[HECnet] Intermittent Connection with PyDECnet?

[Paul Koning]

> On Mar 2, 2020, at 6:35 AM, Johnny Billquist <bqt at softjar.se> wrote:
> 
> Hi.
> 
> On 2020-03-02 06:34, Mark J. Blair wrote:
>> No, I'm not complaining about intermittent connectivity with PyDECnet; I'm asking if it's possible!
>> I don't have persistent Internet connectivity or a fixed IP address at my just-barely-rural home. When my home network is connected to the Internet, it's tethered over my cell phone. And even then, my cell service is spotty. I could possibly resume using a separate hotspot at home rather than my regular cell phone, but even when I was doing that, my connectivity wasn't great. Cell service in my neighborhood isn't very good via either AT&T or Verizon, and wired connectivity is not available.
>> Would any of the DECnet routing mechanisms supported by PyDECnet possibly be suitable for intermittent connection of my home network, with a small number of DECnet nodes, to HECnet? Or am I just going to have to remain a HECnet spectator until I manage to obtain better Internet connectivity?
> 
> Yes. It is possible. If you use TCP as the transport, it can work with you having only intermittent connectivity, and different addresses.
> 
> Paul Koning will have to tell if PyDECnet can also act as a listener from some arbitrary remote system. But with RSX I can definitely do that. So if nothing else, you can always set it up so that you connect your PyDECnet to an RSX host...

PyDECnet can handle this in two ways.

First, Multinet TCP in listen mode can be set to accept incoming connections from any address rather than a specific address.  Other datalink types currently don't offer that option (but at least for DDCMP it could be added with a bit of work).

Second, for all IP connectivity, if the other end is identified by name rather than address, PyDECnet will redo the address lookup (gethostbyname call) every hour.  So if you have a dynamic IP address but have dynamic DNS configured, that will restore connectivity once the address update makes its way through caches and an hour passes.

For intermittent "dialup style" connections, the dynamic DNS thing is probably not quick enough so you'll want the other option.  It might make sense to enable DECnet node validation, which PyDECnet supports, for that circuit.  That isn't exactly strong authentication but it's better than a wide open port.

	paul