[HECnet] Multinet peerings...?

[Johnny Billquist]

On 2016-01-14 21:29, Paul_Koning at Dell.com 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.

Yes. But I think that Peter is actually advocating that cost for 
ethernet should be larger than cost for Multinet link at all nodes, in 
order to most of the time decide to favor the multinet links.

Ie. Not have a situation where node a uses the multinet link to talk to 
node b, and b uses ethernet (bridge) to send responses back to a.

DECnet works just fine with such different paths, though. So it's just a 
question of - will the multinet links give better performance than 
ethernet and the bridge?

Both ends could have equal or different costs for the links. As long as 
the relative order of costs between the links are the same, they should 
then both favor the multinet link. However, it can become more 
interesting when there are multiple paths, and multiple hops, as the 
costs are the sum of the cost of all hops, meaning that potentially, 
what cost other people put on their links can affect how your forwarding 
matrix looks like.

	Johnny