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Re: IPMasq disturbing Fetchmail?

On Fri, Mar 01, 2002 at 03:10:24PM +0100, joe user wrote:
> Hello.
> Is it possible that IPMasq can disturb fetchmail?
> The retrieving of messages always stalls when a message is between 2434- or 
> 2448 bytes in size.
> I have a small home-network with two boxes running Woody.
> One of them is acting 'router' using the 'ipmasq'-package.
> The other one is my workstation and there is where I run fetchmail directly 
> against my ISP.
> If I try fetchmail on the router instead, it works fine and retrieves all 
> messages without stalling.

I had a similar problem with my ISP - intermittently. Never got to the
bottom of it. I suspect it had something to do with packet
fragmentation, but I am at a loss. Calling the ISP turned out to be
fruitless, as they are only willing to support windoze (odd: I'm told
that many ISPs actually use linux themselves...)

My symptoms were similar to yours. In addition, some web page graphics
wouldn't load (as if big images couldn't load), and seti@home never
managed to download work units. Got the first few K, then stopped.

But I did find a workaround: lower the MTU on the ppp
connection from the default 1500. In my case, lowering to 800 did the

Where to lower it depends on what you use for dialling up:

For diald:
    add a line "mtu 800" to /etc/diald/diald.options.<your-provider-name>
    (diald doesn't like you to add it to the ppp config nor command line).
    Beware that diald likes to re-generate the /etc/diald/diald.options.*
    files (how *do* you turn that off anyway?), and undo changes in

For ppp:
    add "mtu 800" to /etc/ppp/peers/<your-provider-name>

> If this is a unknown behaviour, what can I do to get more information on 
> what is happening?

Don't know. Pls post here if you find out more

> I am not a netfilter guru so I don't have an idea on how to turn on 
> extensive logging on the router..

Neither am I. The above worked for me, but I'm sure there is more to it.

Karl E. Jørgensen
==== Today's fortune:
    if (argc > 1 && strcmp(argv[1], "-advice") == 0) {
	printf("Don't Panic!\n");
	-- Arnold Robbins in the LJ of February '95, describing RCS

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