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DHCP server does not send DHCPNAK

Martin Cerveny
Occasional Advisor

DHCP server does not send DHCPNAK



I have problem with comware DHCP server (5.20 1808P08).

It is not compliant with RFC2131 (DHCP) section "4.3.2 DHCPREQUEST message"/"INIT-REBOOT state":


1) client (Solaris) generate DHCPREQUEST (tested directly and dhcp relay)

   - 'requested IP address' is from DIFFERENT (previous) ip network

   - all other other fields are set correctly as described in RFC2131

2) server accept message (incremented 'display dhcp server statistics' - DHCPREQUEST)

3) server remains silent !!!!!



Server SHOULD send a DHCPNAK message to the client if the 'requested IP address' is incorrect, or is on the wrong  network.


If the client has been assigned address previously from that DHCP server eg. entry still exist in 'dhcp server ip-in-user all'

DHCP correctly response correctly with DHCPNAK !

There is no problem with other DHCP (non comware) servers.


Is that feature or bug ?

Is there public bugtrack ?


Thanks, Martin Cerveny


Trusted Contributor

Re: DHCP server does not send DHCPNAK

I too am having problems understanding how my H3C switches (Commware7) are doing DHCP.


A few things just don't seem to work quite right. Broadcasted DHCP requests within a VLAN seem to be being dropped on the switch, for example, and the server never sees them.


I'd like to read an in-depth analysis, white paper, or configuration/testing example to see how others deal with it.

Martin Cerveny
Occasional Advisor

Re: DHCP server does not send DHCPNAK

The problem still persists (Comware 5.20.105 R1808P17).



Trusted Contributor

Re: DHCP server does not send DHCPNAK

The sad thing is that SHOULD != SHALL, so HP could continue to ignore that part of the RFC and still be compliant.


But I agree with you, for compatibility reasons HP should fix this.


Have you filed this as a bug report - what did the support answer you (if any)?


What does the internal debugging of the HP-device tell you about its activity?


That is:


terminal monitor

terminal debugging

debugging dhcp server all


Then your ssh session should start to display the dhcp acitivity.


To disable the above you can do


undo debugging all

undo terminal debugging

undo terminal monitor


Also the statistics contain the DHCPNAK, what does its value tell you?


display dhcp server statistics


If that DHCPNAK counter goes up then you should be able to see this in the debugging of the dhcp server aswell. Perhaps the packet is sent wrong direction or something?