What does the Cisco Web Security Appliance (WSA) do, and how does it control web traffic?

The WSA (Web Security Appliance) is a web proxy that provides malware protection, application visibility, acceptable use policy enforcement, and reporting for all web traffic leaving the network.

WSA capabilities:

• URL (Uniform Resource Locator) blacklisting — block access to known malicious or policy-violating websites
• URL filtering — categorize websites (social media, gambling, streaming) and apply policies per category
• Malware scanning — inspect downloaded files for malware
• URL categorization — dynamically classify unknown URLs
• Web application filtering — control access to specific web applications (e.g., block personal Dropbox but allow corporate)
• Encryption/decryption — decrypt HTTPS (Hypertext Transfer Protocol Secure) traffic for inspection, then re-encrypt

Policy enforcement examples:

• Block all social media during work hours
• Allow streaming video but limit bandwidth to 1 Mbps
• Block file uploads to personal cloud storage
• Allow access to news sites but log all visits

Tip: The WSA works as a web proxy — client browsers are configured (or transparently redirected) to send all HTTP (Hypertext Transfer Protocol)/HTTPS traffic through the WSA. This gives it complete visibility and control over web activity.

Go deeper:

• Proxy server (Wikipedia) — the content-filtering / transparent-proxy mechanism behind a WSA's visibility and HTTPS inspection.