CCNP Route Lab 5-1 , Configure and Verify Path Control

CCNP Route Lab 5-1 , Configure and Verify Path Control

Topology

ccnp-route-lab-configure-verify-path-control

Objectives

  • Configure and verify policy-based routing.
  • Select the required tools and commands to configure policy-based routing operations.
  • Verify the configuration and operation by using the proper show and debug commands.

Background
You want to experiment with policy-based routing (PBR) to see how it is implemented and to study how it could be of value to your organization. To this end, you have interconnected and configured a test network with four routers. All routers are exchanging routing information using EIGRP.

Note: This lab uses Cisco 1841 routers with Cisco IOS Release 12.4(24)T1, and the Advanced IP Services image c1841 -advipservicesk9-mz.124-24.T1 .bin. You can use other routers (such as 2801 or 2811) and Cisco IOS Software versions if they have comparable capabilities and features. Depending on the router and software version, the commands available and output produced might vary from what is shown in this lab.

Required Resources

  • 4 routers (Cisco 1841 with Cisco IOS Release 12.4(24)T1 Advanced IP Services or comparable)
  • Serial and console cables

Step 1: Prepare the routers for the lab.
Cable the network as shown in the topology diagram. Erase the startup configuration, and reload each router to clear previous configurations.

Step 2: Configure router hostname and interface addresses.
a. Using the addressing scheme in the diagram, create the loopback interfaces and apply IP addresses to these and the serial interfaces on R1, R2, R3, and R4. On the serial interfaces connecting R1 to R3 and R3 to R4, specify the bandwidth as 64 Kb/s and set a clock rate on the DCE using the clock rate 64000 command. On the serial interfaces connecting R1 to R2 and R2 to R3, specify the bandwidth as 128 Kb/s and set a clock rate on the DCE using the clock rate 128000 command.

You can copy and paste the following configurations into your routers to begin.

Note: Depending on the router model, interfaces might be numbered differently than those listed. You might need to alter them accordingly.

Router R1

Router R2

Router R3

Router R4

b. Verify the configuration with the show ip interface brief, show protocols, and show interfaces description commands. The output from router R3 is shown here as an example.

Step 3: Configure basic EIGRP.
a. Implement EIGRP AS 1 over the serial and loopback interfaces as you have configured it for the other EIGRP labs.

b. Advertise networks 172.16.12.0/29, 172.16.13.0/29, 172.16.23.0/29, 172.16.34.0/29, 192.168.1.0/24, 192.168.2.0/24, 192.168.3.0/24, and 192.168.4.0/24 from their respective routers.

You can copy and paste the following configurations into your routers.

Router R1

Router R2

Router R3

Router R4

You should see EIGRP neighbor relationship messages being generated.

Step 4: Verify EIGRP connectivity.
a. Verify the configuration by using the show ip eigrp neighbors command to check which routers have EIGRP adjacencies.

Did you receive the output you expected?
The output should be similar to that shown above.

b. Run the following Tcl script on all routers to verify full connectivity.

You should get ICMP echo replies for every address pinged. Make sure to run the Tcl script on each router.

Step 5: Verify the current path.
Before you configure PBR, verify the routing table on R1.

a. On R1, use the show ip route command. Notice the next-hop IP address for all networks discovered by EIGRP.

b. On R4, use the traceroute command to the R1 LAN address and source the ICMP packet from R4 LAN A and LAN B.

Note: You can specify the source as the interface address (for example 192.168.4.1) or the interface designator (for example, Fa0/0).

Notice that the path taken for the packets sourced from the R4 LANs are going through R3 –> R2 –> R1.

Why are the R4 interfaces not using the R3 –> R1 path?
Because the serial interfaces between routers R1 and R3 have been configured with a lower bandwidth of 64 Kb/s, giving it a higher metric. All other serial interfaces are using the bandwidth setting of 128 Kb/s. R3 chooses to send all packets to R2 because of its lower metric.

c. On R3, use the show ip route command and note that the preferred route from R3 to R1 LAN 192.168.1.0/24 is via R2 using the R3 exit interface S0/0/1.

d. On R3, use the show interfaces serial 0/0/0 and show interfaces s0/0/1 commands.

Notice that the bandwidth of the serial link between R3 and R1 (S0/0/0) is set to 64 Kb/s, while the bandwidth of the serial link between R3 and R2 (S0/0/1) is set to 128 Kb/s.

e. Confirm that R3 has a valid route to reach R1 from its serial 0/0/0 interface using the show ip eigrp topology 192.168.1.0 command.

As indicated, R4 has two routes to reach 192.168.1.0. However, the metric for the route to R1 (172.16.13.1) is much higher (40640000) than the metric of the route to R2 (21152000), making the route through R2 the successor route.

Step 6: Configure PBR to provide path control.
Now you will deploy source-based IP routing by using PBR. You will change a default IP routing decision based on the EIGRP-acquired routing information for selected IP source-to-destination flows and apply a different next-hop router.

Recall that routers normally forward packets to destination addresses based on information in their routing table. By using PBR, you can implement policies that selectively cause packets to take different paths based on source address, protocol type, or application type. Therefore, PBR overrides the router’s normal routing behavior.

Configuring PBR involves configuring a route map with match and set commands and then applying the route map to the interface.

The steps required to implement path control include the following:

  • Choose the path control tool to use. Path control tools manipulate or bypass the IP routing table. For PBR, route-map commands are used.
  • Implement the traffic-matching configuration, specifying which traffic will be manipulated. The match commands are used within route maps.
  • Define the action for the matched traffic using set commands within route maps.
  • Apply the route map to incoming traffic.

As a test, you will configure the following policy on router R3:

  • All traffic sourced from R4 LAN A must take the R3 –> R2 –> R1 path.
  • All traffic sourced from R4 LAN B must take the R3 –> R1 path.

a. On router R3, create a standard access list called PBR-ACL to identify the R4 LAN B network.

b. Create a route map called R3-to-R1 that matches PBR-ACL and sets the next-hop interface to the R1 serial 0/0/1 interface.

c. Apply the R3-to-R1 route map to the serial interface on R3 that receives the traffic from R4. Use the ip
policy route-map command on interface S0/1/0.

d. On R3, display the policy and matches using the show route-map command.

Note: There are currently no matches because no packets matching the ACL have passed through R3 S0/1/0.

Step 7: Test the policy.
Now you are ready to test the policy configured on R3. Enable the debug ip policy command on R3 so that you can observe the policy decision-making in action. To help filter the traffic, first create a standard ACL that identifies all traffic from the R4 LANs.

a. On R3, create a standard ACL which identifies all of the R4 LANs.

b. Enable PBR debugging only for traffic that matches the R4 LANs.

c. Test the policy from R4 with the traceroute command, using R4 LAN A as the source network.

Notice the path taken for the packet sourced from R4 LAN A is still going through R3 –> R2 –> R1.

As the traceroute was being executed, router R3 should be generating the following debug output.

Why is the traceroute traffic not using the R3 –> R1 path as specified in the R3-to-R1 policy?
It does not take the PBR-specified path because LAN A does not meet the criteria specified in the PBRACL access list.

d. Test the policy from R4 with the traceroute command, using R4 LAN B as the source network.

Now the path taken for the packet sourced from R4 LAN B is R3 –> R1, as expected.

The debug output on R3 also confirms that the traffic meets the criteria of the R3-to-R1 policy.

e. On R3, display the policy and matches using the show route-map command.

Note: There are now matches to the policy because packets matching the ACL have passed through R3 S0/1/0.

Router Interface Summary Table

Router Interface Summary
Router Model Ethernet Interface
#1
Ethernet Interface
#2
Serial Interface
#1
Serial Interface
#2
1700 Fast Ethernet 0
(Fa0)
Fast Ethernet 1
(Fa1)
Serial 0 (S0) Serial 0/0/1
(S0/0/1)
1800 Fast Ethernet 0/0
(Fa0/0)
Fast Ethernet 0/1
(Fa0/1)
Serial 0/0/0
(S0/0/0)
Serial 0/0/1
(S0/0/1)
2600 Fast Ethernet 0/0
(Fa0/0)
Fast Ethernet 0/1
(Fa0/1)
Serial 0/0 (S0/0) Serial 0/1 (S0/1)
2800 Fast Ethernet 0/0
(Fa0/0)
Fast Ethernet 0/1
(Fa0/1)
Serial 0/0/0
(S0/0/0)
Serial 0/0/1
(S0/0/1)
Note: To find out how the router is configured, look at the interfaces to identify the type of router and how many interfaces the router has. Rather than list all combinations of configurations for each router class, this table includes identifiers for the possible combinations of Ethernet and serial interfaces in the device. The table does not include any other type of interface, even though a specific router might contain one. For example, for an ISDN BRI interface, the string in parenthesis is the legal abbreviation that can be used in Cisco IOS commands to represent the interface.

Device Configurations (Instructor version)

Router R1

Router R2

Router R3

Router R4

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