1) IPv4

IPv4 address formats

Overview of common IPv4 subnets and masks

Mask Hosts  Usable Netmask          Hex Mask
/30  4      2  fffffffc  this is 1/64 of a Class C net
/29  8      6  fffffff8  this is 1/32 of a Class C net
/28  16     14  fffffff0  this is 1/16 of a Class C net
/27  32     30  ffffffe0  this is 1/8 of a Class C net
/26  64     62  ffffffc0  this is 1/4 of a Class C net
/24  256    254    ffffff00  this is a Class C net
/23  512    510    fffffe00  these are 2 Class C net
/22  1024   1022    fffffc00  these are 4 Class C net
/21  2048   2046    fffff800  these are 8 Class C net
/20  4096   4094    fffff000  these are 16 Class C net
/19  8192   8190    ffffe000  these are 32 Class C net
/18  16384  16382    ffffc000  these are 64 Class C net
/17  32768  32766    ffff8000  these are 128 Class C net
/16  65536  65534      ffff0000  these are 256 Class C net = Class B net

IPv4 Multicast addresses (

All multicast addresses can easily be recognized because they start with the bit pattern "1110".
Well known multicast addresses are listed at

Multicast addresses use a destination Mac-address in the range from
01:00:5E:00:00:00 to 01:00:5E:7F:FF:FF
The IP address maps directly to a Mac address. The lower 23 Bits of the multicast IPv4 Address are added to the lower 23 Bits of the Mac address. Example: would be send to the Mac address 01:00:5E:00:00:D2.
Ethernet frames with a value of 1 in the least-significant bit of the first octet of the destination address (logical AND with 01:00:00:00:00:00) are sent to all ports on the same switch unless the switch is VLAN aware and there is a VLAN tag between ethernet and IP layer. In other words the Ethernet address and the VLAN tag define together to which ports a packets is sent.

IPv4 special and private address ranges

Private address ranges are not routed on the Internet and can be freely allocated in any private network. NAT (network address translation) is required when connecting such a network to the Internet.

Private network addresses (RFC1597/RFC1918 addresses):
Special addresses:

2) IPv6 address types

Some of this information is taken from

Written by Guido Socher, MIT license