[HECnet] Multinet peerings...?

[hvlems at zonnet.nl]

Yes, I'd forgotten that endnodes can do that on a local LAN. Provided there's no router in that area, be it level 1 or level 2.

Verzonden vanaf mijn BlackBerry 10-smartphone.
  Origineel bericht  
Van: Johnny Billquist
Verzonden: donderdag 14 januari 2016 22:35
Aan: hecnet at Update.UU.SE
Beantwoorden: hecnet at Update.UU.SE
Onderwerp: Re: [HECnet] Multinet peerings...?

On 2016-01-14 22:26, hvlems at zonnet.nl wrote:
> Johnny,
> When the area routers in the other area are on the same LAN then the bridge w‎ill only be involved if there is another area router in that other area on the remote side of the bridge program.
> And will (very likely) slow down communications.

The bridge have no clue about areas at all. No more than a physical 
ethernet cable would. There don't have to be area routers on any side. 
But if there are, they are no different from any other ethernet node.

> 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.
(I hope the explanation makes sense, otherwise I can try and explain it 
more. I tried doing this many years ago, and ended up realized it cannot 
be done.)

Johnny

> Hans
>
> Verzonden vanaf mijn BlackBerry 10-smartphone.
> Origineel bericht
> Van: Johnny Billquist
> Verzonden: donderdag 14 januari 2016 22:06
> Aan: hecnet at Update.UU.SE
> Beantwoorden: hecnet at Update.UU.SE
> Onderwerp: Re: [HECnet] Multinet peerings...?
>
> On 2016-01-14 21:38, Peter Lothberg wrote:
>>>
>>>> On Jan 14, 2016, at 3:02 PM, Peter Lothberg <roll at Stupi.SE> wrote:
>>>>
>>>>> The values are somewhat arbitrary; it doesn't really matter what
>>>>> scheme you use but if you are inconsistent the routing may be
>>>>> surprising.
>>>>>
>>>>> The routing spec has a suggested algorithm (100,000/line speed)
>>>>> which may have made sense in the old days but for modern networks
>>>>> isn't terribly useful.
>>>>> paul
>>>>
>>>> What I wanted to get to was a scenario where traffic was symetric
>>>> between two nodes, eg, use the same links from a-b as b-a, it makes it
>>>> much easier to understand what's wrong when things behave funny...
>>>
>>> If costs are the same at both ends of a link, that will certainly
>>> help. Then again, it is quite possible for two paths to have equal
>>> cost, and if so, DECnet implementations will pick one of the two, in
>>> a way that is not specified.
>>> paul
>>
>> If all links in HECNet where point-to-point, with the same metric on
>> both sides, it will most likely be almost *perfect* by itself.
>>
>> The complex movie is when they *THINK* they are all on the same
>> ethernet with metric 1.....
>
> Well, in all honesty, default cost for ethernet links in VMS is 4, and
> in RSX is 3...
> So, if you want to favor a different link, set the cost to less.
>
> But you are blindly assuming that Multinet (or other) point-to-point
> links are better. That one I still do not see. There are definitely
> cases where it can be worse.
> The worst thing about the bridge is, as I wrote in another mail, is when
> you are on an ethernet segment, and you want to talk to a different
> area, which have several area routers on that same ethernet segment you
> are on, in which case you might end up going through pretty bad hopping.
>
> Johnny
>