Slide *Student ObjectivesUpon completion of this module, you will be able to: Describe the RIP routing protocol.Identify the limitations of RIP version 1.List the benefits of RIP version 2.Interpret RIP routing table entries.Describe the Split Horizon and Poison Reverse loop resolution protocols.Describe the operation of triggered updates.Configure the RIP routing protocol.Verify the RIP configuration.Test RIP operation.Note: Depending on the needs of the students, the instructor may choose to reduce or eliminate the protocol overview portion of this module.

Slide *Limitations of Manual ConfigurationWhat if you have 50 switches, 10 subnetworks, a meshed topology, and 500 devices, what now?

Slide *Routing Information ProtocolA distance-vector protocol used as an Interior Gateway Protocol.First used in the Advanced Research Projects Agency Network (ARPAnet) as early as 1969. It is primarily intended for use in homogeneous networks of moderate size (20-30 switches or less).Relatively simple to understand and implement. Each router creates its routing table based on route information exchanged between neighbors.Supported by all Extreme Networks switches.Distance-VectorDistance - Hop CountVector - Next Hop RouterRIP Network?

Slide *Routing Information Protocol (Continued)The router exchanges update messages with each neighbor every 30 seconds.Stale routes are removed from the routing table.There are two versions of RIP.In RIP V1, 25 routes can be advertised in a single packet. This limits the maximum packet size to 512 octets.Supports 2 types of loop resolution protocols.Split Horizon, Poison ReverseSupports triggered updates.RIP Network?

Slide *Limitations of RIP Version 1Only understands class A, B, and C IP addresses.Does not propagate subnetwork mask information in its updates.Cannot support variable length subnetwork masks.Uses broadcasts for update delivery.It is an insecure routing protocol.Updates:Sent as broadcastNetworks only (no subnetwork masks)RIP Network?

Slide *RIP Version 2Fixes many of the limitations of RIP-1.Is a classless routing protocol.Supports variable length subnetwork masking.Supports Classless Internet Domain Routing (CIDR).Has features to make it backward compatible with RIP Version 1.Supports authentication (not supported on Extreme Switches).Clear text passwordMD5 checksum (RFC 2082)Uses multicast for update delivery.RIPv2 networkNetwork 129.128.128.0Subnet 255.255.192.0Network 129.128.128.0Subnet 255.255.192.0Network 129.128.0.0

Slide *Routing Table and Route AdvertisementContains an entry for every known destination network.Contains the following information:Origin of the route.IP Address of destination network.IP address of the next router (gateway).Metric (hop count) to the destination network.Duration of time since the last entry update.Route Advertisement of VLANsOnly those VLANs configured with an IP address, configured to forward IP, and running RIP have their subnetworks advertised. Route Table

OriDestinationGatewayMtrFlagsVLANDuration *r10.10.11.0/2410.10.99.1212UG-----um--bbone0d:0h:18m:36s *r10.10.20.0/2410.10.99.1223UG-----um--bbone0d:0h:09m:06s *r10.10.33.0/2410.10.99.1242UG-----um--bbone0d:0h:18m:53s *d10.10.55.0/2410.10.55.1261U------u---white0d:3h:21m:52s d10.10.60.0/2410.10.60.1261-------u---brown0d:3h:21m:00s *d10.10.99.0/2410.10.99.1261U------u---bbone0d:3h:21m:35s *d127.0.0.1/8127.0.0.10U-H----um--white0d:3h:34m:16s

Slide *Routing LoopsRouter A advertises the route to the target network to Router B.Router B advertises the route to the target network learned from A to C.Router C advertises the route back to router B over the port that supplied the route.Router B believes it has two routes to the target network when actually only one exists.When the valid route becomes unavailable the router tries to use the alternate route.Traffic is sent over the original route and looped back again.ACBProblem!!Target NetworkUsing A M=1Target NetworkUsing B M= 2Target NetworkUsing C M=3

B Routing TableTarget network using A M=1Target network using C M=3

C Routing TableTarget network using B M=2

Slide *Counting to Infinity ProblemComplex networks can contain multiple routing loops.Routers re-advertise routes out interfaces from which they were learned.When the valid route becomes unavailable routers advertise routes with ever increasing hop count metrics.Old route entries will be replaced by new route entries.Behavior repeats until the max hop count reaches infinity (16 - unreachable).Causes slow convergence.CBA

C Routing TableTarget network using B M=16

B Routing TableTarget network using A M=1Target Network using C M=16

Slide *Split HorizonUsed to prevent routing loop.Enabled by default on the switch.Router does not advertise a route back out the port that the route was originally learned on.The possibility of a loop has been eliminated using split horizon.Split Horizon prevents route from being sent!!Target NetworkUsing C M=3ACBTarget NetworkUsing A M=0Target NetworkUsing B M= 1

C Routing TableTarget network using B M=2

B Routing TableTarget network using A M=1

Slide *Poison ReverseRouters advertise routes with hop count of 16 (unreachable).Faster convergence.Poison Reverse takes precedence over split horizon when both are enabled to prevent loops.Enabled by default.Possible increased size of routing messages.Target NetworkUsing C M=16ACBTarget Network using C M=16Target Network using A M=1B Routing TableTarget Network using B M=2C Routing TableTarget NetworkUsing A M=0Target NetworkUsing B M= 1Poison Reverse causes Router C to advertises route as unreachable.

Slide *Triggered UpdatesSent out whenever the metric for a route changes and the router is required to send an update immediately.Even if it is not yet time for a regular update message to be sent.Generally result in faster convergence.Results in more RIP-related traffic.Target NetworkBATarget = 0Target = 1Target = 2Target = 4Target = 4Target = 6Target = 3 Target = 5Target = 2 Target = 6Target = 3Target = 1 Target = 7Target = 2 Target = 8failed route

Slide *RIP LimitationsLimit of 15 hops between the source and the destination networks.Bandwidth taken up by periodic broadcasts of entire routing table.Slow convergence.Routing decisions based on hop count.Flat networks; no concept of areas or boundaries.RIP Network

Slide *RIP Configuration StepsCreate and configure VLANs.Configure the VLAN with an IP address.Enable IP Forwarding.Enable RIP on VLANs that do RIP routing.Enable RIP globally on the switch.Verify RIP configuration.

Slide *General IP Configuration CommandsCreate and configure VLANs:create vlan configure vlan add ports Configure VLAN with an IP address:configure vlan ipaddress { | }Enable IP forwarding:enable ipforwarding

Slide *RIP Specific Configuration CommandsEnable RIP on VLANs that do RIP routing:configure rip add vlan [ | all]Enable RIP globally on the switch:enable ripDisable RIP on VLANs:configure rip delete vlan [ | all]Disable RIP globally on the switch:disable ripWhen RIP is disabled on the interface, the parameters are not reset to their defaults.

Slide *RIP Configuration Example Configuration for R1:create vlan vlan1rip configure vlan1rip add ports 1 configure vlan1rip ipaddress 10.1.0.1/24create vlan vlan0rip configure vlan0rip add ports 2,3 configure vlan0rip ipaddress 10.0.0.1/24 enable ipforwarding configure rip add vlan vlan0rip configure rip add vlan vlan1rip enable ripSimilar configurations for R2 and R3.110.0.0.0 / 24 VLAN0rip.2.1.3.210.2.0.0 / 24 VLAN2rip.310.3.0.0 / 24 VLAN3ripR2R3R110.1.0.0 / 24VLAN1ripRIP Network

Slide *RIP Timer and Cost Configuration CommandsConfigure RIP update timer:configure rip updatetime {}Configure RIP route timeout:configure rip routetimeout {}Configure RIP garbage time:configure rip garbagetime {}Configure RIP VLAN cost:configure rip vlan [ | all] cost

Slide *Additional RIP Configuration CommandsConfigure RIP receive version:configure rip rxmode vlan [vlan name | all] [none | v1only | v2only | any]Configure RIP transmit version:configure rip txmode vlan [vlan name | all] [none | v1only | v2only | any]Enable or disable specific RIP features:[enable | disable] rip [aggregation | export | |originate-default | poisonreverse | splithorizon | triggerupdates | use-ip-router-alert]Unconfigure RIP:unconfigure rip {vlan }

Slide *Verifying RIP ConfigurationTimersRIP, Split Horizon, Triggered Updates, Poison Reverse Status

Slide *Verifying RIP Interfaces and Routes

Slide *Verifying IP Forwarding and VLAN InterfaceVLAN name and IP address

Slide *Verifying the Route SourcePreferred route flagOrigin of route is RIP

Slide *SummaryYou should now be able to:Describe the RIP routing protocol.Identify the limitations of RIP version 1.List the benefits of RIP version 2.Interpret RIP routing table entries.Describe the Split Horizon and Poison Reverse loop resolution protocols.Describe the operation of triggered updates.Configure the RIP routing protocol.Verify the RIP configuration.Test RIP operation.

Slide *LabTurn to the Routing Information Protocol (RIP) Lab in the ExtremeXOS Operations and Configuration - Lab Guide Rev. 12.1 and complete the hands-on portion of this module.

2008 Extreme Networks, Inc. All rights reserved. ExtremeXOS Operation and Configuration, Version 12.1. Part number DOC-00919.

Review Questions

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This presentation contains forward-looking statements that involve risks and uncertainties, including statements regarding our expectations as to products, trends and our performance. There can be no assurances that any forward-looking statements will be achieved, and actual results could differ materially from forecasts and estimates. For factors that may affect our business and financial results please refer to our filings with the Securities and Exchange Commission, including, without limitation, under the captions: Managements Discussion and Analysis of Financial Condition and Results of Operations, and Risk Factors, which is on file with the Securities and Exchange Commission (http://www.sec.gov). We undertake no obligation to update the forward-looking information in this release.

2008 Extreme Networks, Inc. All rights reserved. ExtremeXOS Operation and Configuration, Version 12.1. Part number DOC-00919.

The End2008 Extreme Networks, Inc. All rights reserved. ExtremeXOS Operation and Configuration, Version 12.1. Part number DOC-00919.2008 Extreme Networks, Inc. All rights reserved. ExtremeXOS Operation and Configuration, Version 12.1. Part number DOC-00919.

*ExtremeXOS Operation and Configuration, Version 12.1 - Configuring RIP*Upon completion of this module, you will be able to: Describe the RIP routing protocolIdentify the limitations of RIP version 1List the benefits of RIP version 2Interpret RIP routing table entriesDescribe the Split Horizon and Poison Reverse loop resolution protocolsDescribe the operation of triggered updatesConfigure the RIP routing protocolVerify the RIP configuration, andTest RIP operation

****As previously discussed, RIP is well known and utilized. However, RIP Version 1 does have several limitations. These include:

Classfull Addressing: RIP Version 1 only understands class A, B, and C IP addresses.

Subnet Masks: RIP Version 1 does not propagate subnet mask information along with other routing information.

Variable Length Subnet Masks: RIP Version 1 does not support variable length subnet masks.

Generates Broadcasts: RIP Version 1 uses broadcasts to deliver routing updates. Remember, broadcast messages must be processed by all stations on the network.

Security: RIP Version 1 does not support any authentication and routers sending updates cannot be verified. *RIP version 2 is an enhancement over RIP version 1 to overcome some of the basic limitations of RIP version 1. Mainly it's a classless routing protocol. It supports variable length subnetwork masks. It supports CIDR or Classless Internet Domain Routing, so you could actually subnet your networks or use, a class C subnet mask on what would otherwise be a class A network and advertise the subnet mask information along with the route.

RIP version 2 has features to make it backwards compatible with RIP version 1 and, lastly, RIP version 2 supports authentication. RIP version 2 supports clear text passwords or MD5. Unfortunately, authentication is not supported on Extreme Networks devices for RIP.

Lastly, RIP version 2 uses multicast for router table updates as opposed to broadcast. Updates are sent to unique or well-known multicast address of 224.0.0.9, that only RIP version 2 routers are listening for as opposed to a broadcast packet that all devices on the network on that particular subnet would be able to hear and would have to then discard.

NOTE - If you are using RIP with supernetting/Classless Inter-Domain Routing (CIDR), you must use RIPv2 only. In addition, RIP route aggregation must be turned off.*The routing table in each device using RIP, contains an entry for every known destination network.

Each routing table entry contains the following information:

Origin of the route. This field indicates how the route was learned. Possible entries include: directly attached, RIP, or OSPF. In the example on the screen, you see an origin of r and d - indicating routes learn by RIP and direct. In the example network 10.10.11 was learned from another router through the RIP protocol. Now if we look down below even further at the 10.10.55.0 network, thats a direct route, meaning that this network is locally configured on that device itself.

IP address of the destination network.

IP address of the next router (gateway).

The Metric field to indicate the number of hops to the destination network.

The Duration field to show how much time has elapsed since the entry was last updated. The router exchanges an update message with each neighbor every 30 seconds (default value), or if there is a change to the overall routed topology (also called triggered updates). If a router does not receive an update message within six update cycles (nominally 180 seconds) from the router that was the source of the original routing table entry, it assumes that either the source router has failed or that the connecting link has become unusable. The router marks the existing route as invalid and eventually removes the route from its routing table. When the router learns of a new route from another neighbor, the new route is used to replace the deleted one. The distance-vector routing algorithm waits for six times the update interval before timing out the route, even though it expects to hear from each neighbor at every update interval. The additional time is used to avoid invalidating routes based on the loss of a single update message.

Note: In addition to having the IP address configured on the VLAN, and having IP forwarding enabled, and having a routing protocol enabled, the VLAN itself must be up. On Extreme Networks' devices, a VLAN is up when it has at least one active port.

If you would like to have a route advertised even when there is no active link on the VLAN, you may enable loop-back on a particular VLAN using the command:

enable loopback-mode

and then the VLAN name. Thatll bring that interface up and get that interface advertised out into your routing protocol.*A problem can occur with a dynamic routing protocol where we can actually create routing loops so that a particular device may think that a network is reachable via two different interfaces. This in itself does not necessarily create a problem, but there are certain circumstances where that can actually create confusion in the routing table.

In the example on the screen, we see that Router A at the top of the right side, advertises the route to the target network, the network off to the left. Router B receives the advertisement from Router A and then advertises the route to the target network to Router C.

Router C then, since were using RIP, will advertise the contents of its routing table out all of its interfaces. Unfortunately, it re-advertises that network back to Router B. Router B, when you look at its routing table, now believes it has a route to the target network through Router A as well as through Router C. This in itself would not necessarily be a problem because the metric to the target network through Router C is larger than the metric to the target network through Router A, so, no problem, Router B will always use the link directly to Router A.

The problem occurs when we lose a physical link to Router A from Router B. Now the only option that Router B has to reach the target network is through Router C. So Router B sends that packet to Router C, Router C thinks the target network is reachable through Router B, so it sends that packet right back to Router B. Again, Router B thinks that the target network is reachable through Router C and sends the packet right back and you see we have this looping of that packet in between Router B and Router C since they dont have an actual path to get back to the target network. This will continue to happen until the time to live in that packet counts up to 16, at which time RIP will simply discard the frame.*The "Counting to Infinity" problem exists because networks can contain multiple routing loops - where the router will advertise a route it learned out of the interface on which the route was learned.

As we stated in the last slide, this isn't usually a problem - until a router fails.

When the valid route becomes unavailable routers continue to advertise the routes with ever increasing hop count metrics.

The hop count on the advertisements keeps increasing as invalid routes with lower hop counts are removed because a new entry is received from a router that already has an entry to the target network in the routing table. This behavior repeats until the max hop count reaches infinity - which is 16 in RIP.

So let's step through this illustration.

1. Router A advertises the route to the target network with 0 hops2. Router B advertises the route to the target network with a metric of 13. Router C advertises the route to the target network with a metric of 2 out of the same interface that it learned the route on.4. Now router B has two entries to the target network, but prefers to use Router A because it has a lower metric. The routing tables will remain in this state until, Router A fails.5. Now that Router A has failed, router B will advertise that it can still get to the target network through router C, and the metric assigned to the route is 36. Router C sees the advertisement from router B with an increased metric, so it deletes the previous entry from that gateway (since it has new information from the gateway) and7. Sends out an update that it is 4 hops away from the the target network. 8. Now, Router B has to update its routing table with the new information. It deletes the previous route to the target network through Router C and now add this new information to the routing table. Of course it now has to advertise the new route with a metric of 5. This continues until both routers show the target network as being unreachable.All of this lead to slow convergence of the network.*A number of modifications can be made to the basic distance-vector routing algorithm to improve performance in a dynamic environment and to help expedite convergence and eliminate routing loops. These include:

Split horizonPoison reverse

By default, both are enabled on Extreme Networks switches when RIP is enabled.

The occurrence of loops between two routers can be greatly reduced by using split-horizon. The count-to-infinity problem can be overcome if the router is careful about where it sends its routing information. Split-horizon is a technique whereby a router does not advertise a route over the same port that supplied the route. In other words, a router does not claim network reachability to a neighbor from which the route was learned.

The illustration demonstrates the use of split-horizon to break a loop of two hops.

Router A advertises that it can reach the target network with a hop count of zero.

Router B enters into its routing table that it can reach the target networks with a hop count of one using router A. It then advertises that fact.

Router C learns in its regular update from router B that it can reach the target network using router B with a hop count of two.

Router C does not advertise the route to the target network back to router B.

As a result of split-horizon, the possibility of a loop has been eliminated and Router B has only one route to the target network. If the link between Router A and Router B fails, Router B times out the entry and advertises the target network as unreachable. *Poison reverse is a technique whereby a router advertises a route over the same port that supplied the route with a hop count of 16, defining it as unreachable. A router claims that a network is unreachable over the interface from which the route was learned, preventing any route loops. Poison reverse speeds up convergence because erroneous routes are eliminated without waiting for a timeout.

Poison Reverse takes precedence over split horizon when both are enabled to prevent loops.

Like split-horizon, poison reverse is enabled by default.

The disadvantage of poison reverse is that it increases the size of the routing update messages. When poison reverse is used, the router must mention all poison routes with a metric of 16. If the system is large, this can result in a large update message, almost all of whose entries indicate unreachable networks. In many cases, the network administrator is willing to accept slower convergence to reduce the overhead that the increased size of the routing table update messages would cause.

The illustration shows a typical exchange of routing information when a router is configured to perform split-horizon with poison reverse. In this example:

Router A advertises that it can get to the target network in one hop.

Router B enters the information that it received from router A its routing table and advertises that it can reach the target network in two hops.

Router C puts the information that it received from router B its routing table. Because split-horizon with poison reverse is enabled, it advertises that it CANNOT reach the target network on the port where the network was learned. *Triggered updates occur whenever the metric for a route changes. Triggered updaters are required to be sent out immediately, even if it is not yet time for a regular update message to be sent. The metric may change because a network has become unavailable. It may change because the router interface has gone down, or maybe all the physical links on a VLAN were somehow disconnected. Remember, with Extreme Networks switches, what defines whether an interface is up or down is whether there is at least one active link on the associated VLAN. If all active links on a VLAN are lost, and that VLAN is being advertised by RIP, RIP will do a triggered update and send a new copy of its router table to its neighbors.

Using Triggered Updates generally results in faster convergence, but also results in more RIP-related traffic. Triggered updates can cause excessive loads on networks with limited bandwidth or networks with many routers. A simple solution to this problem is to set a timer to a random number between one and five seconds after a triggered update is sent. If other changes occur that would trigger another update before the timer expires, the router must wait until the timer expires before sending the update. A triggered update may also be suppressed if a regular timed update is due by the time the triggered update would be sent.

The illustration shows a network in two states:

Before the triggered update was issued (crossed-out entries)

After all routers have converged their router tables

Finally, if your network is experiencing excessive amounts of triggered updates, check the stability of your network connections to include the cabling, interfaces, connectors, and ports. A flapping link could cause RIP to constantly send out triggered updates that must be propagated throughout the entire network.*RIP is easy to configure and understand, but it does have a few limitations:

RIP has a limit of 15 hops between the source and destination networks. As mentioned previously, 16 hops in RIP terms is considered unreachable.

Bandwidth can be taken up by the periodic broadcasts of the entire routing table. Remember, RIP does not limit its updates to information about networks which have changed. Rather, RIP broadcasts the entire contents of the routing table. If the router has a large routing table and also has a flapping interface, the router is going to be using a great deal of bandwidth just sending out continued large route table updates. RIP updates may not be a concern to you if you have a lot of bandwidth, or if your network is relatively small.

RIP generally is considered somewhat slow to converge compared to other protocols such as OSPF. Remember, if a router fails, it may take as many as 180 seconds for the entries that reference that router to be removed from the routing table.

Routing decisions, again, are based solely on hop count. If a router running RIP has to choose between two routes, one with more bandwidth and the other with fewer hops, the router chooses the path with fewer hops, even though the path is of poorer quality.

RIP assumes that the network is flat and has no hierarchy. There is no concept of areas or network boundaries.

Finally, each router periodically transmits all its routing information to its neighbors. The information transmitted by each router is based on the information that it receives from its immediate neighbors.

A change in the routing table of a single router can result in a chain of updates, even if the change is erroneous. Eventually, this information will reach all other routers in the routing domain, and all will broadcast the erroneous data. This makes the identification of a router that originally supplied the inaccurate data quite difficult.

*This page presents the general steps and specific commands to configure RIP on a switch. To configure RIP, perform the following general steps:

Create and configure VLANs

Configure the VLAN with an IP Address. i.e. Create the Router Interface (RIF)

Enable IP Forwarding

Enable RIP on the VLANs that do RIP routing and on the VLANs you want to advertise through RIP

Enable RIP globally, and

Verify the configuration and operation using show commands

*Before you can enable RIP, you need to create a routing interface. Before you can create the routing domain, you need to create a VLAN and add ports to that VLAN.

To create a VLAN, use the command:

create VLAN

To add ports to the VLAN, use the command:

configure vlan add ports

That concludes the VLAN portion of the setup. Now you need to create the router interface. To do that, you simply need to issue the command:

configure vlan ipaddress { | }

Now, the router interface is setup, but routing has not been enabled. To enable routing, issue the command:

enable ipforwarding

These basic steps must be used regardless of the routing protocol you will be using in subsequent steps.

*VLANs that are configured with an IP address, but are not configured to forward IP or are not configured to run RIP, do not have their subnets advertised by RIP. Only those VLANs that are configured with an IP address, are configured to forward IP, and run RIP, have their subnets advertised.

To configure the Routing Information Protocol (RIP) on the router, you will need to add RIP to one or more VLANS, and then enable it. To add RIP to a VLAN, enter the command:

configure rip add vlan [ | all]

The next step is to actually enable the routing protocol. The following command will accomplish that task:

enable rip

There may be instances were you do not wish to run RIP on every VLAN, or you may wish to remove RIP functionality for one or more VLANs. To remove RIP from a VLAN, issue the command:

configure rip delete vlan [ | all]

Finally, if you have a need to completely disable RIP completely on the router, you may use the following command:

disable rip

When RIP is disabled on the interface, RIP parameters are not reset to their default values.

**As I'm sure you know or at least have guessed, there are some timers and other parameters that can be configured and customized to better suit the needs of your network. We'll go through those right now.

As we've discussed previously, RIP sends out periodic updates to inform neighboring routers about the contents of the host router's routing table. By default, these updates are sent out every 30 seconds. You may choose to modify that update time by issuing the following command:

configure rip updatetime {}

The range of acceptable values is 10 to 180 and must be less than the route timeout value.

If a route entry has not been updated within a specific period of time, the route entry will expire and is considered invalid. To configure the route timeout period, enter the following command:

configure rip routetimeout {}

The default routetimeout value is 180 seconds. The range of acceptable values is 0 - 4294967295 and must be greater than the update timer.

After a route entry has been marked as invalid, it will be retained in the routing table and be advertised as being unreachable. This garbage collection period is there to ensure that all neighboring routers have an opportunity to learn that the route is no longer reachable. To configure how long a route entry is retained after expiration, and advertised as unreachable, use the following command:

configure rip garbagetime {}

The default is garbage collection period 120 seconds.

Finally, you may change the cost metric that a router advertises on a per VLAN basis. To configure the cost metric of the VLAN router interface, enter the following command:

configure rip vlan [ | all] cost

The range of acceptable values for the cost metric is 1 - 14.

*There are other ways that you may configure RIP behavior. For example, you may want to filter whether or not the router accepts RIP advertisements from other routers. You may want to identify the version of RIP advertisements that the router will accept or the VLANs that the router will accept advertisements from. To filter the types of RIP advertisements the router will accept, use the following command:

configure rip rxmode vlan

The filter types available are:

none - accept no RIP advertisements from any neighborsv1only - accept only RIP Version 1 advertisementsv2only - accept only RIP Version 2 advertisementsany - accept RIP Version 1 and RIP version 2 advertisements

The vlan parameter allows you to specify the VLANs from which the device will accept advertisements. Of course, you can also control the types of RIP advertisements that will be transmitted using the command:

configure rip txmode vlan

The parameters are identical to those used by the rxmode command. Other RIP features that you may configure are:

aggregation - Controls whether the system aggregates subnet information on a RIP version 2 (RIPv2) interfaceexport - Controls whether RIP redistributes routes from other routing protocolsoriginate-default - Controls how the default route is advertised by RIPpoisonreverse - Controls whether or not poison-reverse is enabled as part of RIPsplithorizon - Controls whether or not split-horizon is enabled as part of RIPtriggerupdates - Controls whether or not triggered updates are enabled as part of RIPuse-ip-router-alert - Controls whether the router alert IP option is included in the outgoing RIP control packets

Finally, to set paramters back to their default values, use the command:

unconfigure rip*Once youve completed the RIP configuration, you can use the show rip command to verify the router's configuration.

Notice at the top of the screen that RIP Routing is enabled.

Split Horizons, Triggered Updates, and Poison Reverse are enabled also enabled. This is by default.

Next are the timers. The update interval is set to the default value of 30 seconds. The Route timeout, is also set to the default value -180 seconds. The Garbage Timeout is set to 120 seconds - again, the default value.*The next step in verifying your RIP configuration is to use the command:

show rip interface

The screen shows the name of the VLAN, the IP address and mask that are associated with the VLAN, followed by the flags. The flags r, i, and f should be displayed. The flag - lowercase "r" - indicates that RIP is enabled on this router. The flag - lowercase i - indicates that RIP is enabled on this interface. Finally, the flag - lowercase f - indicates that IP forwarding is enabled on the interface. If you do not see the letters r, i, and f listed in the flags field, then RIP will not be functioning properly on that interface.

The next command we'll discuss is the command:

show rip routes

This command shows you all routes that have been learned specifically by the RIP Routing Protocol. An alternative to the show RIP Routes command is:

show iproute origin RIP

This command shows you the contents of the Routing Table, but filters the contents of the Routing Table to only display RIP learned route entries.*Next, the command

show ipconfig

provides additional routing information. Most importantly, youll see in the center of the screen the VLAN name, the IP address, and sub-net mask configured on the VLAN.

Next, focus your attention on the flags.

When the device is configured for IP routing, always expect to see the flags E, U, and f (enabled, up, and forwarding).

If you do not see the E, U, and f flags, you will not be able to route on this interface.

If you ever encounter difficulties with IP routing, the very first thing you should do is look at the output of the show ipconfig command and look to see if the E, U, and f flags are displayed. If they are not displayed, the system is configured incorrectly.

*The next thing that you'll want to do when verifying your route configuration is to use the

show IProute

command to verify that this router is receiving route information from neighboring routers

On the left-hand side of the screen, youll see the routing protocol that is associated with route entry.

In this example, the letter r indicates network 12.0.0.0 was learned via RIP.

We learned about that network from gateway 10.0.0.2.

Additionally, see the pound sign next to each route? The pound sign indicates that this is the preferred route to the that particular network.

Its possible to have more than one route to each remote network. In some cases, multiple entries with an equal metric. The router indicates which path its using by setting the Preferred Route Flag. You may see multiple routes to a network in the table, but only one will have the # sign indicating that thats the preferred route.**