Re: 'bogus savefile header'

[Aaron Turner <synfinatic () gmail com>]

On Mon, Aug 23, 2010 at 12:08 PM, Guy Harris <guy () alum mit edu> wrote:
> On Aug 22, 2010, at 4:15 PM, Aaron Turner wrote:
>
> > Long story short, tcpreplay allows users to replay traffic in "verbose
> > mode" which basically involves forking tcpdump and writing each packet
> > over a socketpair().  This has worked for quite a while (years now)
> > but recently I've realized something broke along the way and I'm at a
> > loss to as why.
>
> What changed between when it worked and when it broke?  tcpreplay, libpcap, tcpdump, some of the above, all of the 
> above?

Since I don't have a unit test case for this, I can't say what has
changed exactly (guess what I'm doing tonight :).  Looking at my svn
history, my code has been pretty stable for quite a long time (over a
year).   I know I've upgraded libpcap a number of times since I last
executed this code so that's my best guess right now without debugging
more then I have so far.

> > Basically, when I write my first packet over the socket to tcpdump, i
> > get the error:
> >
> > tcpdump: pcap_loop: bogus savefile header
> >
> > I believe I've tracked that down to sf-pcap.c in libpcap, which
> > indicates that the caplen > 65535.  Seems straight forward, until I
> > start debugging and see the pcap_t struct I'm using for
> > pcap_dump_fopen()
>
> That's for the side of the socket pair to which tcpreplay is writing, I presume.

Correct.

> > has snapshot set to 65535:
>
> That just means you're claiming that the max packet size is 65535; you could then write a packet with a caplen > 
> 65535 with pcap_dump().  Doing so would be considered impolite, but it's not impossible....

Not the case here, standard ethernet, no jumbo frames- first frame is
93 bytes.  Problem seems to happen with any pcap file which contains
packets.

Anyways, I'm going to build libpcap with gcc -g and see what is being
sent across the socket... maybe that will explain things.


-- 
Aaron Turner
http://synfin.net/         Twitter: @synfinatic
http://tcpreplay.synfin.net/ - Pcap editing and replay tools for Unix & Windows
Those who would give up essential Liberty, to purchase a little temporary
Safety, deserve neither Liberty nor Safety.
    -- Benjamin Franklin
"carpe diem quam minimum credula postero"
-
This is the tcpdump-workers list.
Visit https://cod.sandelman.ca/ to unsubscribe.