[HECnet] Phase III<--->Phase IV limitations?

[Paul_Koning at Dell.com]

No, Phase III is not aware of areas.  The node number is a simple integer.  In every implementation I know of, it’s an integer in the range 1 to 255.

So while in theory a Phase III node could send to node number 56327, which a Phase IV node would interpret as 55.7, in the real world no Phase III node has that ability.

	paul

> On May 13, 2015, at 2:20 PM, Hans Vlems <hvlems at zonnet.nl> wrote:
> 
> Paul, is a phase III node "aware"‎ of being in an area?
> Put differently, would a phase III node be able to talk to machines in, say, area 55, provided their node numbers are below 255?
> Hans
> 
> Verzonden vanaf mijn BlackBerry 10-smartphone.
>   Origineel bericht  
> Van: Paul_Koning at Dell.com
> Verzonden: woensdag 13 mei 2015 19:38
> Aan: hecnet at Update.UU.SE
> Beantwoorden: hecnet at Update.UU.SE
> Onderwerp: Re: [HECnet] Phase III<--->Phase IV limitations?
> 
> 
>> On May 12, 2015, at 8:05 AM, Johnny Billquist <bqt at softjar.se> wrote:
>> 
>> On 2015-05-12 06:09, Cory Smelosky wrote:
>>> Hey,
>>> 
>>> I can't remember the limitations between a Phase IV and a Phase III node
>>> interacting...aside from the limited area and node numbers.
>>> 
>>> Can Phase IV be used as a bridge to access Phase III nodes?
>> 
>> Yes. As long as the phase III nodes are in the same area.
>> It is pretty obvious and straight forward. Phase III nodes can talk to III or IV nodes in the same area only, as they do not explicitly say anything about the area. Ph IV routers will route III packets just fine within an area. Obviously, a ph III node can only address nodes with number < 256.
> 
> Those are the rules in practice. (Well, more precisely the node address may be limited to a smaller number, if the node is a router and uses a small packet size so the highest address that fits in the routing message is limited to less than 255.)
> 
> The specs are somewhat more lenient, but in practice you don’t see that. For example, Phase III routing nodes could in theory be built with a Max Address value higher than 255. In addition, the packet processing rule for Phase IV nodes talking to a Phase III neighbor say that the phase III node can send packets with area numbers in them, and can receive packets from out of area (in which case the area number is left intact during forwarding). Again, in practice that isn’t done, and I wonder why the spec allows these strange cases.
> 
> paul