interval. It's weird because .103 was (and is) my IP address, it just seems like it doesn't like to keep it.

    To get it fixed I tried to restart my cable modem, followed by my pfsense box. That didn't work, so I restarted my pfsense box again and it still didn't work. For kicks I checked the "relinquish lease" box on the WAN interface to release/renew it. Then it finally got the IP applied and things are working again.

    Next times this happens, I'll definitely get a capture. I was just hoping maybe somebody had an idea of what to look for or maybe try, since I'm not sure when this will happen again.



  • Some more information.... I relinquished my IP and took out my mac spoof on the WAN connection. I did a release/renew and couldn't get a new IP address. I was able to get a tcpdump file of this off the WAN interface.

    The weird thing is that when I released the IP, it would blank everything out. When I renewed it and it timed out, it would show the Gateway IPv4 address and the status was 'up', but the IPv4 Address was not properly displayed. I can't recall if it was just 0.0.0.0 or wasn't even displaying.

    In order to get a new IP, I had to relinquish and release the WAN interface, issue a restart command of the cable modem through the Xfinity app on my phone, wait a few minutes, then finally renew the IP.


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