SUBNETTING AND IP ROUTING

IP ADDRESS

An IP address is a software address, not a hardware address—the latter is hard-coded on a network interface card (NIC) and used for finding hosts on a local network. IP addressing was designed to allow hosts on one network to communicate with a host on a different network regardless of the type of LANs the hosts are participating in.

IP TERMINOLOGY

Network address This is the designation used in routing to send packets to a remote network—for example, 10.0.0.0, 172.16.0.0, and 192.168.10.0

Broadcast address The address used by applications and hosts to send information to all nodes on a network is called the broadcast address 172.16.0.0; and 10.255.255.255, which . Examples include 255.255.255.255, which is any network, all nodes; 172.16.255.255, which is all subnets and hosts on network broadcasts to all subnets and hosts on network

CLASSES OF IP

CLASS A The designers of the IP address scheme said that the first bit of the first byte in a Class A network address must always be off, or 0. This means a

Class A address must be between 0 and 127 in the first byte, inclusive.

Consider the following network address: 0xxxxxxx If we turn the other 7 bits all off and then turn them

all on, we’ll find the Class A range of network addresses:

00000000 = 0 01111111 = 127

CONT…

CLASS B In a Class B network, the RFCs state that the first bit of the first byte must always be turned on but the second bit must always be turned off. If you

turn the other 6 bits all off and then all on, you will find the range for a Class B network:

10000000 = 128 10111111 = 191 As you can see, a Class B network is defined

when the first byte is configured from 128 to 191.

CONT…

CLASS C For Class C networks, the RFCs define the first 2 bits of the first octet as always turned on, but the third bit can never be on. Following the same

process as the previous classes, convert from binary to decimal to find the range. Here’s the range for a Class C network:

11000000 = 192 11011111 = 223 So, if you see an IP address that starts at 192 and

goes to 223, you’ll know it is a Class C IP address.

RESERVED IP

Address Function Network address of all 0s Interpreted to mean “this network or segment.” Network address of all 1s Interpreted to mean “all networks.” Network 127.0.0.1 Reserved for loopback tests. Designates the local node

and allows that node to send a test packet to itself without generating network traffic.

Node address of all 0s Interpreted to mean “network address” or any host on a specified network.

Node address of all 1s Interpreted to mean “all nodes” on the specified network; for example, 128.2.255.255 means “all nodes” on network 128.2 (Class B address).

Entire IP address set to all 0s Used by Cisco routers to designate the default route. Could also mean “any network.”

Entire IP address set to all 1s (same as 255.255.255.255) Broadcast to all nodes on the current network; sometimes called an “all 1s broadcast” or limited broadcast

SUBNET MASK

To create sub networks, you take bits from the host portion of the IP address and reserve them to define the subnet address. This means fewer bits for hosts, so the more subnets, the fewer bits available for defining hosts.

SUBNET MASK AND CIDR VALUES

255.0.0.0 /8 255.128.0.0 /9 255.192.0.0 /10 255.224.0.0 /11 255.240.0.0 /12 255.248.0.0 /13 255.252.0.0 /14 255.254.0.0 /15 255.255.0.0 /16 255.255.128.0 /17 255.255.192.0 /18 255.255.224.0 /19 255.255.240.0 /20 255.255.248.0 /21 255.255.252.0 /22 255.255.254.0 /23 255.255.255.0 /24 255.255.255.128 /25 255.255.255.192 /26 255.255.255.224 /27 255.255.255.240 /28 255.255.255.248 /29 255.255.255.252 /30

SUBNETTING OF C CLASS

255.255.255.128 (/25) Since 128 is 10000000 in binary, there is only 1 bit for subnetting and 7 bits for hosts. We’re going to subnet the Class C network address 192.168.10.0.

192.168.10.0 = Network address 255.255.255.128 = Subnet mask Now, let’s answer the big five: How many subnets? Since 128 is 1 bit on (10000000), the answer would be 21 = 2. How many hosts per subnet? We have 7 host bits off (10000000), so the equation

would be 27 – 2 = 126 hosts. What are the valid subnets? 256 – 128 = 128. Remember, we’ll start at zero and count in

our block size, so our subnets are 0, 128. What’s the broadcast address for each subnet? The number right before the value of the

next subnet is all host bits turned on and equals the broadcast address. For the zero subnet, the next subnet is 128, so the broadcast of the 0

subnet is 127. What are the valid hosts? These are the numbers between the subnet and broadcast

address. The easiest way to find the hosts is to write out the subnet address and the broadcast address. This way, the valid hosts are obvious.

The following table shows the 0 and 128 subnets, the valid host ranges of each, and the broadcast address of both subnets:

IP ROUTING

There are two types of routing system

STATIC ROUTING

DYNAMIC ROUTING

COMPARISON

STATIC DYNAMIC

Static routing occurs when you manually add routes in each router’s routing table. There are pros and cons to static routing, but that’s true for all routing processes.

Dynamic routing is when protocols are used to find networks and update routing tables on routers. True, this is easier than using static or default routing, but it’ll cost you in terms of router CPU processing and bandwidth on the network links. A routing protocol defines the set of rules used by a router when it communicates routing information between neighboring routers.

ROUTING CONT..

STATIC SAYS—

Router(config)#ip route 172.16.3.0 255.255.255.0 192.168.2.4

ROUTING CONT…

DYNAMIC IS OF FIVE TYPES RIP(routing information protocol) RIPV2(routing information protocol

version 2) IGRP(interior gateway routing protocol) EIGRP(extended interior gateway

routing protocol) OSPF(open shortest path first)

ROUTING CONT…

RIP R1#config t R1(config)#router rip R1(config-router)#network 10.0.0.0 R1(config-router)#network 192.168.10.0 R1(config-router)#network 192.168.20.0 RIPV2 R1(config)#router rip R1(config-router)#network 192.168.40.0 R1(config-router)#network 192.168.50.0 R1(config-router)#version 2

ROUTING CONT…

IGRP or EIGRP Router#config t Router(config)#router eigrp 20 Router(config-router)#network

172.16.0.0 Router(config-router)#network

10.0.0.0

ROUTING CONT…

OSPF Test#config t R1(config)#router ospf 1 R1(config-router)#network 192.168.10.64 0.0.0.15 area 0 R1(config-router)#network 192.168.10.80 0.0.0.15 area 0 R1(config-router)#network 192.168.10.96 0.0.0.15 area 0 R1(config-router)#network 192.168.10.8 0.0.0.3 area 0 GIVEN THAT You have a router with these four subnets

connected to four different interfaces: 192.168.10.64/28 192.168.10.80/28 192.168.10.96/28 192.168.10.8/30

??? ANY QUERY