Multichannel mount failures to Samba depending on IP address (single channel works)

[Steve French]

On a loosely related note is there a way to configure the "interfaces"
line in smb.conf to be "everything that would show up by default AND
localhost too" (man smb.conf indicates that localhost and 127.0.0.1
are filtered out of the interface list by default - but of course it
works to mount non-multichannel to localhost)

On Tue, Nov 18, 2025 at 5:46 PM Steve French <smfrench at gmail.com> wrote:
>
> Saw an interesting multichannel failure scenario to Samba today:
>
> Samba server smb.conf has
>    "server multi channel support = yes"
> in the [global] section but it does not include a line for
> "interfaces" (uses the default)
>
> On localhost, mounting to current Samba from Linux (tried various
> versions of cifs.ko so does not appear to be a recent regression),
> noticed:
>
> 1) mount -t cifs //locahost/share /mnt                                    worked
> 2) mount -t cifs //localhost/share /mnt -o multichannel          failed
> 3) mount -t cifs //127.0.0.1/share /mnt                                   worked
> 4) mount -t cifs //127.0.0.1/share /mnt -o multichannel          failed
> 5) mount -t cifs //192.168.1.190/share /mnt -o multichannel   worked
>
> When mounting with "localhost" or "127.0.0.1" as the server name (non
> multichannel) note that it does not show [CONNECTED] in
> /proc/fs/cifs/DebugData
>
> Server interfaces: 3 Last updated: 3 seconds ago
> 1) Speed: 1Gbps
> Capabilities: None
> IPv4: 192.168.1.198
> Weight (cur,total): (0,1)
> Allocated channels: 0
>
> 2) Speed: 1Gbps
> Capabilities: None
> IPv6: 2603:8080:2200:13fc:c82b:b16f:52c8:2329
> Weight (cur,total): (0,1)
> Allocated channels: 0
>
> 3) Speed: 1Gbps
> Capabilities: None
> IPv6: 2603:8080:2200:13fc:5b60:a7d6:77d7:72cc
> Weight (cur,total): (0,1)
> Allocated channels: 0
>
> Note that when mounting to "192.168.1.190" (non-multichannel) it only
> shows two instead of three interfaces (not sure why it drops one of
> the IPv6 ones) but it does correctly show [CONNECTED]
>
> Server interfaces: 2 Last updated: 1 seconds ago
> 1) Speed: 1Gbps
> Capabilities: None
> IPv4: 192.168.1.198
> Weight (cur,total): (1,1)
> Allocated channels: 1
> [CONNECTED]
>
> 2) Speed: 1Gbps
> Capabilities: None
> IPv6: 2603:8080:2200:13fc:5b60:a7d6:77d7:72cc
> Weight (cur,total): (0,1)
> Allocated channels: 0
>
> The mount failures with multichannel to 127.0.0.1 are weird - the
> first negprot/sessionsetup/tcon works fine but the second negprot then
> sessionsetup fails with the server returning with
> "STATUS_SESSION_DELETED" which seems strange (since the session is
> valid, and channel one session setup worked fine).  Any idea if this
> is a Samba server bug?
>
> Presumably the workaround is to add an "interfaces" line to smb.conf
> to force it to return 127.0.0.1 as a valid interface, but this still
> seems like it could be a server bug.  And quite confusing to users (as
> "Resource temporarily unavailable" won't make sense to them since
> single channel works fine) Any thoughts?
>
> And log messages are unlikely to help the user figure out the server
> config (or bug) issue.
>
> [12421.964837] CIFS: Attempting to mount //localhost/test
> [12422.032199] CIFS: VFS: \\localhost Send error in SessSetup = -11
> [12422.032234] CIFS: VFS: failed to open extra channel on
> iface:192.168.1.198 rc=-11
> [12422.137163] CIFS: successfully opened new channel on
> iface:2603:8080:2200:13fc:c82b:b16f:52c8:2329
> [12422.137401] CIFS: VFS: reconnect tcon failed rc = -11
>
> Thoughts?
>
> --
> Thanks,
>
> Steve



-- 
Thanks,

Steve