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IP Addressing and Routing

Every device on a network needs an address so data can find it. This unit explains IPv4 and IPv6 addressing, the difference between public and private addresses, static versus dynamic assignment, how NAT stretches a limited supply of addresses, and how routers decide where packets go using static and dynamic routing. Static and dynamic routing is AHL content.

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IPv4 and IPv6 addressing

Two ways to address a deviceIPv4 · 32-bitDotted-decimal, four 8-bit octets (0-255)192.8 bits168.8 bits1.8 bits18 bits~4.3 billion addressesIPv6 · 128-bitEight groups of 4 hex digits, colon-split2001:0db8:85a3:0000:8 groups × 16 bits = 128 bits~340 undecillion addressesIPv6 wins: simpler header · far larger space · IPsec mandatoryIPv4: more complex header · IPsec optionalLoopback (talk to self): 127.0.0.1 (v4) · ::1 (v6)
  • IPv4 uses a 32-bit address written in dotted-decimal notation, for example 192.168.1.1. Each of the four octets is an 8-bit number from 0 to 255, giving about 4.3 billion addresses.
  • IPv6 uses a 128-bit address written as eight groups of four hexadecimal digits separated by colons, for example 2001:0db8:85a3:0000:0000:8a2e:0370:7334, giving about 340 undecillion addresses.
  • IPv6 has a simpler header, a vastly larger address space and mandatory IPsec support, whereas IPv4's header is more complex and IPsec is optional.
  • The loopback address, which a device uses to send traffic to itself, is 127.0.0.1 in IPv4 and ::1 in IPv6.

Check you've got it

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1. How many bits are used in an IPv4 address?

2. Which technology maps many private IP addresses onto a single public IP address to reduce the number of public addresses a network needs?

3. Which best describes a dynamic IP address?

4. Which statement correctly describes dynamic routing rather than static routing?

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