Site-Local/Unique-Local Addressing (IPv6)

William Herrin bill at
Mon Jan 8 18:12:33 UTC 2018

On Mon, Jan 8, 2018 at 12:03 PM, Nicholas Warren <nwarren at>

> 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?

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

William Herrin ................ herrin at  bill at
Dirtside Systems ......... Web: <>

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