Information Technology Reference
In-Depth Information
If one or more fragments are lost, the entire packet must be retransmitted. Retransmission is the
responsibility of the higher-layer protocol (such as TCP). Also, the flags field in the IP header
might be set to not fragment the packet. If set to not fragment, the packet is discarded if the
outgoing MTU is smaller than the packet.
IP Addressing
This section covers the IP address classes, network subnets, and address assignments. The
CCIE candidate must be an expert in handling IP addresses.
IP addresses assign a unique logical number to a network device. The number is 32-bits long.
To make the number easier to read, you use the dotted decimal format. The bits are combined
into four 8-bit groups, each converted into decimal numbers that are separated with dots. The
following example shows an IP address in binary and decimal formats:
Binary IP address: 00110000010101011001001000001010
Grouping into four octets: 00110000 01010101 10010010 00001010
Convert each octet into decimal:
00110000 = 48
01010101 = 85
10010010 = 146
00001010 = 10
The IP address is: 48.85.146.10
IP Address Classes
IP addresses are divided into five classes. The most significant bits of the first octet help
determine the address class of the IP address. Table 6-2 shows the high-order bits of each
IP address class.
High-Order Bits of IP Address Classes
Table 6-2
Address Class
High Order Bits
A
0xxxxxxx
B
10xxxxxx
C
110xxxxx
D
1110xxxx
E
1111xxxx
x can be either 1 or 0, regardless of the address class.
The IP Classes A, B, and C are set aside for unicast addresses. Class D is for multicast
addresses; Class E is reserved for experimental use.
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