Insert delay in dhcp3-relay ?

Benjamin hexor38 at
Wed May 4 19:18:02 UTC 2011

Le 04/05/2011 18:02, dhcp-users-request at a écrit :
> Adding a delay to the relay agent will NOT stop this.
> For a client that already has a working lease, it will continue to
> renew the lease with the remote server. Delaying the packet a couple
> if seconds won't stop this.
> You would have to block the request altogether, and then the client
> would start to broadcast renewal requests which the local server
> would pick up.
> In practice, clients will normally take an initial lease from the
> first server to offer a valid offer. In a setup like yours, it is
> going to be normal for the fastest server to be the one on the local
> network.
> The question that comes up next is how you are doing the fault
> tolerance - yes I understand what you mean.
> ISC DHCP server has a failover mode where two servers can co-ordinate
> their offers so as to share a common address space. If one fails,
> then the other can take over and run everything by itself.
> As an alternative, you can simply run two independent servers with
> non-overlapping ranges. As long as each server has enough addresses
> to service all the clients then the worst case is a failure of one
> server which is longer than half the lease time* - at which point
> clients will start to switch addresses as their leases expire.
> But, in both cases it shouldn't really matter which server a client
> is bound to.
> * By default, clients renew their leases when they are half way
> through. So few (if any) client will have less than half a lease left
> and can continue without an active DHCP server for at least this long.

I'm not agree with you, if I can put a delay, the network will work as I 
want. (I have make some test with 'request analys'(with wireshark))
This network is an application of an company network.
I want use fault tolerance, so if the DHCP A is offline the client use 
the DHCP C with the help of the relay. This is a case of problem on the 
network (DHCP A is Down) in normal case, computer of network A use DHCP 
A and computer of network C use DHCP C.

When DHCP A is online a new time, I want the client uses DHCP A and not 
the C (not necessary immediatly), for example after a reboot of the 
client (for example after a night, the worker go to the company and put  
the computer on).
After the reboot of the computer, the computer send on the broadcast a 
"Request" (with the old IP address: ip address in the range of DHCP C), 
so if I put a delay, the Relay not send the request to DHCP C and after 
a few second the client send a "DHCP - Discover" (to find a DHCP) and 
DHCP A send an offer, which the client accept (Request - ACK ).

But I can't put a delay .... (it is possible on Windows Server, but I 
don't like to work with windows)
(I'm going to see the "failover mode", but if it possible I prefer to do 
this the relay)
If anyone have an idea to put a delay I waiting you ;)

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