Chapter 4 Notes

Chapter 4 Notes - Chapter 4 Distance Vector Routing...

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Chapter 4 – Distance Vector Routing Protocols Introduction to Distance Vector Routing Protocols RIP – Router Information Protocol Originally specified in RFC 1058 Hop count is used as metric for path selection If hop count for network > 15, RIP cannot supply a route to that network Router updates are broadcast / multicast every 30 seconds by default IGRP – Interior Gateway Routing Protocol Proprietary protocol dev. By Cisco Bandwidth, delay, load, & reliability used to create a composite metric Routing updates are broadcast every 90 seconds, by default Predecessor of EIGRP – now obsolete EIGRP – Enhanced IGRP Cisco proprietary distance vector routing protocol Can perform unequal cost load balancing Uses Diffusing Update Algorithm (DUAL) to calc. shortest path No periodic updates Updates only sent when change in topology Distance Vector Technology Distance vector – routes are advertised as vectors of distance and direction Distance – in terms of a metric (hop count) Direction – the next-hop router / exit interface Router only knows: Direction or interface in which packets should be forwarded Distance or how far it is to destination network Distance vector routing protocols share certain characteristics Periodic updates Neighbors All routers that share a link are configured to use same routing protocol Routers using distance vector routing are not aware of network topology Broadcast Updates
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Sent to 255.255.255.255 Neighboring routers will process updates All devices will process update up to Layer 3 before discarding Entire Routing Table Updates Sent periodically to all neighbors Neighbors must process entire update to find pertinent info and discard rest Routing Protocol Algorithms Purpose of the Algorithm: Used to calculate the best paths and send that info to the neighbors Defines the following processes: Sending and receiving routing info Calculating the best paths and installing routes in the routing table Detecting and reacting to topology changes Routing Protocol Characteristics Based on: Time to Convergence – how quickly routers in network topology share routing information & reach a state of consistent knowledge Scalability – how large a network can become based on routing protocol that is deployed Classless or Classful – Classless include subnet mask in updates (supports VLSM) Classful – do not include subnet mask, do not support VLSM Resource Usage – requirements of a routing protocol (mem. Space, CPU utilization, link bandwidth utilization)
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Chapter 4 Notes - Chapter 4 Distance Vector Routing...

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