Original URL: http://www.theregister.co.uk/2007/08/20/skype_outage_post-mortem/

Patch Tuesday update triggered Skype outage

Mass reboot exposes VoIP network stability bug

By John Leyden

Posted in VoIP, 20th August 2007 09:44 GMT

Skype has blamed last week's prolonged outage on the effects of Microsoft's Patch Tuesday.

The latest security update from Microsoft required a system reboot. The effect of so many machines rebooting and subsequently trying to log onto the Skype VoIP network triggered system instability and a prolonged outage of almost two days starting on Thursday1. Services have now been restored.

The necessity for system reboots after Microsoft patches happens almost every month. Skype said the problems it experienced were down to a failure in its system recovery functions due to a previously unidentified software bug.

In a system update, Skype said:" The abnormally high number of restarts affected Skype’s network resources. This caused a flood of log-in requests, which, combined with the lack of peer-to-peer network resources, prompted a chain reaction that had a critical impact.

"Normally Skype’s peer-to-peer network has an inbuilt ability to self-heal, however, this event revealed a previously unseen software bug within the network resource allocation algorithm which prevented the self-healing function from working quickly. Regrettably, as a result of this disruption, Skype was unavailable to the majority of its users for approximately two days," it added.

Skype said the bug in its systems was not security related, denying speculation that a newly-announced denial of service "bug" was involved in the outage. The potency of the bug came into question in a posting to a full disclosure mailing list on Friday, hours after it was published.

The last security update from Skype itself came out last October, Secunia reports. ®

1Microsoft's publishes its monthly patches on the second Tuesday of every month. Many clients will automatically download the updates on Wednesday and apply them on the next system reboot, which could be Thursday morning. Many will apply patches before then but are unlikely to do so en masse at the same time.