[HECnet] One more for the Cisco GRE mesh: Seeking Tunnel End-Points

[Johnny Billquist]

Supratim...

On 2019-02-26 23:05, Supratim Sanyal wrote:
> Thanks Johnny for taking the time to write and explain (instead of 
> saying "go read DECnet manuals"). So, basically, CTAKAH cannot decide to 
> use one path for 1.13 and another one for 1.559 since they are both area 1.

CTAKAH don't even care about where 1.13 is. CTAKAH knows it is not in 
area 1, so it tries to find the cheapest path to area 1. It is not 
looking at the node number, or anything beyond the area routing at that 
point. In short, if you need to go to another area, the only thing 
DECnet does is try to find the cheapest path to that area.
And in the case of ties, it takes the node with the highest number, and 
1.599 is a higher number than 1.13, even if your end destination is 
1.13, it would pick 1.599.

> Got it, no easy way out other than move my bunch to a new area. Please 
> assign me an area. It will take me a while, though, to move across all 
> the toys.

Right. Allocated area 31 for you. Go ahead and start moving things over. 
Let me know when you want me to update the nodename database.

> BTW, interestingly, MIM has also decided that IMPVAX is the way to reach 
> area 12 (Tim in Perth, Australia), despite Tim having 3 or more other 
> direct GRE tunnels to other area routers. Is this because IMPVAX happens 
> to be in the same area as MIM (unlike his other tunnels)?

No. It just happens to be the cheapest path to area 12. MIM is an area 
router, so it has the full picture of all other area routers, and it can 
figure out the cheapest way to get to area 12, which is through IMPVAX.
With IMPVAX, it becomes the cost to get to IMPVAX, which carries a cost 
of 4 at MIM, and then at IMPVAX, the next hop is IMPRTR on QNA-1. That 
hop has a cost of 4 as well. What the cost of the link between IMPRTR 
and area 12 is I don't know, but this has a cost of 8+N, whatever that N 
is. Any other path to area 12 from MIM will likely go through several 
hosts as well, as I do not have any direct connection to area 12. And 
other places then have higher costs in the end for the whole path from MIM.

   Johnny

> 
> 
>>
>> DECnet routing is kindof stupid. When a node in one area wants to talk 
>> to a node in another area, the only thing it does is figure out how to 
>> get to that area. And that just means find the lowest cost path to any 
>> node in that area. And here it where it gets silly.
>>
>> Until a couple of days ago, CTAKAH:: had the same cost for all 
>> circuits. That resulted in CTAKAH choosing IMPVAX for all 
>> communication to area 1. So even though CTAKAH and MIM have a direct 
>> circuit between them, packets from CTAKAH (in Russia) and MIM (in 
>> Sweden) were travelling over New York.
>>
>> CTAKAH have now dropped the cost for the circuits to MIM to a little 
>> lower, meaning it will prefer this link. But that also means that even 
>> through CTAKAH and IMPVAX have a direct connection, all packets from 
>> CTAKAH to IMPVAX will pass over MIM.
>>
>> In essence, this is how DECnet works, and you cannot get around this. 
>> When multiple connections to a different area exists, it is going to 
>> be suboptimal. The one thing would could do to improve things a bit 
>> would be to move you to an area of your own. Then both links would 
>> become useful for more than redundancy backup.
>>
>>    Johnny
>>
>> On 2019-02-26 20:53, Supratim Sanyal wrote:
>>> This email is directed to owners of Cisco routers with GRE tunnels; 
>>> to the best of my limited knowledge, Dave McGuire, Ian McLaughlin, 
>>> Brian Hechinger, Mark Darvill, Cory Smelosky, Peter Löthberg ... who 
>>> else?
>>>
>>> I already have a stable GRE tunnel to A12RTR for a while now, and am 
>>> looking for end-points on other Cisco routers on HECnet to connect 
>>> to. I will be coming in from IP address 45.62.248.66, DECnet node 1.919.
>>>
>>> If possible, please let me know what GRE end-points I can connect to. 
>>> You can, of course, DM me too.
>>>
>>> Thank you.
>>>
>>> Supratim
>>> +1-240-483-8572 (cell)
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>
>>
> 
> 


-- 
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