Server Down - How should Client Act?

Simon Hobson dhcp at
Mon May 1 14:59:03 UTC 2006

Melody Helt wrote:

>I have my default lease set up for 3 mins for experimentation.  I am giving
>out a static IP based on MAC address.
>My server does down.  Using ethereal to watch the network traffic, I see
>that at about 1/2 the time of the lease, the client sends out a DHCPREQUEST
>message then 5 seconds later sends out another DHCPREQUEST.  Nothing else
>After the lease time expires, the server starts up again.  No communication
>occurs between client & server.  The client has to be rebooted in order for
>it to communicate & get an IP from the server.
>From reading on the internet, I thought that once the lease expired, the
>client would keep broadcasting a message trying to find a host.  This
>doesn't seem to be the case in my experiment.  Should the client keep

You are right, the client should keep trying - at least for a while. 
I suspect many implementations don't keep trying indefinitely on the 
assumption that if it gets no reply to the first few requests then it 
isn't likely to get one later.

>In this situation, is there anyway to get the client & server to communicate
>without having to reboot the client?

Only intervention at the client end will help, try these :

Manually tell the client to renew using whatever tools the client OS provides.

Disable & re-enable the network interface (eg "ifdown eth0 ; ifup 
eth0" on Linux). DHCP client should then kick in.

Similar to above, unplug and reconnect the network cable.

Ditto, put the system to sleep and wake it.


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