Distance Vector Routing Protocols Routing Protocols and Concepts – Chapter 4 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public ITE PC v4.0 Chapter 1 1 Objectives Identif y the characteristics of distance vector routin g p rotocols. ygp Describe the network discovery process of distance vector routing protocols using Routing Information Protocol (RIP). Describe the processes to maintain accurate routing tables used by distance vector routing protocols. Id tif th diti l di t ti l d l i th Id en tif y th e con diti ons l ea di ng t o a rou ti ng l oop an d exp l a i n th e implications for router performance. Recognize that distance vector routing protocols are in use today Recognize that distance vector routing protocols are in use today ITE PC v4.0 Chapter 1 2 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Distance Vector Routing Protocols Dynamic routing protocols help the network administrator overcome the time- consuming and exacting process of configuring and maintaining static routes consuming and exacting process of configuring and maintaining static routes . Examples of Distance Vector routing protocols: Routing Information Protocol (RIP) RFC 1058 – RFC 1058 . –Hop count is used as the metric for path selection. –If the hop count for a network is greater than 15, RIP cannot supply a route to that network. R ti d t b d t lti t 30 d b d f lt – R ou ti ng up d a t es are b roa d cas t or mu lti cas t every 30 secon d s, b y d e f au lt . Interior Gateway Routing Protocol (IGRP) –proprietary protocol developed by Cisco. – Bandwidth, delay, load and reliability are used to create a composite metric. Bandwidth, delay, load and reliability are used to create a composite metric. –Routing updates are broadcast every 90 seconds, by default. –IGRP is the predecessor of EIGRP and is now obsolete. Enhanced Interior Gatewa y Routin g Protocol ( EIGRP ) yg () –Cisco proprietary distance vector routing protocol. –It can perform unequal cost load balancing. –It uses Diffusing Update Algorithm (DUAL) to calculate the shortest path. – There are no periodic updates as with RIP and IGRP Routing updates are sent only ITE PC v4.0 Chapter 1 3 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public – There are no periodic updates as with RIP and IGRP . Routing updates are sent only when there is a change in the topology. Distance Vector Routing Protocols The Meaning of Distance Vector : The Meaning of Distance Vector : –A router using distance vector routing protocols knows 2 things: Distance to final destination Distance to final destination The distance or how far it is to the destination network Vector or direction traffic should be directed Vector , or direction , traffic should be directed The direction or interface in which packets should be forwarded For example, in the figure, R1 knows that the distance to reach network 172.16.3.0/24 is 1 hop and that the direction is out the i t f S0/0/0 t d R2 ITE PC v4.0 Chapter 1 4 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public i n t er f ace S0/0/0 t owar d R2 . Distance Vector Routing Protocols Distance Vector Routing Protocols Characteristics of Distance Vector routing protocols: Periodic u p dates p •Periodic Updates sent at regular intervals (30 seconds for RIP). Even if the topology has not changed in several days, Neighbors The router is only aware of the network addresses of its own interfaces and the remote network addresses it can reach through its neighbors. It has no broader knowledge of the network topology Broadcast updates Broadcast Updates are sent to 255.255.255.255. Some distance vector routing protocols use multicast addresses instead of broadcast addresses addresses instead of broadcast addresses . Entire routing table is included with routing update Entire Routing Table Updates are sent, with some e x cept i o n s to be d i scussed l ate r , pe ri od i ca ll y to a ll exceptions to be discussed later, periodically to all neighbors. Neighbors receiving these updates must process the entire update to find pertinent information and discard the rest. Some distance vector routing protocols like EIGRP do not ITE PC v4.0 Chapter 1 5 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Some distance vector routing protocols like EIGRP do not send periodic routing table updates. Distance Vector Routing Protocols Distance Vector Routing Protocols Routing Protocol Algorithm: Th l ith i d t l l t th b t th d th d – Th e a l gor ith m i s use d t o ca l cu l a t e th e b es t pa th s an d th en sen d that information to the neighbors. – Different routin g p rotocols use different al g orithms to install routes gp g in the routing table, send updates to neighbors, and make path determination decisions. ITE PC v4.0 Chapter 1 6 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Distance Vector Routing Protocols Routing Protocol Characteristics Criteria used to compare routing protocols includes – Criteria used to compare routing protocols includes Time to convergence Time to convergence defines how quickly the routers in the network topology share routing information and reach a state of consistent knowledge. The faster the convergence, the more preferable the protocol. Scalability Scalability defines how large a network can become based on the routing protocol that is deployed deployed . The larger the network is, the more scalable the routing protocol needs to be. Resource usage Resource usa g e includes the re q uirements of a routin g p rotocol such as memor y s p ace , gq gp yp, CPU utilization, and link bandwidth utilization. Higher resource requirements necessitate more powerful hardware to support the routing protocol operation Classless ( Use of VLSM ) or Classful () Classless routing protocols include the subnet mask in the updates. This feature supports the use of Variable Length Subnet Masking (VLSM) and better route summarization. Implementation & maintenance ITE PC v4.0 Chapter 1 7 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Implementation & maintenance Implementation and maintenance describes the level of knowledge that is required for a network administrator to implement and maintain the network based on the routing protocol deployed. Distance Vector Routing Protocols Distance Vector Routing Protocols ITE PC v4.0 Chapter 1 8 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Network Discovery Router initial start up (Cold Starts) Cold Starts Router initial start up (Cold Starts) When a router cold starts or powers up, it knows nothing about the network topology. It does not even know that there are devices on the other end of its links. The only information that a router has is from its own saved configuration file stored in NVRAM. Initial network discovery - Initial network discovery Directly connected networks are initially placed in routing table routing table ITE PC v4.0 Chapter 1 9 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Network Discovery I iti l E h Network Discovery Initial Exchange of Routing Information – If a routing protocol is configured then I n iti a l E xc h ange If a routing protocol is configured then •Routers will exchange routing information •Initially, these updates only include information about their directly connected networks. Routing updates received from other routers –Router checks update for new information •If there is new information: –Metric is updated –New information is stored in routing table After this first round of update exchanges, each tk btth td t kfthi rou t er k nows a b ou t th e connec t e d ne t wor k s o f th e i r directly connected neighbors. However, did you notice that R1 does not yet know about 10400andthatR3does not yet know about about 10 . 4 . 0 . 0 and that R3 does not yet know about 10.1.0.0? –Full knowledge and a converged network will not take place until there is another exchange of routing information ITE PC v4.0 Chapter 1 10 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public information . [...]... by: -Incorrectly configured static routes -Incorrectly configured route redistribution -Slow convergence -Incorrectly config red discard ro tes Incorrectl configured routes Routing loops can create the following issues -Excess use of bandwidth Excess -CPU resources may be strained -Network convergence is degraded Network -Routing updates may be lost or not processed in a timely manner ITE PC v4.0 Chapter. .. and not with switches) Packet Solution to problems with synchronized updates - Used of random variable called RIP_JITTER •A good reference is : Routing TCP/IP (Jeff Doyle) page 19 3-1 96 Update •Update timers : timer for periodic update (default 30s) - RIP_JITTER (random to prevent colision - 15% of the update timers) ITE PC v4.0 Chapter 1 © 2007 Cisco Systems, Inc All rights reserved Cisco Public 22 Routing... velopment/source/157870 041 8/ch05lev1sec1.html#ch05fig1 ITE PC v4.0 Chapter 1 © 2007 Cisco Systems, Inc All rights reserved Cisco Public 23 Routing Loops R ti L Routing loops are A condition in which a packet is continuously transmitted within a series of routers i f t without ever reaching its destination ITE PC v4.0 Chapter 1 © 2007 Cisco Systems, Inc All rights reserved Cisco Public 24 Routing Loops Routing... calculating best path routes using the new routing information collected 4 For example: It takes five rounds of periodic update intervals before most of the branch routers in Regions 1 2 and 3 1, 2, learn about the new routes advertised by B2-R4 ITE PC v4.0 Chapter 1 5 3 2 1 © 2007 Cisco Systems, Inc All rights reserved Cisco Public 14 Routing Table Maintenance Periodic Updates: RIPv1 & RIPv2 –These are... incorrect updates about network 10 .4. 0.0 10 4 0 0 ITE PC v4.0 Chapter 1 © 2007 Cisco Systems, Inc All rights reserved Cisco Public 34 Preventing loops with TTL IP & TTL –Purpose of th TTL field P f the fi ld The TTL field is found in an IP header and is i used t prevent packets from endlessly d to t k t f dl l traveling on a network How th TTL field works H the fi ld k -TTL field contains a numeric value... the triggered update update ITE PC v4.0 Chapter 1 © 2007 Cisco Systems, Inc All rights reserved Cisco Public 20 Triggered Extensions to RIP Problems and Prerequisites Prerequisites P i it –RIP must be enabled for this feature to function –This feature runs on a point-to-point, serial interface only –Triggered extensions to IP RIP increase efficiency of RIP on point-top point, serial interfaces , •interface... around a network ITE PC v4.0 Chapter 1 © 2007 Cisco Systems, Inc All rights reserved Cisco Public 27 Preventing loops by Setting a maximum Setting a maximum g Distance Vector routing protocols set a specified metric value to indicate infinity y Once a router “counts to infinity” it marks the route as unreachable RIP defines infinity as 16 hops - an "unreachable" metric ITE PC v4.0 Chapter 1 © 2007 Cisco... reinstating a route that may have gone bad -Holddown ti H ldd timers allow a router t not accept any changes to a ll t to t t h t route for a specified period of time - Do not appept the update when the route is flapping -Point of using holddown timers Allows routing updates to propagate through network with the most current information information ITE PC v4.0 Chapter 1 © 2007 Cisco Systems, Inc All rights... http://cisco.com/en/US/docs/ios/12_0t/12_0t1/feature/guide/trigrip.html ITE PC v4.0 Chapter 1 © 2007 Cisco Systems, Inc All rights reserved Cisco Public 21 Routing Table Maintenance Random Jitter Synchronized updates A condition where multiple routers on multi access LAN segments transmit routing updates at the same time Problems with synchronized updates P bl ith h i d d t -Bandwidth consumption -Packet collisions... Note: The IP protocol has its own mechanism to prevent the possibility of a packet traversing the network endlessly IP has a Time-to-Live ( (TTL) f ) field and its value is decremented by 1 at each router –If the TTL is zero, the router drops the packet If zero packet ITE PC v4.0 Chapter 1 © 2007 Cisco Systems, Inc All rights reserved Cisco Public 26 Preventing loops with Count to Infinity Count t I fi . Vector Routing Protocols Routing Protocols and Concepts – Chapter 4 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public ITE PC v4.0 Chapter 1 1 Objectives Identif y the characteristics. knows that the distance to reach network 172.16.3.0/ 24 is 1 hop and that the direction is out the i t f S0/0/0 t d R2 ITE PC v4.0 Chapter 1 4 © 2007 Cisco Systems, Inc. All rights reserved. Cisco. information collected 4 5 For example: It takes five rounds of periodic update intervals before most of the branch routers in Regions 1 2 and 3 2 3 ITE PC v4.0 Chapter 1 14 © 2007 Cisco Systems,