Intel ER8100STUS - Express 8100 Router, Reference Manual

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Reference.bok : Chapter08 48 Wed Apr 22 10:58:08 1998
48
IP Concept
IP Routing
Frame types and type
codes
IP Frame types are described in Appendix D “IP Frame Formats”, p. 126 . The
following Ethernet type codes are used in IP environment, also see Appendix C
“Ethernet Type Codes”, p. 121 :
IP Addresses Structure
Address notation
IP addresses are 32-bit numbers. The most common notation for IP addresses di-
vides the 32-bit address into four 8-bit fields and specifies the value of each field
as a decimal number (from
0
to
255
, each representing an 8-bit octet). Each num-
ber field is separated by a period (for example 14.0.65.3). This is called the dotted
decimal notation.
Network numbers
The 32-bit address field consists of a network and a local host part. They are di-
vided into different address classes which differ in the number of bits allocated
to the network part and the hosts part (local address) of the address. The value of
the first octet in the IP address defines the address class (classes A, B, C, D).
Class A address
The class A address comprises a 7-bit network number and a 24-bit local address.
The highest order bit is set to
0
. This allows 126 class A networks.
Class B address
The class B address comprises a 14-bit network number and a 16-bit local ad-
dress. The two highest-order bits are set to
1 0
. This allows 16,256 class B net-
works.
Type field Description
0800 DOD Internet Protocol (IP)
0806 Address Resolution Protocol
1 2 3 4
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
0 Network Local Address
1 2 3 4
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
10 Network Local Address