Cisco GRE and IPSec - GRE over IPSec - Selecting and Configuring GRE IPSec Tunnel or Transport Mode

This article aims to explain the differences between GRE IPSec Tunnel and GRE IPSec Transport mode and how they can be configured and implemented in a Secure Cisco VPN Network. Packet Analysis of both modes with detailed diagrams and Cisco IOS configuration commands, ensures the reader will not be left with any unanswered questions on this topic!

http://www.firewall.cx/cisco-technical-knowledgebase/cisco-routers/872-cisco-router-gre-ipsec-tunnel-transport.html

Analysing The IP Routing Process - Step-by-Step Analysis

This article explains the IP Routing process with the help of detailed diagrams. We examine step-by-step how a packet is created, sent to a gateway (router) and routed outside the local network. Ethernet, MAC Addresses, ARP, RARP, DNS, ICMP, TCP and other protocol roles are analysed in the example provided.

http://www.firewall.cx/networking-topics/routing/181-routing-process.html