Chapter 5 RIP version 1 CIS 82 Routing Protocols and Concepts

Chapter 5 RIP version 1 CIS 82 Routing Protocols and Concepts
Rick Graziani Cabrillo College Last Updated: 3/10/2009

Note This presentation will be updated prior to March. 25, 2008
The audio of the lecture for this presentation will be available on my web site after March. 25, 2008 My web site is For access to these PowerPoint presentations and other materials, please me at

For further information
This presentation is an overview of what is covered in the curriculum/book. For further explanation and details, please read the chapter/curriculum. Book: Routing Protocols and Concepts By Rick Graziani and Allan Johnson ISBN: ISBN-13:

Topics RIPv1: Distance Vector, Classful Routing Protocol
Background and Perspective RIPv1 Characteristics and Message Format RIP Operation Basic RIPv1 Configuration RIPv1 Scenario A Enable RIP: router rip Command Specifying Networks Verification and Troubleshooting Verifying RIP: show ip route Verifying RIP: show ip protocols Verifying RIP: debu ip rip Passive Interfaces Automatic Summarization Modified Topology B Boundary Routers and Automatic Summarization Processing RIP Updates Sending RIP Updates Advantages and Disadvantages of Automatic Summarization Default Route and RIPv1 Modified Topology C Propagating the Default Route in RIPv1

RIPv1 Download Packet Tracer Topology: cis82-RIPv1-A-student.pkt

RIPv1: A Distance Vector, Classful Routing Protocol
Background and Perspective RIPv1 Characteristics and Message Format RIP Operation

RIPv1: Distance Vector, Classful Routing Protocol
Why learn RIP? Still in use today. Help understand fundamental concepts and comparisons of protocols Classful (RIPv1) vs classless (RIPv2)

Background and Perspective
RIP is not a protocol “on the way out.” In fact, an IPv6 form of RIP called RIPng (next generation) is now available..

Background and Perspective
Charles Hedrick wrote RFC 1058 in 1988, in which he documented the existing protocol and specified some improvements. RFC 1058 can be found at

RIPv1 Characteristics and Message Format
RIP characteristics: Distance Vector or Link State? Distance vector routing protocol. Metric? Hop count Maximum Hop count? Greater than 15 are considered unreachable. Routing table updates are broadcasted every…? 30 seconds. (RIPv2 uses multicasts)

Each Route Entry (three fields): Address Family Identifier (set to 2 for IP unless a router is requesting a full routing table, in which case the field is set to 0) IP Address: Network address of an advertised route Metric: How many hops to get to this network via this router (incremented by each router) One RIP update can contain up to 25 route entries.

IP Address Classes and Classful Routing
No subnet mask RIPv1: Classful routing protocol. Does not send subnet mask in update. A router either uses the subnet mask: (discussed later) configured on a local interface or applies the default classful subnet mask Because of this limitation, RIPv1 networks cannot be discontiguous, nor can they implement VLSM. Startup 1. Each RIP-configured interface sends out a Request message Asking for their complete routing tables. 2. A Response message is sent back by RIP-enabled neighbors. If new route: Installs in routing table. If existing route: Replace if better hop count. Startup router then sends a triggered update out all RIP-enabled interfaces containing its own routing table so that RIP neighbors can be informed of any new routes. RIPv1: Classful routing protocol. Does not send subnet mask in update.

IP Address Classes and Classful Routing
Routing Table ? Network-add/mask RIP Update network-add /16 R2 receives an RIP update with a network address. R2 adds the network address and mask to the routing table. A router either uses the subnet mask: (discussed later) Local interface or Default classful subnet mask Because of this limitation, RIPv1 networks cannot be discontiguous, nor can they implement VLSM. RIPv1: Classful routing protocol. Does not send subnet mask in update. A router either uses the subnet mask: (discussed later) configured on a local interface or applies the default classful subnet mask Because of this limitation, RIPv1 networks cannot be discontiguous, nor can they implement VLSM. Startup 1. Each RIP-configured interface sends out a Request message Asking for their complete routing tables. 2. A Response message is sent back by RIP-enabled neighbors. If new route: Installs in routing table. If existing route: Replace if better hop count. Startup router then sends a triggered update out all RIP-enabled interfaces containing its own routing table so that RIP neighbors can be informed of any new routes.

Basic RIPv1 Configuration
RIPv1 Scenario A Enable RIP: router rip Command Specifying Networks

RIPv1 Scenario A RIPv1 is a classful or classless routing protocol?
Notice that this topology uses five Class C network addresses. Remember, RIPv1 is a classful routing protocol We will see that the class of the network is used by RIPv1 to determine the subnet mask. RIPv1 is a classful or classless routing protocol? Classful How many classful networks are there and of what class? 5 Class C network addresses. We will see that the class of the network is used by RIPv1 to determine the subnet mask.

Enabling RIP: router rip Command
R1# conf t Enter configuration commands, one per line. End with CNTL/Z. R1(config)# router ? bgp Border Gateway Protocol (BGP) egp Exterior Gateway Protocol (EGP) eigrp Enhanced Interior Gateway Routing Protocol (EIGRP) igrp Interior Gateway Routing Protocol (IGRP) isis ISO IS-IS iso-igrp IGRP for OSI networks mobile Mobile routes odr On Demand stub Routes ospf Open Shortest Path First (OSPF) rip Routing Information Protocol (RIP) R1(config)# router rip R1(config-router)# Enter router configuration mode for RIP, enter router rip at the global configuration prompt. Notice that the prompt changes. What routing protocols does this router support? (PT is limited) Configure RIP…

Enabling RIP: router rip Command
R1# conf t R1(config)# router rip R1(config-router)# network R1(config-router)# network R1(config-router)# exit R1(config)# no router rip no router rip To remove the RIP routing process from a device Stops the RIP process Erases all existing RIP configuration commands. router rip Does not directly start the RIP process. Provides access to configure routing protocol settings. No routing updates are sent until additional commands are configured. no router rip To remove the RIP routing process from a device Stops the RIP process Erases all existing RIP configuration commands.

Specifying Networks Router(config-router)# network directly-connected-classful-network-address To enable RIP routing for a network, use the network command in router configuration mode Enter the classful network address for each directly connected network. The network command performs the following functions: Enables RIP on all interfaces that belong to a specific network. Associated interfaces will now both send and receive RIP updates. Advertises the specified network in RIP routing updates sent to other routers every 30 seconds. To enable RIP routing for a network, use the network command in router configuration mode Enter the classful network address for each directly connected network.

Specifying Networks R1(config)# router rip R1(config-router)# network R1(config-router)# network RIP Update To enable RIP routing for a network, use the network command in router configuration mode Enter the classful network address for each directly connected network. The network command performs the following functions: Enables RIP on all interfaces that belong to a specific network. Associated interfaces will now both send and receive RIP updates. Advertises the specified network in RIP routing updates sent to other routers every 30 seconds. The network command performs the following functions: Enables RIP on all interfaces that belong to a specific network. Associated interfaces will now both send and receive RIP updates. Advertises the specified network in RIP routing updates sent to other routers every 30 seconds (no mask).

Specifying Networks Only directly connected classful network addresses! R1(config)# router rip R1(config-router)# network R1(config-router)# network R2(config)# router rip R2(config-router)# network R2(config-router)# network R2(config-router)# network R3(config)# router rip R3(config-router)# network R3(config-router)# network If you enter a subnet or host IP address, IOS automatically converts it to a classful network address. For example, if you enter the command network , the router will convert it to network Configure RIP for all three routers What happens if you enter a subnet or host IP address? (Try it) IOS automatically converts it to a classful network address. For example, if you enter the command network , the router will convert it to network

Only directly connected classful network addresses!

Administrative Distance
R3# show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, <some output omitted> * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route Gateway of last resort is not set R /24 [120/2] via , 00:00:13, Serial0/0/1 R /24 [120/1] via , 00:00:25, Serial0/0/1 R /24 [120/1] via , 00:00:25, Serial0/0/1 C /24 is directly connected, Serial0/0/1 C /24 is directly connected, FastEthernet0/0 R3# R = RIP RIP has a default administrative distance of 120. When compared to other interior gateway protocols, RIP is the least-preferred routing protocol. Note: This is irrelevant because you usually do not run multiple routing protocols in the same domain, and even if you did you can modify these AD values. What is the administrative distance of a network route learned via RIP? 120

Administrative Distance
R3# show ip protocols <output omitted> Routing Protocol is “rip” Routing Information Sources: Gateway Distance Last Update :00:10 Distance: (default is 120) RIP has a default administrative distance of 120. When compared to other interior gateway protocols, RIP is the least-preferred routing protocol. Note: This is irrelevant because you usually do not run multiple routing protocols in the same domain, and even if you did you can modify these AD values. Where is the administrative distance displayed using this command?

Verification and Troubleshooting
Verifying RIP: show ip route Verifying RIP: show ip protocols Verifying RIP: debu ip rip Passive Interfaces

Verifying RIP: show ip route on all three routers…
R1# show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, <output omitted> Gateway of last resort is not set R /24 [120/1] via , 00:00:02, Serial0/0/0 R /24 [120/2] via , 00:00:02, Serial0/0/0 C /24 is directly connected, FastEthernet0/0 C /24 is directly connected, Serial0/0/0 R /24 [120/1] via , 00:00:02, Serial0/0/0 An R in the output indicates RIP routes. Because this command displays the entire routing table, including directly connected and static routes, it is normally the first command used to check for convergence. Routes might not immediately appear when you execute the command because networks take some time to converge.. The routing table, includes what kind of routes? Directly connected networks Static routes Dynamic routes Why might a RIP route not be immediately displayed in the routing table? Networks will take some time to converge.

Verifying RIP: show ip route Command
R2# show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, <output omitted> Gateway of last resort is not set C /24 is directly connected, Serial0/0/1 R /24 [120/1] via , 00:00:12, Serial0/0/1 R /24 [120/1] via , 00:00:24, Serial0/0/0 C /24 is directly connected, Serial0/0/0 C /24 is directly connected, FastEthernet0/0 Using R2, which routes do you expect to see in our scenario? Directly connected networks of R2 RIP routes for remote networks What routes do you expect not to see? Networks not in our scenario – not configured with network statements on the routers. Static default route

R3# show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, <output omitted> Gateway of last resort is not set C /24 is directly connected, Serial0/0/1 C /24 is directly connected, FastEthernet0/0 R /24 [120/2] via , 00:00:08, Serial0/0/1 R /24 [120/1] via , 00:00:08, Serial0/0/1 R /24 [120/1] via , 00:00:08, Serial0/0/1

R1# show ip route <output omitted> R /24 [120/2] via , 00:00:23, Serial0/0/0

Examine and discuss the show ip protocols Command
1. Verifies that RIP routing is configured and running on Router R2 At least one active interface with an associated network command is needed before RIP routing will start. 2. These are the timers that show when the next round of updates will be sent out from this router—23 seconds from now, in the example. 3. This information relates to filtering updates and redistributing routes, if configured on this router. Filtering and redistribution are both CCNP-level topics. 4. Information about which RIP version is currently configured and which interfaces are participating in RIP updates. 5. Router R2 is currently summarizing at the classful network boundary By default, will use up to four equal-cost routes to load-balance. Automatic summarization is discussed later in this chapter. 6. Classful networks configured with the network command are listed next. These are the networks that R2 will include in its RIP updates. (with other learned routes) 7. RIP neighbors Gateway: Next-hop IP address of the neighbor that is sending R2 updates. Distance is the AD that R2 uses for updates sent by this neighbor. Last Update is the seconds since the last update was received from this neighbor.

Verifying RIP: show ip protocols Command
1. Verifies that RIP routing is configured and running on Router R2 At least one active interface with an associated network command is needed before RIP routing will start. 2. These are the timers that show when the next round of updates will be sent out from this router—23 seconds from now, in the example. 3. This information relates to filtering updates and redistributing routes, if configured on this router. Filtering and redistribution are both CCNP-level topics. 4. Information about which RIP version is currently configured and which interfaces are participating in RIP updates. 5. Router R2 is currently summarizing at the classful network boundary By default, will use up to four equal-cost routes to load-balance. Automatic summarization is discussed later in this chapter. 6. Classful networks configured with the network command are listed next. These are the networks that R2 will include in its RIP updates. (with other learned routes) 7. RIP neighbors Gateway: Next-hop IP address of the neighbor that is sending R2 updates. Distance is the AD that R2 uses for updates sent by this neighbor. Last Update is the seconds since the last update was received from this neighbor. Verifies that RIP routing is configured and running on Router R2 At least one active interface with an associated network command is needed before RIP routing will start.

These are the timers that show when the next round of updates will be sent out from this router—23 seconds from now, in the example.

This information relates to filtering updates and redistributing routes, if configured on this router. Filtering and redistribution are both CCNP-level topics.

Information about which RIP version is currently configured and which interfaces are participating in RIP updates.

Router R2 is currently summarizing at the classful network boundary By default, will use up to four equal-cost routes to load-balance. Automatic summarization is discussed later in this chapter.

Classful networks configured with the network command are listed next. These are the networks that R2 will include in its RIP updates. (with other learned routes)

RIP neighbors Gateway: Next-hop IP address of the neighbor that is sending R2 updates. Distance is the AD that R2 uses for updates sent by this neighbor. Last Update is the seconds since the last update was received from this neighbor.

Use debug ip rip to view RIP updates that are sent and received…
The debug command is a useful tool to help diagnose and resolve networking problems, providing real-time, continuous information. The debug command is a useful tool to help diagnose and resolve networking problems, providing real-time, continuous information.

RIP: received v1 update from 192.168.2.1 on Serial0/0/0
in 1 hops Update coming in from R1 on interface Serial 0/0/0. R1 only sends one route: No other routes are sent because doing so would violate the split horizon rule. R1 is not allowed to advertise networks back to R2 that R2 previously sent to R1. Assuming all routers have converged, why were no other routes from R1’s routing table sent to R2? Split horizon rule. R1 is will not advertise networks back to R2 that were learned from R2.

RIP: received v1 update from 192.168.4.1 on Serial0/0/1
in 1 hops The next update that is received is from R3. Because of the split horizon rule, R3 only sends one route: the network.

RIP: sending v1 update to 255.255.255.255 via FastEthernet0/0
( ) RIP: build update entries network metric 2 network metric 1 network metric 1 network metric 2 Learned via RIP from R1 Learned via RIP from R3 R2 sends out its own updates. FastEthernet 0/0 interface: Includes the entire routing table except for network , which is attached to FastEthernet 0/0. Directly Connected

RIP: sending v1 update to 255.255.255.255 via Serial0/0/1
( ) RIP: build update entries network metric 2 network metric 1 network metric 1 Directly Connected Learned via RIP from R1 R2 sends update to R3. Three routes are included. R2 does not advertise the network R2 and R3 share, nor does it advertise the network because of split horizon.

RIP: sending v1 update to 255.255.255.255 via Serial0/0/0
( ) RIP: build update entries network metric 1 network metric 1 network metric 2 R2# undebug all All possible debugging has been turned off Directly Connected Learned via RIP from R3 R2 sends update to R1. Three routes are included. R2 does not advertise the network that R2 and R1 share, nor does it advertise the network because of split horizon. In another 30 seconds, all the debug output will repeat (every 30 seconds).

Passive Interfaces Got Router?
Does R2 need to send RIP updates out Fa 0/0? What are the disadvantages to this? No, there is no RIP router or any router. Bandwidth is wasted transporting unnecessary updates. All devices on the LAN must process the RIPv1 update up to the transport layer. Security risk (Authentication would is a better solution - later) Some routers can have interfaces that do not connect to another router. You can use the passive-interface command with RIP to configure an interface not to send those updates. Bandwidth is wasted transporting unnecessary updates. All devices on the LAN must process the RIPv1 update up to the transport layer. Security risk (Authentication would is a better solution - later)

Passive Interfaces What about using on R2:
Router(config-router)# passive-interface interface-type interface-number What about using on R2: R2(Config-router)# no network But then R2 would not advertise this LAN as a route in updates sent to R1 and R3. Correct solution is to use the passive-interface command What about using on R2: R2(Config-router)# no network R2 would not advertise this LAN as a route in updates sent to R1 and R3. Correct solution is to use the passive-interface command

Passive Interfaces – Use it on R2…
R2(config)# router rip R2(config-router)# passive-interface FastEthernet 0/0 X

Passive Interfaces R2# show ip protocols <output omitted>
Interface Send Recv Triggered RIP Key-chain Serial0/0/ Serial0/0/ Automatic network summarization is in effect Routing for Networks: Passive Interface(s): FastEthernet0/0 Routing Information Sources: Gateway Distance Last Update :00:27 :00:23 Distance: (default is 120) FastEthernet 0/0 no longer included LAN network still included in RIP updates that are sent FastEthernet 0/0 is a passive interface

Automatic Summarization
Modified Topology B Boundary Routers and Automatic Summarization Processing RIP Updates Sending RIP Updates Advantages and Disadvantages of Automatic Summarization

Modified Topology: Scenario B
/24 /16 /24 Fewer routes in a routing table means that the routing table process can more quickly locate the route needed to forward the packet. Summarizing several routes into a single route is known as route summarization or route aggregation. Some routing protocols, such as RIP, automatically summarize routes on certain routers. Where is the separation of classful networks? Summarizing several routes into a single route is known as route summarization or route aggregation. Fewer routes = smaller routing tables = faster lookups Some routing protocols, such as RIP, automatically summarize routes on certain routers.

Modified Topology: Scenario B
/24 /16 /24 What are the classful networks? /16 /24 /24 How is /16 network subnetted? /24 /24 /24 Is /24 subnetted? /30.

Configuration Changes for R1
R1(config)# interface fa0/0 R1(config-if)# ip address R1(config-if)# interface S0/0/0 R1(config-if)# ip address R1(config-if)# no router rip R1(config)# router rip R1(config-router)# network R1(config-router)# network R1(config-router)# passive-interface FastEthernet 0/0 R1(config-router)# end R1# show run <output omitted> ! router rip passive-interface FastEthernet0/0 network IOS automatically corrects subnet entries to classful network address The no shutdown and clock rate commands are not needed because these commands are still configured from Scenario A.

R2(config)# interface S0/0/0 R2(config-if)# ip address R2(config-if)# interface fa0/0 R2(config-if)# ip address R2(config-if)# interface S0/0/1 R2(config-if)# ip address R2(config-if)# no router rip R2(config)# router rip R2(config-router)# network R2(config-router)# network R2(config-router)# passive-interface FastEthernet 0/0 R2(config-router)# end R2# show run <output omitted> ! router rip passive-interface FastEthernet0/0 network network ! <output omitted> IOS automatically corrects subnet entries to classful network address

R3(config)# interface fa0/0 R3(config-if)# ip address R3(config-if)# interface S0/0/1 R3(config-if)# ip address R3(config-if)# no router rip R3(config)# router rip R3(config-router)# network R3(config-router)# network R3(config-router)# passive-interface FastEthernet 0/0 R3(config-router)# end R3# show run <output omitted> ! router rip passive-interface FastEthernet0/0 network network

Boundary Routers and Automatic Summarization
RIP is a classful routing protocol that automatically summarizes classful networks across major network boundaries. RIP is a classful routing protocol that automatically summarizes classful networks across major network boundaries.

Does R2 have interfaces on more than one major classful network?
R2 has interfaces in more than one major classful network. This makes R2 a boundary router in RIP. Both Serial 0/0/0 and FastEthernet 0/0 interfaces on R2 are inside the boundary. The Serial 0/0/1 interface is inside the boundary. Boundary routers summarize RIP subnets from one major network to the other, updates for the , , and networks will automatically be summarized into when sent out R2’s Serial 0/0/1 interface. Does R2 have interfaces on more than one major classful network? Yes, and This makes R2 a boundary router in RIP. Boundary routers summarize RIP subnets from one major network to the other: , , and networks automatically summarized into when sent out R2’s Serial 0/0/1 interface.

Processing RIP Updates
R2# show ip route /24 is subnetted, 3 subnets R [120/1] via , 00:00:18, Serial0/0/0 C is directly connected, Serial0/0/0 C is directly connected, FastEthernet0/0 /30 is subnetted, 1 subnets C is directly connected, Serial0/0/1 R /24 [120/1] via , 00:00:16, Serial0/0/1 Classful routing protocols such as RIPv1 do not include the subnet mask in the routing update. However, the routing table includes RIPv1 routes with both the network address and the subnet mask. So how does a router running RIPv1 determine what subnet mask it should apply to a route when adding it to the routing table? Do Classful routing protocols such as RIPv1 include the subnet mask in the routing update. No. So how does a router running RIPv1 determine what subnet mask it should apply to a route when adding it to the routing table?

Rules for Processing RIPv1 Updates
Routing Update and Interface Routing Update Subnet Mask Same Classful Major Network Use mask of interface Different Classful Major Network Use default classful mask The following two rules govern RIPv1 updates: If a routing update and the interface on which it is received belong to the same major network, the subnet mask of the interface is applied to the network in the routing update. If a routing update and the interface on which it is received belong to different major networks, the classful subnet mask of the network is applied to the network in the routing update.. The following two rules govern RIPv1 updates: If a routing update and the interface on which it is received belong to the same major network, the subnet mask of the interface is applied to the network in the routing update. If a routing update and the interface on which it is received belong to different major networks, the classful subnet mask of the network is applied to the network in the routing update..

Example of RIPv1 Processing Updates
R2# debug ip rip (selected output) RIP: received v1 update from on Serial0/0/0 in 1 hops R2# show ip route (selected output) /24 is subnetted, 3 subnets R [120/1] via , 00:00:18, Serial0/0/0 Same classful network as the incoming update. Update: in 1 hops Interface received: Serial 0/0/ /24 Same classful network address ( ) Applies subnet mask of its S0/0/0 interface, /24. The /24 subnet was added to the routing table. /24 The following two rules govern RIPv1 updates: If a routing update and the interface on which it is received belong to the same major network, the subnet mask of the interface is applied to the network in the routing update. If a routing update and the interface on which it is received belong to different major networks, the classful subnet mask of the network is applied to the network in the routing update..

Sending RIP Updates 192.168.4.0/24 192.168.5.0/24 R2# debug ip rip
RIP protocol debugging is on RIP: sending v1 update to via Serial0/0/0 ( ) RIP: build update entries network metric 1 network metric 1 network metric 2 RIP: sending v1 update to via Serial0/0/1 ( ) network metric 1 Sending RIP Updates /24 /24

Sending RIP Updates

Determining the mask and network address
Receiving an Update: Determining subnet mask for routing table What is the major classful network address of the receiving interface? What is the major classful network address of the network in the routing update? Are they the same major classful network address? Yes: Apply subnet mask of the receiving interface for this network address in the routing table. No: Apply classful subnet mask for this network address in the routing table. Sending an Update: Determining whether or not to summarize route sent What is the major classful network address of the sending interface? Yes: Send subnet network address No: Send summary address – the classful network address Receiving an Update: Determining subnet mask for routing table What is the major classful network address of the receiving interface? What is the major classful network address of the network in the routing update? Are they the same major classful network address? Yes: Apply subnet mask of the receiving interface for this network address in the routing table. No: Apply classful subnet mask for this network address in the routing table. Sending an Update: Determining whether or not to summarize route sent What is the major classful network address of the sending interface? Yes: Send subnet network address No: Send summary address – the classful network address

Verifying Routing Updates
R1# show ip route <output omitted> Gateway of last resort is not set /24 is subnetted, 3 subnets C is directly connected, FastEthernet0/0 C is directly connected, Serial0/0/0 R [120/1] via , 00:00:17, Serial0/0/0 R /24 [120/1] via , 00:00:17, Serial0/0/0 R /24 [120/2] via , 00:00:17, Serial0/0/0 R3# show ip route <output omitted> Gateway of last resort is not set R /16 [120/1] via , 00:00:15, Serial0/0/1 /30 is subnetted, 1 subnets C is directly connected, Serial0/0/1 C /24 is directly connected, FastEthernet0/0

Classful routing protocols do not support VLSM
Routers running RIPv1 are limited to using the same subnet mask for all subnets with the same classful network. As you will learn in later chapters, classless routing protocols such as RIPv2 allow the same major (classful) network to use different subnet masks on different subnets, better known as variable-length subnet masking (VLSM).. Routers running RIPv1 are limited to using the same subnet mask for all subnets with the same classful network. Classless routing protocols such as RIPv2 allow the same major (classful) network to use different subnet masks (VLSM).

Advantages of Automatic Summarization
R3# show ip route <output omitted> Gateway of last resort is not set R /16 [120/1] via , 00:00:15, Serial0/0/1 /30 is subnetted, 1 subnets C is directly connected, Serial0/0/1 C /24 is directly connected, FastEthernet0/0 Smaller routing updates Smaller routing updates are sent and received, which uses less bandwidth for routing updates between R2 and R3. R3 has a single route for the /16 network, regardless of how many subnets there are or how it is subnetted. Using a single route results in a faster lookup process in the routing table for R3.

Disadvantage of Automatic Summarization
Discontiguous network, two or more subnets separated by at least one other major network. /16 is a discontiguous network. /16 /16 Discontiguous network, two or more subnets separated by at least one other major network. /16 is a discontiguous network.

Discontiguous Networks Do Not Converge with RIPv1
R1(config)# router rip R1(config-router)# network R1(config-router)# network R2(config)# router rip R2(config-router)# network R2(config-router)# network R3(config)# router rip R3(config-router)# network R3(config-router)# network RIPv1 configuration is correct, but it is unable to determine all the networks in this discontiguous topology. RIPv1 configuration is correct, but it is unable to determine all the networks in this discontiguous topology.

Both routers, however, will advertise the major network address, a summary route to R2. /16 /16 What routing update will be sent by R1 and R3? major network address, a summary route to R2.

R1# show ip route /24 is subnetted, 3 subnets C is directly connected, FastEthernet0/0 C is directly connected, FastEthernet0/1 R3# show ip route C is directly connected, FastEthernet0/0 C is directly connected, FastEthernet0/1 What networks/subnets do you expect to see in R1’s routing table? What networks/subnets do you expect to see in R3’s routing table? Note: The book/curriculum mistakenly has the following routes for R1 and R3 (Book: Figure 5-15 and 5-17). These routes are NOT in the routing tables. R1: R [120/2] via , 00:00:26, Serial0/0/0 R3: R [120/2] via , 00:00:22, Serial0/0/1 R1 does not have routes to the LANs attached to R3. R3 does not have routes to the LANs attached to R1. Note: The book/curriculum mistakenly has the following routes for R1 and R3 (Book: Figure 5-15 and 5-17). These routes are NOT in the routing tables. R1: R [120/2] via , 00:00:26, Serial0/0/0 R3: R [120/2] via , 00:00:22, Serial0/0/1

R2# show ip route R /16 [120/1] via , 00:00:14, Serial0/0/1 [120/1] via , 00:00:19, Serial0/0/0

R2# show ip route R /16 [120/1] via , 00:00:14, Serial0/0/1 [120/1] via , 00:00:19, Serial0/0/0 R2 has two equal-cost paths to the network. R2 will load-balance traffic destined for any subnet of This means that R1 will get half of the traffic and R3 will get the other half of the traffic, whether or not the destination of the traffic is for one of their LANs. /16 /16 R2 has two equal-cost paths to the network. What will R2 do when it receives traffic for a host on a network ie ? R2 will load-balance traffic destined for any subnet of This means that R1 will get half of the traffic and R3 will get the other half of the traffic, whether or not the destination of the traffic is for one of their LANs.

R2# show ip route R /16 [120/1] via , 00:00:14, Serial0/0/1 [120/1] via , 00:00:19, Serial0/0/0 Classful routing protocols do not support discontiguous networks because they do not include the subnet mask in the routing update. Classless routing protocols (RIPv2, EIGRP, OSPF, IS-IS, BGP) do support discontiguous networks. Classful routing protocols do not support discontiguous networks because they do not include the subnet mask in the routing update. Classless routing protocols (RIPv2, EIGRP, OSPF, IS-IS, BGP) do support discontiguous networks.

Modified Topology C Propagating the Default Route in RIPv1
Default Route and RIPv1 Modified Topology C Propagating the Default Route in RIPv1

Modified Topology: Scenario C
/24 /24 Default routes are used by routers to represent all routes that are not specifically in the routing table. A default route is commonly used to represent routes that are not in the locally administered network, such as the Internet.. /24 Default routes are used by routers to represent all routes that are not specifically in the routing table.

Default Routes In today’s networks, customers:
Do not necessarily have to exchange routing updates with their ISP. Do not need a listing for every route on the Internet. Default route that sends all traffic to the ISP router. ISP configures a static route pointing to the customer router for addresses inside the customer’s network. In today’s networks, customers do not necessarily have to exchange routing updates with their ISP. Customer routers that connect to an ISP do not need a listing for every route on the Internet. Instead, these routers have a default route that sends all traffic to the ISP router when the customer router does not have a route to a destination. The ISP configures a static route pointing to the customer router for addresses inside the customer’s network.

Configuration Changes for R2 and R3
R2(config)# router rip R2(config-router)# no network R2(config-router)# exit R2(config)# ip route serial 0/0/1 R3(config)# no router rip R3(config)# ip route serial 0/0/1

Routing Table R1# show ip route <output omitted> Gateway of last resort is not set /24 is subnetted, 3 subnets C is directly connected, FastEthernet0/0 C is directly connected, Serial0/0/0 R [120/1] via , 00:00:05, Serial0/0/0 R1 has all /24 subnets, but will drop packets for all other networks. No default route (coming) R1 has all /24 subnets, but will drop packets for all other networks. No default route (coming)

Routing Table R2 has routes for 172.30.0.0/16 subnets.
R2# show ip route <output omitted> Gateway of last resort is to network /24 is subnetted, 3 subnets R [120/1] via , 00:00:03, Serial0/0/0 C is directly connected, Serial0/0/0 C is directly connected, FastEthernet0/0 /30 is subnetted, 1 subnets C is directly connected, Serial0/0/1 S* /0 is directly connected, Serial0/0/1 R2 has routes for /16 subnets. R2 has static default route for all other networks R2 has routes for /16 subnets. R2 has static default route for all other networks

Routing Table R3 has static route for 172.30.0.0/16 network.
R3# show ip route <output omitted> Gateway of last resort is not set /22 is subnetted, 1 subnets S is directly connected, Serial0/0/1 /30 is subnetted, 1 subnets C is directly connected, Serial0/0/1 C /24 is directly connected, FastEthernet0/0 R3 has static route for /16 network. Doesn’t matter if or how /16 is subnetted, R3 will forward packets to R2. R3 has static route for /16 network. Doesn’t matter if or how /16 is subnetted, R3 will forward packets to R2.

Propagating the Default Route in RIPv1
R1# show ip route <output omitted> Gateway of last resort is not set /24 is subnetted, 3 subnets C is directly connected, FastEthernet0/0 C is directly connected, Serial0/0/0 R [120/1] via , 00:00:05, Serial0/0/0 Can configure static default route on every router but: inefficient does not react to topology changes In many routing protocols, including RIP, you can use the default-information originate command in router configuration mode to specify that this router is to originate default information, by propagating the static default route in RIP updates. Can configure static default route on every router but: inefficient does not react to topology changes In many routing protocols, including RIP, you can use the default-information originate command in router configuration mode to specify that this router is to originate default information, by propagating the static default route in RIP updates.

R2(config)# router rip R2(config-router)# default-information originate R2(config-router)# end R2# debug ip rip RIP: sending v1 update to via Serial0/0/0 ( ) RIP: build update entries subnet metric 1 subnet metric 1

R1# show ip route <output omitted> * - candidate default, U - per-user static route, o - ODR Gateway of last resort is to network /24 is subnetted, 3 subnets C is directly connected, Serial0/0/0 R [120/1] via , 00:00:16, Serial0/0/0 C is directly connected, FastEthernet0/0 R* /0 [120/1] via , 00:00:16, Serial0/0/0 The static default route on R2 has been propagated to R1 in a RIP update. R1 has connectivity to the LAN on R3 and any destination on the Internet. The static default route on R2 has been propagated to R1 in a RIP update. R1 has connectivity to the LAN on R3 and any destination on the Internet.

Topics RIPv1: Distance Vector, Classful Routing Protocol
Background and Perspective RIPv1 Characteristics and Message Format RIP Operation Basic RIPv1 Configuration RIPv1 Scenario A Enable RIP: router rip Command Specifying Networks Verification and Troubleshooting Verifying RIP: show ip route Verifying RIP: show ip protocols Verifying RIP: debu ip rip Passive Interfaces Automatic Summarization Modified Topology B Boundary Routers and Automatic Summarization Processing RIP Updates Sending RIP Updates Advantages and Disadvantages of Automatic Summarization Default Route and RIPv1 Modified Topology C Propagating the Default Route in RIPv1

Chapter 5 RIP version 1 CIS 82 Routing Protocols and Concepts
Rick Graziani Cabrillo College Last Updated: 3/10/2009

Chapter 5 RIP version 1 CIS 82 Routing Protocols and Concepts

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Chapter 5 RIP version 1 CIS 82 Routing Protocols and Concepts

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