[cisco-voip] DHCP Problems | CME / Windows

Mon Mar 15 14:02:45 EDT 2010

Remember DHCP is broadcast from the client to the server, so it's not the PC seeing the DHCP server it's the DHCP server seeing the PC request an address.  Because your router has an interface on the data vlan it is going to see the broadcast from the PC and the DHCP server on the router will try and serve the client an address.

You may be able to configure ip helper on the router's data vlan to  point to the data dhcp server.  While that shouldn't be necessary it may keep the DHCP server on the router from doing anything for that vlan.

You can also try looking at the DHCP database on the router to see if other PCs are getting assigned addresses.

-Ryan

On Mar 15, 2010, at 11:29 AM, Kim, Hyoun S wrote:

What’s strange is that the DHCP pool I set up for the phones is on a private IP range that is unadvertised outside from the CME router.

On the router, I’ve defined the DHCP pool “phone” with the range of 10.10.10.0/24.  There is nothing specified in the ip routes on the CME.  On the switches connected to the network, the voice vlan goes to the interface on the CME with the IP 10.10.10.1.

I don’t see how in the debug log, how the PC even knows about the other DHCP server if you can’t even ping it or see it.

Hyoun Kim
Network Administrator I
Charter Media - East Division
640 Broadmor Blvd, Suite 80
Murfreesboro, TN 37129

Email: Hyoun.Kim at chartercom.com
Office: 615.217.6245
Fax: 615.217.6255

From: Ryan Ratliff [mailto:rratliff at cisco.com] 
Sent: Thursday, March 11, 2010 3:17 PM
To: Chris Ward (chrward)
Cc: Kim, Hyoun S; cisco-voip at puck.nether.net
Subject: Re: [cisco-voip] DHCP Problems | CME / Windows

That debug tells me that the dhcp database on the router had a previous entry for this client and is now seeing the request on a different vlan.

You can see that after the DHCPNak is sent it sees the request come in, confirms it doesn't have a pool for that address range, and doesn't send another Nak.  

I think you need to see the debugs that result in this client getting into the dhcp database to begin with.

-Ryan

On Mar 11, 2010, at 4:03 PM, Chris Ward (chrward) wrote:

“010542: Mar 11 15:35:27.595 EST: DHCPD: client has moved to a new subnet.”

That doesn’t seem good. Any ip-helpers in use here?

+Chris

From: cisco-voip-bounces at puck.nether.net [mailto:cisco-voip-bounces at puck.nether.net] On Behalf Of Kim, Hyoun S
Sent: Thursday, March 11, 2010 3:41 PM
To: Ryan Ratliff (rratliff)
Cc: cisco-voip at puck.nether.net
Subject: Re: [cisco-voip] DHCP Problems | CME / Windows

I do have another router, but it doesn’t point anything to the CME router.   All I did was configure the CME router to use a valid IP within the subnet.

Here is the output I’ve gotten so far:
010540: Mar 11 15:33:46.498 EST: DHCPD: checking for expired leases.
010541: Mar 11 15:35:27.595 EST: DHCPD: DHCPREQUEST received from client 0100.247e.1137.4c.
010542: Mar 11 15:35:27.595 EST: DHCPD: client has moved to a new subnet.
010543: Mar 11 15:35:27.595 EST: DHCPD: Sending notification of ASSIGNMENT FAILURE:
010544: Mar 11 15:35:27.595 EST:   DHCPD: htype 1 chaddr 0024.7e11.374c
010545: Mar 11 15:35:27.595 EST:   DHCPD: remote id 020a0000ac15c8c100000000
010546: Mar 11 15:35:27.595 EST:   DHCPD: circuit id 00000000
010547: Mar 11 15:35:27.595 EST: DHCPD: Sending notification of ASSIGNMENT_FAILURE:
010548: Mar 11 15:35:27.599 EST:  DHCPD: due to: Reason with no text explanation
010549: Mar 11 15:35:27.599 EST:   DHCPD: htype 1 chaddr 0024.7e11.374c
010550: Mar 11 15:35:27.599 EST:   DHCPD: remote id 020a0000ac15c8c100000000
010551: Mar 11 15:35:27.599 EST:   DHCPD: circuit id 00000000
010552: Mar 11 15:35:27.599 EST: DHCPD: Sending DHCPNAK to client 0100.247e.1137.4c.
010553: Mar 11 15:35:27.599 EST: DHCPD: broadcasting BOOTREPLY to client 0024.7e11.374c.
010554: Mar 11 15:35:28.623 EST: DHCPD: Sending notification of DISCOVER:
010555: Mar 11 15:35:28.623 EST:   DHCPD: htype 1 chaddr 0024.7e11.374c
010556: Mar 11 15:35:28.623 EST:   DHCPD: remote id 020a0000ac15c8c100000000
010557: Mar 11 15:35:28.623 EST:   DHCPD: circuit id 00000000
010558: Mar 11 15:35:28.623 EST: DHCPD: DHCPDISCOVER received from client 0100.247e.1137.4c on interface FastEthernet0/0.
010559: Mar 11 15:35:28.623 EST: DHCPD: Seeing if there is an internally specified pool class:
010560: Mar 11 15:35:28.623 EST:   DHCPD: htype 1 chaddr 0024.7e11.374c
010561: Mar 11 15:35:28.623 EST:   DHCPD: remote id 020a0000ac15c8c100000000
010562: Mar 11 15:35:28.623 EST:   DHCPD: circuit id 00000000
010563: Mar 11 15:35:28.623 EST: DHCPD: there is no address pool for 172.24.200.193.
010564: Mar 11 15:35:28.651 EST: DHCPD: DHCPREQUEST received from client 0100.247e.1137.4c.
010565: Mar 11 15:35:28.651 EST: DHCPD: no subnet configured for 172.24.217.73.
010566: Mar 11 15:35:28.651 EST: DHCPD: Finding a relay for client 0100.247e.1137.4c on interface FastEthernet0/0.
010567: Mar 11 15:35:28.651 EST: DHCPD: Seeing if there is an internally specified pool class:
010568: Mar 11 15:35:28.651 EST:   DHCPD: htype 1 chaddr 0024.7e11.374c
010569: Mar 11 15:35:28.651 EST:   DHCPD: remote id 020a0000ac15c8c100000000
010570: Mar 11 15:35:28.651 EST:   DHCPD: circuit id 00000000
010571: Mar 11 15:35:28.651 EST: DHCPD: there is no pool for 172.24.200.193.
010572: Mar 11 15:35:46.500 EST: DHCPD: checking for expired leases.

That MAC address is a PC.

Hyoun Kim
Network Administrator I
Charter Media - East Division
640 Broadmor Blvd, Suite 80
Murfreesboro, TN 37129

Email: Hyoun.Kim at chartercom.com
Office: 615.217.6245
Fax: 615.217.6255

From: Ryan Ratliff [mailto:rratliff at cisco.com] 
Sent: Thursday, March 11, 2010 11:48 AM
To: Kim, Hyoun S
Cc: cisco-voip at puck.nether.net
Subject: Re: [cisco-voip] DHCP Problems | CME / Windows

debug dhcp detail
debug ip dhcp server event
debug ip dhcp packet

I don't believe the ios dhcp server will attempt to serve requests on an interface it doesn't have a dhcp pool defined for.  Do you happen to have another router with a data vlan address and ip-helper pointed to the CME router?

-Ryan

On Mar 11, 2010, at 12:21 PM, Kim, Hyoun S wrote:

After implementing the last Cisco VoIP solution for our offices, I’ve stumbled across a problem with machines (all Windows) that occasionally drop their network connection just briefly every couple of hours.  While this normally wouldn’t be a problem, it is for us because we redirect several of the default Windows folders to a Windows server.  When the connection drops, Windows loses these folders and you have to log off/log on to get them back.

Looking into the Event Properties of various windows machines, it intermittently gets a DHCPNACK message from another DHCP server.  Unfortunately, that DHCP server is the DHCP pool I set up on the CME.

One of the Ethernet ports on the CME is configured for the data VLAN.  This is connected to our switch with only the data VLAN being shown when I perform a show spanning-tree on that interface.
The other Ethernet port is strictly configured for the voice VLAN and displays only the voice VLAN in a show spanning-tree on that interface.

Each PC port has both the data VLAN & voice vlan defined in the configuration w/ the phone containing “switchport voice vlan 100”.

Do you guys have any suggestions on why the Windows machines are trying to pull an IP from the Cisco DHCP server I set up for the phones?

Thanks in advance.

<image001.jpg>
Hyoun Kim • Network Administrator I – East Division
640 Broadmor Blvd • Suite 80 • Murfreesboro, TN 37129
' 615.217.6245 • ' 859.312.6941 • 7 615.217.6255 • * Hyoun.Kim at chartercom.com

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