On 01/02/2015 09:17 PM, Johnny Billquist wrote: One can tunnel most anything over GRE, even raw Ethernet frames, regardless of the higher-level protocols. Hence the 'G' for "Generic". Yes. But you need some ingress and egress that makes use of it. Or else we could just as well argue that UDP can tunnel anything. ...which it can. ;) On a Cisco, assigning a DECnet cost to an interface (and a GRE endpoint is a pseudo-interface on a Cisco) forms that ingress/egress. (I know YOU know this; I'm saying it for the benefit of those here who are just learning about this) Actually, I don't know the details, even though I pretty much know how it *could* be done. I've pretty much never actually worked on a Cisco box. :-) However, DECnet costs cannot possibly be related, as we're now not talking about DECnet protocols. (LAT and MOP are not using DECnet...) You need to somehow tell the Cisco box to grab all ethernet packets with a certain protocol number, and pass those on over the tunnel, and have the other end do the reverse. Assigning a DECnet cost to a tunnel endpoint pseudo-interface causes it to pay attention to DECnet packets. Which is not LAT and MOP. Which is what I've written multiple times now. :-) Right. I didn't say it was. Seemed to me you implied it. Oh well. Me and english... :-) Oh, nono...I'm sorry if it seemed that way. DECnet packets are routed by the Cisco router. MOP and LAT are not protocols running on top of DECnet, but are their own protocols directly on ethernet. Which is also why they in essence are "local only", as they cannot be routed. ...but they can be bridged, which you can ALSO do with a GRE tunnel. The very same GRE tunnel as is handling DECnet, in fact. Yes. And this is where it comes to me not knowing Ciscos. I know how you do it in general if we talk networking. And this is just what my bridge does, except it don't use GRE, but is more simple and stupid. :-) I wouldn't say that; I think it's just that GRE is more standardized, and typically ends in a router, which gives it more powerful capabilities...but not by virtue of it being GRE. But I assume there must be a way to tell a Cisco to bridge an arbitrary ethernet protocol, using GRE as the tunneling protocol. Yes there is. You can also bridge ALL packets on a network to a different network, regardless of protocol. I remember looking at the GRE interface under NetBSD many years ago when I wanted to setup HECnet, but the documentation confused me in the details, and I just wanted something really simple, so I wrote my own bridge instead. It was a dirty hack on a dark night. It does (more or less) do what I needed, but it's really just a quick hack. Yes. Computer operating system-based implementations tend to be a bit ridiculous. In a router it's more natural. I'm sure being written by "router people" has a big positive influence on its implementation as well, as opposed to being written by "operating system people". -Dave -- Dave McGuire, AK4HZ/3 New Kensington, PA