VMware released update 3b on the 8th of December 2015. With this release comes some important changes, 1 of which is disabling SSLv3. This was disabled due to vulnerabilities which were found. This is very important as ESXi hosts communicate to the vCenter via SSLv3. If you update the host before updating the vCenter to update 3b, the host will no longer be able to communicate to the vCenter and be in a not responding state in the vCenter.
If you are using Horizon View older than 6.2, this will also cause the View Composer service to stop communicating as it also uses SSLv3.
You can find out more information of why this was disabled in VMware blog here – https://blogs.vmware.com/vsphere/2015/12/sslv3-protocol-disabled-by-default-in-vsphere-5-5-update-3b.html
To resolve this issue if you have already updated a host to the latest update you have two options. One is to re enable SSLv3 which you can do by following this article, please bear in mind that this is a workaround and is not advised as SSLv3 is disabled because of security vulnerabilities – http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2139396
The recommended steps to resolve this issue is to update the vCenter server to update 3b, this can be done after a host has been patched to bring the host back into communication with vCenter.
The release notes of ESXi 5.5 update 3b can be found here which also clearly state the correct order of updating ESXi and vCenter – http://pubs.vmware.com/Release_Notes/en/vsphere/55/vsphere-esxi-55u3b-release-notes.html
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