IP Addressing

Lecture 11October 30, 2000

Background

The goal of Universal Service is such that all computers on all physically different networks can communicate.

Physical addresses allow communication between computers on one network.

A new level of abstraction must be be introduced for internet communication.

IP Addresses

An IP address is the next layer of abstraction. The IP address provides virtual addressing.

The address is software controlled, whereas the address for the network card is hardware based.

The IP addressing scheme is quite complex, and there have been many revisions to the IP scheme.

IP Addresses (cont.)

IP addressing allows for seamless integration amongst heterogeneous networks.

To send a packet, the destination address is the IP address of the computer, not the hardware address! This allows for communication across networks.

IP Addresses (cont.)

32 bits in length (IPv4) 64 bits in length (IPv6) Addresses are divided into a prefix and suffix The suffix is the host address The prefix is the network number

IP Classes

People commonly throw around terms like “Class C”, but it should really be termed “Class C address” or “Class C address space.”

Class A: 16777216 hosts! Class B: 65536 Class C: 256

IP Class Scheme

IP Class Scheme

From the previous figure, we see that the 32-bit address is split into 4 octets.

IP addresses are self identifying. If the first 4 bits of the first octet are

– 0xxx: Class A address– 10xx: Class B address– 110x: Class C address– 1110: Class D address (Multicast)– 1111: Class E address

Dotted Decimal

IP addresses are generally read in dotted decimal format.

0.0.0.0 through 255.255.255.255

Much better than reading: 10000001 00110100 00000110 00000000

Dotted Decimal with Classes

Class A: – 1 prefix octet (128 networks)– 3 suffix octets (16777216 hosts)

Class B: – 2 prefix octets (16384 networks)– 2 suffix octets (65536 hosts)

Class C:– 3 prefix octets (2097152 networks)– 1 suffix octet (256 hosts)

Address Space

Address Delegation

A central authority exists for IP address delegation.

In the US, it’s ARIN – American Registry for Internet Numbers (http://www.arin.net)

People just can’t arbitrarily use any IP network if their network is publicly accessible! That would lead to routing conflicts.

Address Delegation (cont.)

RFC 1597 – Private networks– 10.0.0.0 – 10.255.255.255 (Full Class A)– 172.16.0.0 – 172.31.255.255 (16 Class B’s)– 192.168.0.0 – 192.168.255.255 (Full Class B)

Special Addresses

Network address– Host 0 address for specific class type– 16.0.0.0 is the network address for the Class A

prefix of 16.– 130.111.0.0 is the network address for the Class B

prefix of 130.111.

Special Addresses (cont.)

Directed Broadcast Address (Network Broadcast Address)– A network suffix of all 1’s.– 16.255.255.255 is the directed broadcast address

for the Class A prefix of 16.– 130.111.255.255

Special Addresses (cont.)

Limited Broadcast Address– All 1’s in the entire address.– Limited broadcast address is restricted to the local

subnet.– 255.255.255.255

Special Addresses (cont.)

Loopback addresses– Loopbacks are used for testing. An IP looback is

application-level testing.– Any information sent to the loopback address is

never passed to the network segment. It is handled internally in the TCP/IP stack.

– 127.x.x.x

Special Addresses (cont.)

This computer’s address– If a computer doesn’t know what it’s own address is,

but needs to communicate to another machine, it designates the address of 0.0.0.0 for itself.

– Applications include DHCP, BOOTP

IP and Routers

IP and Routers (cont.)

We’ve seen from our project that routers do not necessarily have a single IP address.

Commonly have 2 (or more addresses)– IP address for the LAN interface– IP address for the WAN interface