Distance vector routing updates

Distance Vector Routing 

Distance vector routing updates 

7.1.1 

This page will explain how distance vector routing updates occur.
Routing table updates occur periodically or when the topology in a distance vector protocol network changes. It is important for a routing protocol to update the routing tables efficiently. As with the network discovery process, topology change updates proceed systematically from router to router. Distance vector algorithms call for each router to send its entire routing table to each of its adjacent neighbors. The routing tables include information about the total path cost. The path cost is defined by the metrics and the logical address of the first router on the path to each network in the table.
The next page will explain how routing loops occur.

Module 7: Distance Vector Routing Protocols / Overview

Module 7: Distance Vector Routing Protocols 

Overview

Dynamic routing makes it possible to avoid the configuration of static routes. Dynamic routing makes it possible to avoid the time-consuming and exacting process of configuring static routes. Dynamic routing also makes it possible for routers to react to changes in the network and to adjust their routing tables accordingly, without the intervention of the network administrator. However, dynamic routing can cause problems. Some of the problems associated with dynamic distance vector routing protocols are discussed in this module, along with some of the steps that designers of the protocols have taken to solve the problems.
RIP is a distance vector routing protocol that is used in thousands of networks throughout the world. The fact that RIP is based on open standards and is easy to implement makes it attractive to some network administrators. However, RIP lacks the power and features of more advanced routing protocols. Because of its simplicity, RIP is a good basic protocol for networking students. This module will also introduce RIP configuration and troubleshooting.
IGRP is another distance vector routing protocol. Unlike RIP, IGRP is a Cisco-proprietary protocol rather than a standards-based protocol. IGRP is also very simple to implement. However, IGRP is a more complex routing protocol than RIP and can use many factors to determine the best route to a destination network. This module will introduce IGRP configuration and troubleshooting.
This module covers some of the objectives for the CCNA 640-801, INTRO 640-821, and ICND 640-811 exams. -
Students who complete this module should be able to perform the following tasks:

• Describe how routing loops can occur in distance vector routing
• Describe several methods used by distance vector routing protocols to ensure that routing information is accurate
• Configure RIP
• Use the ip classless command
• Troubleshoot RIP
• Configure RIP for load balancing
• Configure static routes for RIP
• Verify RIP
• Configure IGRP
• Verify IGRP operation 
• Troubleshoot IGRP 
  

Module 6: Summary

Module 6: Summary

This page summarizes the topics discussed in this module.
The process that a router uses to forward packets toward the destination network is called routing. Decisions are based upon the destination IP address of each packet. When routers use dynamic routing, they learn about remote networks from other routers. When static routing is used, a network administrator configures information about remote networks manually.
Static route operations can be divided into these three parts. First a network administrator uses the ip route command to configure a static route. Then the router installs the route in the routing table. Finally, the route is used to route packets.
Static routes can be used for backup purposes. A static route can be configured on a router that will only be used when the dynamically learned route has failed.
After static routes are configured, verify they are present in the routing table and that routing works as expected. Use the command show running-config to view the active configuration in RAM. The show ip route command is used to make sure that the static route is present in the routing table.
The communication used between routers is referred to as a routing protocol. The goal of a routing protocol is to build and maintain the routing table.
A routed protocol is used to direct user traffic. A routed protocol provides enough information in its network layer address to allow a packet to be forwarded from one host to another based on the addressing scheme.
An AS is a collection of networks under the same administration that share a common routing strategy. Autonomous systems divide the global internetwork into smaller and more manageable networks. Each AS has its own set of rules and policies and a number that distinguishes it from all other autonomous systems.
The distance vector routing approach determines the direction, or vector, and distance to any link in an internetwork. The link-state approach recreates the exact topology of an entire internetwork.
Distance vector routing algorithms pass periodic copies of a routing table from router to router. These regular updates between routers communicate topology changes. The distance vector routing algorithm is also known as the Bellman-Ford algorithm.
The second basic algorithm used for routing is the link-state algorithm. The link-state algorithm is also known as the Dijkstra algorithm or as the SPF algorithm. Link-state routing algorithms maintain a complex database of topology information. The distance vector algorithm has nonspecific information about distant networks and no knowledge of distant routers. A link-state routing algorithm maintains full knowledge of distant routers and how they interconnect.
Interior routing protocols are designed for use in a network whose parts are under the control of a single organization. An exterior routing protocol is designed for use between two different networks that are under the control of two different organizations. These are typically used between ISPs or between a company and an ISP.