Dynamic routing protocols are used to maintain newest routing information in communications between network devices, discover other networks and choose the best paths to forward messages. One of the earliest dynamic routing protocols was RIPv1 (Routing Information Protocol). This protocol used hop count as a communication element and it was not appropriate for larger network implementations. RIPv1 does not support VLSM implementations. Newer dynamic protocols were invented to cover RIP limitations, RIPv2, EIGRP (Enhanced Interior Gateway Routing Protocol – Cisco proprietary protocol), OSPF (Open Shortest Path First) and IS-IS (Intermediate System-to-Intermediate System). These type of protocols were called Interior Gateway Protocols because they were implemented inside a network. Another type of dynamic routing protocols is the Exterior Gateway Protocols, these kind of dynamic routing protocols are used to interconnect networks. A well known exterior gateway protocol is BGP (Border Gateway Protocol).
When talking about Interior Gateway Protocols (IGP) or Exterior Gateway Protocols (EGP), we have to say something about Autonomous Systems, also known as AS. Autonomous Systems are basically networks that have one ownership and a single point of administration. IGPs are implemented inside networks while EGPs are implemented outside of them (used to interconnect Autonomous Systems).
When working with dynamic routing protocols, you’ll have to remember the following elements:
Load balancing – is a computer networking method to distribute workload across multiple computers or a computer cluster, network links, central processing units, disk drives, or other resources, to achieve optimal resource utilization, maximize throughput, minimize response time, and avoid overload (Wikipedia : http://en.wikipedia.org/wiki/Load_balancing_(computing))
Metric– is used by routing protocols to evaluate paths for packets to follow. Dynamic routing protocols use different metrics, RIP uses hop count, EIGRP uses bandwidth and delay and OSPF uses bandwidth etc. A network can use multiple routing protocols and each one would have it’s own routing methods, paths and metrics. These are the metrics used in IP networks:
Hop count – used by RIP, it counts the number of routers a packet must travel to reach it’s destination.
Bandwidth – used by different routing protocols, the path with the highest bandwidth is chosen.
Cost – a numeric value that can be configured by Administrators to determine the priority of a certain path.
Delay – counts the time that a packet will take to travel from source to destination.
Load – measures the amount of traffic of a path.
Reliability – measures the probability of link failure.
Classful Routing Protocols – do not send network mask in routing update messages. Cannot be used when implementing VLSM (when using different network mask).
Administrative distance – is the measure used by Cisco routers to select the best path when there are two or more different routes to the same destination from two different routing protocols (Wikipedia: http://en.wikipedia.org/wiki/Administrative_distance). The routing protocol with the lowest AD wins. Below is the list of dynamic routing protocols administrative distance:
|EIGRP summary route||5|
In the following video tutorial, I will show you how to view the administrative distance and metric on a Cisco router, how to configure static routing and other useful configuration commands. I hope this was informative folks, have a wonderful day.