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TsooRad is a blog for John Weber. John was a Skype for Business MVP (2015-2018) - before that, a Lync Server MVP (2010-2014). My day job is titled "Technical Lead, MS UC" - I work with an awesome group of people at CDW, LLC. I focus on collaboration and infrastructure. This means Exchange of all flavors, Skype, LCS/OCS/Lync, Windows, business process, and learning new stuff. I have a variety of interests - some of which may rear their ugly head in this forum. I have a variety of certifications dating back to Novell CNE and working up through the Microsoft MCP stack to MCITP multiple times. FWIW, I am on my third career - ex-USMC, retired US Army. I have a fancy MBA. One of these days, I intend to start teaching. The opinions expressed on this blog are mine and mine alone.


Maximum Number of names in a SAN Extension

In what is sure to be a long standing record (of sorts) for me (and maybe only me) – I just submitted a CSR to a public provider with 53 domains in the SAN field.  This raised the question:  “how many entries or names can be in that one field?”  I know there has to be some sort of limit. 

Handy Dandy, we had a TMG guy in the room, so we asked him.  While he did not know off the top of his head, he did have an answer in mere minutes (where I had googled for about 10 and found squat).


So, now we know the field is defined by a database, that a Windows PKI CA is limited to 4k of names, and that somewhere around 150 25 character domain names eat up just under 4k.  By extension, we can assume (and we know what that means) that the Public cert providers are following the same RFC and that they will have a similar limit.

How about that?  An answer to a question you did not know you had!


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