Chapter 2 The Internet Address Architecture

Table 2-1. Example IPv4 addresses written in dotted-quad and binary notation Dotted-Quad RepresentationBinary Representation

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 > ::ffff: IPv4-compatible IPv6 address ::0102:f001 -> ::

Table 2-2. Examples of IPv6 addresses and their binary representations Hex NotationBinary Representation 5f05:2000:80ad:5800:58:800:2023:1d :: :: or ::102:f

:7344]:443/ :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 AddressSimplified Notation FF01:0000:0000:0000:0000:0000:0000:0001ff01::1 2031:0000:130F:0000:0000:09C0:876A:130B2031:0:130f::9c0:876a:130b 0000:0000:0000:0000:0000:0000:0000:0001::1 FE80:0000:0000:5EFE: fe80::5efe: FE80: 0000:0000:0000:1585:4868:495F:D521fe80::1585:4868:495f:d521

IPv4 addresses: original partitioning

The original (“classful”) IPv4 address space partitioning Clas sAddress Range High-Order BitsUse Fraction of TotalNumber of Nets Number of Hosts A – Unicast1/212816,777,216 B – Unicast1/416,38465,536 C – Unicast1/82,097, D – Multicast1/16N/A E – Reserved1/16N/A

Class B Address

Subnetting

IPv4 subnet mask examples in various formats Dotted-Decimal RepresentationShorthand (Prefix Length)Binary Representation / / / / / / /

IPv6 subnet mask examples in various formats Hex NotationShorthand (Prefix Length)Binary Representation ffff:ffff:ffff:ffff::/ ff00::/

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 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: – – 28 free bits provides 2^28 addresses : local network control; never forwarded – is for All hosts in the network – : Internetwork control; forwarded normally – 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 ( /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 /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