In my case the ISP had setup a temporary account for me to use for testing. so I
dialled into a Linux command prompt, plus I rang him and asked him. He also said he
had done extensive testing and determined that 296 was the optimum, and he was
hesitant to change it. I had configured the pppd options file to not negotiate MTU,
and the messages file showed the ISP sending the MTU negotiation message, which was
ignored by my linux box. When I set mine back to 296 and turned MTU negotiation back
on, the ISP sent the MTU negotiation stuff, and my Linux replied.
Dave
----------
From: Jann Linder[SMTP:[EMAIL PROTECTED]]
Sent: Wednesday, 3 June 1998 0:15
To: 'Dave'
Cc: 'linux-net'; 'masq'
Subject: RE: [masq] Chapter 2: masqueraded http slows down
how do you check the mtu at the ISP? i assumed they were auto-adjusting
and have left that out of my pppd command to dial.
Jann
Jann Linder
Web Developer/CH2M Hill - SFO
[EMAIL PROTECTED]
Home Page:
http://www.jann.com/
CalendarPlus Web Site:
http://www.calendarplus.com/
-----Original Message-----
From: Dave [SMTP:[EMAIL PROTECTED]]
Sent: Monday, June 01, 1998 11:14 PM
To: 'Linux_masq'
Subject: Re: [masq] Chapter 2: masqueraded http slows down
Greetings.
It appears that the problem may have been caused by a difference in MTU
between the modem on my Linux box and the modem on the ISP's Linux box.
MTU matched everywhere on my side of the link (at 1500), but not on the
ISP's modem. So I changed everything on my side (ppp0, eth0 and my Win95
client) to 296, which is the same as the ISP's, and everything works fine.
The web pages I could not access previously now fly past (well, as fast as
you'd expect from a 33600 baud modem, but quite acceptable).
I had a few suggestions about checking MTU, but I didn't think to go as far
as I did until I noticed sendmail was reporting "collect: I/O error on
connection" messages fairly consistently for several sites that were trying
to send us email. A quick look at the sendmail FAQ web page (fortunately
one of those I could access) said that this message might appear for a
small number of sites, and may even not appear depending on the size of the
emails being transferred. The FAQ suggested checking the MTU between the
client and host systems. I did and they were different, and the rest is
history. Recent history, granted, but history has to start somewhere. :)
Next question. I have seen documented in several places that the MTU on
the ppp0 and eth0 interfaces must be the same due to a bug or something in
the Linux kernel (I have kernel 2.0.33). I have also seen a patch which is
supposed to fix this, but the same site that had the patch noted that all
patches had been incorporated into kernel 2.0.33. So the question is,
given that I did seem to experience some problems, do I need to install the
patch on my 2.0.33 kernel and would doing so help?
Btw I checked my kernel configuration and IP_ALWAYS_DEFRAG *is* set.
Many thanx to those who responded to my first question, especially Matt
Roberts.
Dave
----------
From: Dave[SMTP:[EMAIL PROTECTED]]
Sent: Friday, 29 May 1998 8:48
To: 'Linux_masq'
Subject: [masq] masqueraded http slows down
Greetings.
I have finally got my Linux box connected to our ISP and basically working
doing masquerading amongst other things. Not through problems, just lack
of time on my part. (Or on my hands.)
Slackware Linux 3.4, kernel 2.0.33 (compiled with IP_MASQUERADING etc.
etc.), um, pppd 2.2.0 etc. The rest is a standard Slackware 3.4
distribution. Running on a 486DX4/100 16M RAM, 38400 modem. During tests
the CPU was idle about 97% (according to vmstat). The client is a Windows
95 pc with the Linux box configured as the default gateway and dns.
Eventually about 8 PCs will be connected to the internet via the Linux
box, internet usage is not huge tho.
DNS works fine.
pppd works fine.
Email works fine.
ftp works fine (provided I load the appropriate module :)
http (using Netscape and Internet Explorer) works fine ... but ... after a
while, usually around 15 or 20 minutes, loading web pages will slow to a
crawl. At first response is fine, the modem lights flash and there is lots
of receiving. But after this there is no activity. Occasionally the send
light flashes. Minutes pass, then the receive light flashes a couple of
times. According to Netscape transfer speed is something like 9 bytes/sec,
that's just before the transfer stalls. At the same time tho, other things
like ftp, traceroute, pings, emails still seem to work fine.
MTU is 1500, ftp transfers of megabyte files happens very quickly and very
smoothly.
Any ideas about what might be going wrong and/or what I can do to fix it
are more than welcome.
tia
Dave
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