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Date:      Mon, 26 Apr 2021 15:12:38 +0000
From:      "Poul-Henning Kamp" <phk@phk.freebsd.dk>
To:        "Rodney W. Grimes" <freebsd-rwg@gndrsh.dnsmgr.net>
Cc:        freebsd-hackers@freebsd.org
Subject:   Re: Are there any RFCs for address selection for IPv4
Message-ID:  <76798.1619449958@critter.freebsd.dk>
In-Reply-To: <202104261456.13QEuXEa098219@gndrsh.dnsmgr.net>
References:  <202104261456.13QEuXEa098219@gndrsh.dnsmgr.net>

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--------
Rodney W. Grimes writes:

> > It is OK to have a LL as next-hop.
> > 
> > It is not OK to send a packet with dst=LL to any next-hop.
>
> No, that is explicity forbidden:
> RFC 3927 at 2.7 paragraph 2:
>
>    An IPv4 packet whose source and/or destination address is in the
>    169.254/16 prefix MUST NOT be sent to any router for forwarding, and
>    any network device receiving such a packet MUST NOT forward it,
>    regardless of the TTL in the IPv4 header.

Right the second criteria should be:

It is not OK to send a packet with src=LL or dst=LL to any next-hop.

But it /is/ OK to have a next-hop router on a LL, but it is no use,
unless your host has another interface with a "real" IP on it.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.



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