CCNA LAB30: Passive Interfaces for RIPv2 Updates

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Lab Objective:
The objective of this lab exercise is for you to learn and understand how to prevent RIPv2 from sending unnecessary updates by using passive interfaces.

Lab Purpose:
Preventing unnecessary RIPv2 updates using passive interfaces is a fundamental skill. By default, RIPv2 sends updates via multicast on all interfaces for which RIPv2 has been enabled. For example, it is not possible to ever have another device connected to a Loopback interface, so it is a waste of router processing power to have RIPv2 continuously sending updates to a Loopback interface. As a Cisco engineer, as well as in the Cisco CCNA exam, you will be expected to know how to prevent RIPv2 from sending unnecessary updates.

Certification Level:
This lab is suitable for CCNA certification exam preparation.

Lab Difficulty:
This lab has a difficulty rating of 6/10.

Readiness Assessment:
When you are ready for your certification exam, you should complete this lab in no more than 10 minutes.

Lab Topology:
Please use the following topology to complete this lab exercise:




Task 1:
This lab will use only two routers. Configure the hostnames on routers R1 and R2 as illustrated in the topology.

Task 2:
Configure a back-to-back Serial connection between R1 and R2. Configure the DCE interface Serial0/0 in R2 to provide clocking to R1 at a clock speed of 2 Mbps.

Task 3:
Configure IP addresses 192.168.0.1/30 and 192.168.0.2/30 on R1 and R2 Serial0/0 interfaces, respectively. Configure the Loopback interfaces on R1 with the IP addresses illustrated in the topology. Enable RIPv2 for the Serial0/0 interface on R2 and R1 and attached Loopback subnets.


Task 4:
First, use the show ip protocols command to see the interfaces on which RIPv2 is sending updates. Next, enable debugging on R1 and verify that RIPv2 updates are being sent on all RIPv2-enabled interfaces. When you have verified this, disable debugging.

Task 5:
Prevent RIPv2 from sending updates on the Loopback interfaces. Verify your configuration by enabling debugging. Disable debugging when done.

Configuration and Verification
Task 1:
For reference information on configuring hostnames, please refer to earlier labs.

Task 2:
For reference information on configuring DCE clocking, please refer to earlier labs.


Task 3:
For reference information on configuring Loopback interfaces and RIPv2, please refer to earlier labs.

Task 4:

Loopback interfaces are logical interfaces that have the majority of the characteristics of physical interfaces. However, one important thing to remember is that no host can ever reside on a subnet configured for a Loopback interface. If you assign a Loopback interface as a /24 subnet mask, for example, you are simply wasting valuable IP address space. Given that no host can every reside on the same subnet as a Loopback interface, it is a waste of router resources to have a routing protocol send updates to a Loopback interface, as there will never be another router (or other device) that will ever respond back to these updates. Hence, when you configure Loopback interfaces, it is always considered best practice to disable routing protocols that can send updates to them using the passive-interface command as illustrated in Task 5 below:

Task 5:

NOTE: Suppose you have a router with one Serial interface and 600 Loopback interfaces. Given such a scenario, issuing the passive-interface command for every one of those Loopback interfaces would take a great deal of time. Fortunately, Cisco recognized this and created the passive-interface default command in Cisco IOS. When this command is issued, all interfaces are configured as passive. In order to send updates on a particular interface, you would negate that interface as not being passive by issuing the no passive-interface command followed by the interface(s) you want to send routing protocol updates to. This is illustrated below:


R1#conf t
Enter configuration commands, one per line.  End with CTRL/Z.
R1(config)#router rip
R1(config-router)#passive-interface default
R1(config-router)#no passive-interface serial0/0
R1(config-router)#end
R1#
The configuration above makes all interfaces configured for RIP passive with the exception of interface Serial0/0. Make sure you remember this command, not only for the purposes of the CCNA exam but also for use in the real world.
来源: CCNA LAB20: Configuring Static Routing via Interfaces
来源: CCNA LAB21:  Configuring Static Routing via IP addresses
来源: CCNA LAB22: Configuring and Naming Static Routes
来源: CCNA LAB23: Configuring Default Static Routes
来源: CCNA LAB24: Configuring IPv6 Static Routes
来源: CCNA LAB25: Configuring IPv6 Default Routes
来源: CCNA LAB26: Configuring IP Floating Static Routes
来源: CCNA LAB27: Configuring RIP version 2
来源: CCNA LAB28: RIPv2 Automatic Summarization
来源: CCNA LAB29: Debugging and Verifying RIP Version 2 Updates

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呀小亮

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