Windows, TCP, and a Compatible Router HELP!
Weston Houghton/Unsane
dedicated ISDN line connected to a local internet service provider. This
connection is then brought into our work by a Compatible Systems
RiscRouter. Our network consists of mainly PowerMac machines, and is
growing rapidly with Windows 95 and Win NT machines. Our Win 95, Win NT,
and PowerMacs with OpenTransport all seem to have a problem resegmenting
TCP packets. If we try to reach many sites (via ftp, www, all methods) we
can get small packets of information, but anything large (say >10k) such
as images and files, just don't make it.
Yet, our PowerMacs without OpenTransport do not have any problems (I don't
know about Win 3.11, as we no longer have any machines with 3.11). We had
originally thought that perhaps the TCP stack in Windows was no good, but
now it is happening on our OT Macs as well. Somehow I'm beginning to doubt
that it is the TCP stack. As well as the fact that an OT mac operates fine
via a 28.8 modem PPP connection from home. I'm looking for any thoughts on
what could be causing our problems.
Oh, yeah, most of the sites we cannot reach are in the silicon valley area
I believe (Sun, Macromedia, etc...) Any thoughts would be greatly
appreciated, as well as if you could possibly email them to me to make
sure that I get them.
Weston Houghton
whou...@medialab.com
Chris Baker
If your routers are connected via PPP, your MTU size is probably 1600 bytes and
therefore the routers will have to fragment the data. This may be were your
problem lies.
See if you can change the MTU size on your hosts as a test.
Chris Baker
http://www.xyplex.com
Brian R. Bertan
It may be the combination of a large host MTU with a smaller router MTU. NT does
runs with the IP Don't Fragment bit set. If your host MTU exceeds your router
MTU, the router must return ICMP message "Fragmentation required - DF set".
Some routers do not, and data transfer simply fails as you describe.
Microsoft recommends tweaking on of the following value parameters in the
registry:
EnablePMTUDiscovery
EnablePMTUBHDiscovery
TCPWindowSize.
This is described in detail in Technet article Q127023. All have performance
implications. Also, reducing the MTU size on the host to below the router value
will also help.
--
Brian Bertan
b.be...@ieee.org
http://www.li.net/~brb
Brian R. Bertan
Weston Houghton/Unsane wrote:
>
> I'm looking for any help or ideas on our system at work. We have a
> dedicated ISDN line connected to a local internet service provider. This
> connection is then brought into our work by a Compatible Systems
> RiscRouter. Our network consists of mainly PowerMac machines, and is
> growing rapidly with Windows 95 and Win NT machines. Our Win 95, Win NT,
> and PowerMacs with OpenTransport all seem to have a problem resegmenting
> TCP packets. If we try to reach many sites (via ftp, www, all methods) we
> can get small packets of information, but anything large (say >10k) such
> as images and files, just don't make it.
>
> Yet, our PowerMacs without OpenTransport do not have any problems (I don't
> know about Win 3.11, as we no longer have any machines with 3.11). We had
> originally thought that perhaps the TCP stack in Windows was no good, but
> now it is happening on our OT Macs as well. Somehow I'm beginning to doubt
> that it is the TCP stack. As well as the fact that an OT mac operates fine
> via a 28.8 modem PPP connection from home. I'm looking for any thoughts on
> what could be causing our problems.
>
> Oh, yeah, most of the sites we cannot reach are in the silicon valley area
> I believe (Sun, Macromedia, etc...) Any thoughts would be greatly
> appreciated, as well as if you could possibly email them to me to make
> sure that I get them.
>
> Weston Houghton
> whou...@medialab.comIt may be the combination of a large host MTU with a smaller router MTU. NT does