Repeated network failures

[Bob Eager <bob@eager.cx>]

Scenario:

I am doing daily backups using tarsnap, on about seven different
systems. I have been doing this for almost two years.

Six of the systems are fine. But, several days ago, one system started
failing. That system is actually not being used at present, so no
changes have been made.

I can successfully do:

rikki# tarsnap --list-archives                                         ~  10:11
rikki-daily-2016-08-14_05:15:00-etc
rikki-daily-2016-11-15_06:15:00-var
rikki-daily-2017-02-09_06:15:00-usr_local_etc
rikki-monthly-2016-03-01_07:30:00-boot
rikki-daily-2017-02-14_06:15:00-usr_local_etc
rikki-daily-2016-07-29_05:15:00-root
...etc

But a simple backup of one file fails:

rikki# sh -x z
+ tarsnap -c -v -v -v -f test --noisy-warnings testfile
a testfile
tarsnap: Connection lost, waiting 1 seconds before reconnecting
tarsnap: Connection lost, waiting 2 seconds before reconnecting
tarsnap: Connection lost, waiting 4 seconds before reconnecting
tarsnap: Connection lost, waiting 8 seconds before reconnecting
tarsnap: Connection lost, waiting 15 seconds before reconnecting
tarsnap: Connection lost, waiting 30 seconds before reconnecting
tarsnap: Connection lost, waiting 60 seconds before reconnecting
tarsnap: Connection lost, waiting 90 seconds before reconnecting
tarsnap: Connection lost, waiting 90 seconds before reconnecting
tarsnap: Too many network failures
tarsnap: Error closing archive
tarsnap: Error exit delayed from previous errors.
rikki# 

Any ideas, please? I have rebooted the system, in case it's a resource
leak problem. I've also reinstalled tarsnap.
-- 
Bob