What's the difference between DHCP and Static?


The shortest, simplest answer is this:

  • "Static" refers to manual IP Address configuration which never changes unless you change it.
  • "DHCP" (Dynamic Host Configuration Protocol) refers to automatic IP Address configuration which changes on its own


To better understand DHCP and Static IP, read on:


In order to be part of a network, every device needs an IP Address. This address is the device's "spot" on the network in relation to the router, which is in charge of the network.

Dynamic Host Configuration Protocol (DHCP) and Static Allocation ("static") are the two methods used to assign an IP address to a device on a network:


DHCP

Dynamic Host Configuration Protocol is the more common of the two methods, and can be thought of as the "automatic" version of IP assignment. Any router you buy off the shelf will use DHCP by default.


Example:

DHCP can be though of like a hotel. You show up, ask for a room, and the front desk agent gives you one. They show you where the amenities are and how to get to your room. While you're there, the room is yours. You can get phone calls, meals, and deliveries to your room. However, next time you visit, you will probably get a different room. 


In the case of IP addresses, this is how your cell phone and laptop can connect to networks they have never seen before using only the password. The router acts like the front desk agent at the hotel, assigning devices to specific IP Addresses as they join the network (provided they have the right password).


There is a specific "Lease Time" on the IP Address given to each device, and when that time is halfway up, the router asks the device if it would like to renew the lease. As long as the device is within range and powered on, it will keep answering "yes" and it will keep the same IP address. If the device is out of range, it can't answer "yes" and the lease will eventually expire. This leaves the IP address free for another device to use.



Static

Static Allocation is less common in residential settings, and can be thought of as the "manual" version of IP assignment.


Example:

Static Allocation can be thought of like a PO box. You have your key, and you know where it is and how to get there. When you arrive, there might be no one to help you, but you already know where you're supposed to be. You go to the same box every time, and it belongs to you and no one else.


To connect to a static network, a device must already know all of the network's configuration information before it can successfully connect. If any of the information is wrong, the device will either not connect, or may have issues after connecting.


What information does a device need for a static connection?

  • IP Address
    • The device needs to know where it should sit (what IP address it should occupy). It's up to the network administrator to make sure he doesn't give the same IP address to two different devices, lest there be an IP Address Conflict.
    • Example: 192.168.001.025
  • Gateway IP Address
    • This is the IP Address of the router. The device needs to know the router's address so that it can send information out of the network (through the "gateway").
    • Example: 192.168.001.001
  • Subnet IP / Subnet Mask
    • This is a number in the same form as an IP address that tells all the devices on the network what the size and scope of the network is. A device needs to know the size and scope of its own network, so that it can recognize when you ask it for a resource that is not inside the network.
    • Example: 255.255.255.000
  • DNS IP (Domain Name Service)
    • This is the IP address of the server (or group of servers) that match "Domain Names" to actual IP Addresses. The "Domain Name" of a website is the address as you probably know it (like www.Netsurion.com). However, in order to access a website, your computer needs to know the actual IP Address where the site lives. The role of the Domain Name Servers is to keep these addresses up to date and answer requests from your computer when you want to access websites.
    • Example: 008.008.008.008 (This is Google's actual DNS Server Address)
NOTE:
  • Netsurion Firewalls are set up to handle DNS requests themselves. Therefore, it is safe to put the Gateway IP in place as the DNS IP if you are connecting to a Netsurion Firewall.
  • Most devices also ask for a "Secondary DNS." This is just used as a back-up in case the first server fails, and is usually not required. It is usually OK to put Google's DNS address in as the secondary.