DHCP relay stops working after DHCP server maintenance

[VladoK]

Hi,

I have a Cisco 2911 branch router with quite simple config and there is also DHCP relay configured on LAN subinterfaces. The helper-address points to a server located in datacenter.

Regularly after the datacenter maintenance window (when DHCP server is inaccessible and then comes back online) the DHCP relay on branch router stops working. Rebooting the router solves the problem.

There is 15.4(3)M7 IOS. Have somebody an idea what's wrong? 

[marce1000]

 - 1) Perhaps the router checks the reach ability of the DHCP server (though I  am not sure) 2) Does it also help to remove the relay-config from the router configuration and re-add it again ? 3) Check if the problem get's resolved if the router uses a  more recent software release (if appropriate). Whilst all these points may be cumbersome , DHCP services on a local Intranet should be up all the time. In our case it quasi-never happens that DHCP services are unreachable.

M.

[paul driver]

Hello

On the router can you open up a debug and capture a client transaction.-
debug ip dhcp server packet
debug ip udp

or possible a acl to debug bootpc and bootps UDP

access-list 100 permit ip host 0.0.0.0 host 255.255.255.0

access-list 100 permit udp host <helper-address> host dhcp server eq 67
access-list 100 permit udp host <helper-address> host dhcp server eq 68
access-list 100 permit udp host <dhcp server> host <helper-address> 67
access-list 100 permit udp host <dhcp server> host <helper-address> 68

debug ip packet detail 100