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Troubleshooting DHCP issues

q-le
Explorer
Explorer

Hi All,

We have 2 x Nexus 7 cores and several access switches 3750 + 2960 and several VLANs.

All working well until recently we have a couple of users in VLAN say 200 reported they can not get an IP address from our Windows DHCP server.

ie hence they can not log to the Domain and we temporarly assign them a static IP addresses  until we figure out what went wrong!!!

We checked the trunk , the DHCP server but can not see anything wrong

How do we troubleshooting this issues ? 

Any advices are much appreciated

Thanks

Peter

 

1 Accepted Solution

Accepted Solutions

try removing the config :

hsrp 0     

from interface vlan 200.

 

hope you got it resolved.

 

-

Parvesh

Remember marking as correct answer / helpful answer.

View solution in original post

17 Replies 17

Wilson Bonilla
Participant
Participant

Hello Peter. 

1- Make sure your DHCP server has enough available IP addresses to assign. 

2- Double check all trunk interface allow vlan 200 across the entire path from end user to dhcp server. 

3- Is the DHCP server hosted in the same vlan as the end users?

4- If DHCP server resides in a different vlan, make sure relay-agent is properly configured.

5- Can you take two sniffer captures simultaneos;

     - Install wireshark in the end user, take a capture while trying to obtain an ip address.

     - Install wireshark in the dhcp server, at the same time you are capturing packets in the pc, capture the dhcp server NIC and check if the DHCP discover coming from the PC arrives to the server NIC, analyze further the conversation between these two end points.

 

Let me know if that helps. 

Wilson B. 

 

Hi Wilson,

1) yes, dhcp has plenty of addresses

2) all trunk interfaces are good

3)DHCP server is in a different VLAN

4) Relay agents are in the Core Nexus 7

5) DHCP server is a virtual server and can not install wireshark on it.

Wireshark on a User PC and can not see any D.O.R.A process

 

Are there any debug commands I can try on the Nexus Core 7 and the access switches ?

Thanks

Much appreciated.

 

Check if there is any rouge DHCP there in the segment people usually use the VMware in there pc and it has a built in DHCP and that causes the problem. because I went through a similar issue sniff the packets with wireshark check if there is a NAck packet of DHCP.

q-le
Explorer
Explorer

Hi ,

I will try Wireshark on the port of the users PC and see what happen.

Will post the result tomorrow.

Thanks ALL.