[HECnet] Decnet over internet

[Robert Armstrong]

  FWIW, on LEGATO I currently have 8 defined Multinet DECnet links.  Three
are TCP and the rest are UDP.  Historically I've had 18 different remote
links, although not all were in use at the same time.  Again, some were TCP
and some UDP.

  The TCP and UDP links both exhibit the occasional "adjacency down" then
"adjacency up" behavior.  I haven't analyzed the relative frequency, but I
can conclusively say that TCP doesn't fix the problem, at least for
Multinet.  I don't see it as a serious problem, although it is an annoyance.
Searching my OPERATOR.LOG files just now, I'm going to say there are around
2 or 3 "flaps" per day. 

  The UDP links are significantly easier to administer, however, and I've
stopped adding new TCP links.  

  1) Multinet has no ability to configure the TCP option for you, and you
have to manually edit the DECNET-CIRCUITS file to create one.  And once you
manually edit this file, you can no longer use the MULTINET CONFIGURE/DECNET
tool (or rather, you can, but it'll erase all your hand edits!).

  2) UDP is symmetrical - both ends are configured the same.  TCP is
inherently asymmetrical because you need an active (connecting) and passive
(listening) end.  Multinet does both, but you have to coordinate with the
other end about who will play which role

  3) All UDP connections can share the same port; all TCP connections
require a unique port.  This is another issue that has to be coordinated for
each link.

  4) Since each TCP link needs a unique port, that means each TCP link needs
another rule added to my firewall.  All the UDP links share one port and one
rule.  (Actually if you're the active end and your firewall allows outgoing
connections then this doesn't apply, but everybody can't be active.
Somebody has to lose the coin flip and be the listening end.)

  Admittedly #1 is unique to Multinet, but the rest are just consequences of
a connection oriented vs non-connection oriented protocol.

Bob