Is it possible to install the symantec endpoint 12.3 from 11.7?

 Yes it is possible to upgrade

Upgrading or migrating to Symantec Endpoint Protection 12.1.3 (RU3)

http://www.symantec.com/docs/TECH206823

Upgrade and Migration paths

Symantec Endpoint Protection 12.1.3 (RU3) can upgrade seamlessly over the following:

• Symantec Endpoint Protection 12.1.2100.2093 (RU2 MP1)
• Symantec Endpoint Protection 12.1.2015.2015 (RU2)
• Symantec Endpoint Protection 12.1.1101.401 (RU1 MP1)
• Symantec Endpoint Protection 12.1.1000.157 (RU1)
• Symantec Endpoint Protection 12.1.671.4971 (RTM)
• Symantec Endpoint Protection 11.x (can be upgraded to enterprise version only)
• Symantec Endpoint Protection Small Business Edition 12.0

https://www-secure.symantec.com/connect/blogs/latest-symantec-endpoint-protection-released-sep-121ru3

https://www-secure.symantec.com/connect/blogs/whats-new-latest-symantec-endpoint-protection-sep-121ru3

Is it possible to install the symantec endpoint 12.3 from 11.7?

Yes it supported

Supported upgrade paths to Symantec Endpoint Protection Manager 12.1 from Symantec Endpoint Protection Manager 11.x

Upgrading or migrating to Symantec Endpoint Protection 12.1.3 (RU3)

You can upgrade from any previous version of 11.x or 12.1 to SEP 12.1.3

Hi,

Thank you for posting in Symantec community.

I would be more than happy to assist you.

You can refer this video to complete the upgrade from SEP 11.7 to SEP 12.1 RU3.

SEPM 11 RU7 MP3 to SEP 12.1.2 (SEP 12.1 RU2) Upgrade Process Graphical Overview.

https://www-secure.symantec.com/connect/videos/sepm-11-ru7-mp3-sep-1212-sep-121-ru2-upgrade-process-graphical-overview

Also can refer this article, it's an old article but still can be helpful.

SEP 11.x to SEP 12.1 Upgrade process graphical overview

https://www-secure.symantec.com/connect/articles/sep-11x-sep-121-upgrade-process-graphical-overview

& latest article about SEP 12.1 RU3 migration.

Upgrading or migrating to Symantec Endpoint Protection 12.1.3 (RU3)

http://www.symantec.com/docs/TECH206823

Hi,

Please check this below link:

http://www.symantec.com/docs/TECH163602

Hello,

Yes, you can Upgrade the SEPM to the Latest version 12.1 RU3 from SEPM 11.0.7

If you are planning to upgrade or migrate to Symantec Endpoint Protection 12.1.3, please take a look at the latest how-to article created by our very own SEP content council team.

Best practices for upgrading to Symantec Endpoint Protection 12.1.x

http://www.symantec.com/business/support/index?page=content&id=TECH163700

Hope that helps!!