[Info-vax] Cutting down on routing nodes

[Kari Uusimäki]

John Wallace wrote:
> On Jul 31, 10:04 am, IanMiller <g... at uk2.net> wrote:
>> A routing node can give faster notification of a node being
>> unavailable. If there is no routing node then a node sends a
>> connection request out on the LAN and waits.
>> A routing node on the LAN could reply and say its not available (based
>> on listening to end node hello messages).
>>
>> IIRC The aforementioned configurator module collects the SYSID
>> broadcast messages. This are quite interesting as they can contain
>> information as to node type (Vax, Alpha) and VMS version. I don't
>> recall if the configurator module displays everything that it could
>> collect. The format of SYSID is documented. I once wrote something
>> that collected these.
> 
> Sounds right to me.
> 
> My favourite NCP incantation ever:
> NCP> set module configurator known circuits surveillance enabled
> 
> One of my favourite network apps ever: EtherNIM, which took the SYSID
> info and drew terminal-based network pictures based on them.
> 
> IP-world equivalent: nothing really. The thing about SYSIDs is that
> they were part of an "architecture" (a "vision", even!), and the IP
> world doesn't do "architecture" as such, let alone vision. It does do
> lots of connectivity which mostly works, but I can't even reliably
> tell what's on my home LAN, never mind what's on the corporate
> networks.
> 
> 
> Not Ian's, but Jim's:
> "ISTR that if there is no defined routing node, then one will get
> magically picked.  Like the lowest (highest?) address in the area. "
> 
> That'll be the "designated router". A Decnet network would work
> without one, because of the AA-00-04 business, but there were benefits
> (such as the instant error status Ian mentions) to having a router on
> your LAN, even if it wasn't actually doing much routing.
> 
> There is an architected (that word again) mechanism for DECnet nodes
> choosing a router from among several possible candidates. A router
> priority is associated with each possible router. If all candidates
> have the same priority, then a winner is chosen based on address
> (can't remember if highest address or lowest won, it's all somewhere
> in the architecture documents).
> 
> If I remember rightly, it used to be great fun (not) on the rare
> occasions when something low powered unintentionally became designated
> router on a busy LAN and ended up handling rather more traffic than it
> could cope with.


The highest node address (e.g. xx.1023) in an Area has the highest 
priority when choosing the designated router (if all routers have the 
same router priority configured). Normally the Network Manager should 
define different priorities for each router.

If you have only one DECnet Area, you don't need more than one L1 router 
in that area - in case you have a LAN which spans a building. And it 
would work without it also as said before, but a L1 router makes your 
life easier - especially on a busy network.

If you have a campus-wide LAN (and lots of DECnet nodes) you might 
benefit of configuring one L1 router in each building. That depends on 
your LAN configuration. If your area includes WAN links, you definetely 
will benefit of L1 a router at each site.

If you have several DECnet Areas on your network, you need at least one 
L2 (Area) router. Usually one area router per area is the best solution.
All L2 routers work as L1 routers as well, which means that you don't 
need a separate L1 router when you have a L2 router.