On Jan 2, 2015, at 8:41 PM, Johnny Billquist <bqt at softjar.se> wrote: On 2015-01-03 02:13, Paul_Koning at Dell.com wrote: On Jan 2, 2015, at 7:57 PM, Johnny Billquist <bqt at softjar.se> wrote: On 2015-01-02 19:07, Paul_Koning at Dell.com wrote: On Jan 2, 2015, at 12:34 PM, Johnny Billquist <bqt at softjar.se> wrote: On 2015-01-02 18:28, Hans Vlems wrote: Is there an advantage if you use a tunnel in stead of Johnny's bridge program which I use? It scales better and use less network bandwidth, if that is a concern. Less network bandwidth because the GRE tunnel doesn t use Ethernet padding and regular Ethernet headers, while the JB bridge is a bridge so it does have both of those? That seems like the only difference; from the DECnet routing layer point of view, both are LAN links and the protocol operation is the same for both. No, you're not thinking about the larger picture, Paul. :-) Like I responded myself. One "problem" is all the routers that are broadcasting. Both hello messages and routing updates. And they need to go to all bridges connected. While if you had a tunnel between two routers, you'll end up with just the chatter between those two routers. Any routers located on each end, or elsewhere, is of no concern for the link. But you re comparing different cases. GRE is like a two-station Ethernet; your bridge is more general. The flooding case of a bridge makes a difference only if you have more than two stations. Right. But we should not talk about GRE here, because that just confuse the issue. The thing is, the Ciscos are routers, with a tunnel between the two routers. So you only have these two routers talking to each other over the tunnel. With the bridge, you do not get that isolation. You will instead have every router on each side (even if you just have two points to the bridge) talking across the bridge. So the number of packets over the bridge is essentially proportional to the number of routers connected to the ethernet segments. And in the HECnet specific case, the bridge actually have around 10 active points, and atleast one router at each point Ok. But if someone wanted the efficiency of a GRE tunnel without having a device capable of talking that protocol, one could set up another instance of a JB bridge, with just those two systems on it. Then it would be just as efficient. I agree that if you compare a point to point topology tunnel with a 10-point bridge, the two necessarily look rather different. paul