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IP address

An internet protocol address (IP address) is a numerical label such as 192.0.2.1 that is connected to a computer network that uses the Internet Protocol for communcation. An IP address serves two main functions: computer network interface identification and location addressing.
— Wikipedia

IP address is: unique address, used to identify each computer on the internet.

IP address provided by: ICANN, and ensure that 2 organizations don’t use the same address.

IPv4 format, 32-bit

IP address consist of: 4 octets and 3 periods: nnn.nnn.nnn.nnn nnn - is octet, decimal value 0-255 (256 total values). . - is period

  • 1.2.3.4
  • 01.102.103.104

IPv6 format, 128-bit

IPv6 can have 2 formats:

  • normal, pure IPv6 format FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF, FFFF - is segment, total 8 segments, hexadecimal value 0-FFFF, separated by colons IPv6 support short notations - no leading zeros The following list shows examples of valid IPv6 (Normal) addresses:
    • 2001 : db8: 3333 : 4444 : 5555 : 6666 : 7777 : 8888
    • 2001 : db8 : 3333 : 4444 : CCCC : DDDD : EEEE : FFFF
    • : : (implies all 8 segments are zero)
    • 2001: db8: : (implies that the last six segments are zero)
    • : : 1234 : 5678 (implies that the first six segments are zero)
    • 2001 : db8: : 1234 : 5678 (implies that the middle four segments are zero)
    • 2001:0db8:0001:0000:0000:0ab9:C0A8:0102 (This can be compressed to eliminate leading zeros, as follows: 2001:db8:1::ab9:C0A8:102)
  • dual, IPv6 + IPv4 format Combines IPv6 and IPv4 address, and has this format: FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:nnn.nnn.nnn.nnn

The following list shows examples of valid IPv6 (Dual) addresses:

  • 2001 : db8: 3333 : 4444 : 5555 : 6666 : 1 . 2 . 3 . 4
  • : : 11 . 22 . 33 . 44 (implies all six IPv6 segments are zero)
  • 2001 : db8: : 123 . 123 . 123 . 123 (implies that the last four IPv6 segments are zero)
  • : : 1234 : 5678 : 91 . 123 . 4 . 56 (implies that the first four IPv6 segments are zero)
  • : : 1234 : 5678 : 1 . 2 . 3 . 4 (implies that the first four IPv6 segments are zero)
  • 2001 : db8: : 1234 : 5678 : 5 . 6 . 7 . 8 (implies that the middle two IPv6 segments are zero)

IP ranges - CIDR

CIDR - Classless Inter-Domain Routing, was adopted to simplify the addressing scheme. In CIDR each subnet has own subnet mask, and the subnet mask is part of the IP address.

IPv4 CIDR blocks

Address formatDifference to last addressMaskAddressTypical use
a.b.c.d/32+0.0.0.0255.255.255.2551Host route
a.b.c.d/31+0.0.0.1255.255.255.2542Point-to-point links (RFC 3021)
a.b.c.d/30+0.0.0.3255.255.255.2524Point-to-point links (glue network)
a.b.c.d/29+0.0.0.7255.255.255.2488Smallest multi-host network
a.b.c.d/28+0.0.0.15255.255.255.24016Small LAN
a.b.c.d/27+0.0.0.31255.255.255.22432
a.b.c.d/26+0.0.0.63255.255.255.19264
a.b.c.d/25+0.0.0.127255.255.255.128128Large LAN
a.b.c.0/24+0.0.0.255255.255.255.0256
a.b.c.0/23+0.0.1.255255.255.254.0512
a.b.c.0/22+0.0.3.255255.255.252.01024Small business
a.b.c.0/21+0.0.7.255255.255.248.02048Small ISP/ large business
a.b.c.0/20+0.0.15.255255.255.240.04096
a.b.c.0/19+0.0.31.255255.255.224.08192ISP/ large business
a.b.c.0/18+0.0.63.255255.255.192.016384
a.b.c.0/17+0.0.127.255255.255.128.032768
a.b.0.0/16+0.0.255.255255.255.0.065536
a.b.0.0/15+0.1.255.255255.254.0.0131072
a.b.0.0/14+0.3.255.255255.252.0.0262144
a.b.0.0/13+0.7.255.255255.248.0.0524288
a.b.0.0/12+0.15.255.255255.240.0.01048576
a.b.0.0/11+0.31.255.255255.224.0.02097152
a.b.0.0/10+0.63.255.255255.192.0.04194304
a.b.0.0/9+0.127.255.255255.128.0.08388608
a.0.0.0/8+0.255.255.255255.0.0.016777216Largest IANA block allocation
a.0.0.0/7+1.255.255.255254.0.0.033554432
a.0.0.0/6+3.255.255.255252.0.0.067108864
a.0.0.0/5+7.255.255.255248.0.0.0134217728
a.0.0.0/4+15.255.255.255240.0.0.0268435456
a.0.0.0/3+31.255.255.255224.0.0.0536870912
a.0.0.0/2+63.255.255.255192.0.0.01073741824
a.0.0.0/1+127.255.255.255128.0.0.02147483648
0.0.0.0/0+255.255.255.2550.0.0.04294967296Entire IPv4 Internet

IP utility

Universal network utility, which can be used to many network tasks.

  • Check network interfaces: ip [-brief] link or ip [-brief] address
  • Find neighbors: ip neighbor
  • Up/down network interface: ip link set dev eth0 up or ip link set dev eth0 down

Online tools

IP reputation check

Backlinks

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