This tutorial is based on IPV4 and RFC1918 private address space as assigned by the IANA - which is commonly used by most small businesses and home networks.
In networking we refer to the following: "A name indicates what we seek, an IP address indicates where it is and a route tells us how to get there"
DHCP
Every host or device on your network needs a minimum amount of configuration data if it is to successfully connect to the internet. This data is commonly obtained from a DHCP server but could be configured manually. DHCP - Dynamic Host Configuration Protocol is a mechanism that provides the IP address, Subnet Mask, Default Gateway and DNS info to a host on the network. When the host starts it's networking services it looks to see how it should configure the interface, via DHCP or using manually entered data. Most routers, cable/DSL modems contain a DHCP server.
NAT
RFC 1918 describes blocks of IP address that are assigned by the IANA Internet Assigned Numbers authority - for use in private networks - therefor many private networks can use the same IP address range - for this to work an additional feature called NAT Network Address Translation (common form is IP Masquerading) was introduced.
IP Address (ipconfig)
An IP address is an Internet Protocol Address and is unique within any given subnet. The Internet Protocol is used to route data packets between networks and the IP address includes information about the network and the device on the network. Using the method, local devices and devices on networks around the world can communicate with each other.
Subnet Mask (ipconfig)
This misunderstood parameter is extremely important. Subnet masks are used to split IP networks into logically smaller networks thus giving control over discrete networks. Your DSL provider does this all the time when they setup a SLIP link to your modem. The SLIP link address is created by apply a subnet mask to the original IP address range in such a way that it creates a network with 2 IP addresses, 1 broadcast address and 1 network address. The 2 IP address are assigns for each end of the SLIP link.
The more standard use of the subnet mask is to determine which network (or subnet) a host is connected to. For example the IP address 192.168.16.2 is not very useful without the subnet mask. Why? The subnet mask is the key that defines how the network is partitioned. For example, you can define a subnet mask that partitions a network into 4 parts - if you don't have this key you'll not know which network a host is connected to.
Mike has assigned the network address 192.168.10.0 to his IT support company. Normally this would have a subnet mask of 255.255.255.0, a broadcast address of 192.168.10.255 and accommodate 254 hosts. He has decided to partition his network into 4 subnets. He will further partition one of these subnets into 16 subnets for point-to-point SLIP applications. The Hierarchical subneting is covered in RFC1219. Mikes network now look like this:
Network Address 192.168.10.0
Subnet ID 0, 192.168.10.0, subnet mask 255.255.255.192, broadcast 192.168.10.63, 62 hosts
Subnet ID 1, 192.168.10.64, subnet mask 255.255.255.192, broadcast 192.168.10.127, 62 hosts
Subnet ID 2, 192.168.10.128, subnet mask 255.255.255.192, broadcast 192.168.10.191, 62 hosts
Subnet ID 3, 192.168.10.192, subnet mask 255.255.255.192, broadcast 192.168.10.255, 62 hosts
Subnet ID 3 is further partitioned as follows:
Network Address 192.168.10.192
Subnet ID 0, 192.168.10.192, subnet mask 255.255.255.252, broadcast 192.168.10.195. 2 hosts
Subnet ID 1, 192.168.10.196, subnet mask 255.255.255.252, broadcast 192.168.10.199. 2 hosts
...
Subnet ID 15, 192.168.10.252, subnet mask 255.255.255.252, broadcast 192.168.10.255. 2 hosts
Example: Which network is host 192.168.10.197 on? Looking at the above information we can see that it is host 1 on Subnet ID 1 (network 192.168.10.196). If we are given the subnet mask along with the IP address, 192.168.10.197/255.255.255.252, we can calculate the same information without knowing how the network is partitioned, as follows:
last octet = 197 dec, 252 means 6 bits stolen
bin
110001|00 = network id = 196 = 192.168.10.196
110001|01 = first host = 197 = 192.168.10.197
110001|10 = second host = 198 = 192.168.10.198
110001|11 = broadcast address = 199 = 192.168.10.199
Easy right!
DNS (nslookup)
So you would normally type http://www.google.com into your browser but you could just as well type http://74.125.67.147/. What's going on here? Well Google.com is the domain name and 74.125.67.147 is the IP address of Google's server. The name-to-IP address translation is handled by the DNS - Domain Name Service, without it we would all have to memorize the unfriendly IP addresses. You can use either the DNS info given you by your service provider, a 3rd party DNS provider like OpenDNS or your Default gateway will normally act as DNS proxy.
Default Gateway (ipconfig)
But how did my computer find the Google home page? This is where the routing tables take over - remember one of the parameters that we need to connect to the Internet is the Default Gateway - this is normally our router or cable/DSL modem. It has 2 IP address, one on the private side of the network (which we call the default gateway address) and an external (public) address provided by your service provider. The service provider can offer either a static or dynamic address. You can discover your public IP address by using a service like whatismyip.com
Routing Table (netstat -r)
Every connected host has a routing table that contains at least the default route. This means "if I'm looking for an IP address that is not in my local subnet, please pass the request along to this default route" from there the request will be routed through many nodes - each with some knowledge of the destination - until finally the destination host is contacted. This route is then used for all subsequent communication between the source and destination devices.
DOS Commands
Using some simple DOS commands you can play around and discover some interesting things about your network and the internet.
nslookup - find the ip address of any internet resource using it's name
ipconfig - discover all the config parameters associated with your NIC (Network Interface Card)
netstat - find network statistics including routing table
tracert - find the route your data takes to any internet resource
ping - check the latency and availability of any resource
hostname - get the local computer hostname
Steve Earle is Creative Guy at E2Mktg, call him on 954.806.2188 and get started with a Fast-Track Digital Video for your company today.
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