I have Cisco 871 router for a home office router connected to Comcast via a Motorola Modem: SB5100 SURFBoard. Seems like the DHCP lease ends and then no matter what I do cant get it to pull another one. I can take my PC put it in the modem directly and reboot and my PC will get a good address, but the Cisco External interface just wont do it. Has anyone run into this thing before? Also I have called once already to Comcast and of course they did "nothing" (I think they reset the modem) and then it worked again. Its about a week or 2 later now and It has happened again. So I plug my PC in, Reboot, and my PC is on the internet. Any ideas suggestions, prior experience with the smae problem etc... would be awesome. Thank you.
Motorola Surf Cable modem and Cisco 871: DHCP lease seems to end and then not able to renew
Jan 07, 2009
2 Replies
Is it the PC or the cable modem you reboot to get an IP?
On Jan 7, 10:27=A0am, alexd wrote:
Actually there is the Modem plugged into the 871 then the PCs are plugged in to the 4 port switch in the 871. However I believe stumbled across som information that was on linux usergroup board that may be helpful. It basically says that even linux users who direcly connect to the modem have the same issue and Comcast offers no answer to them. So far the one fix posted said he changed his cable modem to a newer one (RCA) and that the problem went away. Since Cisco IOS is a unix based OS I bet they are on to something. Further the firmware on the cable modem must be the bug here. I have actually tried now with a Cisco 851W, 871, and a 2611XM all with the same messages in the debug. over and over
R2611XM(config)# Jan 8 05:48:13.467: DHCP: SDiscover attempt # 3 for entry: Jan 8 05:48:13.467: DHCP: SDiscover: sending 308 byte length DHCP packet Jan 8 05:48:13.467: DHCP: SDiscover 308 bytes Jan 8 05:48:13.467: B'cast on FastEthernet0/0 interface from 0.0.0.0 R2611XM(config)#%Unknown DHCP problem.. No allocation possible Jan 8 05:48:25.879: DHCP: Waiting for 50 seconds on interface FastEthernet0/0 R2611XM(config)# Jan 8 05:48:56.622: DHCP: deleting entry 88A5F8B4 0.0.0.0 from list R2611XM(config)# Jan 8 05:49:15.881: DHCP: Try 11 to acquire address for FastEthernet0/0 Jan 8 05:49:15.897: DHCP: allocate request Jan 8 05:49:15.897: DHCP: new entry. add to queue, interface FastEthernet0/0 Jan 8 05:49:15.897: DHCP: SDiscover attempt # 1 for entry: Jan 8 05:49:15.897: DHCP: SDiscover: sending 308 byte length DHCP packet Jan 8 05:49:15.897: DHCP: SDiscover 308 bytes Jan 8 05:49:15.901: B'cast on FastEthernet0/0 interface from 0.0.0.0 R2611XM(config)# Jan 8 05:49:19.660: DHCP: SDiscover attempt # 2 for entry: Jan 8 05:49:19.660: DHCP: SDiscover: sending 308 byte length DHCP packet Jan 8 05:49:19.660: DHCP: SDiscover 308 bytes Jan 8 05:49:19.660: B'cast on FastEthernet0/0 interface from 0.0.0.0 R2611XM(config)# Jan 8 05:49:23.666: DHCP: SDiscover attempt # 3 for entry: Jan 8 05:49:23.666: DHCP: SDiscover: sending 308 byte length DHCP packet Jan 8 05:49:23.666: DHCP: SDiscover 308 bytes Jan 8 05:49:23.666: B'cast on FastEthernet0/0 interface from 0.0.0.0
Then after all this I can go get my old $40 linksys home router plug it in, it pulls an address, and away we go. So there must be a bug in the modem/up stream if I can realiably get a PC to work stand alone and so far most anything other than a Cisco IOS device (and linux users have the same issue standalone). I will keep testing. If anone else has some info too that would be great.
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