How does DHCP assigns unique addresses to a network and does DNS lookup need to be changed

I recently got to know about DHCP that it dynamically assigns ip addresses to a computer. But what if two DHCP servers across the world assign a same ip address to two different computers. Doesn't it conflicts with the uniqueness property of ip addresses. For example two DHCP servers assign ip address x to computer1 and computer2 and i wanted to send a mail to computer1 by looking at DNS server it should be send to ip address x. But there is a conflict as two different computers have same ip address x. could someone please clear my doubt.

Let say I want to contact a server whose domain name is example.Com and ip address stored in DNS server is 127.18.1.1 and DHCP changes the ip address for this server to some random value 127.19.1.1 then how is the address resolved since I'm contacting to example.com which has 127.18.1.1

1 answer

  • answered 2018-07-06 14:05 Michael B

    There are a number of ways that this problem is avoided.

    Firstly, by keeping networks small, segregating machines into specific functions, geographic areas, etc you reduce the risk of having a large pool of addresses in use.

    Secondly, if you must have multiple DHCP servers on a network, then the address space should be split between them. So if you have 192.168.0.0/24, one server would handle 192.168.0.0/25 and another would handle 192.168.127.0/25

    Thirdly, most DHCP servers will ping the IP address that they are going to offer before offering it. If the address gets a response it will be marked as Conflicted and won't be offered again.