These are all concepts that we need to understand before we can get into the nitty-gritty of exactly what a specific protocol does, why it does it, why it does it the way that it does it, how it does it and when it does what it does. We also need to be able to distinguish the commonalities and differences that exist between different protocols. So let's get at it.

Routing

Routing is the process of moving data from one network to another network

Routing Protocols

In short routing protocols are the software that sends and receives routing information packets to and from other routers and in so doing allows the router to:

• Dynamically Advertise Routes
• Dynamically Learn Routes
• Determine Possible Routes
• Determine Route Availability
• Determine Route Efficiency
• Determine Best Route to Destination
• Determine Alternative Routes

Here are some of the routing protocols currently in use today:

• RIP - Routing Information Protocol
• RIP II - Routing Information Protocol II
• OSPF - Open Shortest Path First
• IS-IS - Intermediate System to Intermediate System
• IGRP - Interior Gateway Routing Protocol
• EIGRP - Enhanced Interior Gateway Routing Protocol (Cisco proprietary protocol)
• BGP - Border Gateway Protocol

All you need to remember is that routing protocols convey routing information such as routing tables, network IDs, hop counts, administrative distance/cost, other metrics and autonomous numbers to neighbouring routers.

To illustrate this here is a simple version of what routing protocols get up to:

Router1: “Hey! Neighbour here is something really good it's my routing table. Check it out and see if there is anything in it that you don't know already.”

Router2: “Well thanks a lot. Here is mine. Do likewise.”

Routed (Routable) Protocols

A routed protocol is routable meaning that it can be routed by a router. This means that it can be forwarded from one router to another.

Routed protocols contain the data elements; such as IP Addresses, that are required in order for a packet to be sent outside of its host network or network segment.

IP (Internet Protocol) and IPX (Internet Packet Exchange) are examples of routed protocols.

Non-Routable Protocols

Non-routable protocols cannot survive being routed. In short non-routable protocols have a very narrow world view in that they assume that every computer that they will ever need to communicate with exists on the same network segment as them.

Today we find that those protocols that are not multi-segment aware are disappearing from use. The following are examples of non-routable protocols:

• NetBEUI
• DLC
• LAT
• DRP
• MOP

Interior Gateway Protocols (IGP)

Interior Gateway Protocols are used to communicate routing information between routers within an autonomous system. Because they transport (communicate) routing information they are routing protocols and not routed protocols as many people mistakenly believe.

Conclusion

Today the world is very Internet centric and so we find that those elements, protocols, systems etc. that can't get along with the Internet are doomed to fade rather rapidly into oblivion and non-routable protocols are among the first to go.

Well it's now time to go. So until we meet again in a future edition of The CCNA Summary Series enjoy!