Etherip(4) interoperability with NetBSD-9?

[Brian Buhrow <buhrow%nfbcal.org@localhost>]

	hello.  I have a bunch of NetBSD-5.2 machines networked together using
the etherip(4) protocol.  I'm interested in beginning to think about how to
upgrade that fleet of devices to NetBSD-9 in hopes of capturing better
network performance.  I know the etherip(4) driver was removed from
NetBSD-9, so I have the following questions:

1.  I don't remember if the networking stack in NetBSD-9 is multi-threaded
or not.  Can someone say how much concurrency is available in the NetBSD-9
stack?

2.  Is there a way to get the NetBSD-9 stack to speak to NetBSD-5.2 using
the etherip(4) protocol without having to update the NetBSD-5.2 machines?

-thanks
-Brian