inbound ssh ceased on 4 servers at same time

[John Brooks]

today at about noon, all four freebsd servers on a clients lan
quit accepting ssh connections. all were running 4.11-release-p4,
and had been cvsup'd at the same time from cvs-10, cvs-11, or
cvs-12. outbound ssh works as expected to both local openbsd boxes
and to remote locations from the affected boxes. there are no host 
based firewalls involved, and all other network services are 
operating correctly. netstat shows port 22 as listening. at 
11:20 am, ssh was working properly on all boxes.

has anybody encountered a situation like this before? 

--
John Brooks
john at day-light.com