openssh bugs - Nov 2023 - [Bug 3631] New: ssh fe80 -b invalid argument failure

https://bugzilla.mindrot.org/show_bug.cgi?id=3631

            Bug ID: 3631
           Summary: ssh fe80 -b invalid argument failure
           Product: Portable OpenSSH
           Version: 8.9p1
          Hardware: Other
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P5
         Component: ssh
          Assignee: unassigned-bugs at mindrot.org
          Reporter: rainer.burki at asdfg.it

The ssh client does not allow to bind to a local fe80 address if the
address is specified with the option -b <ipv6-addr>. It though works
when specifying it with -B <interface>

The following is from a ubuntu 22.04 trying to connect to another
ubuntu 22.04. 

We will use the local eth0 inet6 address fe80::250:56ff:fe00:243d for
binding:

vmadmin at li224-vmLS1:~$ ip add
...
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel
state UP group default qlen 1000
    link/ether 00:50:56:00:24:3d brd ff:ff:ff:ff:ff:ff
    altname enp3s0
    altname ens160
    inet 192.168.110.61/24 brd 192.168.110.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::250:56ff:fe00:243d/64 scope link 
       valid_lft forever preferred_lft forever
vmadmin at li224-vmLS1:~$ ssh -B eth0 fe80::250:56ff:fe00:241e 
vmadmin at fe80::250:56ff:fe00:241e's password: 
<snip, works>

Same again with -b:

vmadmin at li224-vmLS1:~$ ssh -b fe80::250:56ff:fe00:243d
fe80::250:56ff:fe00:241e 
bind fe80::250:56ff:fe00:243d: Invalid argument
ssh: connect to host fe80::250:56ff:fe00:241e port 22: failure
vmadmin at li224-vmLS1:~$

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |djm at mindrot.org

--- Comment #1 from Damien Miller <djm at mindrot.org> ---
These are interface-scoped addresses, and so only make sense when you
specify the interface along with the address. The output of `ip addr
ls` doesn't make this clear unfortunately.

ssh -b fe80::250:56ff:fe00:243d%etho fe80::250:56ff:fe00:241e 

should do what you want

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https://bugzilla.mindrot.org/show_bug.cgi?id=3631

--- Comment #2 from Damien Miller <djm at mindrot.org> ---
(In reply to Damien Miller from comment #1)
> ssh -b fe80::250:56ff:fe00:243d%etho fe80::250:56ff:fe00:241e
err, make that

ssh -b fe80::250:56ff:fe00:243d%eth0 fe80::250:56ff:fe00:241e

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Rainer <rainer.burki at asdfg.it> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |WORKSFORME
             Status|NEW                         |RESOLVED

--- Comment #3 from Rainer <rainer.burki at asdfg.it> ---
(In reply to Damien Miller from comment #2)
> (In reply to Damien Miller from comment #1)
> > ssh -b fe80::250:56ff:fe00:243d%etho fe80::250:56ff:fe00:241e
> 
> err, make that
> 
> ssh -b fe80::250:56ff:fe00:243d%eth0 fe80::250:56ff:fe00:241e
Okay, this works, thanks.

If someone arrives here through a search:
In most cases the short form is sufficient
ssh <fe80-dest-ip>%eth0

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