What does each security device/service protect against in a defense-in-depth architecture?

Question

Accepted Answer

VPN encrypts traffic, ASA firewall controls inter-network traffic, IPS blocks malicious activity, ESA/WSA filter email/web, and the AAA server controls access.

Device/Service
Full Name
Purpose

VPN
Virtual Private Network
Encrypts traffic over public networks

ASA Firewall
Adaptive Security Appliance
Controls traffic between networks

IPS
Intrusion Prevention System
Detects and blocks malicious activity

ESA
Email Security Appliance
Filters malicious emails

WSA
Web Security Appliance
Filters malicious web content

AAA Server
Authentication, Authorization, Accounting
Controls network access

Go deeper:

Defense in depth (computing) — Wikipedia — how complementary controls like these combine into overlapping layers of protection.

Device/Service	Full Name	Purpose
VPN	Virtual Private Network	Encrypts traffic over public networks
ASA Firewall	Adaptive Security Appliance	Controls traffic between networks
IPS	Intrusion Prevention System	Detects and blocks malicious activity
ESA	Email Security Appliance	Filters malicious emails
WSA	Web Security Appliance	Filters malicious web content
AAA Server	Authentication, Authorization, Accounting	Controls network access