Hi,
i'm wondering how can we insure the availability of a dhcp server in a network?
we know already that we can't set up two servers because it 's decreasing the band width.
could some please help me?
thanks

If you are looking for some sort of redundancy in DHCP you can setup split scopes.

In otherwords, have 2 servers as dhcp. On one server you set them to use one range and the other server gets the rest of the range. You have to make considerations when doing this of course. If one server fails will the other be able to hold all the IP addresses?

Let's say you have 172.16.25.0/24 as your network. An example config would be to have
server1: 172.16.25.10-100
server2: 172.16.25.101-200
.1-.10 and .201-.255 is reserved for static printers, servers and workstations. If you have fewer than 90 clients this will provide redundancy. It doesn't really matter if the client pulls from server1 or server2 as long as the settings are the same for both DHCP servers.

Configure DHCP Failover..

http://www.madboa.com/geek/dhcp-failover/