ch4.pdf

JTO PH-II IT RIP 4 ROUTING INFORMATION PROTOCOL 4.1 OBJECTIVE The objectives of this chapter is to understand  Routing Information Protocol concepts  RIP characteristics & featur...

JTO PH-II IT RIP 4 ROUTING INFORMATION PROTOCOL 4.1 OBJECTIVE The objectives of this chapter is to understand  Routing Information Protocol concepts  RIP characteristics & features  RIP functionality & format of RIPv2 update message  Comparison between RIPv1 and RIPv2  Configuration procedure for RIPv2 4.2 INTRODUCTION TO ROUTING INFORMATION PROTOCOL A brief introduction on static and dynamic routing was given in the last chapters. This chapter discusses about routing information protocol in detail. PURPOSE OF ROUTING PROTOCOLS The roles played by routers are colossal in efficiently interconnecting different networks across Internet. For selection of best path between networks across countries router relies on routing table contents. The routing table contents may be static as dictated by network administrators. Since there are notable drawbacks in using static routing, larger networks prefer dynamic routing by enabling routing protocols. Routing protocols help in populating the routing table contents and keep the contents updated as and when network topology changes. It is not that entire Internet – Network of Networks runs using a single routing protocol. Many routing protocols run in different segments of Internet. Let us categorize them in the next section. Routing protocols‘ primary function is to update the routers‘ routing table. In simple terms routing protocols are languages by which routers speak about different networks they have in their topology. When a routing protocol is enabled on a particular router, that router will talk to other routers in which the same routing protocol is enabled in order to share network related information by exchanging route announcements. Most significant point to note is that, different routing protocols behave differently in exchanging network information. Based on the properties of routing protocols namely…. To which routers they share information? In what periodicity they exchange routing updates? What contents they exchange? JTO PH-II IT Version Page 46 of 136 For Restricted Circulation  JTO PH-II IT RIP …… routing protocols are classified as shown in Figure below Figure 20: Classification of Routing Protocols Figure 21: Role of EGP & IGP Autonomous system An autonomous system (AS) is a collection of connected Internet Protocol (IP) routing prefixes along with their routers which are controlled under a single administration that follows a defined routing policy. Interior Gateway Protocols An interior gateway protocol (IGP) is a routing protocol that is used to exchange routing information within routers of an autonomous system (AS). Examples of IGP are RIP Routing Information Protocol, OSPF Open shortest Path First Protocol and EIGRP Enhanced Interior Gateway Routing Protocol. Exterior Gateway Protocols A routing protocol that exchanges routing information between different autonomous systems is termed as Exterior Gateway Protocol. BGP Border Gateway Protocol is an example of an EGP. JTO PH-II IT Version Page 47 of 136 For Restricted Circulation  JTO PH-II IT RIP 4.3 ROUTING INFORMATION PROTOCOL - FEATURES Routing Information Protocol (RIP) is a distance vector protocol that measures the distance to reach a remote network by calculating hop count. RIP Metric: Figure 22: Calculation RIP metric The term hop count refers to the number of routers that a packet has to passes through from its source router to reach the destination network. RIP protocol uses Bellman Ford algorithm to find best route. Characteristics & features of Routing Information Protocol: 1. RIP is a distance vector routing protocol 2. RIP is an IGP Interior Gateway Protocol – works within AS 3. Administrative distance of RIP is 120 4. Supports classless routing and VLSM (RIPv2) 5. RIP uses metric – HOP COUNT to decide best path to reach a destination 6. RIP sends periodic update messages to next RIP routers 7. Entire routing table is sent each time 8. Maximum number of hops supported by RIP is 15 JTO PH-II IT Version Page 48 of 136 For Restricted Circulation  JTO PH-II IT RIP 9. A route with Hop count 16 is considered as an invalid route. 10. A RIP update message carry a maximum of 25 routes 11. RIP uses UDP as transport layer and identified by port no 520 12. For avoiding routing loops RIP uses the following mechanisms: Split horizon - Don‘t send routes/ route updates learnt by a router back to it... Route poison - Routers send possibly down networks with Hop count 16 and keep them in HOLD DOWN status. Poison reverse - Is an acknowledgment for a route poison message, an exception to split horizon, send back a poisoned route with hop count set as 16. 13. RIP supports equal cost load balancing by default 14. RIP supports both manual and automatic route summarization (across major networks) 15. Timers used by RIP  Update interval - 30 sec (routing updates scheduled)  Invalid timer - 180 sec-(after last update, total 180 Sec) route is marked as invalid, but a part of routing update (metric is marked 16).  Hold down timer - 180 sec (new routes are on hold)  Flush timer - 240 sec - route is deleted Figure 23: RIP Timers 4.4 HOW RIP WORKS? RIP routers send their entire routing table contents of their table only to neighbor routers periodically. See Figure.5 The receiving router processes the route announcements and updates in its routing table if needed and forwards the contents of its own routing table to the next neighbor. This process repeats for all routers periodically. This type of exchanging routing information is referred as ―routing by rumor‖ JTO PH-II IT Version Page 49 of 136 For Restricted Circulation  JTO PH-II IT RIP Figure 24: How RIP works The maximum hop count of the path is limited to 15 hops to prevent infinite routing loops; this limits the size of RIP networks. In RIPv1, the entire routing table contents are sent as route announcements as broadcast messages periodically, for every 30 seconds to only neighbors using the IP address 255.255.255.255. These entire routing contents are sent periodically to all devices as broadcast information. RIPv1 does not support VLSM. The improved version RIPv2 sends the entire routing table contents by using multicast address 224.0.0.9. RIPv2 supports VLSM and routing announcements contains subnet mask details. RIPv2 does automatic network address summarization. 4.5 COMPARISON OF RIPV1 AND RIPV2 FEATURES RIPv1 RIPv2 Supports classful routing Supports classless routing Support only FLSM Supports FLSM & VLSM Don‘t carry SNM in route update Carry SNM in route update messages messages Route updates are sent as broadcast Router updates are sent as multicast messages - 255.255.255.255 messages - 224.0.0.9 Auto summarizes routes across major Auto summarizes routes across network boundaries major network boundaries Supports manual route No manual route summarization support summarization Timed updates - every 30 seconds + Updates are timed - every 30 seconds triggered updates Support protocol authentication Does not support protocol authentication between RIPv2 routers JTO PH-II IT Version Page 50 of 136 For Restricted Circulation  JTO PH-II IT RIP Table 8. Features of RIPv1 & RIPv2. RIP has little overhead regarding used bandwidth, configuration time and management time. It maintains only a single table – routing table. RIP is very easy to implement, suitable for small networks. 4.6 FORMAT OF RIPV2 UPDATE MESSAGE: Figure 25: Update Message Format of RIP 4.7 CONFIGURING RIPV2 When we enable static routes on a router, the unknown networks for that router needs to be configured. But while enable dynamic routing on a router, we configure directly connected routes under a routing protocol as given below… 4.8 STEPS TO CONFIGURE RIPV2: a. On each router, enable RIP by ROUTER RIP command. b. Disable RIPv1 and enable RIPv2 using the VERSION 2 command under RIP. c. Advertise the directly connected networks as classful numbers. d. Repeat steps a to c in all routers. JTO PH-II IT Version Page 51 of 136 For Restricted Circulation JTO PH-II IT RIP Figure 26: RIPv2 Configuration Figure 27: Checking RIP routes in routing table JTO PH-II IT Version Page 52 of 136 For Restricted Circulation  JTO PH-II IT RIP Figure 28: Listing RIP protocol details 4.9 RIP CONFIGURATION COMMANDS Commands Description ROUTER RIP Enable RIP protocol VERSION 2 Enables RIPv2 NETWORK To make RIP to advertise the network To display routing protocols running on a SHOW IP PROTOCOLS router SHOW IP ROUTE To list out routing table contents Table 9. Basic RIP configuration commands 4.10 CONCLUSION Routing Information Protocol (RIP) is a distance vector protocol that uses hop count as its primary metric. RIP defines how routers should share information when moving traffic among an interconnected group of local area networks (LANs). RIP protocol is easy to implement and is convenient for smaller network. JTO PH-II IT Version Page 53 of 136 For Restricted Circulation