Day 6 (Communication between 2 IP subnets)

1. Static route on a computer (Windows)
2. Default route/Default gateway
3. Trunking between a switch and a router

1. Static route on a computer (Windows)
If Host A wants to communicate with Host B, either host must know how to reach to the other. In other words, proper routes must exist on both hosts.
It is a very important and fundamental concept of routing.
Ask at least 2 questions, all the time.
- Does host A have a route to reach host B?
- And does host B have a route to get back to host A?

On a windows computer, static routes are configured as in following format
route add mask gateway
e.g. route add 192.168.10.0 mask 255.255.255.0 172.16.31.126

On a Cisco router, static routes are configured as in follwing format.
ip route
e.g. ip route 192.168.10.0 255.255.255.0 172.16.31.126

2. Default route/Default gateway
Default route is used when a host/router does not have more specific route.
On a home computer network, default route is the only route and it is automatically assigned to a home computer by the home router via DHCP.
Default route is represented by network address 0.0.0.0, mask 0.0.0.0.

Default gateway is the IP address used by default route.
On a home computer network, default gateway is the IP address of LAN interface of the home router.

On a Cisco router, default gateway is also known as "gateway of last resort".

To configure a default gateway on a Cisco router, a default route is configured as in following format.
ip route 0.0.0.0 0.0.0.0
e.g. ip route 0.0.0.0 0.0.0.0 172.16.31.1

3. Trunking between a switch and a router
A trunk is a single physical connection that can carry more than 1 Vlan.

Day 5 (IP Address)

As discussed in Day 2, there are 3 IP classes. IP classes are based on first octect.
1 - 126, Class A
128 - 191, Class B
192 - 223, Class C

Class A default netmask is 8 bits, described as /8 or 255.0.0.0
Class B default netmask is 16 bits, described as /16 or 255.255.0.0
Class C default netmask is 24 bits, described as /24 or 255.255.255.0

Netmask defines the number of hosts that can be used in a given network.
Class A default netmask allows 16 million addresses in a network.
Class B default netmask allows 65536 addresses in a network.
Class C default netmask allows 256 addresses in a network.

When network addresses are used along with default netmask, they are said to be "classful addressing."

First address of the network cannot be assigned to a host. It is used to identify the network itself and it is known as "network address" or "subnet" address.

Last address of the network cannot be assigend to a host. It is used to identify all hosts in the network and it is called "broadcast address". (e.g. Ping to a broadcast address will be heard by all the hosts in the network.)

Using a netmask value greater than default value is called "Subnetting".
Using a netmask value smaller than default value is called "Supernetting".

Subnetting is used to reduce the number of hosts in a network.
Supernetting is used to increase the number of hosts in a network.

Subnetting and supernetting is called "classless addressing".