Example 10-1 Configuring EIGRP on R2 and Placing S0 into EIGRP Autonomous System 100 | CCNA Practical Studies (Cisco Certification & Training)

Lab Objective: Configuring EIGRP

In this chapter, you will learn how to configure EIGRP by accomplishing the following lab objectives, based on the network topology in Figure 10-2:

Figure 10-2. IP EIGRP Routers

graphics/10fig02.gif

Place R3's S0, R2's S0, R4's S0, and R4's Loopback0 networks into EIGRP autonomous system (AS) 100.
Place R3's E0 and R4's E0 networks into EIGRP 100.
Create two loopback interfaces on R4 with the following addresses: loopback1=200.200.1.4/24 and loopback2=200.200.2.4/24.
Add these two networks into the EIGRP routing domain, and configure R4 so that all other routers see only one route to these two addresses.

Review the routers that will be configured for EIGRP. Figure 10-2 depicts that portion of the lab in which EIGRP will be configured.

Configuring EIGRP Between R2, R3, and R4

Table 10-1 outlines the two required steps and corresponding commands for configuring EIGRP.

Table 10-1. Steps for Configuring EIGRP

Step	Command
1. Enable the EIGRP routing process in global configuration mode.	Router(config)# router eigrp [ autonomous-system ]
2. Associate networks with an EIGRP routing process in router configuration mode.	Router(config-router)# network [ network-number ]

EIGRP will send updates only to the interfaces in the networks specified. If you do not specify an interface's network, it will not be advertised in any IP EIGRP update.

Lab Task 1: Place R3's S0, R2's S0, R4's S0, and R4's Loopback0 Networks into EIGRP AS 100

Begin by configuring EIGRP as the routing protocol between R2, R3, and R4. Use the autonomous system 100. Resume the connection to R2 and place S0 into EIGRP 100, as shown in Example 10-1.

 Termserver#  2  [Resuming connection 2 to r2 ... ] R2#  conf t  Enter configuration commands, one per line. End with CNTL/Z. R2(config)#  router eigrp 100  R2(config-router)#  network 192.168.100.0  R2(config-router)#

Now return to the terminal server, and resume the connection to R3 and subsequently to R4. Enable the EIGRP routing process on each router. Then add R3 and R4's S0 interface into EIGRP AS 100, and add R4's loopback0 into EIGRP AS 100, as shown in Example 10-2.

Example 10-2 Enabling EIGRP on R3 and R4 and Placing R3 and R4's S0 Interface and R4's Loopback0 Interface Into EIGRP Autonomous System 100

 Termserver#  3  [Resuming connection 3 to r3 ... ] R3#  conf t  Enter configuration commands, one per line. End with CNTL/Z. R3(config)#  router eigrp 100  R3(config-router)#  network 192.168.100.0  R3(config-router)#  ^Z  R3# %SYS-5-CONFIG_I: Configured from console by console R3# _________________________________________________________________________ Termserver#  4  [Resuming connection 4 to r4 ... ] R4#  conf t  Enter configuration commands, one per line. End with CNTL/Z. R4(config)#  router eigrp 100  R4(config-router)#  network 192.168.100.0  R4(config-router)#  network 192.169.4.0  R4(config-router)#  ^Z  R4# %SYS-5-CONFIG_I: Configured from console by console R4#

After EIGRP has been configured, R2 and R4 each should form a neighbor relationship to R3. In addition, R3 should form two neighbor relationships, one to R2 and one to R4. You can verify that this has occurred using the following command:

 Router#  show ip eigrp neighbors

Now go to each individual router in EIGRP AS 100 and verify that you have the proper EIGRP neighbor relationships. First, examine the neighbor relationship on R2, as shown in Example 10-3.

Example 10-3 R2 EIGRP Neighbor Relationship to R3

 Termserver#  2  [Resuming connection 2 to r2 ... ] R2#  show ip eigrp neighbors  IP-EIGRP neighbors for process 100 H   Address                 Interface   Hold Uptime   SRTT   RTO  Q  Seq                                         (sec)         (ms)       Cnt Num 0   192.168.100.3           Se0          162 00:07:39    0  5000  0  1 R2#

The output in Example 10-3 shows that R2 has successfully formed a neighbor relationship to R3's S0 address of 192.168.100.3.

Next , examine the neighbor relationship on R4, as shown in Example 10-4.

Example 10-4 R4 EIGRP Neighbor Relationship to R3

 Termserver#  4  [Resuming connection 4 to r4 ... ] R4#  show ip eigrp neighbors  IP-EIGRP neighbors for process 100 H   Address                 Interface   Hold Uptime   SRTT   RTO  Q  Seq                                         (sec)         (ms)       Cnt Num 0   192.168.100.3           Se0          170 00:07:45    0  5000  0  1 R4#

Again, the output from show ip eigrp neighbors shows that R4 has successfully formed a neighbor relationship to R3's S0 address of 192.168.100.3.

Finally, examine R3 to see its neighbor relationships, as shown in Example 10-5.

Example 10-5 R3 Neighbor Relationships to R4 and R2

 Termserver#  3  [Resuming connection 3 to r3 ... ] R3#  show ip eigrp neighbors  IP-EIGRP neighbors for process 100 H   Address                 Interface   Hold Uptime   SRTT   RTO  Q  Seq                                         (sec)         (ms)       Cnt Num 1   192.168.100.4           Se0          163 00:08:26    0  5000  0  1 0   192.168.100.2           Se0          147 00:08:40    0  3000  0  1 R3#

The output in Example 10-5 shows that R3 has two neighbor relationships, one to R2 and one to R4, as expected.

Although EIGRP has been configured properly, if you examine the routing table on R3, you can see that only one EIGRP route exists in the routing table to R4's loopback0 network of 192.169.4.0. The letter D precedes the EIGRP route to depict internal routes learned through EIGRP. Example 10-6 displays the routing table on R3.

Example 10-6 Only One EIGRP Route on R3

 R3#  show ip route  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP  D - EIGRP  , EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set C    192.168.100.0/24 is directly connected, Serial0 C    192.168.35.0/24 is directly connected, Serial1 I    192.168.50.0/24 [100/8539] via 192.168.35.5, 00:01:02, Serial1 C    192.169.3.0/24 is directly connected, Loopback0 C    192.168.3.0/24 is directly connected, Ethernet0 I    192.169.5.0/24 [100/8976] via 192.168.35.5, 00:01:02, Serial1  D    192.169.4.0/24 [90/2297856] via 192.168.100.4, 00:06:28, Serial0  R3#

The output shows only one EIGRP route on R3, even though you placed two networks into EIGRP on R4. This is expected because the network of 192.168.100.0 is already in the routing table as a directly connected route. So, even though it was added to EIGRP, you should expect to see it as a directly connected route, not an EIGRP route. This appears in the routing table where 192.168.100.0 appears as a directly connected route represented by a C preceding the route instead of an EIGRP route represented by and EX.

Lab Task 2: Add R3 and R4's EO Network into EIGRP AS 100

Next, add R3 and R4's E0 network into EIGRP AS 100. After doing so, you should expect to see additional EIGRP routes being advertised to these networks through EIGRP. Example 10-7 shows how these networks are added on R3 and R4.

Example 10-7 Configuring R3 and R4's E0 Network as Part of AS 100

 R3#  conf t  Enter configuration commands, one per line. End with CNTL/Z. R3(config)#  router eigrp 100  R3(config-router)#  network 192.168.3.0  R3(config-router)#  end  R3# %SYS-5-CONFIG_I: Configured from console by console R3# Termserver#  4  [Resuming connection 4 to r4 ... ] ________________________________________________________________________ R4#  conf t  Enter configuration commands, one per line. End with CNTL/Z. R4(config)#  router eigrp 100  R4(config-router)#  network 192.168.4.0  R4(config-router)#  end  R4# %SYS-5-CONFIG_I: Configured from console by console R4#

Now, if you display the routing table on R3, you should see that R3 has learned R4's E0 network in addition to R4's Loopback0 network, which were advertised through EIGRP, as shown in Example 10-8.

Example 10-8 R3 Displays EIGRP Route to R4's E0 Network of 192.168.4.0 and to R4's Loopback0 Network of 192.169.4.0

 Termserver#  3  [Resuming connection 3 to r3 ... ] R3#  show ip route  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set C    192.168.100.0/24 is directly connected, Serial0 C    192.168.35.0/24 is directly connected, Serial1 I    192.168.50.0/24 [100/8539] via 192.168.35.5, 00:00:35, Serial1 C    192.169.3.0/24 is directly connected, Loopback0 C    192.168.3.0/24 is directly connected, Ethernet0  D    192.168.4.0/24 [90/2195456] via 192.168.100.4, 00:00:49, Serial0   D    192.169.4.0/24 [90/2297856] via 192.168.100.4, 00:06:28, Serial0  I    192.169.5.0/24 [100/8976] via 192.168.35.5, 00:00:35, Serial1 R3#

Conversely, R4's routing table shows that R3's E0 network of 192.168.3.0 was learned through EIGRP, as shown in the highlighted section of Example 10-9.

Example 10-9 R4 Displays EIGRP Route to R3's E0 Network of 192.168.3.0

 R4#  show ip route  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set C    192.168.100.0/24 is directly connected, Serial0  D    192.168.3.0/24 [90/2195456] via 192.168.100.3, 00:04:15, Serial0  192.168.4.0/24 is variably subnetted, 2 subnets, 2 masks D    192.168.4.0/24 is a summary, 00:04:33, Null0 C    192.168.4.0/27 is directly connected, Ethernet0 C    192.169.4.0/24 is directly connected, Loopback0 R4#

Finally, examine the routing table of R2, as shown in Example 10-10. Based on what you've seen regarding how EIGRP works on R3 and R4, at first glance you might expect R2 to learn, through EIGRP, routes to R4 and R3's E0 networks and R4's Loopback0 networkmore specifically , routes to 192.168.3.0, 192.168.4.0, and 192.169.4.0.

Example 10-10 R2's Routing Table Shows Route to 192.168.3.0 but Not to 192.168.4.0

 Termserver#  2  [Resuming connection 2 to r2 ... ] R2#  show ip route  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set C    192.168.1.0/24 is directly connected, Ethernet0 R    192.169.1.0/24 [120/1] via 192.168.1.1, 00:00:08, Ethernet0 C    192.168.2.0/24 is directly connected, Ethernet1 C    192.169.2.0/24 is directly connected, Loopback0 C    192.168.100.0/24 is directly connected, Serial0  D    192.168.3.0/24 [90/2195456] via 192.168.100.3, 00:00:56, Serial0  R2#

Notice that R2 has learned the route to 192.168.3.0 through EIGRP but not to 192.168.4.0 or 192.169.4.0. Because you know that R4 advertised the 192.168.4.0 and 192.169.4.0 routes to R3 and each route shows up correctly in R3's routing table (see Example 10-8), you might wonder why these routes were not passed on to R2. The rule of split horizon explains this:

Information about routes is prevented from exiting the router interface through which that information was received.

Although these routes were learned by R3, split horizon prevents them from being passed out R3's S0 interface to R2 because it is the same interface that the routes were learned on initially. To disable split horizon for EIGRP, enter interface configuration mode and use the following command:

 Router(config-if)#  no ip split-horizon eigrp  [  autonomous-system  ]

Split horizon is a key consideration in hub-and-spoke Frame Relay networks when not using point-to-point subinterfaces. Disable EIGRP split horizon on R3 by entering the interface configuration mode of S0 and executing the command shown in Example 10-11.

Example 10-11 Disabling EIGRP Split Horizon on R3's S0 Interface

 R3#  conf t  Enter configuration commands, one per line.  End with CNTL/Z. R3(config)#  int s0  R3(config-if)#  no ip split-horizon eigrp 100  R3(config-if)#  end  R3#

Now that split horizon has been disabled for EIGRP on R3's S0 interface, when you return to R2 and display the routing table, you should see that R2 has learned the routes to network 192.168.4.0 and 192.169.4.0, as shown in Example 10-12. These routes were passed on to R2 through R3 after split horizon was disabled on the R3's S0 interface.

Example 10-12 After Split Horizon Is Disabled on R3's S0 Interface, R2 Successfully Learns Routes to 192.168.4.0 and 192.169.4.0

 R2#  show ip route  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set  D    192.168.4.0/24 [90/2707456] via 192.168.100.3, 00:02:08, Serial0   D    192.169.4.0/24 [90/2809856] via 192.168.100.3, 00:02:08, Serial0  C    192.168.1.0/24 is directly connected, Ethernet0 R    192.169.1.0/24 [120/1] via 192.168.1.1, 00:00:11, Ethernet0 C    192.168.2.0/24 is directly connected, Ethernet1 C    192.169.2.0/24 is directly connected, Loopback0 C    192.168.100.0/24 is directly connected, Serial0 D    192.168.3.0/24 [90/2195456] via 192.168.100.3, 00:02:09, Serial0 R2#

Now that R2 has a route to R4's E0 network of 192.168.4.0 and to R4's Loopback0 network of 192.169.4.0, R2 should be capable of ping ing 192.168.4.4 and 192.169.4.4, as shown in Example 10-13.

Example 10-13 R2 Can Ping R4's E0 and Loopback0 Interfaces After the Route Is Learned Through EIGRP

 R2#  ping 192.168.4.4  Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 192.168.4.4, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 88/92/104 ms R2# R2#  ping 192.169.4.4  Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 192.168.4.4, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 88/92/104 ms R2#

With the proper routes in the routing table, R2 successfully ping s R4's E0 and loopback0 interfaces.

Lab Task 3 & 4: Create Two Loopback Interfaces on R4 with Specified Network Addresses, and Place R4's Loopback0 into EIGRP 100

Next, resume the connection to R4 and configure two new additional loopback interfaces. Create loopback1 with an address of 200.200.1.4 and loopback2 with an address of 200.200.2.4, as shown in Example 10-14.

Example 10-14 Configuring R4 with Loopback Interfaces 200.200.1.4 and 200.200.2.4

 Termserver#  4  [Resuming connection 4 to r4 ... ] R4#  conf t  Enter configuration commands, one per line. End with CNTL/Z. R4(config)#  int loopback1  R4(config-if)#  ip addre  %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback1, changed state to up R4(config-if)#  ip address 200.200.1.4 255.255.255.0  R4(config-if)#  exit  R4(config)#  int loopback2  R4(config-if)# %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback2, changed state to up R4(config-if)#  ip address 200.200.2.4 255.255.255.0  R4(config-if)#  ^Z  R4#

Lab Task 5: Add the Two Networks into the EIGRP Routing Domain, and Configure R4 So That All Other Routers See Only One Route to These Two Addresses

Each loopback interface represents a network. These two networks are advertised in the EIGRP routing process on R4 to R3 and R2 and are used to demonstrate route summarization. Route summarization is the process of condensing routing information. This process also is referred to as route aggregation, classless interdomain routing (CIDR), or supernetting. Without summarization, each router in a network must retain a route to every subnet in the network. With summarization, routers can reduce a group of routes to a single advertisement called a summary route. Route summarization reduces the load on the router by decreasing the number of CPU processing cycles required for route propagation and routing information overhead.

In large networks, summarization is a useful technique to consolidate hundreds or possibly thousands of routes propagated within an autonomous system. Instead, a summary route is advertised that represents the path to multiple routes. As the network increases in size , the more important route summarization becomes. The simplest form of route summarization is collapsing all the subnet routes into a single network route at the classful bit boundary. By default, EIGRP automatically summarizes in this fashion; however, EIGRP also supports route summarization at any bit boundary rather than just at the major network number boundary. This is possible because EIGRP supports VLSM.

Next, add the two loopback networks created on R4 to EIGRP AS 100, as shown in Example 10-15.

Example 10-15 Adding Loopback1 and Loopback2 to EIGRP AS 100 on R4

 R4#  conf t  Enter configuration commands, one per line. End with CNTL/Z. R4(config)#  router eigrp 100  R4(config-router)#  network 200.200.1.0  R4(config-router)#  network 200.200.2.0  R4(config-router)#  ^Z  R4#

Go to R3 and examine the routing table of R3 to verify that the loopback networks added on R4 are being advertised through EIGRP. Example 10-16 shows that networks 200.200.1.0 and 200.200.2.0 have been advertised and that R3 learned these through EIGRP.

Example 10-16 Networks 200.200.1.0 and 200.200.2.0 Advertised to R3 Through EIGRP

 Termserver#  3  [Resuming connection 3 to r3 ... ] R3#  show ip route  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set  D    200.200.1.0/24 [90/2297856] via 192.168.100.4, 00:00:03, Serial0   D    200.200.2.0/24 [90/2297856] via 192.168.100.4, 00:00:03, Serial0  C    192.168.100.0/24 is directly connected, Serial0 C    192.168.35.0/24 is directly connected, Serial1 I    192.168.50.0/24 [100/8539] via 192.168.35.5, 00:00:03, Serial1 C    192.169.3.0/24 is directly connected, Loopback0 C    192.168.3.0/24 is directly connected, Ethernet0 I    192.169.5.0/24 [100/8976] via 192.168.35.5, 00:00:03, Serial1 D    192.168.4.0/24 [90/2195456] via 192.168.100.4, 00:00:03, Serial0 D    192.169.4.0/24 [90/2297856] via 192.168.100.4, 00:00:03, Serial0 R3#

To ensure that split horizon is not an issue, verify that R2 is receiving these EIGRP loopback networks through EIGRP from R3, as shown in Example 10-17.

Example 10-17 R2 Receives R4 Loopback Networks as Expected

 Termserver#  2  [Resuming connection 2 to r2 ... ] R2#  show ip route  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set  D    200.200.1.0/24 [90/2809856] via 192.168.100.3, 00:01:13, Serial0   D    200.200.2.0/24 [90/2809856] via 192.168.100.3, 00:01:14, Serial0  D    192.168.4.0/24 [90/2707456] via 192.168.100.3, 00:01:14, Serial0 C    192.168.1.0/24 is directly connected, Ethernet0 R    192.169.1.0/24 [120/1] via 192.168.1.1, 00:00:16, Ethernet0 C    192.168.2.0/24 is directly connected, Ethernet1 C    192.169.2.0/24 is directly connected, Loopback0 C    192.168.100.0/24 is directly connected, Serial0 D    192.168.3.0/24 [90/2195456] via 192.168.100.3, 00:36:35, Serial0 D    192.169.3.0/24 [90/2809856] via 192.168.100.3, 00:36:35, Serial0 R2#

You can see that R2 has received network 200.200.1.0 and 200.200.2.0 as desired and that split horizon is not an issue. Verify that R2 can ping these newly created loopbacks on R4, as shown in Example 10-18.

Example 10-18 R2 Can ping R4's Newly Created Loopback Addresses

 R2#  ping 200.200.1.4  Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 200.200.1.4, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 88/92/104 ms R2#  ping 200.200.2.4  Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 200.200.2.4, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 88/91/100 ms R2#

So far, so good. However, the lab objective explicitly states that these two loopbacks should be added to the EIGRP routing domain and that you need to configure R4 so that all other routers see only one route to these two addresses. This objective is accomplished through configuring route summarization. By doing so, you will summarize the two Class C loopback addresses into one Class B summary address that will be advertised from R4 to R3 and R2 through EIGRP. As mentioned previously, because EIGRP supports VLSM, you can summarize these two addresses at any bit boundary rather than just at the major Class B network number boundary if you desire . For the purposes here, however, you need to summarize at the Class B boundary.

A summary address is configured in interface configuration mode of the interface from which you want the summarized address to be advertised. In the lab, a summary address of 200.200.0.0 is configured on R4's S0 interface and is advertised out to the rest of the network. In addition, you will need to turn off autosummary within the EIGRP routing process of R4. Autosummary is on by default when the EIGRP routing process is started. Turn off autosummary so that only the summarized Class B route is advertised from R4. If autosummary was not turned off, R4 would advertise the Class B summary address that you will configure on R4's S0 interface in addition to the two Class C addresses of each loopback (that is, 200.200.1.0 and 200.200.2.0). By turning off autosummary, you ensure that only the Class B summary address is advertised to the rest of the network.

To configure a summary address and ensure that only one summary route is advertised from R4, two steps are required, as shown in Table 10-2.

Table 10-2. Configuring a Summary Address and Ensuring That Only One Summary Route Is Advertised

Step	Command
1. Disable automatic route summarization in router configuration mode.	Router(config-router)# no auto-summary
2. Configure a summary address in interface configuration mode of the desired interface from which the summary address will be advertised.	Router(config-if)# ip summary-address eigrp [ autonomous-system # ] [ network address ] [ mask ]

After a summary address is configured, if there are any more specific routes in the routing table, EIGRP will advertise the summary address out the interface with a metric equal to the minimum of all more specific routes.

First, disable autosummary within the EIGRP routing process on R4, as shown in Example 10-19.

Example 10-19 Disabling Autosummary on R4 to Prevent Route Advertisements of 200.200.1.0 and 200.200.2.0

 R4#  conf t  Enter configuration commands, one per line.  End with CNTL/Z. R4(config)#  router eigrp 100  R4(config-router)#  no auto-summary  R4(config-router)#  ^Z  R4# %SYS-5-CONFIG_I: Configured from console by console R4#

As mentioned previously, this prevents routes 200.200.1.0 and 200.200.2.0 from being automatically summarized at their default major network boundary and being subsequently advertised through EIGRP to R3 and R2.

Next, configure a summary address of 200.200.0.0 on R4's SO. This is the interface that you want the summary address to be advertised from. Example 10-20 shows the summary address configuration.

Example 10-20 Configuring a Summary Address on R4 of 200.200.200.0 to Be Advertised Out S0

 R4#  conf t  Enter configuration commands, one per line. End with CNTL/Z. R4(config)#  int s0  R4(config-if)#  ip summary-address eigrp 100 200.200.0.0 255.255.0.0  R4(config-if)#  ^Z  R4# %SYS-5-CONFIG_I: Configured from console by console R4#

R4 now has been configured to advertise the summary address of 200.200.0.0 out its S0 interface to the rest of the network. Now examine the routing table on R4 to see how the summary address appears in the routing table as shown in Example 10-21.

Example 10-21 R4 Routing Table Show How the Summary Address Appears After Configuration

 R4#  show ip route  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set C    200.200.1.0/24 is directly connected, Loopback1 C    200.200.2.0/24 is directly connected, Loopback2 C    192.168.100.0/24 is directly connected, Serial0 D    192.168.3.0/24 [90/2195456] via 192.168.100.3, 00:00:00, Serial0      192.168.4.0/27 is subnetted, 1 subnets C    192.168.4.0 is directly connected, Ethernet0 C    192.169.4.0/24 is directly connected, Loopback0  D    200.200.0.0/16 is a summary, 00:00:36, Null0  R4#

R4's routing table has added a summary route of 200.200.0.0/16 pointing to Null0. Null0 is also known as the bit bucket, meaning that the router drops all packets routed to Null0. Essentially, the summary address route is displayed on R4's routing table for informational purposes. It does not affect the routing of packets because R4 has more specific routes pointing to the specific networks of 200.200.1.0 and 200.200.2.0. Thus, the summary route of 200.200.0.0 is advertised to the rest of the network, but when packets are forwarded to R4 destined for either network, R4 forwards the packets to the more specific routes of 200.200.1.0 or 200.200.2.0. In this way, you can consolidate these two routes using summarization and then advertise the summary route to the remainder of the network, while still maintaining specific routes to these destinations on R4.

NOTE

This concept is known as longest match routing. The router selects a route from its routing table that has the longest matching value to the destination IP address in the IP packet. For example, assume that router R4 receives an IP packet with a destination IP address of 200.200.1.1. The router will parse through its routing table to determine which route has the longest match to 200.200.1.1. R4 will choose 200.200.1.0 instead of 200.200.0.0 because 200.200.1.0 matches the first three octets instead of only the first two octets. When the longest match is found, the router forwards the packet to the loopback interface.

Now that you've configured a summary address of 200.200.0.0 on R4, check R3 and R2's routing table to see if the summary route has been advertised as designed. Resume the connection to R3 to check the routing table, as demonstrated in Example 10-22.

Example 10-22 Summary Address of 200.200.0.0 Advertised Successfully from R4 to R3

 Termserver#  3  [Resuming connection 3 to r3 ... ] R3#  show ip route  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set C    192.168.100.0/24 is directly connected, Serial0 C    192.168.35.0/24 is directly connected, Serial1 I    192.168.50.0/24 [100/8539] via 192.168.35.5, 00:01:06, Serial1 C    192.169.3.0/24 is directly connected, Loopback0 C    192.168.3.0/24 is directly connected, Ethernet0      192.168.4.0/27 is subnetted, 1 subnets D    192.168.4.0 [90/2195456] via 192.168.100.4, 00:01:24, Serial0 D    192.169.4.0 [90/2297856] via 192.168.100.4, 00:01:24, Serial0 I    192.169.5.0/24 [100/8976] via 192.168.35.5, 00:01:07, Serial1  D    200.200.0.0/16 [90/2297856] via 192.168.100.4, 00:01:24, Serial0  R3#

The output in Example 10-22 shows that R3 has received the summary address configured on R4's S0 interface. Next, check R2's routing table. Remember that before configuring a summary address on R4, R3 and R2 were receiving two loopback routesone to 200.200.1.0 and one to 200.200.2.0 (see Example 10-17). Now, if you display R2's routing table, you should see the results in Example 10-23.

Example 10-23 Summary Address of 200.200.0.0 Advertised Successfully Propagated to R2

 Termserver#  2  [Resuming connection 2 to r2 ... ] R2#  show ip route  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set      192.168.4.0/27 is subnetted, 1 subnets D    192.168.4.0 [90/2707456] via 192.168.100.3, 00:01:35, Serial0 C    192.168.1.0/24 is directly connected, Ethernet0 R    192.169.1.0/24 [120/1] via 192.168.1.1, 00:00:10, Ethernet0 C    192.168.2.0/24 is directly connected, Ethernet1 C    192.169.2.0/24 is directly connected, Loopback0 C    192.168.100.0/24 is directly connected, Serial0 D    192.168.3.0/24 [90/2195456] via 192.168.100.3, 00:42:24, Serial0 D    192.169.3.0/24 [90/2809856] via 192.168.100.3, 00:42:24, Serial0  D    200.200.0.0/16 [90/2809856] via 192.168.100.3, 00:01:35, Serial0  R2#

R2 now is getting only the summarized route of 200.200.0.0, as designed. Thus, you know that these two Class C routes have been properly summarized on R4 and advertised successfully through EIGRP to R3 and R2, per the lab objective.

With only a summary address in the routing table of R2, you need to determine whether R2 can still ping the loopback addresses of R4 by initiating a ping to each of R4's loopback addresses, as shown in Example 10-24.

Example 10-24 After Receiving the Summary Address of 200.200.0.0, R2 Still Can Successfully ping Each of R4's Loopback Addresses

 R2#  ping 200.200.1.4  Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 200.200.1.4, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 88/92/100 ms R2#  ping 200.200.2.4  Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 200.200.2.4, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 88/93/104 ms R2#

You now have successfully configured EIGRP between R2, R3, and R4, adding the required networks into EIGRP AS 100. In addition, you have summarized the two loopback networks of 200.200.1.0 and 200.200.2.0 on R4 into one route of 200.200.0.0, and you have advertised this summary address to the rest of your network. The next section examines some commands useful to verifying the configuration and operation of EIGRP.

Verifying EIGRP Configuration and Operation

To verify the EIGRP configuration and ensure that the proper networks are configured for EIGRP, a few commands are helpful. These two important show commands are used quite extensively while configuring EIGRP between R2, R3, and R4:

  show ip eigrp neighbors   show ip route

The show ip eigrp neighbors command is useful for verifying that two neighboring routers configured for EIGRP have established a neighbor relationship and thus will be capable of exchanging EIGRP routing information. The show ip route command is useful for verifying that expected EIGRP routes have been learned and have made it into the routing table. If additional review of either command is needed, refer back within this chapter to see how each command was used to verify and troubleshoot the EIGRP configuration in the lab environment.

The remaining commands that provide helpful information concerning EIGRP configuration as well as foster an understanding of how the EIGRP configuration should appear in the running configuration are as follows :

  show ip protocols   show running-config   show ip eigrp topology

show ip protocols Command

Begin by returning to R3 and executing the show ip protocols command. Currently, R3 is configured for two routing protocolsIGRP and EIGRP. Execute the command on R3, and examine the EIGRP information as shown in Example 10-25.

Example 10-25 Output of show ip protocols on R3

 R3#  show ip protocols  Routing Protocol is "igrp 200"   Sending updates every 90 seconds, next due in 41 seconds   Invalid after 270 seconds, hold down 280, flushed after 630   Outgoing update filter list for all interfaces is not set   Incoming update filter list for all interfaces is not set   Default networks flagged in outgoing updates   Default networks accepted from incoming updates   IGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0   IGRP maximum hopcount 100   IGRP maximum metric variance 1   Redistributing: igrp 200   Routing for Networks:     192.168.35.0     192.169.3.0   Routing Information Sources:     Gateway         Distance      Last Update     192.168.35.5         100      00:00:02   Distance: (default is 100)  Routing Protocol is "eigrp 100"  Outgoing update filter list for all interfaces is not set   Incoming update filter list for all interfaces is not set   Default networks flagged in outgoing updates   Default networks accepted from incoming updates   EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0   EIGRP maximum hopcount 100   EIGRP maximum metric variance 1   Redistributing: eigrp 100   Automatic network summarization is in effect   Automatic address summarization:     192.168.100.0/24 for Ethernet0     192.168.3.0/24 for Serial0   Routing for Networks:     192.168.100.0     192.168.3.0   Routing Information Sources:     Gateway         Distance      Last Update     192.168.100.4         90      00:55:52     192.168.100.2         90      00:55:52   Distance: internal 90 external 170 R3#

The output shows that that R3 is running IGRP and EIGRP. The EIGRP section shows that you are running EIGRP with AS 100, as displayed by the following information:

 Routing Protocol is "eigrp 100"

Next, you can see that automatic network summarization is in effect for networks 192.168.100.0/24 (E0) and 192.168.3.0/24 (S0). When the EIGRP routing process is started on a router, automatic network summarization is on by default, and EIGRP automatically summarizes at the major network boundary, as you can see for E0 and S0. To turn it off, as you did on R4, you need to use the no auto-summary command under the EIGRP routing process.

Next, the output shows that EIGRP is advertising networks 192.168.100.0 and 192.168.3.0, as indicated by the following information:

 Routing for Networks:     192.168.100.0     192.168.3.0

Finally, you can see that R3 has two EIGRP neighborsone to R2 and one to R4. From these two sources, R3 is receiving EIGRP routing information, as shown from the following portion of the output:

 Routing Information Sources:     Gateway         Distance      Last Update     192.168.100.4         90      00:55:52     192.168.100.2         90      00:55:52

Now that you have a basic idea of some of the information available using the show ip protocols command for EIGRP, go to R4 and see how R4 differs from R3. Execute the show ip protocols command on R4 results in the output displayed in Example 10-26.

Example 10-26 show ip protocols Output on R4

 R4#  show ip protocols  Routing Protocol is "eigrp 100"   Outgoing update filter list for all interfaces is not set   Incoming update filter list for all interfaces is not set   Default networks flagged in outgoing updates   Default networks accepted from incoming updates   EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0   EIGRP maximum hopcount 100   EIGRP maximum metric variance 1   Redistributing: eigrp 100  Automatic network summarization is not in effect   Address Summarization:   200.200.0.0/16 for Serial0  Summarizing with metric 128256  Routing for Networks:   192.168.100.0   192.168.4.0   200.200.1.0   200.200.2.0   192.169.4.0  Routing Information Sources:     Gateway         Distance      Last Update     (this router)          5      3d05h     192.168.100.3         90      00:36:05   Distance: internal 90 external 170 R4#

R4 shows that automatic network summarization is not in effect. This is expected because you disabled autosummary on R4. In addition, R4 shows that you are summarizing 200.200.1.0 and 200.200.2.0 to 200.200.0.0/16 and that you are advertising this summarized route out the Serial0 interface. Lastly, you can see that R4 has five networks being advertised in EIGRP AS 100, two of which have been summarized.

show running-config Command

If you look at the running configuration on R4, you should be able to derive much of the same information as the output from show ip protocols. The highlighted area of Example 10-27 shows the EIGRP configuration on R4.

Example 10-27 Running Configuration on R4 Shows EIGRP Configuration

 R4#  show running-config  Building configuration... Current configuration: ! version 11.2 no service password-encryption no service udp-small-servers no service tcp-small-servers ! hostname R4 ! enable password falcons ! ip subnet-zero no ip domain-lookup ip host R1 192.169.1.1 ip host R2 192.169.2.2 ip host R3 192.169.3.3 ip host R4 192.169.4.4 ip host R5 192.169.5.5 ip host R6 192.169.6.6 ! interface Loopback0  ip address 192.169.4.4 255.255.255.0 ! interface Loopback1  ip address 200.200.1.4 255.255.255.0 ! interface Loopback2  ip address 200.200.2.4 255.255.255.0 ! interface Ethernet0  description This interface does not connect to another IP device  ip address 192.168.4.4 255.255.255.224 ! interface Serial0  description This interface connects to R3's S0 (DLCI 101)  ip address 192.168.100.4 255.255.255.0  ip summary-address eigrp 100 200.200.0.0 255.255.0.0  encapsulation frame-relay  frame-relay map ip 192.168.100.2 101 broadcast  frame-relay map ip 192.168.100.3 101 broadcast  frame-relay lmi-type ansi ! interface Serial1  no ip address  shutdown !  router eigrp 100   network 192.168.100.0   network 192.168.4.0   network 200.200.1.0   network 200.200.2.0   network 192.169.4.0   no auto-summary  ! no ip classless ! banner motd ^CC This is Router 4 ^C ! line con 0  exec-timeout 0 0  password falcons  logging synchronous line aux 0 line vty 0 4  password falcons  login R4#

You can verify that what you see in the running configuration parallels what you saw in the show ip protocols outputnamely, that five networks have been placed in EIGRP AS 100, two of which have been summarized to 200.200.0.0/16 and advertised out S0. In addition, autosummary has been disabled on R4 using the no auto-summary command. The EIGRP configuration looks exactly as expected.

show ip eigrp topology Command

Another useful EIGRP troubleshooting command is show ip eigrp topology, which gives you the capability to view the EIGRP topology table, as demonstrated for R3 in Example 10-28.

Example 10-28 EIGRP Topology Table on R3 Indicates That All Routes Are in the Passive State

 R3#  show ip eigrp topology  IP-EIGRP Topology Table for process 100 Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,        r - Reply status P 200.200.0.0/16, 1 successors, FD is 2297856          via 192.168.100.4 (2297856/128256), Serial0 P 192.168.100.0/24, 1 successors, FD is 2169856          via Connected, Serial0 P 192.168.3.0/24, 1 successors, FD is 281600          via Connected, Ethernet0 P 192.168.4.0/27, 1 successors, FD is 2195456          via 192.168.100.4 (2195456/281600), Serial0 P 192.169.4.0/24, 1 successors, FD is 2297856          via 192.168.100.4 (2297856/128256), Serial0 R3#

As discussed earlier, EIGRP maintains a topology table that contains all destinations advertised by neighboring routers. A destination is moved from the topology table to the routing table when there is a feasible successor. An entry in the topology table can have one of two statespassive or active. A route in the topology table is in the passive state when the router is not performing a route recomputation. It is in an active state when undergoing a route recomputation. If there are always feasible successors, a route never has to go into the active state and avoids a route recomputation. Viewing the topology table can help you determine whether a route recomputation is occurring, causing you not to see expected EIGRP routes in the routing table. Currently, you can see that all of R3's routes in the topology table are in the passive state, so expected routes should be advertised properly into the routing table.

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