The open systems interconnect (OSI) model provides the standardization of a communication system by breaking it into seven layers. From lowest to highest, these are physical,data link, network, transport,session, presentation, application. At each level, the peers communicate using protocol data units (PDUs). These are maintained by ISO(International Organization for Standardization) as part of identification ISO/IEC 7498-1.
Practically, the TCP/IP model with four layered approach for end to end connectivity for data transmission overtook the OSI model in implementation of devices. From lowest to highest, these layers are link, internet, transport and application. TCP/IP model is maintained by Internet Engineering Task Force.
Routers and Switches are two of the essential device elements of any network. With respect to the OSI model, a router operates at layer 3 to store IP addresses in a routing table and maintain an address of its own. A network switch operates at layer 2 of the OSI model. A network switch stores MAC addresses in a look-up table and resolves the destination IP address using the stored MAC address.
Routers serve as interconnections between multiple networks, receive the incoming TCP/IP packets, read the packet internals to identify source and target the IP address — and forward the packets to ensure the data reaches its final target address. Additional features like security maybe performed within routers.
A network switch joins multiple devices on the same network using a MAC address lookup mechanism. It is unable to join multiple networks or work as gateway for internet sharing.
The two primary functions of a router are to identify the best path for forwarding packets and forwarding the packets to their destination on the path.
Routing Protocols discusses the three methods of packet forwarding mechanisms: process switching, fast switching , cisco express forwarding. The authors advise best practices for maintaining two useful network documents — topology diagram and addressing table. Starting from basic router setup and configuration, there is a walk through of essential concepts like static routing, dynamic routing, link state routing protocols, distance vector routing protocols, enhanced interior gateway routing protocol (EIGRP), open shortest path first link state routing protocol (single area and multi area) to advanced concepts like access control lists and Cisco IOS (earlier Internetwork Operating System).
The book discusses EIGRP, which is a distance vector routing protocol that includes features from link state routing protocols, in detail. EIGRP can scale to include multiple topologies and provide essential quick convergence times with minimal network traffic. This protocol was released initially as proprietary protocol for Cisco Devices. Recently Cisco has released a basic functionality of EIGRP as an open standard to the IETF as an informational RFC. Advanced features of EIGRP will not be released to IETF.
There is also detailed introduction to OSPF which was a replacement over the distance vector routing protocol RIP. The book discusses how OSPF is a classless routing protocol that uses concept of areas for scalability.There is discussion how OSPF creates and maintains three databases — adjacency database, link state database and forwarding database which contains a list of neighbouring routers to exchange routing information which is kept and maintained in router memory.
Being a Cisco Network Academy title, there is care taken to present this text as an introduction for career network professionals as well as others requiring updated and on the job information about routing protocols. The book does a neat job of covering the essentials of routing protocols. One of the drawbacks in this book is the requirement of an additional supplementary book Routing Protocols Lab Manual for labs and class activities from this companion guide.[amazon template=iframe image&chan=default&asin=B009O3376S]