Sniffing a VPN

[Joe Nall <joe@nall.com>]

I have set up a test VPN and have been trying to verify that packets are
encrypted.  From a third BSD box on the lan between the two gateways I
was able to use sniffit and ngrep to see tcp/udp traffic before the VPN,
now neither tool can see any packets when the two subnets are talking. 
Any clues on a sniffit configuration or another more appropriate tool to
see the packets?  I want to verify that the traffic is encrypted.

Thanks,
Joe