[slime-devel] Lisp connection closed unexpectedly

[Stelian Ionescu]

On Sun, 2009-12-06 at 20:16 +0100, Helmut Eller wrote:
> * Plato Wu [2009-12-06 15:33+0100] writes:
> 
> >> I've seen it too at work, but only if I ssh to my work place from home
> >> and use emacs -nw; it does not appear with the gui version. It's also
> >> 23.1.x, I think.
> >>
> >>   -T.
> >
> > Yes, I am at the same situation: ssh and -nw and 23.1.x
> 
> I was able to produce a network capture with tshark.  I changed
> swank.lisp so that it always creates the port on 4444 and captured with
> tshark -i lo -w /tmp/x.dump port 4444
> 
> The file is attached below and can be opened with Wireshark.  Some TCP
> packets have a "TCP CHECKSUM INCORRECT".  This seems very odd to me.
> Does somebody know what it means?

When creating TCP/UDP packets, the kernel could compute the checksum
itself but that's slow so most of the times nowadays it delegates the
checksum calculation to the network card. Since wireshark intercepts the
packet before being sent to the NIC, it sees incorrect checksums.

Furthermore, for packets sent on the loopback interface Linux avoids
calculating or checking the checksum at all(one could always use ECC RAM
for safety).

-- 
Stelian Ionescu a.k.a. fe[nl]ix
Quidquid latine dictum sit, altum videtur.
http://common-lisp.net/project/iolib
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