Yes indeed, the typesettings for these books are really awesome. The template is also being used by other authors notably by Jon Snader in his VPNs Illustrated book and if it's not obvious enough the name of the book is paying homage to the original TCP Illustrated series [1]. Co-incidentally Jon also wrote 44 Tips for TCP/IP network socket programming before the VPN book [2].

[1] VPNs Illustrated: Tunnels, VPNs, and IPsec: Tunnels, VPNs, and IPsec:

https://www.oreilly.com/library/view/vpns-illustrated-tunnel...

[2] Effective TCP/IP Programming: 44 Tips to Improve Your Network Programs:

https://www.informit.com/store/effective-tcp-ip-programming-...