IPv6 summary notes
Largely taken from
Address length and format
The IPv6 address is 128 bits (i.e. 16 bytes) long and is written in 8 groups of 2 bytes in hexadecimal numbers separated by colons:
FDDD:F00D:CAFE:0000:0000:0000:0000:0001
Leading zeros of each block can be omitted, the above address can hence be written like this:
FDDD:F00D:CAFE:0:0:0:0:1
We can abbreviate whole blocks of zeros with :: and write:
FDDD:F00D:CAFE::1
This can only be done once in order to void ambiguity:
FF:0:0:0:1:0:0:1 (correct)
FF::1:0:0:1 (correct)
FF:0:0:0:1::1 (correct)
FF::1::1 (ambiguous, wrong)
Protocols
| Number | Protocol | Purpose |
|---|---|---|
| 58 | IPv6-ICMP | |
| 6 | TCP | Stateful - controls if packets arrived |
| 17 | UDP | Stateless - streaming applications etc. |
Ways to assign IPv6 addresses:
- Static - fixed address
- SLAAC - Stateless Address Autoconfiguration (host generates itself)
- DHCPv6 - Dynamic host configuration protocol (assigned by central server)
Scopes and special addresses
- GLOBAL - everything (i.e. the whole internet)
- UNIQUE LOCAL - everything in our LAN (behind the internet gateway)
- LINK LOCAL - (will never be routed, valid in one collision domain, i.e. on the same switch)
| range | Purpose |
|---|---|
| ::1/128 | Loopback address (localhost) |
| ::/128 | unspecified address |
| 2000::/3 | GLOBAL unicast (Internet) |
| FC00::/7 | Unique-local (LAN), note 1 |
| FE80::/10 | Link-Local Unicast (same switch) |
Notes:
- Unique local is actually FD00::/8 and is generally not recommended nor needed for small networks
- Always use the smallest possible scope for communication
- A host can have multiple addresses in different scopes
Subnetting
| bits (MSB) | Purpose |
| First 48 bits: | Network address |
| Next 16 bits: | Subnet address |
| Last 64 bits: | Device address |
Network+Subnet = Prefix
The following address
2003:1000:1000:1600:1234::1 would have the network 2003:1000:1000, the subnet 1600, so together the prefix 2003:1000:1000:1600. If the ISP provider delegated a part of the prefix to me (e.g. 2003:1000:1000:1600/56) then I could use the subnets from 2003:1000:1000:1600 to 2003:1000:1000:16FF for my own purposes (i.e. define 256 subnets in this example)
IPv6 addresses in URIs/URLs
Because IPv6 address notation uses colons to separate hextets, it is necessary to encase the address in square brackets in URIs. For example http://[2a00:1450:4001:82a::2004]. If you want to specify a port, you can do so as normal using a colon: http://[2a00:1450:4001:82a::2004]:80.