On Mon, Jan 08, 2018 at 05:03:14PM +0000, Nicholas Warren wrote: > 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?
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.
