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Re: SMTP/HTTP/Tor Connections Timing Out

On Sun, 14 Jun 2015 10:41:18 +0200
<tomas@tuxteam.de> wrote:

> Hash: SHA1
> On Sun, Jun 14, 2015 at 12:51:14PM +1000, Riley Baird wrote:
> > Hi,
> > 
> > Many of my connections are timing out. For example, I can't use SMTP to
> > send a message if it's over ~1500 bytes [...]
> This sounds suspiciously as if your box were using an MTU[1] which is too
> big for the path (1500 is about the Ethernet MTU. Perhaps along the path
> there is a link with a smaller MTU (typically something encapsulating
> the packets, which needs some room for headers, so the available payload
> per packet schrinks accordingly).
> In the Good Old Days, your box would get an ICMP reply from the router
> in-between by this router, telling that the MTU is too big, but these
> days, over-eager firewalls tend to filter out these things.
> Try to reduce the MTU of your interface, with something along the lines
> of
>   sudo ifconfig eth0 mtu 1400
> (of course, you'd have to replace eth0 by the real name of your interface.
> Just come back here if you don't know what I'm babbling about :-)
> If that works, we can talk about how to make this change more permanent.

This works! I'd recently switched from wicd to /etc/network/interfaces,
and I didn't realise that I needed to set the MTU manually.

I've also found out how to make the change persistent
(adding the line "mtu 1400" to /etc/network/interfaces).

Thanks for your help; now I can use the internet normally again!

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