Network, IP address and VLAN 101

I do not usually deal with VLANs, IPv4/6 … but when I do, maybe I can remember some of this.

IPv6 101

What’s the deal with the ‘:’ in IPv6 ?

IPv6’s 128 bits are represented as 8 groups of 4 hex chars, separated by :. Consecutive : denote 1 or more groups with value 0. :: can only appear once (otherwise ambiguous).

0000:0000:0000:0000:0000:0001:0002:0003 => ::1:2:3
fe80:0001:0000:0000:dead:beef:dead:0000 => fe80:1::dead:beef:0

Network and subnet

/ notation is used to denote the network prefix.

fe80::/64 denotes all addresses like fe80:0:0:0:X:Y:W:Z

Standard dictates maximum prefix length of /64 (otherwise stateless configuration protocols break).

This allows a subnet address to be unique (although not mandatory) across the whole internet !

MAC, EUI-48, EUI-64, wtf ?!

MAC = EUI-48
You can transform EUI-48 into EUI-64

de:ad:aa:cc:be:ef => dead:aa + ff:fe + cc:beef
Invert bit at index 6 (start from left)
dead:aaff:fecc:beef => 11011110 ad:aaff:ccfe:beef => 11011100 ad:aaff:ccfe:beef => dcad:aaff:ccfe:beef
EUI-64 transformation is a stateless way to obtain an unique IP within a subnet

Special IP ranges

Multicast address semantics

Stateless auto configuration in IPv6 is based on well known multicast groups. A multicast address can be decomposed as follows :

ff<4-bit flag><4-bit scope><16-bit reserved><64-bit network id><32-bit group id>

Where scope denotes the part of the network addressed.

0x1 interface local loopback
0x2 link local (L2)
0x8 organisation local
0xe global internet

Some well known link local well known multicast groups :

All nodes in link : ff02::1
All routers in link : ff02::2