Annex SL 27001 or annex A 27001

Please note that there is no ISO document called "Annex SL 27001". ISO 27001 standard has only one annex, called Annex A.

The Annex SL is a section of the ISO/IEC Directives part 1 that prescribes how the ISO Management System Standard (MSS) standards should be written.

Considering that, for network security, you need to use annex A from ISO 27001.

These  articles will provide you a further explanation about ISO 27001 Annex A and network security controls:

• A quick guide to ISO 27001 controls from Annex A https://advisera.com/27001academy/iso-27001-controls/
• How to manage network security according to ISO 27001 A.13.1 https://advisera.com/27001academy/blog/2016/06/27/how-to-manage-network-security-according-to-iso-27001-a-13-1/

These materials will also help you regarding ISO 27001 Annex A:

• ISO 27001 Annex A Controls in Plain English https://advisera.com/books/iso-27001-annex-controls-plain-english/
• ISO 27001 Foundations Course https://advisera.com/training/iso-27001-foundations-course/