Ethan Banks Not writing about IT.

OECG – Chapter 4 Definitions

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subnet – some portion of a larger network. Subnets can be classful or classless.

prefix – the portion of a classless IP network that comes before the host. Often noted with / notation, where the number following the slash represents the number of bits that makes up the subnet.

classful IP addressing – defined by RFC ????. A scheme whereby IP blocks are divided into classes, with 1-126 being /8’s (class A), 128 – 192 being /16’s (class B), and 193 – 223 being /24’s (class C). Class D = 224 – 239 and Class E = 240 – 255. Class D & E are special use.
CIDR – classless interdomain routing. Having a router ignore the classful boundaries through the use of subnetting and supernetting.

NAT – network address translation. RFC 1631. Translating one IP address into another, often for the purpose of turning a private IP address into a public address that is Internet routable.

IPv6 – a 128-bit binary address, represented by 8 quartets of hexadecimal numbers separated by colons. Designed to make sure that we never, ever run out of IP addresses again. Ever.

IPv4 – a 32-bit binary address, represented by 4 decimal numbers separated by dots.

subnet broadcast address – an IP address in which the host portion is all “1’s”, signifying a broadcast.

subnet number – the “network” address of a subnet range, in which the host portion is all “0’s”.

subnet zero – When subnetting a class A, B or C address, this is the subnet for which all the subnet bits are binary “0’s”.

broadcast subnet – Opposite of subnet zero. When all subnet bits are “1’s”.
subnet mask – A number that helps us define what portion is the subnet, and what portion is the host portion of an IP address. 1’s = subnet, 0’s = host.

private addresses – defined in RFC1918 for use in private enterprise. Anyone can use them. Not Internet routable. 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16.

aggregatable global unicast address – an IPv6 address that’s Internet routable.

SLSM – static length subnet mask. Chopping up a classful network such that every subnet is the same size.

VLSM – variable length subnet mask. Chopping up a classful network into subnets of different sizes.

Inside Local address – in NAT, this is the address on the logical inside of the router before NAT takes place.

Inside Global address – in NAT, this is the address on the logical inside of the router after NAT takes place.

Outside Local address – in NAT, this is the address on the logical outside of the network after NAT takes place.

Outside Global address – in NAT, this is the address on the logical outside of the router before NAT takes place.

PAT – port address translation. In NAT, it’s when a router translates not only the address but also the ports themselves. This allows you to hide many local addresses behind a single global outside address.

overloading – It’s PAT!

quartet – one part of an IPv6 address. And a great way to hear capable men sing harmony gospel music.

EUI-64 – the standard format for the host portion of an IPv6 address, consisting of 24-bits of the first half of the MAC, 16-bits of FFFE, and 24 more bits of the last half of the MAC.

dual stack – a device running both IPv4 and IPv6

global routing prefix – the portion of a global IPv6 address that comes before the subnet and host portion. Designed to be summarizable. First 48 bits.

subnet ID – the 16 bits that come after the global routing prefix, but before the 64-bit host.

interface ID – the 64 bits at the end of an IPv6 address, used to uniquely define the host.

By Ethan Banks
Ethan Banks Not writing about IT.

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