What happens if there is more than one DHCP server available

[R Manjunatha]

What happens if there is more than one DHCP server available? How do my clients know which one to use?

[MHM Cisco World]

the first one reply to client will be use. 
there is no certira decide which one will be use. 
one more info. if the client already connect to DHCP-x and get IP from this server before, the client can send to re-assign same IP to this DHCP server and hence never ask new IP from both DHCP server. 

[R Manjunatha]

OK...

DHCP-x and DHCP-y in the same segment on what sequence the first DHCP will replay to the client. What is the terminology here it will use?

[MHM Cisco World]

there is no fix criteria that DHCP-x or DHCP-y will reply first, 
it depend one the link/queue/DHCP response time that decide which one will reply first.
but if you want to make some kind of load balance then you can separate the subnet into two half, 
one half in each server 
this make DHCP-x when dont have any IP to assign not reply to client request and hence the client will select DHCP-y that have free IP to assign. 

[Joseph W. Doherty]

NB: Already correctly answered by @MHM Cisco World, but perhaps stating answer in a slightly different way will help.

"How do my clients know which one to use?"

They don't know.  They don't choose.

"What happens if there is more than one DHCP server available?"

Each will determine whether it can provide an IP.  If it can, it will offer it to the client.

Client uses the first IP it receives back.

[Spooster IT Services]

Hi R Manjunatha , 

The client uses a Discover packet to look for the DHCP servers in the Network , then the server would reply back with an offer packet  which contains details about the IP address lease . The client would accept the IP from the server  whose Offer message the client receives the first .