IP Masq and no NNTP / slow Web problem SOLVED

IP Masq and no NNTP / slow Web problem SOLVED

Post by Phil DeBecke » Sun, 09 Aug 1998 04:00:00

I just solved a * problem with IP Masquerading and NNTP connections;
I saw that there were some others who had the same problem on DejaNews
but no solutions were posted.  For the benefit of these folks I'll post
what I found out:

The situation is one where a linux box is IP Masquerading for an
internal network.  The masq server is connected to an ISP across a ppp
phone connection.  The symptom of the problem is that, while most Web
site and other type of connections work, nntp and some sites do not.
Typically, a connection actually starts, but little or no data comes

The problem seems to be that automatic MTU path discovery does not
happen across the IP Masq connection.  It is therefore necessary to set
the MTU of the outgoing PPP connection (on the masq server) to a low
value - I used 552 (512 bytes data + 40 byte header) and the same on the
client boxes.  This prevents the stalling problem normally seen.

I note that 552 is the maximum that works for me - setting it to 576
(another frequently recommended value) doesn't work.

Anyway, I hope this helps those folks that were reporting this problem.

Phil D.


1. IP Masq: Win95 -> linux -> internet - Problem solved!

I was trying to get IP masquerading working, and as far as I could
tell, everything appeared to be set-up correctly.

One of the machined behind my IP masq. linux box is a dual-boot
Win95/Linux machine.
I was able to get out to the internet when it was in Linux, but not
from Win95.

This machine has a modem (I was still using dial up ppp to connect, as
I was not going to remove it until I had IP masq fully working), and a
network card.

I was able to contact the linux box being used for IP masq, but I was
not able to get past it (used telnet to test).

I checked, double-checked, and triple checked my IP address settings
(I am using the 192.168.1.x local network numbers) in win95 and
everything appeared exactly as it should be (based on the how-to).

Eventually I deleted the entry for dial-up ppp on my win95 box
(Control Panel/Network/ Dial-up Adapter, and TCP/IP - dial up
settings), and much to my delight IP masq worked. I was able to use
telnet, http, ftp, etc, out past my gw.

I have not had a great time with Win95, I find Linux much easier to
work with (better documentation). Does Win95 ASSUME that if I had a
dial up ppp installed before the network card, and had previously used
it for external connection, that I would continue to do so, and that
no other interface would be used?

Perhaps it was foolish to think that Win95 would behave any
differently, even though I had been able to be connected externally
through dial up ppp, and to my local ethernet at the same time.

But then again, this may have been a problem with my particular

Please send a response to this NG if you are having this problem, and
the above fix works for you.

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