Saturday, June 24, 2017

AWS : VPC : What is DHCP

It stands for Dynamic Host Configuration Protocol (DHCP) is a standardized network protocol used on Internet Protocol (IP) networks.

Its an application layer protocol, used by hosts for obtaining network setup configuration information.

For our computers to work over a network they need an ip address , not just any ip address .... That address has to be unique on the network. Cant do it manually for network with large number of PCs.

So how does this work?
  1. Each computer runs a DHCP client that allows it to ask for an ip address
  2. Somewhere on the network there will be a DHCP server , this is where ip addresses are managed. 
    1. on a home network dhcp server can be on router
    2. on an enterprise network this is usually on an enterprise server.

Step 1 : Broad cast msg , all devices get it and drop it

Step 2 : Offers an ip address

Step 3 : DHCP Requesr

Step 4 : DHCP Acknowledgement

Step 5 : When DHCP server gives out an address it also gives out an expiration time. after which the host will need to renew its address.

So in general , this is what happened

In terms of AWS , there is "DHCP Option Set"

Note that
  • Different VPC can have different DHCP option set
  • you cant have 2 DHCP option set for a single VPC
  • Once you create a DHCP option set you cant modify it ( as seen from above )

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