If you want to be able to sniff your IPsec traffic with OpenSwan, you'll need to get KLIPS instead of the default NETKEY IPsec protocol stack.

Installing that on Ubuntu/Karmic should be a matter of:

~# apt-get install openswan-modules-source
~# cd /usr/src
/usr/src# tar jxvf openswan-modules.tar.bz2
/usr/src# cd modules/openswan
/usr/src/modules/openswan# make KERNELSRC=/lib/modules/`uname -r`/build module module_install

But it's not.

Right now, we're running the default Linux kernel 2.6.31-23-server on this Karmic machine. And as it happens, in 2.6.31 they removed networking compatibility ...