Getting into Network Security.

Hi Dears,

Need the advice from your expertise.

-When i search to apply for a Senior Network Engineer positions these days , companies usually combine the position to be Network & Security Engineer , i have a solid background in Enterprise networking but not Security, how can i get into track ? What i notice is that they require experience in Multiple vendors , for example in firewall requirements they want candidates to be aware of ( Cisco ASA & Firepower , Palo Alto , Fortigate , Juniper ) , F5 , are all those firewalls works similarly? How can someone master all these different vendors?

-Any tip of where to start? I am thinking of getting into old CCNA Security curriculum is this a good start?

-I will not be able to practice these technologies and vendors as i dont have access to firewalls on , is there a virtual appliance of those vendors to labbing ?

-What is the best study techniques for Security topics and concepts as i had a tough time understanding and memorising the configuration of IPSec and encryptions.

-What are the best study materials out there?