Transmission Control Protocol / Internet Protocol and Network Utilities

Colin JamisonUniversity of Ulster

Network Protocols

Protocol - used by computers to exchange information over a network

The most common is TCP/IP originated by the U.S department of Defence

If IP is the native language of the InternetthenTCP represents one of many specialised

dialects

Sockets

De facto portable standard for portable applications on TCP/IP

Sockets available on most PC OSs and Mainframes

Internet Address(IP) and Port Address

netid . hostid . portid

Allocation of IP addresses

Network Information Centre (NIC)NIC handles the administration of IP

address allocation to an organisation5-types of IPv4 IP addresses can be

allocatedClass A, Class B, Class C, Class D, Class EThese allow the internet address to be

broken into blocks of small, medium and large networks

IP Address Format

From 000.000.000.000

To 255.255.255.255

Represented by a string of 4-bytes separated by full-stops

Each byte contains 8 bits - so each byte ranges from 0 to 255 decimalor 0000 0000 to 1111 1111 binary

Breakdown of the IP Address

The IP address consists of 2 parts which are, a netid and a hostid

Class A

Class B

Class C

Start-Bits Netid Hostid Total

1 + 7 + 24 = 32

2 + 14 + 16 = 32

3 + 21 + 8 = 32

IP Address Classes

Class A for extremely large networks (up 16 million hosts) - no longer issued

Class B for medium sized networks (65534 hosts)

Class C for small networks (254 hosts)Class D reserved for multicastClass E reserved

Breakdown of IP Address Classes

Class A 1.0.0.0 - 126.0.0.0Class B 129.0.0.0 - 191.255.0.0Class C 192.0.0.0 - 223.255.255.0Class D 224.0.0.0 - 239.255.255.0Class E 240.0.0.0 - 255.255.255.0

Host Addresses (1)

Each computer network interface is identified by a unique IP address

If a computer has more than one interface then it uses multiple IP addresses - one for each interface

Host Addresses (2)

Each packet has a destination address

All hosts on the network examine each broadcast packet

If addressed to them then the host processes it - otherwise it is ignored

Limit to the Number of Hosts

2 IP addresses are reserved in each type of class,and these are 0

e.g. 194.23.12.0 which is the address of the network itself

and255 which is the broadcast addresse.g. 194.23.12.255

Subnets

Each host must determine if a broadcast packet is for it

For a large number of hosts each host must process many packets

To maintain efficiency in a network the network is split into sub-networks (subnets)

The network is divided by sub-netting to create self-contained broadcast domains

Subnet Masks

A subnet mask is a bit mask that allows you to determine which parts of an IP address correspond to the :-

1) network address, and2) subnetWhen you AND an IP address and a

subnet mask the result is an address that contains everything but the hostid

Resolving IP Addresses

Decimal

Class B Class B netid hostid IP Address 131 .204 .27 .27

Binary

Class B Class B netid hostid1000 1100 . 1100 1100 . 0001 1011 . 0001 1011

Subnet Mask 255 .255 .255 .0 1111 1111 . 1111 1111 . 1111 1111 . 0000 0000

1000 1100 . 1100 1100 . 0001 1011 . 0000 0000

Subnet Number 131 .204 .27 .0

Network Utilities

netstatroutearpifconfigpingtraceroute

netstat

Netstat prints information about the Linux networking subsystem

The type of information printed is controlled by the option given

-a displays both listening and non-listening sockets

-r displays the routing table/bin/netstat

route

Used to add or delete to the kernels IP routing table.

Its primary use is to setup static routes to specific hosts or networks

Without options it displays the current contents of the routing table

/sbin/route

arp

Manipulates the kernels address resolution protocol (ARP) cache in various ways

The main use is to setup and clear an address mapping entry

/sbin/arp -a

ifconfig

ifconfig is used to configure the kernels resident network interfaces

it is used at boot time to set up the computers interfaces

If no arguments are specified it displays the status of the given interface only

If -a is specified it displays the status of all interfaces

/sbin/ifconfig

ping

Used to send packets to a destination hostname or IP address and display the response from the destination

Useful to detect intermittent or non-existent network connectivity

ping destination

traceroute

Traces the path of packets through the local network or Internet to the specified destination

The destination can either be a hostname or IP address

Useful as a network debugging aid/usr/sbin/traceroute destination

Questions?