Re: multihomed linux box IP packets sent on wrong subnet

From: prg (rdgentry1_at_cablelynx.com)
Date: 04/23/05 

Date: 22 Apr 2005 20:51:19 -0700

jon bird wrote:
> Hi,
>
> Got a Linux box, fairly old SuSE 6,4 job with 3 network cards all of
> which are internal LANS - as follows:

Hope your Samba is a _lot_ more current than this Suse version. What
is it?

> Kernel IP routing table
> Destination Gateway Genmask Flags Metric Ref
Use
> Iface
> 192.168.2.0 * 255.255.255.0 U 0 0
0
> eth2
> 192.168.1.0 * 255.255.255.0 U 0 0
0
> eth1
> 192.168.0.0 * 255.255.255.0 U 0 0
0
> eth0
> loopback * 255.0.0.0 U 0 0
0
> lo
> default dsl-gw2.onastic 0.0.0.0 UG 0 0
0
> eth0
>
> Samba is configured to run on all 3 interfaces and register with a
WINS
> server (at 192.168.0.200 so subnet 0) however it only seems to
register
> the IP address for the 0 subnet. ...

Do you mean WINS only registers 192.168.0.99? It's common for
multi-homed machines to only successfully register the first request.
Is that what you think is happening? Errors? Logs?

> ... Having a look at the packet trace on
> subnet 0 what appears to be happening is that NBNS registration
packets
> are sent out as follows:
>
> source dest
> 192.168.0.99 -> 192.168.0.200 - Multi-homed registration (registers
> 0.99)
> 192.168.1.99 -> 192.168.0.200 - Multi-homed registration (registers
> 1.99)
> 192.168.2.99 -> 192.168.0.200 - Multi-homed registration (registers
> 2.99)
>
> So somehow it's putting out a source IP address on the wrong subnet -

Not sure what you mean here by "out ... on the wrong subnet". The
registrations are to a server on the 192.168.0.0 subnet, so naturally
the datagrams are routed that way.

> what I would expect is to see the 3 packets as follows:
>
> 192.168.0.99 -> 192.168.0.200 - Multi-homed registration (registers
> 0.99)
> 192.168.0.99 -> 192.168.0.200 - Multi-homed registration (registers
> 1.99)
> 192.168.0.99 -> 192.168.0.200 - Multi-homed registration (registers
> 2.99)

Why? What protocol are these packets (real and presumed)? What do you
think "source" means here? I assumed that they are the source IP of
the registration request, ie., the IP that is to be mapped to NetBios
name. It's been several years since I've looked at SMB packets. Is
that what these are?

> Can't believe this is a Samba problem ...

I'm not sure what the "problem" is that you're referencing, other than
that some packet fields hold IP values you do not expect? Are you
experiencing connection/browsing problems? Errors in logs? What?

> ... because having written some socket
> based software you don't ever specify your source IP address because
the
> OS does that so I'm confused as to why it does this.

I'm not sure what sockets programming has to do with the above
captures. Your Linux machine must register three IPs to what NetBios
name? A group name? Unique name(s)?

Multi-homed boxes often cause headaches with SMB networking. Are you
having any?

The most consice review of multi-home issues I know is:
1.4.3.1.4 Registering Multi-Homed Hosts
found in
"Implementing CIFS" in the Samba docs.
[q]
The annoying thing about multi-homed hosts in an NBT environment is
that they try to register their NetBIOS names on each interface, which
means multiple IP addresses per name. This is not a problem for group
names because group names map to several IP addresses anyway--that's
what NBT group names are all about. Unique names _are_ a problem
because, from the network's point of view, there is no difference
between a multi-homed host and multiple machines. To an NBNS, or to B
nodes on a local LAN, multiple registrations for the same name will
look like a name conflict.
[eq]

It's just not clear to me what the nature of your problem really is.
It could be me -- it's Friday;) Clarify?

You might also try the linux.samba list/ng (via Google if need be)
where the sharper Samba minds may reside.

If you think this _is_ a Suse config/setup problem, why? Just because
of the packets appearring on the 192.168.0.0 subnet? Where else would
they show up; that's where they are being sent?

Am I missing something?

regards,
prg

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