1

Great start into the week ;). I have DHCP running on Windows 2008 R2 server, existing clients can renew IPs but new clients won’t get one, the request times out. Any help would be greatly appreciated.

6 Spice ups
2

Anything in the event log? Are there available IP’s for new clients to take?

3

Are the clients and the server on the same subnet? If not, are your helpers in place on your switches? Def check error logs.

4

Can clients ping the DHCP server? How big is your DHCP scope? Are there enough free IP addresses to service new clients?

5

have you tried restarting the DHCP service?

1 Spice up
6

Thanks for the quick replies. Here the answers to your questions.

Nothing in the Event Logs
More than 100 available IPs
Clients and server are on the same subnet
Clients (that have an IP) can ping the server
Scope 192.168.201.30 - .199
DHCP log shows renewals but no new leases

7

Yes, restarted the server and service.

8

Have you checked the computers that don’t connect that they are not picking up an alternate DHCP server

9

Get WireShark out and start watching the packets…

10

I’m still fairly new to this stuff, but it seems to me I remember running into a computer that wouldn’t pick up a new ip adress from the server and opening a command prompt and entering:

ipconfig /release

ipconfig /renew

solved the problem.

Just out of curiosity…have you entered a static ip address and tried pinging the server just to make sure it’s not a physical layer issue?

1 Spice up
11

Some more info.

If I give a machine a static IP it still can’t get to the network (unidentified).
Any machine that still has a lease can renew (even if it was shut down).
Ipconfig /renew throws an error saying cannot find DHCP server (but again, any machine that is on the network can ping the server and can renew its IP)

12

Are the new clients that can’t get DHCP trying to get it from the right server? Anything new on your network that might be also acting as a DHCP server and causing confusion?

Had similar happen to me once when I hooked up an old server I was going to clean up but forgot that it used to be the DHCP server for the domain and it wanted to try to be again.

13

I ran netmon, here a couple of screenshots.

DHCP.zip (86.2 KB)

14

Is the new client a new computer or just new to you network. Is it operating wired or wireless. Is your cable good, and do you see network activity lights. Does your switch hav seperate VLAN’s set up…

15

DHCP explorer will show all your DHCP servers that are available.

2 Spice ups
16

New clients are 2 laptops that are used for testing. Connected via network cable (used different ones). Network activity lights are on, but data is flowing in one direction only (nothing is received). No VLAN’s on the switch.

17

Can the two laptops ping each other. What are you using for a DHCP server… domain server, firewall, switch, hub, another computer on the network. Are you on a peer-to-peer network, if so make sure your workgroups are correct.

18

jvdm wrote:

New clients are 2 laptops that are used for testing. Connected via network cable (used different ones). Network activity lights are on, but data is flowing in one direction only (nothing is received). No VLAN’s on the switch.

I would check that none are setup as mirrored ports. Mirrored ports often only send traffic to the connected host, and ignore any transmission attempts. I’ve had this screw me up at least once when I forgot to disable the port mirroring after I was done with it.

19

Once they clients have finished booting are you able to release/renew by hand receive an address?

If data is flowing one direction and your are able to collect an address later your switch is most likely setting the porting into blocking mode while STP is being negotiated. A lot of times the STP process is much to slow (30-60 seconds) for a modern day computer and they will be unable to receive an IP packet.

Not sure what model switch you are using but, on a Cisco switch

interface G1/0/1

switchmode mode access
spanning-tree portfast (this will turn off spanning tree and go straight from listening to forwarding).

Just be a little careful, if you have a fairly complex network you don’t want to turn this on for the incorrect port or you may cause switching loops. Access ports will not be an issue though.

20

This may be a long shot, but I once had a user that was having trouble unpluging the network cable. By the time they got it out, they had bent one of the pins on the laptop that makes contact with the network cable. I straightened the pin out and all was fine.