VPN services provide access to remote users and branch offices through IPsec, PPTP, and TLS. Service endpoints can be abused to obtain sensitive data, gain network access, and impact availability through denial of service. This chapter focuses on IPsec and PPTP protocols. TLS is increasingly used to provide secure network access, as described in Chapter 11.
IPsec
IP is an inherently unsafe protocol, lacking confidentiality, integrity, and authentication. When implemented correctly, IPsec negates the following attack classes:
Network sniffing
Source forgery (IP spoofing)
Modification of data within packets
Replay attacks
Internet Key Exchange (IKE)1 is used to authenticate IPsec peers and set VPN parameters. A security association (SA) is established, defining the IPsec protocols used when sending material, plus cryptographic algorithms, keys, and their expiry (known also as lifetime). The process is summarized in Figure 10-1.
Figure 10-1. Setup and use of an IPsec tunnel with IKE
Packet Format
Mutually agreed IPsec SA fields define the security features used between peers. Figure 10-2 shows an example IP datagram using IPsec in tunnel mode. The Authentication Header (AH)2 provides integrity and data origin authentication with an HMAC of the IP datagram. The Encapsulating Security Payload (ESP)3 encapsulates and encrypts IP datagrams, ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month, and much more.
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.
Julian F.
Head of Cybersecurity
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.
Addison B.
Field Engineer
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.
Amir M.
Data Platform Tech Lead
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.
