[slime-devel] Lisp connection closed unexpectedly

[Matthew Mondor]

On Sun, 06 Dec 2009 20:16:50 +0100
Helmut Eller <heller at common-lisp.net> wrote:

> 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?

The text results of tcpdump (especially using -nvvxX flags) or a binary
tcpdump result would be easier for me (and perhaps others?) to read.

When I encountered packet checksum errors here it was due to a
card/driver specific TCP hardware acceleration feature when enabled, or
hardware problems, although a faulty software packet translator or IP
stack bug is not impossible...  Since your test appears to be local, I
doubt NIC TCP acceleration to be the problem however.

In case your question was litteral about "what it means?" (sorry for
stating the obvious if it wasn't), a TCP checksum is wrong for a packet
when it doesn't match the actual checksum of its payload (indicating it
was probably corrupted in transit, or wrongly calculated), and this is
rarely calculated/verified at the application layer, except by userland
packet-level analysis/manipulation tools.

It could even be a tshark-specific problem...
-- 
Matt