# cat /etc/opkg.conf
#src/gz attitude_adjustment http://downloads.openwrt.org/attitude_adjustment/12.09/ar71xx/generic/packages
src/gz trunk http://downloads.openwrt.org/snapshots/trunk/ar71xx/packages
dest root /
dest ram /tmp
dest plugin_root /plugin_root
lists_dir ext /var/opkg-lists
option overlay_root /overlay
#src/gz eko1 http://dl.eko.one.pl/attitude_adjustment/ar71xx/packages
#src/gz gargoylepl_packages http://dl.eko.one.pl/gargoyle-pl/attitude_adjustment/ar71xx/packages
#src/gz gargoylepl_plugins http://dl.eko.one.pl/gargoyle-pl/attitude_adjustment/ar71xx/plugins

# opkg update
Downloading package list for trunk source...
Package list for trunk downloaded successfully.

# opkg list | grep -i fwknop
fwknop - 2.6.2-1 - Fwknop implements an authorization scheme known as Single Packet Authorization
             This package contains the fwknop client.
fwknopd - 2.6.2-1 - Fwknop implements an authorization scheme known as Single Packet Authorization
             This package contains the fwknop daemon.
libfko - 2.0-1 - Fwknop implements an authorization scheme known as Single Packet Authorization

# opkg install fwknop fwknopd libfko
ERROR: No package named fwknop found, try updating your package lists

# ls -al /tmp/opkg-lists/*
-rw-r--r--    1 root     root        497461 Jul 21 13:30 /tmp/opkg-lists/trunk

# ls -al /var/opkg-lists/*
-rw-r--r--    1 root     root        497461 Jul 21 13:30 /var/opkg-lists/trunk