[Dxspider-support] Redundant Links

[Fred Allstadt]

Yes, it IS possible to have your node connected to two or more nodes at the 
same time.  The inherent danger is causing a loop condition, where 
information has multiple paths to move about the various links, causing a 
race condition that floods the networks, effectively bringing it to it's 
knees.  With some (very) creative input and output filtering, you could 
find a way to avoid this.  Until something changes on the network.

As you are part of the cluster in the Northeast US, there's another 
issue:  This group is made up primarily of AR Clusters (though it seems 
that DX Spider installations are increasing).  AR recently added a 
"feature", which can really cause havoc if it sees a cluster on more than 
one route.  To avoid a loop condition, when it sees a node join in a second 
location, it will disconnect the node that contains the path you were first 
on.  Here's an example (as it happened to me):

-- N1ZUK connected to K1TTT, which is connected to N2TX.
-- Now connect N1ZUK to WH1R, which is connected to N2TX.
-- N2TX, seeing N1ZUK on two routes, want's to disconnect the first N1ZUK 
connection.  However, it can't disconnect it directly, as N1ZUK is not 
connected to N2TX directly.  So instead, it drops K1TTT.

Instead, I found it better to run as a 'dead end' node, only having one 
link established, and switching to a backup if your primary node becomes 
unavailable.  I have accomplished this using the following lines in my 
crontab file:

     --- <snip> ---
# Log into K1TTT on the half hour
# Then every 2 minutes check if K1TTT is there, if not, connect K9USA
# Disconnect from K9USA before the half hour

0,30 * * * * start_connect('k1ttt') unless (connected('k1ttt') or 
connected('k9usa'))

2,4,6,8,10,12,14,16,18,20,22,24,26,32,34,36,38,40,42,44,46,48,50,52,54,56 * 
* * * start_connect('k9usa') unless (connected('k9usa') or connected('k1ttt'))

29,59 * * * * disconnect('k9usa') if connected('k9usa')
    --- <snip> ---
(note: the line that starts "2,4,6..." is all one line)

It basically uses K1TTT as my main link.  Every 2 minutes, it checks to see 
if I have any connection to K1TTT or K9USA -- if not, it connects to K9USA 
(which seems to be a very reliable DXSpider link, and get virtually the 
same spots as K1TTT, due to it's link with AB5K).  Then, every half hour, 
it will try to re-establish the link to K1TTT if I'm connected to K9USA, by 
first disconnecting from K9USA, then connecting to K1TTT.

Worst case scenario -- a possible 3 minutes without a link if K1TTT is 
unreachable, from the time that I disconnect from K9USA, to the time I 
reconnect to K9USA.  I could of checked every minute, but I wanted to allow 
enough time to insure that the connects and disconnects were completed.  If 
your links are not as fast as mine (broadband Internet), you may want to 
make your checks less frequent, for the same reason.

73, and good DX --
Fred  N1ZUK
Sysop, DXBVT DX Cluster (N1ZUK)
telnet://n1zuk.dyndns.org
n1zuk at adelphia.net


At 07:03 PM 1/31/02 -0500, you wrote:
>I would like have my node setup with one or more connections to the cluster.
>I have a had a fairly reliable link to the network, but it does go down
>every so often.
>
>Can I have more than one link to the cluster?
>Does DXSpider care?
>What is the down side?
>How do I do it?
>
>TNX Will