[14:30] I discovered today that there have been glitches in connectivity to one or both of the Servology DNS resolvers over the last day or two. The start of the problem appears to coincide with when I installed the latest security updates on resolver B at the weekend, but as far as I can see do not appear to have been caused by those updates – for now I am assuming the timing was coincidental. The cause of the problem seems to be a faulty VRRP process on an older router – two routers were both trying to claim the same IP address on a specific subnet where some of Servology’s internal servers are hosted. I have shut down the faulty VRRP process and this appears to have fixed the connectivity glitches.
I believe the problems were confined to a few IP addresses which are statically configured on routers and distributed via OSPF, so access to most services should not have been affected. Affected services included Servology DNS resolvers and possibly some Servology NTP and SMTP servers. The IP addresses in question most likely worked fine from outside the Servology network (my monitoring server is hosted externally and did not report any problems) – I the glitches were probably only visible from local subnets.
I will continue to monitor this in case of further problems.