Years ago it was really difficult to get tunnels set up, so the AREDN team set up a "global" tunnel server to provide connectivity and many hams took advantage of it.
Since then tunnel became easier to set up and then supernode clusters came into being. Now there are only a few nodes still connected to the global tunnel server. Since there are so few, and the code on the tunnel server is way out of date and problematic, AREDN will pull the plug on it in the near future. Here's the list of nodes still connected to it. If you own or know the owner of one of these nodes, make plans for an alternative link into the network (if you don't have one already).
AJ6GZ-X86-GLOBAL
KB4YFK-GL150
KC6JPG-AREDNCLOUD-01
W7ACS-SEATTLEEOC
K4SPB-HAP-1
KM6IAU-ONAGA-NODE0
K5DLQ-HAP-1
W1HS-UTIK-5AC2ND-1
AE7WY-CLKWY-RTR-MAIN
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Orv W6BI
AREDN Project Manager