I recently tried out vpnc to see if I could use NetBSD instead of
Windows or Linux to connect to work.  It all connects properly, but
once I try to do anything serious (start vim in text mode, do a bunch
of 'ls's, fire up vncviewer), the clients hang.  I can still fire up
new clients, so it's not like the tunnel is busted, just that those
particular streams are hosed.

  As a check, I tried doing pings to work of various sizes.
A ping of up to 500 bytes gets to work and back just fine, but a
ping of 501 bytes or larger will not make it through.  Ordinarily, I
can ping with packets larger than 1K to random spots throughout the
world, so vpnc appears to be introducing something problematic....

  My setup:  NetBSD desktop connected via Ethernet to NetBSD
router box, connected to cable modem.

  I'm clueless about mtu's etc., but on a whim I did:

route change default 10.214.72.11 -mtu 400

  And now route show <workmachine> shows:
 mtu
 400

  But things still don't work.  Can someone send me a clue or two?  

  TIA

  Brian