Rob,

I have already answer for you.

Yes, my Pi is running Raspbian 3.6.11+ #538 PREEMPT Fri Aug 30 20:42:08 BST 2013 armv6l updated&upgraded as often as possible.

Line from config.gz file you're asking about is as follow: #CONFIG_IP_MROUTE is not set

But here is my AMPRNet tunnel interface:

tunl0 Link encap:UNSPEC inet addr: 44.165.2.2 Mask: 255.255.255.248 UP RUNNING NOARP MULTICAST MTU:1480 Metric:1

I've also 3 ax ifces, 3 nr ifces, 1 rose ifce and tun0 ifce from linux to my JNOS.

Traffic flows in both directions IN&OUT just fine.

Best regards. Tom - sp2lob