I wrote:

| I don't see how/why the router should behave differently depending
| on whether there is a NetBSD box bridging or not...
|
| There is no NAT.  (Even if there were, why would the presence of
| a bridging NetBSD box make a difference?)

For the sake of clarity, the question in parentheses is NOT rhetorical,
or meant to be argumentative.  It's the crux of the problem.  :-(

What on earth is munging segments but leaving the checksums intact 
(or fixing them), but only for traffic that leaves the bridged LAN,
or arrives on it from elsewhere?

	Sean.