IP Headers and Address Classes
networkIPv4IP addressingCCNApacket header
Headers in the network layer
- >Version — four bits
- >Internet Header Length (IHL) — four bits
- >Differentiated Services Code Point (DSCP) — six bits
- >Explicit Congestion Notification (ECN) — two bits
- >Total Length — two bytes
- >Identification — two bytes
- >Flags — three bits
- >Fragment Offset — 13 bits
- >Time to Live (TTL) — one byte
- >Protocol — one byte
- >Header Checksum — two bytes
- >Source IP Address — four bytes
- >Destination IP Address — four bytes
- >One or more optional Options headers — variable length
IP addressing
- >Used to identify a network interface on a logical IP network.
- >IP addresses make it possible for any host to communicate with any other, regardless of location or physical network type.
- >An IPv4 address is composed of 32 bits (4 bytes) and has both a host portion, which identifies a specific host and a network portion, which identifies which network the host belongs to.
- >A subnet mask is used to differentiate what portion of the address is the host portion and what portion is the network.
Addressing classes
| IP Address Class | Class A | Class B | Class C |
|---|---|---|---|
| First bit values (binary) | 0 | 10 | 110 |
| First byte value (decimal) | 0-127 | 128-191 | 192-223 |
| Number of network identifier bits | 8 | 16 | 24 |
| Number of host identifier bits | 24 | 16 | 8 |
| Number of possible networks | 126 | 16,384 | 2,097,152 |
| Number of possible hosts | 16,777,214 | 65,534 | 254 |
There is also a Class D, which is used for multicast, and a Class E, which is used for experimental purposes.
Class and header recall5 blanks
A Class A address uses network bits, Class B uses and Class C uses . In the IPv4 header, TTL is byte and the source address is bytes.
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