Nortel BCM50e, Configuration

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BCM50e Integrated Router Configuration - Advanced
Appendix G
IP subnetting
IP addressing
Routers route based on the network number. The router that delivers the data
packet to the correct destination host uses the host ID.
IP classes
An IP address is made up of four octets (eight bits), written in dotted decimal
notation, for example, 192.168.1.1. IP addresses are categorized into different
classes. The class of an address depends on the value of its first octet.
• Class A addresses have a 0 in the left-most bit. In a class A address, the first
octet is the network number and the remaining three octets make up the host
ID.
• Class B addresses have a 1 in the left-most bit and a 0 in the next left most bit.
In a class B address, the first two octets make up the network number and the
two remaining octets make up the host ID.
• Class C addresses begin (starting from the left) with 1 1 0. In a class C
address, the first three octets make up the network number and the last octet is
the host ID.
• Class D addresses begin with 1 1 1 0. Class D addresses are used for
multicasting. (There is also a class “E” address, which is reserved for future
use.)