Repeated DHCP Discover from router

DoctorBrown · 07-30-2006, 09:04 AM

I've been trying to troubleshoot a problem I'm having reliably connecting my laptop to my home network wirelesssly via a D-Link DI-624 router. My ISP is Comcast and I'm using their Motorola modem SB5101.

More on the wireless issue later but the question I have at this time is:

I've noticed that the router continuously sends out DHCP Discover requests. after every 6th or 7th, there is a DHCP Success. Why is this happening, and is it normal and something I can ignore? It fills up the router log and makes it more difficult to troubleshoot the wireless problem. When the WAN port is connected, the cycle repeats every 45 minutes. With the WAN disconnected, it repeats continuously about every minute. Of course in that case, there's a DHCP Discover no response every 6th request.

The wireless issue is that when I successfully get my laptop to connect wirelessly, I come back say a day later I can't connect. The wireless portion authenticates via WPA2-PSK, but the laptop doesn't recognize the DHCP reply from the router for a local LAN address. So, I get a 'Limited connectivity...' and the IP address is a 169.254.7.... network address. The Router DHCP screen shows the router has assigned a 192.168.0... address as expected. The Intel PROSet shows 'Did not receive IP address'. If I reset the router everything is good again and I can connect with no problem. So I'm wondering if the two symptoms are related in some way.

I've gone around and around on the wireless issue and no one has an answer. (except to ditch the D-link, which I'm close to doing...).

So for this post, unless someone has a magic bullet for the wireless part, the question is whether the repeating DHCP Request cycle is normal or not, and can or should I stop or reduce it. If so, how? I recognize that it has to occur sometimes to establish the initial connections and when the WAN connection is lost.

**johnwill** · 08-01-2006, 10:14 AM

The only place the router would be sending DHCP discover commands is to the broadband modem. DHCP clients send the DHCP Discover command, so that would be one of your workstations if it's on the LAN side.

What is the actual contents of a couple entries of the log?

DoctorBrown · 09-03-2006, 03:56 PM

I know it's been awhile since you posted. I hope you're still listening..

From the logs, here's one cycle of the DHCP Request/Reply. Clearly, this is a request from the router to the WAN/ISP side of the world. I'm connected to Comcast cable.

Jul/17/2006 07:12:08 DHCP Request success 67.180.192.88
Jul/17/2006 07:12:08 DHCP Request 67.180.192.88
Jul/17/2006 07:12:07 DHCP Request 67.180.192.88
Jul/17/2006 07:11:07 DHCP Request 67.180.192.88
Jul/17/2006 07:10:05 DHCP Request 67.180.192.88
Jul/17/2006 07:08:02 DHCP Request 67.180.192.88
Jul/17/2006 07:03:54 DHCP Request 67.180.192.88
Jul/17/2006 06:55:41 DHCP Request 67.180.192.88
Jul/17/2006 06:39:13 DHCP Request 67.180.192.88

This cycle repeats every hour and 15 minutes. Why would the router need to do this? Can I make it stop? It's making it more difficult to troubleshoot another issues with my wifi connection.

**Bill_Castner** · 09-03-2006, 05:12 PM

It would have zero effect on your wi-fi connection.

I do no know the lease term the modem is receiving, but the request will be made starting at half the lease expiration. The log traffic seems normal to me, you have 8 UDP packets over 45 minutes.

.

**johnwill** · 09-03-2006, 06:28 PM

It's also from a public IP address, not from inside your network.

**Bill_Castner** · 09-03-2006, 10:37 PM

I suspect it is testing for the purpose of authenticating the MAC address.

.

**johnwill** · 09-04-2006, 02:08 PM

Could be, I see a ton of ARP requests when I monitor my Comcast modem, it started happening when they changed over to a new network configuration.

DoctorBrown · 09-06-2006, 06:29 PM

Quote:

Originally Posted by Bill_Castner

It would have zero effect on your wi-fi connection.
.

I agree, but these messages were filling up the log display when I was trying to see if there were any messages from the LAN side that would help me with the WiFi issue.

07-30-2006, 09:04 AM	#1 (permalink)
DoctorBrown Registered User Join Date: Mar 2006 Posts: 24 OS: Win XP	Repeated DHCP Discover from router I've been trying to troubleshoot a problem I'm having reliably connecting my laptop to my home network wirelesssly via a D-Link DI-624 router. My ISP is Comcast and I'm using their Motorola modem SB5101. More on the wireless issue later but the question I have at this time is: I've noticed that the router continuously sends out DHCP Discover requests. after every 6th or 7th, there is a DHCP Success. Why is this happening, and is it normal and something I can ignore? It fills up the router log and makes it more difficult to troubleshoot the wireless problem. When the WAN port is connected, the cycle repeats every 45 minutes. With the WAN disconnected, it repeats continuously about every minute. Of course in that case, there's a DHCP Discover no response every 6th request. The wireless issue is that when I successfully get my laptop to connect wirelessly, I come back say a day later I can't connect. The wireless portion authenticates via WPA2-PSK, but the laptop doesn't recognize the DHCP reply from the router for a local LAN address. So, I get a 'Limited connectivity...' and the IP address is a 169.254.7.... network address. The Router DHCP screen shows the router has assigned a 192.168.0... address as expected. The Intel PROSet shows 'Did not receive IP address'. If I reset the router everything is good again and I can connect with no problem. So I'm wondering if the two symptoms are related in some way. I've gone around and around on the wireless issue and no one has an answer. (except to ditch the D-link, which I'm close to doing...). So for this post, unless someone has a magic bullet for the wireless part, the question is whether the repeating DHCP Request cycle is normal or not, and can or should I stop or reduce it. If so, how? I recognize that it has to occur sometimes to establish the initial connections and when the WAN connection is lost.

08-01-2006, 10:14 AM	#2 (permalink)
johnwill Manager, Networking Forums Join Date: Sep 2002 Location: S.E. Pennsylvania, US Posts: 41,802 OS: Windows 7, XP-Pro, Vista, Linux Blog Entries: 1	The only place the router would be sending DHCP discover commands is to the broadband modem. DHCP clients send the DHCP Discover command, so that would be one of your workstations if it's on the LAN side. What is the actual contents of a couple entries of the log? __________________ If TSF has helped you, Tell us about it! or Donate to help keep the site up! Microsoft MVP - Windows Desktop Experience

09-03-2006, 05:12 PM	#4 (permalink)
Bill_Castner Users Helping Users Join Date: Aug 2006 Location: Bethesda, MD Posts: 1,029 OS: XP SP2 Vista Win2k	It would have zero effect on your wi-fi connection. I do no know the lease term the modem is receiving, but the request will be made starting at half the lease expiration. The log traffic seems normal to me, you have 8 UDP packets over 45 minutes. . __________________ MS-MVP Windows Networking VSOP AUMHA Forums MVM BroadbandReports / DSLR MVP Tek-Tips

09-03-2006, 06:28 PM	#5 (permalink)
johnwill Manager, Networking Forums Join Date: Sep 2002 Location: S.E. Pennsylvania, US Posts: 41,802 OS: Windows 7, XP-Pro, Vista, Linux Blog Entries: 1	It's also from a public IP address, not from inside your network. __________________ If TSF has helped you, Tell us about it! or Donate to help keep the site up! Microsoft MVP - Windows Desktop Experience

09-03-2006, 10:37 PM	#6 (permalink)
Bill_Castner Users Helping Users Join Date: Aug 2006 Location: Bethesda, MD Posts: 1,029 OS: XP SP2 Vista Win2k	I suspect it is testing for the purpose of authenticating the MAC address. . __________________ MS-MVP Windows Networking VSOP AUMHA Forums MVM BroadbandReports / DSLR MVP Tek-Tips

09-03-2006, 03:56 PM	#3 (permalink)
DoctorBrown Registered User Join Date: Mar 2006 Posts: 24 OS: Win XP	I know it's been awhile since you posted. I hope you're still listening.. From the logs, here's one cycle of the DHCP Request/Reply. Clearly, this is a request from the router to the WAN/ISP side of the world. I'm connected to Comcast cable. Jul/17/2006 07:12:08 DHCP Request success 67.180.192.88 Jul/17/2006 07:12:08 DHCP Request 67.180.192.88 Jul/17/2006 07:12:07 DHCP Request 67.180.192.88 Jul/17/2006 07:11:07 DHCP Request 67.180.192.88 Jul/17/2006 07:10:05 DHCP Request 67.180.192.88 Jul/17/2006 07:08:02 DHCP Request 67.180.192.88 Jul/17/2006 07:03:54 DHCP Request 67.180.192.88 Jul/17/2006 06:55:41 DHCP Request 67.180.192.88 Jul/17/2006 06:39:13 DHCP Request 67.180.192.88 This cycle repeats every hour and 15 minutes. Why would the router need to do this? Can I make it stop? It's making it more difficult to troubleshoot another issues with my wifi connection.

09-04-2006, 02:08 PM	#7 (permalink)
johnwill Manager, Networking Forums Join Date: Sep 2002 Location: S.E. Pennsylvania, US Posts: 41,802 OS: Windows 7, XP-Pro, Vista, Linux Blog Entries: 1	Could be, I see a ton of ARP requests when I monitor my Comcast modem, it started happening when they changed over to a new network configuration. __________________ If TSF has helped you, Tell us about it! or Donate to help keep the site up! Microsoft MVP - Windows Desktop Experience