1. Introduction to Computers
IP Configuration

2. IP Configuration
Hosts on a TCP/IP network need to be configured with various parameters before network communication can occur
Fortunately for most SOHO (small office / home office) situations, this will be automatically done when connecting the computer to the network. However, even if we aren’t spending a lot of time performing initial configurations, it will be helpful to understand the configurations; what they mean, why they were set and where they come from, in order to diagnose them and solve any problems

3. IP address and subnet mask
IP addresses identify a single host on a network, and are composed of two parts - a network address and a host address
As a reminder, the IP address and subnet masks will both be made up of four 8-bit binary numbers called octets. Or, when written in decimal, four numbers from While more complex subnet addresses can exist, for starting purposes, if a subnet mask octet is 255, the matching octet in the IP address is part of the network address. If the subnet mask octet is 0, the matching IP address octet is part of the host IP address
If the IP address or subnet mask is improperly configured, we can have trouble communicating on the network

4. IP address Considerations - Network Address
All hosts on a network must use the SAME network address to be able to communicate
This means that if one computer has the ip address of , and another has , these computer can not communicate if they are physically connected to the same network
This also extends to the subnet mask. For example, if we have two computers with the IP addresses of and with the subnet mask of , they can communicate. They are on the same network
If we change the subnet mask for one of them to , they will no longer be able to communicate. One will be on the network, and the other will be on the network

5. IP address Considerations - Improper Addresses
There are two addresses that cannot be assigned to hosts - all 0’s and all 1’s. Basically the first and last possible addresses
The first address will be the network address. No host can have the same IP address as the network
The last address is the broadcast address. This is reserved for messages that need to be sent without a specific address, for all computers to receive
The final IP address consideration is that all hosts on a network must have a unique address. This means that since all hosts on a network will share a network address, they must all have a unique host address

6. Default Gateway Address
So far, we’ve been talking about communications inside of a single network, but what if we wanted to communicate outside of our network?
To do so, we’d need a default gateway. This is a router that will handle all requests for communications with IP addresses that do not share our network address. This could be other networks inside of our organization, or networks on the internet
To be able to function properly, this router needs to have an IP address with the same network address as our local network, so that we can communicate with it. By convention, this device will usually be given the first available IP address ( for example), because this makes it easy to remember, but this is not a rule

7. DNS server Address
When connecting to websites or other hosts on the internet, we will use the host’s IP address to communicate with them. However, humans are not typically great at remembering multiple long numbers, so we use website names to navigate to hosts instead
The process of translating a URL name into an IP address is called name resolution, and is handled by a Domain Name System (DNS) server. For a host to be able to use website names instead of IP addresses, we’ll need the IP address of a DNS server to ask

8. Types of DNS Servers
Depending on the type of host you are looking to reach there are a few different types of DNS server
Internal DNS servers reside inside a network and are used to provide name resolution for internal hosts and other services
External DNS servers are servers located on the internet and are used to obtain name resolution for websites
Client-side DNS is the settings configured on a single host. This is where your host will look first before contacting a server. This is also called caching

9. Configuration Method - Static
There are a few different ways for a host to obtain their IP configuration
The first is for a network administrator to manually assign the information
This method can work well for small networks, but it can be prone to error from typos and it can result in duplicate IP address assignments if your records are off
This type of configuration is mostly used only for small networks or in special circumstances where a host has to have a specific IP address

10. Configuration Method - DHCP
If we want to automatically configure our IP configuration, we can use the Dynamic Host Configuration Protocol (DHCP). Using this protocol, a DHCP server is used to automatically configure all hosts on a network
As network administrators, we would configure the DHCP server with all the necessary settings, such as an IP address, subnet mask and default gateway
When host connects to a network using DHCP, it sends out a broadcast message to look for a DHCP server. If one exists, then the DHCP server responds with an IP address that the computer can use called a lease and all the necessary configuration settings
The DHCP server also makes sure that no two hosts have the same IP address, however, since the IP address is a lease, it is temporary. The next time the host asks for an address, it may receive a different address

11. Configuration Method - APIPA
The third method isn't so much a configuration type as it is a failsafe. The Automatic Private IP Address (APIPA) is the default TCP/IP configuration method used by hosts when no DHCP server can be found
APIPA will assign the host a network address of , a subnet mask of and a random host address in that range. It does not, however, assign a default gateway so communication outside the network is impossible
The idea behind APIPA is to allow local network communication to continue if a DHCP server goes down or no DHCP server exists. Because all hosts will default to the same network address and subnet mask, they'll be (theoretically) able to communicate with each other
In reality, this rarely works as it should. If anything, it's more of a red flag when troubleshooting network issues. If a host has an IP address in the range of , then you know something is wrong with the DHCP server

12. Configuration Method - Alternate IP Address
One final configuration method is an alternate IP address
With the alternate configuration, you configure the host to use DHCP, however, you also create a static configuration and manually enter an IP address, subnet mask, default gateway and other parameters as a fallback
The host will first use DHCP to obtain an IP address lease. If DHCP fails, the host will then use the alternate configuration instead of using APIPA. This can be used as a more stable failsafe than APIPA