[HECnet] Multinet peerings...?

[Johnny Billquist]

On 2016-01-15 04:05, Mark Pizzolato wrote:
> On Thursday, January 14, 2016 at 6:42 PM, Johnny Billquist wrote:
>> On 2016-01-15 03:25, Brian Hechinger wrote:
>>>
>>>> On Jan 14, 2016, at 8:03 PM, <Paul_Koning at Dell.com>
>> <Paul_Koning at Dell.com> wrote:
>>>>
>>>>
>>>>> On Jan 14, 2016, at 4:40 PM, hvlems at zonnet.nl wrote:
>>>>>
>>>>> ...
>>>>>> Can the bridge program detect whether there are area routers for the
>> 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 until
>>>> this protocol mechanism was added.
>>>>
>>>> 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 Ethernets,
>>>> interconnected by a router (not a bridge).
>>>
>>> And this is what I was (and always have been) thinking. Make “shorter”
>>>> ethernet segments that are less geographically diverse. Put routers between
>>>> them. That should solve most problems, no?
>>
>> 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 implementation.
>
> Certainly, given an already working internet connection, it would never
> make sense for anyone to setup a synchronous serial line again, BUT folks
> who are running simh PDP11 or VAX systems can use the traditional
> DMC/DMR links for point to point WAN connections.  Transport can either
> be TCP or UDP.
>
> I'm pretty sure that Rob Jarratt's router can be an endpoint for one of
> these connections.

Well, I'm thinking actual, physical machines, and not emulated ones... :-)

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol