While doing some more ct_sync testing/debugging, I found out that for some reason my ctnl_dump program didn't work anymore. Instead of fixing it, and updating it to CTSP (conntrack sync protocol) version 2, I decided to write a plugin for the well-known packet analyzer ethereal.
Due to the nature of the CTSP, it passes arch- endian- and configuration-dependent data structures between master and slave. This means that it is virtually impossible to write a analyzer that will work in any of those combinations.My plugin now assumes that you use a little-endian 32bit machine with the pptp-conntrack-nat patch applied.
The plugin turned out to provide very useful information, and I was able to fix some issues in ct_sync using it.