DHCP IP Address

[Peter]

There are two subnets in our network. They are
192.16.13.x and 192.16.16.y. There are two DHCP Servers,
one on each subnet.

We would like to know is it possible for machines in the
subnet 192.16.13.x picks up IP Address from the DHCP
Server in 192.16.16.y subnet ?

Thanks

 

[Pegasus \(MVP\)]

Machines always get their address from the first DHCP
server that responds to a broadcast. If you want to have
two subnets then you must split them physically.

 

[Peter]

They are actually in two different sites linked by frame
relay. Does it mean that they are already physically
separated ?

Thanks

 

[Pegasus \(MVP\)]

No, they would be on the same physical network. However,
they would always get an IP address from the local DCHP
server, simply because it responds first.

 

[Enkidu]

The DHCP server on the opposite subnet is unlikely to be able to serve
an IP address at all without the router configuration being set up
with an "ip helper-address" (Cisco talk) or if the opposite network
has a DHCP relay set up. DHCP broadcasts are not normally sent over
routed networks. If DHCP A has scopes for both networks, and DHCP B
has scopes for both networks too, obviously the first to respond with
an address would be the local DHCP server. It would normally give an
address from the range that is in the same subnet as its IP. However
if the request came via a router configured with an "ip
helper-address" or from a DHCP relay, then a field in the DHCP
"broadcast" indicates that the request is for the other network, and
the server offers an address from the appropriate range.

Hence, even if the local DHCP server is down, then the remote server,
if accessed by a router with "ip helper-address" or via a DHCP relay
should give an address in the correct range (from the correct scope).

So whatever happens, the sites should be served with the correct IP
addresses and other info.

Cheers,

Cliff