IPv6 Global Address, Unicast Local Address and Link Local Address

[FaadiKhan]

IPv6 Addresses are divided into 3 categories

1. Unicast

2. Multicast

3. Anycast

Unicast addresses are further divided into three sub categories based on the scope:

a. Global Address

b. Unicast Local Address

c. Link Local Address

What is the basic difference between these three sub categories and how Unicast Local address can be differentiated from Link Local Address? Also please explain the basic implementation of EUI-64 standard.

[Seb Rupik]

Hi there,
Global Unicast Address:- The three most signicafnt bits are set to 001. Equivalny to IPv4 public address, therefore it is globally identifaable and unqiuely addressable.

Unicast Local Address:- Prefixed with FC00::/7 and a radomly generated 40-bit GlobalID to ensure unqiueness and provide no releation to a global address allocation. Exterior routing protocals oprtaing between adinstravice doains ust be configred to drop prefixed within the FC00::/7 range to ensure the address are only routed within an AD.

Link Local Address:- Prefixed with FE80::/64, provdes addressing for comunication within a network segment. As such there is no gauarentee the adress is unique outside of the segment. All IPv6 interfaces will have a link-local addresss. IPv6 routes must not forward packets with link-local source or destination addresses.

Take as look at the relevant IETF refences for the best source of inforation on these subjects:

Global Unicast Address - https://tools.ietf.org/html/rfc3587
Unicast Local Address - https://tools.ietf.org/html/rfc4193
Link-Local Address - https://tools.ietf.org/html/rfc4291#section-2.5.6
EUI-64 - https://tools.ietf.org/html/rfc4291#section-2.5.1

cheers,
Seb.

[FaadiKhan]

Thank you Seb.

Just to confirm one thing, prefix of /10 or /64 is used for link-local addresses ??

[Seb Rupik · Accepted solution]

Technially it is a /10 , but for deployments use a /64 ; SLAAC for example requires a prefix of that length. 

Also see @Peter Paluch reply here: https://community.cisco.com/t5/ipv6/ipv6-link-local-address-space/m-p/3411919

cheers,

Seb.