Ip Address Notation - Cisco ASR 5000 Series Administration Manual

System Operation and Configuration

IP Address Notation

When configuring a port interface via the CLI you must enter an IP address. The CLI always accepts an IPv4
address, and in some cases accepts an IPv6 address as an alternative.
For some configuration commands, the CLI also accepts CIDR notation. Always view the online Help for the
CLI command to verify acceptable forms of IP address notation.
IPv4 Dotted-Decimal Notation
An Internet Protocol Version 4 (IPv4) address consists of 32 bits divided into four octets. These four octets
are written in decimal numbers, ranging from 0 to 255, and are concatenated as a character string with full
stop delimiters (dots) between each number.
For example, the address of the loopback interface, usually assigned the host name localhost, is 127.0.0.1. It
consists of the four binary octets 01111111, 00000000, 00000000, and 00000001, forming the full 32-bit
address.
IPv4 allows 32 bits for an Internet Protocol address and can, therefore, support 2
IPv6 Colon-Separated-Hexadecimal Notation
An Internet Protocol Version 6 (IPv6) address has two logical parts: a 64-bit network prefix, and a 64-bit host
address part. An IPv6 address is represented by eight groups of 16-bit hexadecimal values separated by colons
(:).
A typical example of a full IPv6 address is 2001:0db8:85a3:0000:0000:8a2e:0370:7334
The hexadecimal digits are case-insensitive.
The 128-bit IPv6 address can be abbreviated with the following rules:
• Leading zeroes within a 16-bit value may be omitted. For example, the address
• One group of consecutive zeroes within an address may be replaced by a double colon. For example,
IPv6 allows 128 bits for an Internet Protocol address and can support 2
(340,282,366,920,938,000,000,000,000,000,000,000,000) internet addresses.
CIDR Notation
Classless Inter-Domain Routing (CIDR) notation is a compact specification of an Internet Protocol address
and its associated routing prefix. It is used for both IPv4 and IPv6 addressing in networking architectures.
CIDR is a bitwise, prefix-based standard for the interpretation of IP addresses. It facilitates routing by allowing
blocks of addresses to be grouped into single routing table entries. These groups (CIDR blocks) share an initial
sequence of bits in the binary representation of their IP addresses.
fe80:0000:0000:0000:0202:b3ff:fe1e:8329 may be written as fe80:0:0:0:202:b3ff:fe1e:8329
fe80:0:0:0:202:b3ff:fe1e:8329 becomes fe80::202:b3ff:fe1e:8329
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ASR 5500 System Administration Guide, StarOS Release 21.4
IP Address Notation
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(4,294,967,296) addresses.
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