[HECnet] Multinet peerings...?

On 2016-01-15 03:25, Brian Hechinger wrote: <Paul_Koning at Dell.com> wrote: dame area at both ends and favor the local one, possibly block advertising of the remote area router? >>> >>> I tried blocking traffic from a node in one area from getting to >>> another area, with the exception of packets from area routers. >>> Unfortunately, it does not work. DECnet can be clever about local >>> ethernet connectivity. If you are on the same ethernet segment, >>> nodes can communicate directly with other nodes on the same >>> ethernet segment, even if they are endnodes, and this exen extends >>> to nodes on different areas. So such filtering in the bridge cause >>> communication to fail for endnodes on the ethernet segment, when >>> the destination is on the same ethernet, even if in a different area. >> >> DECnet expects a "transitive Ethernet" -- if A can talk to B and B >> can talk to C, A must be able to talk to C. That's actually a >> common assumption, other network protocols do the same. DECnet is >> a bit unusual in that it explicitly verifies this property, at >> least for routers -- that's why router hellos have the router list >> in them. We put that in because we had run into some defective >> Ethernets that were non-transitive, causing very strange misbehavior

>> >> End nodes have an on-Ethernet cache: if X talks to Y and both are >> on the same Ethernet, they will do it directly. From the first >> packet if there are no routers; after the initial round-trip if >> there are. If you create a non-transitive Ethernet -- which is >> what filtering does -- this will fail. There is no workaround. If >> you don't want all the nodes on an Ethernet to have direct >> communication, the only solution is to split it into two separate

Yes. This is actually just the traditional way networks are designed. Ethernet is a LAN - as in local. It's not designed for long haul connections. It only works because the internet today have pretty amazing capacity compared to the 80s. But to get a more traditional topology, we need the routers in between somehow - and the WAN links. The problem with that have been that much DECnet gear only supports various links that best would be described as arcane by todays standards, in addition to the ethernet. How many use X.25 nowadays? Or synchronous serial lines? Well, if you were running a Cisco box, you could tunnel DECnet over GRE. Not everyone have one of those. The other option more "generally" available was VMS machines running Multinet, as that supported DECnet links carried over IP. One option that is slowly becoming more and more plausible are specific routers, such as Pauls python router, and Rob Jarrats