Site-Local/Unique-Local Addressing (IPv6)

Layman here, I was reviewing RFCs for a local address for IPv6. I came across two RFCs that seem interesting.

3879 Which deprecates Site Local Addresses.
4193 Which seems to add Unique Local Addresses.

What is the main difference here? Why was this standard removed then added back?

Nich Warren

Site Local Addresses are/were Site Scope, similar to how Link-Local are Link-Local Scope and others are Global Scope.

ULA are Global Scope--but that doesn't mean they are globally routable.

The problem with Scopes being built-in to the addressing model is that software has to be coded to treat different scopes differently. It is hard enough to deal with Link-Local scope, and it was deemed too hard to deal with yet another scope--Site Local. For an example of the pain, try using Link-Local addresses in a web browser, or even with "ping" on the command line.

Hi Nich,

ULA is the IPv6 equivalent to RFC1918. If assigned as instructed
(randomly), it can be used to build multi-organziation private networks
with a relatively low risk of collision, a property lacking in RFC1918.
Other than that, it's exactly the same as RFC 1918.

Site local is deprecated. As explained in the RFC, the concept of a "site"
could not be usefully defined for the purpose of private addressing. You
can safely ignore it.

Bill Herrin