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Date: Fri, 07 Nov 2014 13:54:19 +0100 (CET)
Message-Id: <20141107.135419.41700845.sthaug@nethelp.no>
To: guru@unixarea.de
Subject: Re: IPv6 link-local addr && %interfacename
From: sthaug@nethelp.no
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> it does not work with the link-local addr:
> 
> $ ./ipv6-client fe80::20c:29ff:fe47:a38d    
> host: fe80::20c:29ff:fe47:a38d
> ssh: connect: Network is unreachable

This is expected.

> but with appending %em0 it does work:
> 
> $ ./ipv6-client fe80::20c:29ff:fe47:a38d%em0
> host: fe80::20c:29ff:fe47:a38d%em0
> read: SSH-2.0-OpenSSH_6.6.1_hpn13v11 FreeBSD-20140420
> 
> My question is: What does the %em0 mean in the IPv6 addr and why it is
> not working without it?

A link-local address is *link-local* and needs the interface specifier
to be unique. The same address can be configured on several interfaces.

In principle you could use fe80::1 as the link local address for *all*
of your Ethernet interfaces...

Steinar Haug, Nethelp consulting, sthaug@nethelp.no