Chapter 2The Internet Address Architecture

Table 2-1. Example IPv4 addresses written in dotted-quad and binary notation

Dotted-Quad Representation Binary Representation0.0.0.0 00000000 00000000 00000000 00000000

1.2.3.4 00000001 00000010 00000011 00000100

10.0.0.255 00001010 00000000 00000000 11111111

165.195.130.107 10100101 11000011 10000010 01101011

255.255.255.255 11111111 11111111 11111111 11111111

Expressing IPv6 Addresses• Leading zeros of a block need not be written

• 0:0:0:0:0:0:0:1 -> ::1.

• IPv4-mapped IPv6 address.10.0.0.1 -> ::ffff:10.0.0.1

• IPv4-compatible IPv6 address ::0102:f001 -> ::1.2.240.1.

Table 2-2. Examples of IPv6 addresses and their binary representationsHex Notation Binary Representation5f05:2000:80ad:5800:58:800:2023:1d71

0101111100000101 0010000000000000 1000000010101101 01011000000000000000000001011000 00001000000000000010000000100011 0001110101110001

::1 0000000000000000 0000000000000000 0000000000000000 00000000000000000000000000000000 00000000000000000000000000000000 0000000000000001

::1.2.240.1 or ::102:f001 0000000000000000 0000000000000000 0000000000000000 00000000000000000000000000000000 00000000000000000000000100000010 1111000000000001

• http://[2001:0db8:85a3:08d3:1319:8a2e:0370:7344]:443/

• refers to port number 443 on IPv6 host 2001:0db8:85a3:08d3:1319:8a2e:0370:7344 using the HTTP/TCP/IPv6 protocols.

IPv6 addresses

1. Leading zeros must be suppressed (e.g., 2001:0db8::0022 becomes 2001:db8::22).

2. The :: construct must be used to its maximum possible effect (most blocks of contiguous zeros suppressed) and can go beyond the 16-bit blocks. If multiple blocks contain equal-length runs of zeros, the first is replaced with ::.

3. The hexadecimal digits a through f should be represented in lowercase.

Examples

IPv6 Address Reduction

IPv6 Address Simplified Notation

FF01:0000:0000:0000:0000:0000:0000:0001 ff01::1

2031:0000:130F:0000:0000:09C0:876A:130B 2031:0:130f::9c0:876a:130b

0000:0000:0000:0000:0000:0000:0000:0001 ::1

FE80:0000:0000:5EFE:0192.0168.0001.0123 fe80::5efe:192.168.1.123

FE80: 0000:0000:0000:1585:4868:495F:D521 fe80::1585:4868:495f:d521

IPv4 addresses: original partitioning

The original (“classful”) IPv4 address space partitioning

Class Address Range

High-Order Bits Use

Fraction of Total Number of Nets

Number of Hosts

A 0.0.0.0–127.255.255.255

0 Unicast 1/2 128 16,777,216

B 128.0.0.0–191.255.255.255

10 Unicast 1/4 16,384 65,536

C 192.0.0.0–223.255.255.255

110 Unicast 1/8 2,097,152 256

D 224.0.0.0–239.255.255.255

1110 Multicast 1/16 N/A N/A

E 240.0.0.0–255.255.255.255

1111 Reserved 1/16 N/A N/A

Class B Address

Subnetting

IPv4 subnet mask examples in various formats

Dotted-Decimal Representation Shorthand (Prefix Length) Binary Representation128.0.0.0 /1 10000000 00000000

00000000 00000000

255.0.0.0 /8 11111111 00000000 00000000 00000000

255.192.0.0 /10 11111111 11000000 00000000 00000000

255.255.0.0 /16 11111111 11111111 00000000 00000000

255.255.254.0 /23 11111111 11111111 11111110 00000000

255.255.255.192 /27 11111111 11111111 11111111 11100000

255.255.255.255 /32 11111111 11111111 11111111 11111111

IPv6 subnet mask examples in various formats

Hex Notation Shorthand (Prefix Length) Binary Representationffff:ffff:ffff:ffff:: /64 1111111111111111

1111111111111111 1111111111111111 11111111111111110000000000000000 00000000000000000000000000000000 0000000000000000

ff00:: /8 1111111100000000 0000000000000000 0000000000000000 00000000000000000000000000000000 00000000000000000000000000000000 0000000000000000

Subnet ID (using AND)

Variable-Length Subnet Masks (VLSM)

Broadcast Address

Examples of Prefixes

Scaling Problems with IPv4

1. By 1994, over half of all class B addresses had already been allocated. It was expected that the class B address space would be exhausted by about 1995.

2. The 32-bit IPv4 address was thought to be inadequate to handle the size of the Internet anticipated by the early 2000s.

3. The number of entries in the global routing table (one per network number), about 65,000 in 1995, was growing. As more and more class A, B, and C routing entries appeared, routing performance suffered.

Aggregation

Aggregation: Example

Aggregation reduces the size of routing tables

Multicast

• Any Source Multicast (ASM)– Member can receive data from any participant

• Source Specific Multicast (SSM)– Member can receive data only from one specific source– More Secure– Less Control Traffic in the Internet

IPv4 Multicast Addresses

• Class D: 224.0.0.0 – 239.255.255.255– 28 free bits provides 2^28 addresses

• 224.0.0.0 - 224.0.0.255: local network control; never forwarded– 224.0.0.1 is for All hosts in the network

• 224.0.1.0 – 224.0.1.255: Internetwork control; forwarded normally– 224.0.1.1 used for Network Time Protocol

A typical small to medium size enterprise network

PA vs PI Addresses

Provider-aggregatable and provider-independent IPv4 addresses used in a hypothetical multihomed enterprise. Site operators tend to prefer using PI space if it is available. ISPs prefer PA space because it promotes prefix aggregation and reduces routing table size.

• Scenarios I: S uses PA address space (12.46.129.0/25) from P1’s block– Advertises at C and D to P1 and P2– P1 can aggregate to 12/8 block– P2 can’t aggregate– P2 will advertise 12.46.129.0/25– P2 will route most traffic to S

• (will attract the traffic for Site S due to longest prefix matching)

• Scenario II: S uses PI address space– More symmetric– Best metric route is naturally

chosen