VM's are not receiving DHCP IP on the Cisco 4510R+E switch.

[nikhil.kulkarni]

Folks,

We have some Cisco 4510R+E switches installed in our network. For some reasons the VM's which are using VMWare workstation are not able to receive DHCP address. If I give them a static IP they work fine.

This is a Linux VM that I am trying on. It also gives the following output trying to search for DHCP(attached).

Any suggestion or anyone has come across this? I do not have Windows copy to try this out.

regards,

Nik

[Adrian Jimenez]

Hi Nik,

Is the switch acting as the DHCP server? If not we can do a quick test by creating a pool on the switch and try if in this way we accomplish the DHCP process succesfully. 

Now in case that the DHCP server is on a different server/box as well in a different subnet make sure you have a relay-agent for the DHCPDISCOVER and DHCPREQUEST packets to reach the server on a different subnet. 

Let me know how this goes.

Regards,

Adrian

[Manjunatha Jayaram]

Facing same Kind of issue.. The Linux systems are not working on DHCP while the window system are working fine. Kindly suggest...

[Steve Fuller]

Hi,

The DHCP message from the client has a flag that indicates to the DHCP server whether it expects a broadcast or unicast response.

In Windows the client will try both a 0 (client expects unicast response) and a 1 (client expects a broadcast response). See the DHCP Broadcast flag handling in Windows 7 blog for more details.

Looking at the dhclient and dhclient.conf man pages I don't see any similar statements for Liunux i.e., it will send a unicast or broadcast, but not try both.

Can you try running the dhclient command on your Linux hosts with -B (broadcast) option? This should make the DHCP server reply to the client with a broadcast.

Regards

[Manjunatha Jayaram]

There are so many linux devices in my network. Cant do this thing for every individual device. The Linux devices worked fine for first 10 days but facing this issue since last 3 days.

[Steve Fuller]

Are you able to try this on one or two host to confirm whether this is the issue that you are facing?

If we can prove or eliminate this, we can then consider next steps and long term options for your problem.

Regards

[Manjunatha Jayaram]

Yah I have done this but it isn't working. When I tries with Static IP then they start working. 

[Steve Fuller]

Hi,

So I guess we need to go back to basics.

• Has anything changed in the environment? OS upgrade on your switches for example?
• Are the Windows and Linux clients in the same subnets?
• Do you have any packet captures to confirm whether the DHCP Discover from the Linux clients reach the DHCP server?
• If so are the DHCP offers being sent back and received at the switch?
• What is the model and IOS version of the switch? Is it a version supporting the Embedded Packet Capture? See Configuration Example: Embedded Packet Capture on Cisco IOS and IOS XE for explanation and examples of how to use.

Regards