Juniper IGP - CONFIGURATION GUIDE V11.1.X, Руководство по настройке

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IP implements a system of logical host addresses called IP addresses. The IP addresses
are used by the internetwork and higher layers to identify devices and to perform
internetwork routing. The Address Resolution Protocol (ARP) enables IP to identify
the physical (MAC) address that matches a given IP address. You can use ARP only
on Ethernet and bridged IP 1483 interfaces.
IP is used by all protocols in the layers above and below it to deliver data. This means
that all TCP/IP data flows through IP when it is sent and received, regardless of its
final destination.
Internet Addresses
Internet addressing uses a 32-bit address field. The bits in this address field are
numbered 0 to 31. The 32-bit address field consists of two parts: a network number
and a host number whose boundaries are defined based on the class of IP address.
Hosts attached to the same network must share a common prefix designating their
network number.
Four types of IP classes lend themselves to different network configurations,
depending on the desired ratio of networks to hosts. Figure 2 on page 8 shows the
format of IP address classes.
Figure 2: IP Address Classes
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Class A—The leading bit is set to 0, a 7-bit number, and a 24-bit local host
address. Up to 125 class A networks can be defined, with up to 16,777,214 hosts
per network.
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Class B—The two highest-order bits are set to 1 and 0, a 14-bit network number,
and a 16-bit local host address. Up to 16,382 class B networks can be defined,
with up to 65,534 hosts per network.
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Class C—The three leading bits are set to 1, 1, and 0, a 21-bit network number,
and an 8-bit local host address. Up to 2,097,152 class C networks can be defined,
with up to 254 hosts per network.
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Class D—The four highest-order bits are set to 1, 1, 1, and 0. Class D is used as
a multicast address.
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IP Addressing
JUNOSe 11.0.x IP, IPv6, and IGP Configuration Guide