Claimed incorrect MS behaviour wrt Source and Dest IP ...

Guy G. Sotomayor, Jr. ggs at
Fri Jun 5 14:18:29 GMT 1998

I saw exactly this behavior until I turned on packet filtering on my router
to block ports 137, 138 and 139.  I didn't experiment too much to determine
if it was only 1 of the ports but blocking all 3 did stop the ISDN line from
being brought up.

TTFN - Guy

Richard Sharpe wrote:
> Has anyone heard or seen the following before?  This sounds bogus, in that
> I have never noticed this behaviour, but perhaps I am missing something.
> >From Firewalls Digest:
> >Date: Thu, 4 Jun 1998 14:51:54 -0400
> >From: Laris Benkis <lbenkis at>
> >Subject: Interesting packet trace on inbound packets -Reply
> >
> >[To unsubscribe, send mail to majordomo at with
> >"unsubscribe firewalls" in the body of the message.]
> >- -
> >A snippet from a Usenet posting that may be relevant:
> >
> >>>We have several Win95 machines, WinNT 4.0 workstations and a couple
> >>>of WinNT 4.0 servers running on a LAN with TCP-IP. Some other
> >>>protocols are used but I am interested in TCP-IP.
> >>>
> >>>We also have a Securicor 3net Monet router which is our gateway
> >>> - it manages the ISDN line to our ISP.
> >>>
> >>>We have a problem on our network. Every so often (there is no
> >>>specific time delay between cycles) our ISDN line is brought up regularly,
> >>>and it seems that no one machine is causing this. Something is causing
> >>>the router to dial the ISDN line and keep it open for its minimum
> >>>time out of 45 seconds.
> >
> >The problem occurs when you use microsoft networking over TCP/IP.
> >
> >From what I can tell Microsoft basically 'got it wrong'...
> >
> >Packets which are destined for machines on the local network (hence
> >are delivered via their MAC addresses) have the destination IP
> >address field reversed.
> Well, they got lots of things wrong :-) But this? Seems unlikely!
> >The local destination machine has no problems with this as they
> >identify the packet via the MAC address grab it. Unfortunately most
> >IP routers sitting on the same subnet will recognise the reversed IP
> >address as external and try to route it.
> >
> >Ooops, up goes your ISDN link...
> Could it perhaps be a browser update or something like that?
> >depending on what the destination address is when it's reversed
> >the packet will get routed through the internet until it gets to the
> >actual (reversed) host or some router along the way says 'nope, go
> >away'. The latter usually happens and you will get a
> >ICMP destination unreachable type error returned.
> >
> >We found this problem during the development of our packet analyser
> >product (PacketBoy).
> >
> Regards
> -------
> Richard Sharpe, sharpe at, NIC-Handle:RJS96
> NS Computer Software and Services P/L,
> Ph: +61-8-8281-0063, FAX: +61-8-8250-2080,
> Samba, Linux, Apache, Digital UNIX, AIX, Netscape, Stronghold, C, ...

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