IS-IS and IPv6 LLA next-hop - just Arista, or everyone?

Saku Ytti saku at
Tue May 4 15:20:17 UTC 2021

On Tue, 4 May 2021 at 18:15, Adam Thompson <athompson at> wrote:

Hey Adam,

> I don't see any rationale in RFC 5308 for why the HELLO packet may only contain the LLA - does anyone know/remember why?  (I'm hoping that understanding the rationale will make this an easier pill to swallow.)  Obviously this behaviour/requirement is net-new to the IPv6 TLVs, as there's no LLA-cognate in IPv4 (APIPA doesn't count).  There is in OSI, I think, but I'm still too sane to read those docs.

IPv4 link local is 169.254/16, you may have seen them in Windows.

> It makes sense that you would not want LLAs in LSPs, only GUAs, but does that imply that you must use either ULAs or GUAs in order to establish IPv6 routes in IS-IS, in an IPv6 environment?  That makes about as much sense to me as forcing LLAs for next-hops.

The list may benefit from the context you have, it is not obvious to
me why you'd want anything but LLA.


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