Lecture Week 3 Introduction to Dynamic Routing Protocol Routing Protocols and Concepts

Objectives Describe dynamic routing protocols: Functions Purpose Component s Identify several ways to classify routing protocols. Describe some new concepts of dynamic routing protocols: Convergence Metrics Administrative Distance (AD) Identify the different elements of the routing table.

Dynamic Routing Protocols Dynamic routing protocols are usually used in larger networks to ease the administrative and operational overhead of using only static routes. Typically, a network uses a combination of both a dynamic routing protocol and static routes.

The Evolution of Dynamic Routing Protocols One of the earliest routing protocols was Routing Information Protocol (RIP). –RIP has evolved into a newer version RIPv2. –The newer version of RIP still does not scale to larger network implementations. To address the needs of larger networks, two advanced routing protocols were developed: Open Shortest Path First (OSPF) and Intermediate System- to-Intermediate System (IS-IS). Cisco developed Interior Gateway Routing Protocol (IGRP) and Enhanced IGRP (EIGRP), which also scales well in larger network implementations. Additionally, there was the need to interconnect different internetworks and provide routing among them. Border Gateway Routing (BGP) protocol is now used between ISPs as well as between ISPs and their larger private clients to exchange routing information.

Dynamic Routing Protocols Function(s) of Dynamic Routing Protocols: – -Dynamically share information between routers. – -Automatically update routing table when topology changes. – -Determine best path to a destination. –Compared to static routing, dynamic routing protocols require less administrative overhead. However, the expense of using dynamic routing protocols is dedicating part of a router's resources for protocol operation including CPU time and network link bandwidth. – One of the primary benefits to using a dynamic routing protocol is that routers exchange routing information whenever there is a topology change. This exchange allows routers to automatically learn about new networks and also to find alternate paths when there is a link failure to a current network.

Dynamic Routing Protocols A routing protocol –is a set of processes, algorithms, and messages that are used to exchange routing information and populate the routing table with the routing protocol's choice of best paths The purpose of a dynamic routing protocol is to: – -Discover remote networks – -Maintaining up-to-date routing information – -Choosing the best path to destination networks – -Ability to find a new best path if the current path is no longer available

Dynamic Routing Protocols Advantages of static routing – -It can backup multiple interfaces/networks on a router – -Minimal CPU processing – -Easier for administrator to understand – -Easy to configure – -No extra resources are needed – -More secure Disadvantages of static routing – -Network changes require manual reconfiguration – -Configuration and maintenance is time-consuming – -Does not scale well in large topologies – -Configuration is error-prone, especially in large networks  Advantages of dynamic routing -Administrator has less work maintaining the configuration when adding or deleting networks. -Protocols automatically react to the topology changes. -Configuration is less error-prone. -More scalable, growing the network usually does not present a problem  Disadvantages of dynamic routing -Router resources are used (CPU cycles, memory and link bandwidth). -More administrator knowledge is required for configuration, verification, and troubleshooting.

Dynamic Routing Protocols

Classifying Routing Protocols Dynamic routing protocols are grouped according to characteristics. Examples include: – -RIP – -IGRP – -EIGRP – -OSPF – -IS-IS – -BGP Autonomous System is a group of routers under the control of a single authority.

Classifying Routing Protocols Dynamic routing protocols: –RIP A distance vector interior routing protocol –IGRP The distance vector interior routing developed by Cisco (deprecated from 12.2 IOS and later) –EIGRP The advanced distance vector interior routing protocol developed by Cisco –OSPF A link-state interior routing protocol –IS-IS A link-state interior routing protocol –BGP A path vector exterior routing protocol

Dynamic Routing Protocols Function(s) of Dynamic Routing Protocols: – -Dynamically share information between routers. – -Automatically update routing table when topology changes. – -Determine best path to a destination.

Dynamic Routing Protocols The purpose of a dynamic routing protocol is to: – -Discover remote networks – -Maintaining up-to-date routing information – -Choosing the best path to destination networks – -Ability to find a new best path if the current path is no longer available

Dynamic Routing Protocols Components of a routing protocol – Routing protocol messages These are messages for discovering neighbors and exchange of routing information – Algorithm In the case of a routing protocol algorithms are used for facilitating routing information and best path determination

Classifying Routing Protocols Interior Gateway Routing Protocols (IGP) – -Used for routing inside an autonomous system & used to route within the individual networks themselves. – -Examples: RIP, EIGRP, OSPF Exterior Routing Protocols (EGP) – -Used for routing between autonomous systems – -Example: BGPv4 Autonomous System is a group of routers under the control of a single authority.

Autonomous systems An autonomous system (AS) is a collection of networks under a common administration sharing a common routing strategy. – To the outside world, an AS is viewed as a single entity. The AS may be run by one or more operators while presenting a consistent view of routing to the external world. The American Registry of Internet Numbers (ARIN), a service provider, or an administrator assigns an identifying number to each AS. This autonomous system number is a 16 bit number. Routing protocols, such as Cisco’s IGRP, require assignment of a unique, autonomous system number.

Classifying Routing Protocols Types of routing protocols: – -Interior Gateway Protocols (IGP) – -Exterior Gateway Protocols (EGP) –

Classifying Routing Protocols Dynamic routing protocols are grouped according to characteristics. Examples include: – -RIP – -IGRP – -EIGRP – -OSPF – -IS-IS – -BGP

Classifying Routing Protocols IGP: Comparison of Distance Vector & Link State Routing Protocols –Distance vector –routes are advertised as vectors –of distance & direction. –incomplete view of network –topology. –Generally, periodic – updates. –Link state –complete view of network –topology is created. –updates are not – periodic.

Classifying Routing Protocols

Classful routing protocols – Do NOT send subnet mask in routing updates Classless routing protocols – Do send subnet mask in – routing updates.

Dynamic Routing Protocols Concepts Convergence is defined as when all routers’ routing tables are at a state of consistency

Routing Protocols Metrics Metric – A value used by a routing protocol to determine which routes are better than others.

Routing Protocols Metrics Metrics used in IP routing protocols – -Hop count – -Bandwidth – -Cost – -Delay – -Load – -Reliability

Routing Protocols Metrics The Metric Field in the Routing Table Metric used for each routing protocol – -RIP - hop count – -IGRP & EIGRP - Bandwidth (used by default), Delay (used by default), Load, Reliability – -IS-IS & OSPF – Cost, Bandwidth (Cisco’s implementation)

Routing Protocols Metrics Load balancing – This is the ability of a router to distribute packets among multiple same cost paths

Administrative Distance of a Route Purpose of a metric – It’s a calculated value used to determine the best path to a destination Purpose of Administrative Distance – It’s a numeric value that specifies the preference of a particular route

Administrative Distance of a Route Identifying the Administrative Distance (AD) in a routing table – It is the first number in the brackets in the routing table

Administrative Distance of a Route Directly connected routes – Have a default AD of 0 Static Routes – Administrative distance of a static route has a default value of 1

Administrative Distance of a Route Directly connected routes – -Immediately appear in the routing table as soon as the interface is configured

Administrative Distance of a Route Dynamic Routing Protocols

Summary Dynamic routing protocols fulfill the following functions – -Dynamically share information between routers – -Automatically update routing table when topology changes – -Determine best path to a destination Routing protocols are grouped as either – -Interior gateway protocols (IGP)Or – -Exterior gateway protocols(EGP) Types of IGPs include – -Classless routing protocols - these protocols include subnet mask in routing updates – -Classful routing protocols - these protocols do not include subnet mask in routing update

Summary Metrics are used by dynamic routing protocols to calculate the best path to a destination. Administrative distance is an integer value that is used to indicate a router’s “trustworthiness” Components of a routing table include: – -Route source – -Administrative distance – -Metric

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