Objectives
Review a basic EIGRP configuration.
Explore the EIGRP topology table.
Identify successors, feasible successors, and feasible distances.
Use show and debug commands for the EIGRP topology table.
Configure and verify equal-cost load balancing with EIGRP.
Configure and verify unequal-cost load balancing with EIGRP.
Background
As a senior network engineer, you are considering deploying EIGRP in your corporation and want to evaluate its ability to converge quickly in a changing environment. You are also interested in equal-cost and unequal-cost load balancing because your network contains redundant links. These links are not often used by other
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link-state routing protocols because of high metrics. Because you are interested in testing the EIGRP claims that you have read about, you decide to implement and test on a set of three lab routers before deploying EIGRP throughout your corporate network.
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 a 2801 or 2811) and Cisco IOS Software versions if they have comparable capabilities and features. Depending on the router model and Cisco IOS Software version, the commands available and output produced might vary from what is shown in this lab.
Required Resources
3 routers (Cisco 1841 with Cisco IOS Release 12.4(24)T1 Advanced IP Services or comparable)
Serial and console cables
Step 1: Configure the addressing and serial links.
Create three loopback interfaces on each router and address them as 10.1.X.1/30, 10.1.X.5/30, and 10.1.X.9/30, where X is the number of the router. Use the following table or the initial configurations located at the end of the lab.
Router Interface IP Address/Mask
R1 Loopback11 10.1.1.1/30
R1 Loopback15 10.1.1.5/30
R1 Loopback19 10.1.1.9/30
R2 Loopback21 10.1.2.1/30
R2 Loopback25 10.1.2.5/30
R2 Loopback29 10.1.2.9/30
R3 Loopback31 10.1.3.1/30
R3 Loopback35 10.1.3.5/30
R3 Loopback39 10.1.3.9/30
R1(config)# interface Loopback 11
R1(config-if)# ip address 10.1.1.1 255.255.255.252
R1(config-if)# exit
R1(config)# interface Loopback 15
R1(config-if)# ip address 10.1.1.5 255.255.255.252
R1(config-if)# exit
R1(config)# interface Loopback 19
R1(config-if)# ip address 10.1.1.9 255.255.255.252
R1(config-if)# exit
R2(config)# interface Loopback 21
R2(config-if)# ip address 10.1.2.1 255.255.255.252
R2(config-if)# exit
R2(config)# interface Loopback 25
R2(config-if)# ip address 10.1.2.5 255.255.255.252
R2(config-if)# exit
R2(config)# interface Loopback 29
R2(config-if)# ip address 10.1.2.9 255.255.255.252
R2(config-if)# exit
.
R3(config)# interface Loopback 31
R3(config-if)# ip address 10.1.3.1 255.255.255.252
R3(config-if)# exit
R3(config)# interface Loopback 35
R3(config-if)# ip address 10.1.3.5 255.255.255.252
R3(config-if)# exit
R3(config)# interface Loopback 39
R3(config-if)# ip address 10.1.3.9 255.255.255.252
R3(config-if)# exit
Specify the addresses of the serial interfaces as shown in the topology diagram. Set the clock rate to 64 kb/s, and manually configure the interface bandwidth to 64 kb/s.
If you have WIC-2A/S serial interfaces, the maximum clock rate is 128 kb/s. If you have WIC-2T serial interfaces, the maximum clock rate is much higher (2.048 Mb/s or higher depending on the hardware), which is more representative of a modern network WAN link. However, this lab uses 64 kb/s and 128 kb/s settings.
R1(config)# interface Serial 0/0/0 R1(config-if)# description R1-->R2
R1(config-if)# clock rate 64000 R1(config-if)# bandwidth 64
R1(config-if)# ip address 10.1.102.1 255.255.255.248
R1(config-if)# no shutdown R1(config-if)# exit
R1(config)# interface Serial 0/0/1 R1(config-if)# description R1-->R3
R1(config-if)# bandwidth 64
R1(config-if)# ip address 10.1.103.1 255.255.255.248
R1(config-if)# no shutdown R1(config-if)# exit
R2(config)# interface Serial 0/0/0 R2(config-if)# description R2-->R1
R2(config-if)# bandwidth 64
R2(config-if)# ip address 10.1.102.2 255.255.255.248
R2(config-if)# no shutdown R2(config-if)# exit
R2(config)# interface Serial 0/0/1 R2(config-if)# description R2-->R3
R2(config-if)# clock rate 64000 R2(config-if)# bandwidth 64
R2(config-if)# ip address 10.1.203.2 255.255.255.248
R2(config-if)# no shutdown R2(config-if)# exit
R3(config)# interface Serial 0/0/0 R3(config-if)# description R3-->R1
R3(config-if)# clock rate 64000 R3(config-if)# bandwidth 64
R3(config-if)# ip address 10.1.103.3 255.255.255.248
R3(config-if)# no shutdown R3(config-if)# exit
R3(config)# interface Serial 0/0/1 R3(config-if)# description R3-->R2
R3(config-if)# bandwidth 64
R3(config-if)# ip address 10.1.203.3 255.255.255.248
R3(config-if)# no shutdown
R3(config-if)# exit
Verify connectivity by pinging across each of the local networks connected to each router.
Issue the show interfaces description command on each router. This command displays a brief listing of the interfaces, their status, and a description (if a description is configured). Router R1 is shown as an example.
R1# show interfaces description Status Protocol Description
Interface
Fa0/0 admin down down
Fa0/1 admin down down
Se0/0/0 up up R1-->R2
Se0/0/1 up up R1-->R3
Vl1 up down
Lo11 up up
Lo15 up up
Lo19 up up
Issue the show protocols command on each router. This command displays a brief listing of the interfaces, their status, and the IP address and subnet mask configured (in prefix format /xx) for each interface. Router R1 is shown as an example.
R1# show protocols
Global values:
Internet Protocol routing is enabled
FastEthernet0/0 is administratively down, line protocol is down FastEthernet0/1 is administratively down, line protocol is down Serial0/0/0 is up, line protocol is up
Internet address is 10.1.102.1/29
Serial0/0/1 is up, line protocol is up
Internet address is 10.1.103.1/29
Vlan1 is up, line protocol is down
Loopback11 is up, line protocol is up
Internet address is 10.1.1.1/30
Loopback15 is up, line protocol is up
Internet address is 10.1.1.5/30
Loopback19 is up, line protocol is up
Internet address is 10.1.1.9/30
Step 2: Configure EIGRP.
Enable EIGRP AS 100 for all interfaces on R1 and R2 using the commands used in the previous EIGRP lab. Do not enable EIGRP yet on R3. For your reference, these are the commands which can be used:
R1(config)# router eigrp 100
R1(config-router)# network 10.0.0.0
R2(config)# router eigrp 100
R2(config-router)# network 10.0.0.0
Use the debug ip eigrp 100 command to watch EIGRP install the routes in the routing table when your routers become adjacent. You get output similar to the following.
R3# debug ip eigrp 100
IP-EIGRP Route Events debugging is on R3# conf t
Enter configuration commands, one per line. End with CNTL/Z. R3(config)# router eigrp 100
.
R3(config-router)# network 10.0.0.0
R3(config-router)#
*Feb 4 18:44:57.367: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.1.103.1 (Serial0/0/0) is up: new adjacency
*Feb 4 18:44:57.367: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.1.203.2 (Serial0/0/1) is up: new adjacency
*Feb 4 18:44:57.371: IP-EIGRP(Default-IP-Routing-Table:100): Processing incoming UPDATE packet
*Feb 4 18:44:57.379: IP-EIGRP(Default-IP-Routing-Table:100): Processing incoming UPDATE packet
*Feb 4 18:44:57.427: IP-EIGRP(Default-IP-Routing-Table:100): Processing incoming UPDATE packet
*Feb 4 18:44:57.427: IP- EIGRP(Default-IP-Routing-Table:100): Int 10.1.102.0/29 M 41024000 - 40000000 1024000 SM 40512000 - 40000000 512000 *Feb 4 18:44:57.427: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.102.0 ()
*Feb 4 18:44:57.427: IP-EIGRP(Default-IP-Routing-Table:100): Int 10.1.1.0/30 M40640000 - 40000000 640000 SM 128256 - 256 128000
*Feb 4 18:44:57.427: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.1.0 ()
*Feb 4 18:44:57.427: IP-EIGRP(Default-IP-Routing-Table:100): Int 10.1.1.4/30 M 40640000 - 40000000 640000 SM 128256 - 256 128000
*Feb 4 18:44:57.427: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.1.4 ()
*Feb 4 18:44:57.431: IP-EIGRP(Default-IP-Routing-Table:100): Int 10.1.1.8/30 M40640000 - 40000000 640000 SM 128256 - 256 128000
*Feb 4 18:44:57.431: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.1.8 ()
Essentially, the EIGRP DUAL state machine has just computed the topology table for these routes and installed them in the routing table.
Check to see that these routes exist in the routing table with the show ip route command.
R1# show ip route
Codes: C - connected, S - static, 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
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, * - candidate default, U - per-user static
route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
10.0.0.0/8 is variably subnetted, 12 subnets, 2 masks
D 10.1.3.8/30 [90/40640000] via 10.1.103.3, 00:19:28, Serial0/0/1 D 10.1.2.8/30 [90/40640000] via 10.1.102.2, 00:21:59, Serial0/0/0
10.1.1.8/30 is directly connected, Loopback19
10.1.3.0/30 [90/40640000] via 10.1.103.3, 00:19:28, Serial0/0/1
10.1.2.0/30 [90/40640000] via 10.1.102.2, 00:21:59, Serial0/0/0
10.1.1.0/30 is directly connected, Loopback11
D 10.1.3.4/30 [90/40640000] via 10.1.103.3, 00:19:28, Serial0/0/1 D 10.1.2.4/30 [90/40640000] via 10.1.102.2, 00:21:59, Serial0/0/0 C 10.1.1.4/30 is directly connected, Loopback15
.
10.1.103.0/29 is directly connected, Serial0/0/1
10.1.102.0/29 is directly connected, Serial0/0/0
10.1.203.0/29 [90/41024000] via 10.1.103.3, 00:19:28, Serial0/0/1
[90/41024000] via 10.1.102.2, 00:19:28, Serial0/0/0
After you have full adjacency between the routers, ping all the remote loopbacks to ensure full connectivity or use the following Tcl script. If you have never used Tcl scripts or need a refresher, see Lab 1–1.
R1# tclsh
foreach address { 10.1.1.1 10.1.1.5 10.1.1.9 10.1.2.1 10.1.2.5 10.1.2.9 10.1.3.1 10.1.3.5 10.1.3.9 10.1.102.1 10.1.102.2 10.1.103.1 10.1.103.3 10.1.203.2 10.1.203.3
} { ping $address }
You should receive ICMP echo replies for each address pinged. Make sure that you run the Tcl script on each router and verify connectivity before you continue with the lab.
Verify the EIGRP neighbor relationships with the show ip eigrp neighbors command.
R1# show ip eigrp neighbors
IP-EIGRP neighbors for process 100 Hold Uptime SRTT RTO Q Seq
H Address Interface
0 10.1.102.2 Se0/0/0 (sec) 00:00:22 (ms) 5000 Cnt Num
10 1 2 0
1 10.1.103.3 Se0/0/1 13 00:04:36 24 2280 0 14
R2# show ip eigrp neighbors
IP-EIGRP neighbors for process 100 Hold Uptime SRTT RTO Q Seq
H Address Interface
0 10.1.102.1 Se0/0/0 (sec) 00:00:37 (ms) 5000 Cnt Num
14 1 1 22
1 10.1.203.3 Se0/0/1 11 00:03:29 143 2280 0 15
R3# show ip eigrp neighbors
IP-EIGRP neighbors for process 100 Hold Uptime SRTT RTO Q Seq
H Address Interface
1 10.1.203.2 Se0/0/1 (sec) 00:03:43 (ms) 2280 Cnt Num
14 241 0 18
0 10.1.103.1 Se0/0/0 14 00:05:05 38 2280 0 17
.
Step 3: Examine the EIGRP topology table.
EIGRP builds a topology table containing all successor routes. The course content covered the vocabulary for EIGRP routes in the topology table. What is the feasible distance of route 10.1.1.0/30 in the R3 topology table in the following output?
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R3# show ip eigrp topology
IP-EIGRP Topology Table for AS(100)/ID(10.1.3.9)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 10.1.3.8/30, 1 successors, FD is 128256 via Connected, Loopback39
P 10.1.2.8/30, 1 successors, FD is 40640000
via 10.1.203.2 (40640000/128256), Serial0/0/1 P 10.1.1.8/30, 1 successors, FD is 40640000
via 10.1.103.1 (40640000/128256), Serial0/0/0 P 10.1.3.0/30, 1 successors, FD is 128256
via Connected, Loopback31
P 10.1.2.0/30, 1 successors, FD is 40640000
via 10.1.203.2 (40640000/128256), Serial0/0/1 P 10.1.1.0/30, 1 successors, FD is 40640000
via 10.1.103.1 (40640000/128256), Serial0/0/0 P 10.1.3.4/30, 1 successors, FD is 128256
via Connected, Loopback35
P 10.1.2.4/30, 1 successors, FD is 40640000
via 10.1.203.2 (40640000/128256), Serial0/0/1 P 10.1.1.4/30, 1 successors, FD is 40640000
via 10.1.103.1 (40640000/128256), Serial0/0/0 P 10.1.103.0/29, 1 successors, FD is 40512000
via Connected, Serial0/0/0
P 10.1.102.0/29, 2 successors, FD is 41024000
via 10.1.103.1 (41024000/40512000), Serial0/0/0 via 10.1.203.2 (41024000/40512000), Serial0/0/1
P 10.1.203.0/29, 1 successors, FD is 40512000 via Connected, Serial0/0/1
The most important thing is the two successor routes in the passive state on R3. R1 and R2 are both advertising their connected subnet of 10.1.102.0/30. Because both routes have the same feasible distance of 41024000, both are installed in the topology table. This distance of 41024000 reflects the composite metric of more granular properties about the path to the destination network. Can you view the metrics before the composite metric is computed?
Use the show ip eigrp topology 10.1.102.0/29 command to view the information that EIGRP has received about the route from R1 and R2.
R3# show ip eigrp topology 10.1.102.0/29
IP-EIGRP (AS 100): Topology entry for 10.1.102.0/29
State is Passive, Query origin flag is 1, 2 Successor(s), FD is 41024000 Routing Descriptor Blocks:
10.1.103.1 (Serial0/0/0), from 10.1.103.1, Send flag is 0x0 Composite metric is (41024000/40512000), Route is Internal
Vector metric:
Minimum bandwidth is 64 Kbit Total delay is 40000 microseconds Reliability is 255/255
Load is 1/255 Minimum MTU is 1500 Hop count is 1
10.1.203.2 (Serial0/0/1), from 10.1.203.2, Send flag is 0x0 Composite metric is (41024000/40512000), Route is Internal Vector metric:
Minimum bandwidth is 64 Kbit Total delay is 40000 microseconds Reliability is 255/255
Load is 1/255 Minimum MTU is 1500 Hop count is 1
The output of this command shows the following information regarding EIGRP:
The bandwidth metric represents the minimum bandwidth among all links comprising the path to the destination network.
The delay metric represents the total delay over the path.
The minimum MTU represents the smallest MTU along the path.
If you do not have full knowledge of your network, you can use the hop count information to check how many Layer 3 devices are between the router and the destination network.
Step 4: Observe equal-cost load balancing.
EIGRP produces equal-cost load balancing to the destination network 10.1.102.0/29 from R1. Two equal-cost paths are available to this destination per the topology table output above.
Use the traceroute 10.1.102.1 command to view the hops from R3 to this R1 IP address. Notice that both R1 and R2 are listed as hops because there are two equal-cost paths and packets can reach this network via either link.
R3# traceroute 10.1.102.1
Type escape sequence to abort. Tracing the route to 10.1.102.1
1 10.1.203.2 12 msec 10.1.103.1 12 msec 10.1.203.2 12 msec
Recent Cisco IOS releases enable Cisco Express Forwarding (CEF), which, by default, performs per-destination load balancing. CEF allows for very rapid switching without the need for route processing. However, if you were to ping the destination network, you would not see load balancing occurring on a packet level because CEF treats the entire series of pings as one flow.
CEF on R3 overrides the per-packet balancing behavior of process switching with per-destination load balancing.
To see the full effect of EIGRP equal-cost load balancing, temporarily disable CEF and route caching so that all IP packets are processed individually and not fast-switched by CEF.
R3(config)# no ip cef
R3(config)# interface S0/0/0 R3(config-if)# no ip route-cache R3(config-if)# interface S0/0/1 R3(config-if)# no ip route-cache
Typically, you would not disable CEF in a production network. It is done here only to illustrate load balancing. Another way to demonstrate per-packet load balancing, that does not disable CEF, is to use the per-packet load balancing command ip load-share per-packet on outgoing interfaces S0/0/0 and S0/0/1.
Verify load balancing with the debug ip packet command, and then ping 10.1.102.1. You see output similar to the following:
R3# debug ip packet
IP packet debugging is on R3# ping 10.1.102.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.1.102.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/3/4 ms R3#
*Feb 5 12:58:27.943: IP: tableid=0, s=10.1.103.3 (local), d=10.1.102.1 (Serial0/0/0), routed via RIB
*Feb 5 12:58:27.943: IP: s=10.1.103.3 (local), d=10.1.102.1 (Serial0/0/0), len 100, sending
*Feb 5 12:58:27.947: IP: tableid=0, s=10.1.102.1 (Serial0/0/0), d=10.1.103.3 (Serial0/0/0), routed via RIB
*Feb 5 12:58:27.947: IP: s=10.1.102.1 (Serial0/0/0), d=10.1.103.3 (Serial0/0/0), len 100, rcvd 3
*Feb 5 12:58:27.947: IP: tableid=0, s=10.1.203.3 (local), d=10.1.102.1 (Serial0/0/1), routed via RIB
*Feb 5 12:58:27.947: IP: s=10.1.203.3 (local), d=10.1.102.1 (Serial0/0/1), len 100, sending
Notice that EIGRP load-balances between Serial0/0/0 (s=10.1.103.3) and Serial0/0/1 (s=10.1.203.3). This behavior is part of EIGRP. It can help utilize underused links in a network, especially during periods of congestion.
Step 5: Analyze alternate EIGRP paths not in the topology table.
Issue the show ip eigrp topology all-links command to see all routes that R3 has learned through EIGRP. This command shows all entries that EIGRP holds on this router for networks in the topology, including the exit serial interface and IP address of the next hop to each destination network, and the serial number (serno) that uniquely identifies a destination network in EIGRP.
R3# show ip eigrp topology all-links
IP-EIGRP Topology Table for AS(100)/ID(10.1.3.9)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - reply Status, s - sia Status
P 10.1.3.0/30, 1 successors, FD is 128256, serno 1 via Connected, Loopback31
P 10.1.3.4/30, 1 successors, FD is 128256, serno 2 via Connected, Loopback35
P 10.1.3.8/30, 1 successors, FD is 128256, serno 3 via Connected, Loopback39
P 10.1.2.8/30, 1 successors, FD is 40640000, serno 24
via 10.1.203.2 (40640000/128256), Serial0/0/1 via 10.1.103.1 (41152000/40640000), Serial0/0/0
P 10.1.1.8/30, 1 successors, FD is 40640000, serno 17 via 10.1.103.1 (40640000/128256), Serial0/0/0 via 10.1.203.2 (41152000/40640000), Serial0/0/1
P 10.1.2.0/30, 1 successors, FD is 40640000, serno 22 via 10.1.203.2 (40640000/128256), Serial0/0/1 via 10.1.103.1 (41152000/40640000), Serial0/0/0
P 10.1.1.0/30, 1 successors, FD is 40640000, serno 15 via 10.1.103.1 (40640000/128256), Serial0/0/0 via 10.1.203.2 (41152000/40640000), Serial0/0/1
P 10.1.2.4/30, 1 successors, FD is 40640000, serno 23 via 10.1.203.2 (40640000/128256), Serial0/0/1 via 10.1.103.1 (41152000/40640000), Serial0/0/0
P 10.1.1.4/30, 1 successors, FD is 40640000, serno 16 via 10.1.103.1 (40640000/128256), Serial0/0/0 via 10.1.203.2 (41152000/40640000), Serial0/0/1
P 10.1.103.0/29, 1 successors, FD is 40512000, serno 13 via Connected, Serial0/0/0
P 10.1.102.0/29, 2 successors, FD is 41024000, serno 42 via 10.1.103.1 (41024000/40512000), Serial0/0/0
.
via 10.1.203.2 (41024000/40512000), Serial0/0/1 P 10.1.203.0/29, 1 successors, FD is 40512000, serno 12
via Connected, Serial0/0/1
What is the advertised distance of the R1 loopback network routes from R1 and R2?
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Use the show ip eigrp topology 10.1.2.0/30 command to see the granular view of the alternate paths to 10.1.2.0, including ones with a higher reported distance than the feasible distance.
R3# show ip eigrp topology 10.1.2.0/30
IP-EIGRP (AS 100): Topology entry for 10.1.2.0/30
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 40640000 Routing Descriptor Blocks:
10.1.203.2 (Serial0/0/1), from 10.1.203.2, Send flag is 0x0 Composite metric is (40640000/128256), Route is Internal Vector metric:
Minimum bandwidth is 64 Kbit Total delay is 25000 microseconds Reliability is 255/255
Load is 1/255 Minimum MTU is 1500 Hop count is 1
10.1.103.1 (Serial0/0/0), from 10.1.103.1, Send flag is 0x0 Composite metric is (41152000/40640000), Route is Internal Vector metric:
Minimum bandwidth is 64 Kbit Total delay is 45000 microseconds Reliability is 255/255
Load is 1/255 Minimum MTU is 1500 Hop count is 2
When using the show ip eigrp topology command, why is the route to 10.1.2.1 through R1 not listed in the topology table?
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What is its advertised distance from R1?
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.
What is its feasible distance?
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If the R2 Serial0/0/1 interface were shut down, would EIGRP route through R1 to get to 10.1.2.0/30? Would the switch be immediate?
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Record your answer, and then experiment by shutting down the R1 s0/0/01 interface while an extended ping is running as described below.
Start a ping with a high repeat count on R3 to the R1 Serial0/0/0 interface 10.1.102.1.
R3# ping 10.1.102.1 repeat 10000
Enter interface configuration mode on R1 and shut down port Serial0/0/1, which is the direct link from R1 to R3.
R1(config)# interface serial 0/0/1
R1(config-if)# shutdown
When the adjacency between R1 and R3 goes down, some pings will be lost. After pings are again being successfully received, stop the ping using Ctrl+Shift+^.
R3# ping 10.1.102.1 repeat 10000
Type escape sequence to abort.
Sending 10000, 100-byte ICMP Echos to 10.1.102.1, timeout is 2 seconds:
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!.
*Dec 11 18:41:55.843: %LINK-3-UPDOWN: Interface Serial0/0/0, changed state to down
*Dec 11 18:41:55.847: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.1.103.1 (Serial0/0/0) is down: interface down
*Dec 11 18:41:56.843: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0/0, changed state to down
.!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!
Success rate is 99 percent (374/376), round-trip min/avg/max = 28/39/96 ms R3#
How many packets were dropped?
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When examining the EIGRP reconvergence speed after deactivating the serial link between R1 and R3, the focus should not be on the count of lost ping packets but rather on the duration of connectivity loss or how long it took to perform a successful cutover. The router waits for up to two seconds for each sent ICMP ECHO request to receive a reply and only then does it send another ECHO request. If the router did not wait for the reply, the count of lost packets would be much higher. Because two packets were lost, the cutover took approximately 4 seconds.
Another factor to consider is that an interface deliberately delays the information about loss of connectivity for 2 seconds to prevent transient link flaps (link going up and down) from introducing instability into the network. If the real speed of EIGRP is to be observed, this delay can be made as short as possible using the command carrier-delay msec 0 on all serial interfaces.
g. Issue the no shutdown command on the R1 Serial0/0/1 interface before continuing to the next step.
Step 6: Observe unequal-cost load balancing.
Review the composite metrics advertised by EIGRP using the show ip eigrp topology 10.1.2.0/30 command,.
R3# show ip eigrp topology 10.1.2.0/30
IP-EIGRP (AS 100): Topology entry for 10.1.2.0/30
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 40640000 Routing Descriptor Blocks:
10.1.203.2 (Serial0/0/1), from 10.1.203.2, Send flag is 0x0 Composite metric is (40640000/128256), Route is Internal Vector metric:
Minimum bandwidth is 64 Kbit Total delay is 25000 microseconds Reliability is 255/255
Load is 1/255 Minimum MTU is 1500 Hop count is 1
10.1.103.1 (Serial0/0/0), from 10.1.103.1, Send flag is 0x0 Composite metric is (41152000/40640000), Route is Internal Vector metric:
Minimum bandwidth is 64 Kbit Total delay is 45000 microseconds Reliability is 255/255
Load is 1/255 Minimum MTU is 1500 Hop count is 2
The reported distance for a loopback network is higher than the feasible distance, so DUAL does not consider it a feasible successor route.
To demonstrate unequal-cost load balancing in your internetwork, upgrade the path to the destination network through R1 with a higher bandwidth. Change the clock rate and bandwidth on the R1, R2, and R3 serial interfaces to 128 kb/s.
R1(config)# interface serial 0/0/0
R1(config-if)# bandwidth 128
R1(config-if)# clock rate 128000 R1(config-if)# interface serial 0/0/1
R1(config-if)# bandwidth 128
R2(config)# interface serial 0/0/0
R2(config-if)# bandwidth 128
.
R3(config)# interface serial 0/0/0
R3(config-if)# clock rate 128000
R3(config-if)# bandwidth 128
Issue the show ip eigrp topology 10.1.2.0/30 command again on R3 to see what has changed.
R3# show ip eigrp topology 10.1.2.0/30
IP-EIGRP (AS 100): Topology entry for 10.1.2.0/30
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 21152000 Routing Descriptor Blocks:
10.1.103.1 (Serial0/0/0), from 10.1.103.1, Send flag is 0x0 Composite metric is (21152000/20640000), Route is Internal Vector metric:
Minimum bandwidth is 128 Kbit Total delay is 45000 microseconds Reliability is 255/255
Load is 1/255 Minimum MTU is 1500 Hop count is 2
10.1.203.2 (Serial0/0/1), from 10.1.203.2, Send flag is 0x0 Composite metric is (40640000/128256), Route is Internal Vector metric:
Minimum bandwidth is 64 Kbit Total delay is 25000 microseconds Reliability is 255/255
Load is 1/255 Minimum MTU is 1500 Hop count is 1
After manipulating the bandwidth parameter, the preferred path for R3 to the loopback interfaces of R2 is now through R1. Even though the hop count is two and the delay through R1 is nearly twice that of the R2 path, the higher bandwidth and lower FD results in this being the preferred route.
Issue the show ip route command to verify that the preferred route to network 10.1.2.0 is through R1 via Serial0/0/0 to next hop 10.1.103.1. There is only one route to this network due to the difference in bandwidth.
R3# show ip route eigrp
10.0.0.0/8 is variably subnetted, 12 subnets, 2 masks
D 10.1.2.8/30 [90/21152000] via 10.1.103.1, 00:16:52, Serial0/0/0 D 10.1.1.8/30 [90/20640000] via 10.1.103.1, 00:16:52, Serial0/0/0 D 10.1.2.0/30 [90/21152000] via 10.1.103.1, 00:16:52, Serial0/0/0 D 10.1.1.0/30 [90/20640000] via 10.1.103.1, 00:16:52, Serial0/0/0 D 10.1.2.4/30 [90/21152000] via 10.1.103.1, 00:16:52, Serial0/0/0 D 10.1.1.4/30 [90/20640000] via 10.1.103.1, 00:16:52, Serial0/0/0 D 10.1.102.0/29 [90/21024000] via 10.1.103.1, 00:16:52, Serial0/0/0
Issue the debug ip eigrp 100 command on R3 to show route events changing in real time. Then, under the EIGRP router configuration on R3, issue the variance 2 command, which allows unequal-cost load balancing bounded by a maximum distance of (2) × (FD), where FD represents the feasible distance for each route in the routing table.
R3# debug ip eigrp 100
IP-EIGRP Route Events debugging is on
R3# conf t
Enter configuration commands, one per line. End with CNTL/Z.
.
R3(config)# router eigrp 100
R3(config-router)# variance 2 R3(config-router)#
*Feb 5 15:11:45.195: IP- EIGRP(Default-IP-Routing-Table:100): 10.1.3.8/30 routing table not updated thru 10.1.203.2
*Feb 5 15:11:45.195: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.2.8 ()
*Feb 5 15:11:45.199: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.2.8 ()
*Feb 5 15:11:45.199: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.1.8 ()
*Feb 5 15:11:45.199: IP- EIGRP(Default-IP-Routing-Table:100): 10.1.1.8/30 routing table not updated thru 10.1.203.2
*Feb 5 15:11:45.199: IP- EIGRP(Default-IP-Routing-Table:100): 10.1.3.0/30 routing table not updated thru 10.1.203.2
*Feb 5 15:11:45.199: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.2.0 ()
*Feb 5 15:11:45.199: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.2.0 ()
*Feb 5 15:11:45.199: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.1.0 ()
*Feb 5 15:11:45.199: IP- EIGRP(Default-IP-Routing-Table:100): 10.1.1.0/30 routing table not updated thru 10.1.203.2
*Feb 5 15:11:45.199: IP- EIGRP(Default-IP-Routing-Table:100): 10.1.3.4/30 routing table not updated thru 10.1.203.2
*Feb 5 15:11:45.199: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.2.4 ()
*Feb 5 15:11:45.199: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.2.4 ()
*Feb 5 15:11:45.199: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.1.4 ()
*Feb 5 15:11:45.199: IP- EIGRP(Default-IP-Routing-Table:100): 10.1.1.4/30 routing table not updated thru 10.1.203.2
*Feb 5 15:11:45.199: IP- EIGRP(Default-IP-Routing-Table:100): 10.1.103.0/29 routing table not updated thru 10.1.203.2
*Feb 5 15:11:45.199: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.102.0 ()
*Feb 5 15:11:45.203: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.102.0 ()
Issue the show ip route command again to verify that there are now two routes to network 10.1.2.0.
R3# show ip route eigrp
10.0.0.0/8 is variably subnetted, 12 subnets, 2 masks
D 10.1.2.8/30 [90/40640000] via 10.1.203.2, 00:02:27, Serial0/0/1 [90/21152000] via 10.1.103.1, 00:02:27, Serial0/0/0 D 10.1.1.8/30 [90/20640000] via 10.1.103.1, 00:02:27, Serial0/0/0
D 10.1.2.0/30 [90/40640000] via 10.1.203.2, 00:02:27, Serial0/0/1 [90/21152000] via 10.1.103.1, 00:02:27, Serial0/0/0 D 10.1.1.0/30 [90/20640000] via 10.1.103.1, 00:02:27, Serial0/0/0
D 10.1.2.4/30 [90/40640000] via 10.1.203.2, 00:02:27, Serial0/0/1 [90/21152000] via 10.1.103.1, 00:02:27, Serial0/0/0 D 10.1.1.4/30 [90/20640000] via 10.1.103.1, 00:02:27, Serial0/0/0
D 10.1.102.0/29 [90/41024000] via 10.1.203.2, 00:02:27, Serial0/0/1 [90/21024000] via 10.1.103.1, 00:02:27, Serial0/0/0
.
These unequal-cost routes also show up in the EIGRP topology table, even though they are not considered feasible successor routes. Use the show ip eigrp topology command to verify this.
R3# show ip eigrp topology
IP-EIGRP Topology Table for AS(100)/ID(10.1.3.9)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - reply Status, s - sia Status
P 10.1.3.8/30, 1 successors, FD is 128256 via Connected, Loopback39
P 10.1.2.8/30, 1 successors, FD is 21152000
via 10.1.103.1 (21152000/20640000), Serial0/0/0 via 10.1.203.2 (40640000/128256), Serial0/0/1
P 10.1.1.8/30, 1 successors, FD is 20640000
via 10.1.103.1 (20640000/128256), Serial0/0/0 P 10.1.3.0/30, 1 successors, FD is 128256
via Connected, Loopback31
P 10.1.2.0/30, 1 successors, FD is 21152000
via 10.1.103.1 (21152000/20640000), Serial0/0/0 via 10.1.203.2 (40640000/128256), Serial0/0/1
P 10.1.1.0/30, 1 successors, FD is 20640000
via 10.1.103.1 (20640000/128256), Serial0/0/0 P 10.1.3.4/30, 1 successors, FD is 128256
via Connected, Loopback35
P 10.1.2.4/30, 1 successors, FD is 21152000
via 10.1.103.1 (21152000/20640000), Serial0/0/0 via 10.1.203.2 (40640000/128256), Serial0/0/1
P 10.1.1.4/30, 1 successors, FD is 20640000
via 10.1.103.1 (20640000/128256), Serial0/0/0 P 10.1.103.0/29, 1 successors, FD is 20512000
via Connected, Serial0/0/0
P 10.1.102.0/29, 1 successors, FD is 21024000
via 10.1.103.1 (21024000/20512000), Serial0/0/0 via 10.1.203.2 (41024000/20512000), Serial0/0/1
P 10.1.203.0/29, 1 successors, FD is 40512000 via Connected, Serial0/0/1
Load balancing over serial links occurs in blocks of packets, the number of which are recorded in the routing table’s detailed routing information. Use the show ip route 10.1.2.0 command to get a detailed view of how traffic is shared between the two links.
R3# show ip route 10.1.2.0
Routing entry for 10.1.2.0/30
Known via "eigrp 100", distance 90, metric 21152000, type internal Redistributing via eigrp 100
Last update from 10.1.203.2 on Serial0/0/1, 00:05:41 ago Routing Descriptor Blocks:
10.1.203.2, from 10.1.203.2, 00:05:41 ago, via Serial0/0/1 Route metric is 40640000, traffic share count is 25
Total delay is 25000 microseconds, minimum bandwidth is 64 Kbit Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
* 10.1.103.1, from 10.1.103.1, 00:05:41 ago, via Serial0/0/0 Route metric is 21152000, traffic share count is 48
Total delay is 45000 microseconds, minimum bandwidth is 128 Kbit Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 2
.
Check the actual load balancing using the debug ip packet command. Ping from R3 to 10.1.2.1 with a high enough repeat count to view the load balancing over both paths. In the case above, the traffic share is 25 packets routed to R2 to every 48 packets routed to R1.
To filter the debug output to make it more useful, use the following extended access list.
R3(config)# access-list 100 permit icmp any any echo
R3(config)# end
R3# debug ip packet 100
IP packet debugging is on for access list 100 R3# ping 10.1.2.1 repeat 50
Type escape sequence to abort.
Sending 50, 100-byte ICMP Echos to 10.1.2.1, timeout is 2 seconds:
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
*Feb 5 15:20:54.215: IP: tableid=0, s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), routed via RIB
*Feb 5 15:20:54.215: IP: s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), len 100, sending
*Feb 5 15:20:54.231: IP: tableid=0, s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), routed via RIB
*Feb 5 15:20:54.231: IP: s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), len 100, sending
*Feb 5 15:20:54.247: IP: tableid=0, s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), routed via RIB
*Feb 5 15:20:54.247: IP: s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), len 100, sending
*Feb 5 15:20:54.263: IP: tableid=0, s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), routed via RIB
*Feb 5 15:20:54.263: IP: s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), len 100, sending
*Feb 5 15:20:54.279: IP: tableid=0, s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), routed via RIB
*Feb 5 15:20:54.279: IP: s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), len 100, sending
*Feb 5 15:20:54.295: IP: tableid=0, s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), routed via RIB
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
*Feb 5 15:20:54.295: IP: s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), len 100, sending
*Feb 5 15:20:54.311: IP: tableid=0, s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), routed via RIB
*Feb 5 15:20:54.311: IP: s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), len 100, sending
!
!
*Feb 5 15:20:55.395: IP: tableid=0, s=10.1.203.3 (local), d=10.1.2.1 (Serial0/0/1), routed via RIB
!
R3 just switched to load-share the outbound ICMP packets to Serial0/0/1.
!
*Feb 5 15:20:55.395: IP: s=10.1.203.3 (local), d=10.1.2.1 (Serial0/0/1), len 100, sending
.
*Feb 5 15:20:55.423: IP: tableid=0, s=10.1.203.3 (local), d=10.1.2.1 (Serial0/0/1), routed via RIB
*Feb 5 15:20:55.423: IP: s=10.1.203.3 (local), d=10.1.2.1 (Serial0/0/1), len 100, sending
*Feb 5 15:20:55.451: IP: tableid=0, s=10.1.203.3 (local), d=10.1.2.1 (Serial0/0/1), routed via RIB
*Feb 5 15:20:55.451: IP: s=10.1.203.3 (local), d=10.1.2.1 (Serial0/0/1), len 100, sending
*Feb 5 15:20:55.483: IP: tableid=0, s=10.1.203.3 (local), d=10.1.2.1 (Serial0/0/1), routed via RIB
*Feb 5 15:20:55.483: IP: s=10.1.203.3 (local), d=10.1.2.1 (Serial0/0/1), len 100, sending
If a deliberate metric manipulation is necessary on a router to force it to prefer one interface over another for EIGRP-discovered routes, it is recommended to use the interface-level command "delay" for these purposes. While the "bandwidth" command can also be used to influence the metrics of EIGRP-discovered routes through a particular interface, it is discouraged because the "bandwidth" will also influence the amount of bandwidth reserved for EIGRP packets and other IOS subsystems as well. The "delay" parameter specifies the value of the interface delay that is used exclusively by EIGRP to perform metric calculations and does not influence any other area of IOS operation.
Review a basic EIGRP configuration.
Explore the EIGRP topology table.
Identify successors, feasible successors, and feasible distances.
Use show and debug commands for the EIGRP topology table.
Configure and verify equal-cost load balancing with EIGRP.
Configure and verify unequal-cost load balancing with EIGRP.
Background
As a senior network engineer, you are considering deploying EIGRP in your corporation and want to evaluate its ability to converge quickly in a changing environment. You are also interested in equal-cost and unequal-cost load balancing because your network contains redundant links. These links are not often used by other
. 19
link-state routing protocols because of high metrics. Because you are interested in testing the EIGRP claims that you have read about, you decide to implement and test on a set of three lab routers before deploying EIGRP throughout your corporate network.
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 a 2801 or 2811) and Cisco IOS Software versions if they have comparable capabilities and features. Depending on the router model and Cisco IOS Software version, the commands available and output produced might vary from what is shown in this lab.
Required Resources
3 routers (Cisco 1841 with Cisco IOS Release 12.4(24)T1 Advanced IP Services or comparable)
Serial and console cables
Step 1: Configure the addressing and serial links.
Create three loopback interfaces on each router and address them as 10.1.X.1/30, 10.1.X.5/30, and 10.1.X.9/30, where X is the number of the router. Use the following table or the initial configurations located at the end of the lab.
Router Interface IP Address/Mask
R1 Loopback11 10.1.1.1/30
R1 Loopback15 10.1.1.5/30
R1 Loopback19 10.1.1.9/30
R2 Loopback21 10.1.2.1/30
R2 Loopback25 10.1.2.5/30
R2 Loopback29 10.1.2.9/30
R3 Loopback31 10.1.3.1/30
R3 Loopback35 10.1.3.5/30
R3 Loopback39 10.1.3.9/30
R1(config)# interface Loopback 11
R1(config-if)# ip address 10.1.1.1 255.255.255.252
R1(config-if)# exit
R1(config)# interface Loopback 15
R1(config-if)# ip address 10.1.1.5 255.255.255.252
R1(config-if)# exit
R1(config)# interface Loopback 19
R1(config-if)# ip address 10.1.1.9 255.255.255.252
R1(config-if)# exit
R2(config)# interface Loopback 21
R2(config-if)# ip address 10.1.2.1 255.255.255.252
R2(config-if)# exit
R2(config)# interface Loopback 25
R2(config-if)# ip address 10.1.2.5 255.255.255.252
R2(config-if)# exit
R2(config)# interface Loopback 29
R2(config-if)# ip address 10.1.2.9 255.255.255.252
R2(config-if)# exit
.
R3(config)# interface Loopback 31
R3(config-if)# ip address 10.1.3.1 255.255.255.252
R3(config-if)# exit
R3(config)# interface Loopback 35
R3(config-if)# ip address 10.1.3.5 255.255.255.252
R3(config-if)# exit
R3(config)# interface Loopback 39
R3(config-if)# ip address 10.1.3.9 255.255.255.252
R3(config-if)# exit
Specify the addresses of the serial interfaces as shown in the topology diagram. Set the clock rate to 64 kb/s, and manually configure the interface bandwidth to 64 kb/s.
If you have WIC-2A/S serial interfaces, the maximum clock rate is 128 kb/s. If you have WIC-2T serial interfaces, the maximum clock rate is much higher (2.048 Mb/s or higher depending on the hardware), which is more representative of a modern network WAN link. However, this lab uses 64 kb/s and 128 kb/s settings.
R1(config)# interface Serial 0/0/0 R1(config-if)# description R1-->R2
R1(config-if)# clock rate 64000 R1(config-if)# bandwidth 64
R1(config-if)# ip address 10.1.102.1 255.255.255.248
R1(config-if)# no shutdown R1(config-if)# exit
R1(config)# interface Serial 0/0/1 R1(config-if)# description R1-->R3
R1(config-if)# bandwidth 64
R1(config-if)# ip address 10.1.103.1 255.255.255.248
R1(config-if)# no shutdown R1(config-if)# exit
R2(config)# interface Serial 0/0/0 R2(config-if)# description R2-->R1
R2(config-if)# bandwidth 64
R2(config-if)# ip address 10.1.102.2 255.255.255.248
R2(config-if)# no shutdown R2(config-if)# exit
R2(config)# interface Serial 0/0/1 R2(config-if)# description R2-->R3
R2(config-if)# clock rate 64000 R2(config-if)# bandwidth 64
R2(config-if)# ip address 10.1.203.2 255.255.255.248
R2(config-if)# no shutdown R2(config-if)# exit
R3(config)# interface Serial 0/0/0 R3(config-if)# description R3-->R1
R3(config-if)# clock rate 64000 R3(config-if)# bandwidth 64
R3(config-if)# ip address 10.1.103.3 255.255.255.248
R3(config-if)# no shutdown R3(config-if)# exit
R3(config)# interface Serial 0/0/1 R3(config-if)# description R3-->R2
R3(config-if)# bandwidth 64
R3(config-if)# ip address 10.1.203.3 255.255.255.248
R3(config-if)# no shutdown
R3(config-if)# exit
Verify connectivity by pinging across each of the local networks connected to each router.
Issue the show interfaces description command on each router. This command displays a brief listing of the interfaces, their status, and a description (if a description is configured). Router R1 is shown as an example.
R1# show interfaces description Status Protocol Description
Interface
Fa0/0 admin down down
Fa0/1 admin down down
Se0/0/0 up up R1-->R2
Se0/0/1 up up R1-->R3
Vl1 up down
Lo11 up up
Lo15 up up
Lo19 up up
Issue the show protocols command on each router. This command displays a brief listing of the interfaces, their status, and the IP address and subnet mask configured (in prefix format /xx) for each interface. Router R1 is shown as an example.
R1# show protocols
Global values:
Internet Protocol routing is enabled
FastEthernet0/0 is administratively down, line protocol is down FastEthernet0/1 is administratively down, line protocol is down Serial0/0/0 is up, line protocol is up
Internet address is 10.1.102.1/29
Serial0/0/1 is up, line protocol is up
Internet address is 10.1.103.1/29
Vlan1 is up, line protocol is down
Loopback11 is up, line protocol is up
Internet address is 10.1.1.1/30
Loopback15 is up, line protocol is up
Internet address is 10.1.1.5/30
Loopback19 is up, line protocol is up
Internet address is 10.1.1.9/30
Step 2: Configure EIGRP.
Enable EIGRP AS 100 for all interfaces on R1 and R2 using the commands used in the previous EIGRP lab. Do not enable EIGRP yet on R3. For your reference, these are the commands which can be used:
R1(config)# router eigrp 100
R1(config-router)# network 10.0.0.0
R2(config)# router eigrp 100
R2(config-router)# network 10.0.0.0
Use the debug ip eigrp 100 command to watch EIGRP install the routes in the routing table when your routers become adjacent. You get output similar to the following.
R3# debug ip eigrp 100
IP-EIGRP Route Events debugging is on R3# conf t
Enter configuration commands, one per line. End with CNTL/Z. R3(config)# router eigrp 100
.
R3(config-router)# network 10.0.0.0
R3(config-router)#
*Feb 4 18:44:57.367: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.1.103.1 (Serial0/0/0) is up: new adjacency
*Feb 4 18:44:57.367: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.1.203.2 (Serial0/0/1) is up: new adjacency
*Feb 4 18:44:57.371: IP-EIGRP(Default-IP-Routing-Table:100): Processing incoming UPDATE packet
*Feb 4 18:44:57.379: IP-EIGRP(Default-IP-Routing-Table:100): Processing incoming UPDATE packet
*Feb 4 18:44:57.427: IP-EIGRP(Default-IP-Routing-Table:100): Processing incoming UPDATE packet
*Feb 4 18:44:57.427: IP- EIGRP(Default-IP-Routing-Table:100): Int 10.1.102.0/29 M 41024000 - 40000000 1024000 SM 40512000 - 40000000 512000 *Feb 4 18:44:57.427: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.102.0 ()
*Feb 4 18:44:57.427: IP-EIGRP(Default-IP-Routing-Table:100): Int 10.1.1.0/30 M40640000 - 40000000 640000 SM 128256 - 256 128000
*Feb 4 18:44:57.427: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.1.0 ()
*Feb 4 18:44:57.427: IP-EIGRP(Default-IP-Routing-Table:100): Int 10.1.1.4/30 M 40640000 - 40000000 640000 SM 128256 - 256 128000
*Feb 4 18:44:57.427: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.1.4 ()
*Feb 4 18:44:57.431: IP-EIGRP(Default-IP-Routing-Table:100): Int 10.1.1.8/30 M40640000 - 40000000 640000 SM 128256 - 256 128000
*Feb 4 18:44:57.431: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.1.8 ()
Essentially, the EIGRP DUAL state machine has just computed the topology table for these routes and installed them in the routing table.
Check to see that these routes exist in the routing table with the show ip route command.
R1# show ip route
Codes: C - connected, S - static, 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
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, * - candidate default, U - per-user static
route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
10.0.0.0/8 is variably subnetted, 12 subnets, 2 masks
D 10.1.3.8/30 [90/40640000] via 10.1.103.3, 00:19:28, Serial0/0/1 D 10.1.2.8/30 [90/40640000] via 10.1.102.2, 00:21:59, Serial0/0/0
10.1.1.8/30 is directly connected, Loopback19
10.1.3.0/30 [90/40640000] via 10.1.103.3, 00:19:28, Serial0/0/1
10.1.2.0/30 [90/40640000] via 10.1.102.2, 00:21:59, Serial0/0/0
10.1.1.0/30 is directly connected, Loopback11
D 10.1.3.4/30 [90/40640000] via 10.1.103.3, 00:19:28, Serial0/0/1 D 10.1.2.4/30 [90/40640000] via 10.1.102.2, 00:21:59, Serial0/0/0 C 10.1.1.4/30 is directly connected, Loopback15
.
10.1.103.0/29 is directly connected, Serial0/0/1
10.1.102.0/29 is directly connected, Serial0/0/0
10.1.203.0/29 [90/41024000] via 10.1.103.3, 00:19:28, Serial0/0/1
[90/41024000] via 10.1.102.2, 00:19:28, Serial0/0/0
After you have full adjacency between the routers, ping all the remote loopbacks to ensure full connectivity or use the following Tcl script. If you have never used Tcl scripts or need a refresher, see Lab 1–1.
R1# tclsh
foreach address { 10.1.1.1 10.1.1.5 10.1.1.9 10.1.2.1 10.1.2.5 10.1.2.9 10.1.3.1 10.1.3.5 10.1.3.9 10.1.102.1 10.1.102.2 10.1.103.1 10.1.103.3 10.1.203.2 10.1.203.3
} { ping $address }
You should receive ICMP echo replies for each address pinged. Make sure that you run the Tcl script on each router and verify connectivity before you continue with the lab.
Verify the EIGRP neighbor relationships with the show ip eigrp neighbors command.
R1# show ip eigrp neighbors
IP-EIGRP neighbors for process 100 Hold Uptime SRTT RTO Q Seq
H Address Interface
0 10.1.102.2 Se0/0/0 (sec) 00:00:22 (ms) 5000 Cnt Num
10 1 2 0
1 10.1.103.3 Se0/0/1 13 00:04:36 24 2280 0 14
R2# show ip eigrp neighbors
IP-EIGRP neighbors for process 100 Hold Uptime SRTT RTO Q Seq
H Address Interface
0 10.1.102.1 Se0/0/0 (sec) 00:00:37 (ms) 5000 Cnt Num
14 1 1 22
1 10.1.203.3 Se0/0/1 11 00:03:29 143 2280 0 15
R3# show ip eigrp neighbors
IP-EIGRP neighbors for process 100 Hold Uptime SRTT RTO Q Seq
H Address Interface
1 10.1.203.2 Se0/0/1 (sec) 00:03:43 (ms) 2280 Cnt Num
14 241 0 18
0 10.1.103.1 Se0/0/0 14 00:05:05 38 2280 0 17
.
Step 3: Examine the EIGRP topology table.
EIGRP builds a topology table containing all successor routes. The course content covered the vocabulary for EIGRP routes in the topology table. What is the feasible distance of route 10.1.1.0/30 in the R3 topology table in the following output?
_______________________________________________________________________________
_______________________________________________________________________________
R3# show ip eigrp topology
IP-EIGRP Topology Table for AS(100)/ID(10.1.3.9)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 10.1.3.8/30, 1 successors, FD is 128256 via Connected, Loopback39
P 10.1.2.8/30, 1 successors, FD is 40640000
via 10.1.203.2 (40640000/128256), Serial0/0/1 P 10.1.1.8/30, 1 successors, FD is 40640000
via 10.1.103.1 (40640000/128256), Serial0/0/0 P 10.1.3.0/30, 1 successors, FD is 128256
via Connected, Loopback31
P 10.1.2.0/30, 1 successors, FD is 40640000
via 10.1.203.2 (40640000/128256), Serial0/0/1 P 10.1.1.0/30, 1 successors, FD is 40640000
via 10.1.103.1 (40640000/128256), Serial0/0/0 P 10.1.3.4/30, 1 successors, FD is 128256
via Connected, Loopback35
P 10.1.2.4/30, 1 successors, FD is 40640000
via 10.1.203.2 (40640000/128256), Serial0/0/1 P 10.1.1.4/30, 1 successors, FD is 40640000
via 10.1.103.1 (40640000/128256), Serial0/0/0 P 10.1.103.0/29, 1 successors, FD is 40512000
via Connected, Serial0/0/0
P 10.1.102.0/29, 2 successors, FD is 41024000
via 10.1.103.1 (41024000/40512000), Serial0/0/0 via 10.1.203.2 (41024000/40512000), Serial0/0/1
P 10.1.203.0/29, 1 successors, FD is 40512000 via Connected, Serial0/0/1
The most important thing is the two successor routes in the passive state on R3. R1 and R2 are both advertising their connected subnet of 10.1.102.0/30. Because both routes have the same feasible distance of 41024000, both are installed in the topology table. This distance of 41024000 reflects the composite metric of more granular properties about the path to the destination network. Can you view the metrics before the composite metric is computed?
Use the show ip eigrp topology 10.1.102.0/29 command to view the information that EIGRP has received about the route from R1 and R2.
R3# show ip eigrp topology 10.1.102.0/29
IP-EIGRP (AS 100): Topology entry for 10.1.102.0/29
State is Passive, Query origin flag is 1, 2 Successor(s), FD is 41024000 Routing Descriptor Blocks:
10.1.103.1 (Serial0/0/0), from 10.1.103.1, Send flag is 0x0 Composite metric is (41024000/40512000), Route is Internal
Vector metric:
Minimum bandwidth is 64 Kbit Total delay is 40000 microseconds Reliability is 255/255
Load is 1/255 Minimum MTU is 1500 Hop count is 1
10.1.203.2 (Serial0/0/1), from 10.1.203.2, Send flag is 0x0 Composite metric is (41024000/40512000), Route is Internal Vector metric:
Minimum bandwidth is 64 Kbit Total delay is 40000 microseconds Reliability is 255/255
Load is 1/255 Minimum MTU is 1500 Hop count is 1
The output of this command shows the following information regarding EIGRP:
The bandwidth metric represents the minimum bandwidth among all links comprising the path to the destination network.
The delay metric represents the total delay over the path.
The minimum MTU represents the smallest MTU along the path.
If you do not have full knowledge of your network, you can use the hop count information to check how many Layer 3 devices are between the router and the destination network.
Step 4: Observe equal-cost load balancing.
EIGRP produces equal-cost load balancing to the destination network 10.1.102.0/29 from R1. Two equal-cost paths are available to this destination per the topology table output above.
Use the traceroute 10.1.102.1 command to view the hops from R3 to this R1 IP address. Notice that both R1 and R2 are listed as hops because there are two equal-cost paths and packets can reach this network via either link.
R3# traceroute 10.1.102.1
Type escape sequence to abort. Tracing the route to 10.1.102.1
1 10.1.203.2 12 msec 10.1.103.1 12 msec 10.1.203.2 12 msec
Recent Cisco IOS releases enable Cisco Express Forwarding (CEF), which, by default, performs per-destination load balancing. CEF allows for very rapid switching without the need for route processing. However, if you were to ping the destination network, you would not see load balancing occurring on a packet level because CEF treats the entire series of pings as one flow.
CEF on R3 overrides the per-packet balancing behavior of process switching with per-destination load balancing.
To see the full effect of EIGRP equal-cost load balancing, temporarily disable CEF and route caching so that all IP packets are processed individually and not fast-switched by CEF.
R3(config)# no ip cef
R3(config)# interface S0/0/0 R3(config-if)# no ip route-cache R3(config-if)# interface S0/0/1 R3(config-if)# no ip route-cache
Typically, you would not disable CEF in a production network. It is done here only to illustrate load balancing. Another way to demonstrate per-packet load balancing, that does not disable CEF, is to use the per-packet load balancing command ip load-share per-packet on outgoing interfaces S0/0/0 and S0/0/1.
Verify load balancing with the debug ip packet command, and then ping 10.1.102.1. You see output similar to the following:
R3# debug ip packet
IP packet debugging is on R3# ping 10.1.102.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.1.102.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/3/4 ms R3#
*Feb 5 12:58:27.943: IP: tableid=0, s=10.1.103.3 (local), d=10.1.102.1 (Serial0/0/0), routed via RIB
*Feb 5 12:58:27.943: IP: s=10.1.103.3 (local), d=10.1.102.1 (Serial0/0/0), len 100, sending
*Feb 5 12:58:27.947: IP: tableid=0, s=10.1.102.1 (Serial0/0/0), d=10.1.103.3 (Serial0/0/0), routed via RIB
*Feb 5 12:58:27.947: IP: s=10.1.102.1 (Serial0/0/0), d=10.1.103.3 (Serial0/0/0), len 100, rcvd 3
*Feb 5 12:58:27.947: IP: tableid=0, s=10.1.203.3 (local), d=10.1.102.1 (Serial0/0/1), routed via RIB
*Feb 5 12:58:27.947: IP: s=10.1.203.3 (local), d=10.1.102.1 (Serial0/0/1), len 100, sending
Notice that EIGRP load-balances between Serial0/0/0 (s=10.1.103.3) and Serial0/0/1 (s=10.1.203.3). This behavior is part of EIGRP. It can help utilize underused links in a network, especially during periods of congestion.
Step 5: Analyze alternate EIGRP paths not in the topology table.
Issue the show ip eigrp topology all-links command to see all routes that R3 has learned through EIGRP. This command shows all entries that EIGRP holds on this router for networks in the topology, including the exit serial interface and IP address of the next hop to each destination network, and the serial number (serno) that uniquely identifies a destination network in EIGRP.
R3# show ip eigrp topology all-links
IP-EIGRP Topology Table for AS(100)/ID(10.1.3.9)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - reply Status, s - sia Status
P 10.1.3.0/30, 1 successors, FD is 128256, serno 1 via Connected, Loopback31
P 10.1.3.4/30, 1 successors, FD is 128256, serno 2 via Connected, Loopback35
P 10.1.3.8/30, 1 successors, FD is 128256, serno 3 via Connected, Loopback39
P 10.1.2.8/30, 1 successors, FD is 40640000, serno 24
via 10.1.203.2 (40640000/128256), Serial0/0/1 via 10.1.103.1 (41152000/40640000), Serial0/0/0
P 10.1.1.8/30, 1 successors, FD is 40640000, serno 17 via 10.1.103.1 (40640000/128256), Serial0/0/0 via 10.1.203.2 (41152000/40640000), Serial0/0/1
P 10.1.2.0/30, 1 successors, FD is 40640000, serno 22 via 10.1.203.2 (40640000/128256), Serial0/0/1 via 10.1.103.1 (41152000/40640000), Serial0/0/0
P 10.1.1.0/30, 1 successors, FD is 40640000, serno 15 via 10.1.103.1 (40640000/128256), Serial0/0/0 via 10.1.203.2 (41152000/40640000), Serial0/0/1
P 10.1.2.4/30, 1 successors, FD is 40640000, serno 23 via 10.1.203.2 (40640000/128256), Serial0/0/1 via 10.1.103.1 (41152000/40640000), Serial0/0/0
P 10.1.1.4/30, 1 successors, FD is 40640000, serno 16 via 10.1.103.1 (40640000/128256), Serial0/0/0 via 10.1.203.2 (41152000/40640000), Serial0/0/1
P 10.1.103.0/29, 1 successors, FD is 40512000, serno 13 via Connected, Serial0/0/0
P 10.1.102.0/29, 2 successors, FD is 41024000, serno 42 via 10.1.103.1 (41024000/40512000), Serial0/0/0
.
via 10.1.203.2 (41024000/40512000), Serial0/0/1 P 10.1.203.0/29, 1 successors, FD is 40512000, serno 12
via Connected, Serial0/0/1
What is the advertised distance of the R1 loopback network routes from R1 and R2?
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
Use the show ip eigrp topology 10.1.2.0/30 command to see the granular view of the alternate paths to 10.1.2.0, including ones with a higher reported distance than the feasible distance.
R3# show ip eigrp topology 10.1.2.0/30
IP-EIGRP (AS 100): Topology entry for 10.1.2.0/30
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 40640000 Routing Descriptor Blocks:
10.1.203.2 (Serial0/0/1), from 10.1.203.2, Send flag is 0x0 Composite metric is (40640000/128256), Route is Internal Vector metric:
Minimum bandwidth is 64 Kbit Total delay is 25000 microseconds Reliability is 255/255
Load is 1/255 Minimum MTU is 1500 Hop count is 1
10.1.103.1 (Serial0/0/0), from 10.1.103.1, Send flag is 0x0 Composite metric is (41152000/40640000), Route is Internal Vector metric:
Minimum bandwidth is 64 Kbit Total delay is 45000 microseconds Reliability is 255/255
Load is 1/255 Minimum MTU is 1500 Hop count is 2
When using the show ip eigrp topology command, why is the route to 10.1.2.1 through R1 not listed in the topology table?
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
What is its advertised distance from R1?
_______________________________________________________________________________
.
What is its feasible distance?
_______________________________________________________________________________
If the R2 Serial0/0/1 interface were shut down, would EIGRP route through R1 to get to 10.1.2.0/30? Would the switch be immediate?
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
Record your answer, and then experiment by shutting down the R1 s0/0/01 interface while an extended ping is running as described below.
Start a ping with a high repeat count on R3 to the R1 Serial0/0/0 interface 10.1.102.1.
R3# ping 10.1.102.1 repeat 10000
Enter interface configuration mode on R1 and shut down port Serial0/0/1, which is the direct link from R1 to R3.
R1(config)# interface serial 0/0/1
R1(config-if)# shutdown
When the adjacency between R1 and R3 goes down, some pings will be lost. After pings are again being successfully received, stop the ping using Ctrl+Shift+^.
R3# ping 10.1.102.1 repeat 10000
Type escape sequence to abort.
Sending 10000, 100-byte ICMP Echos to 10.1.102.1, timeout is 2 seconds:
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!.
*Dec 11 18:41:55.843: %LINK-3-UPDOWN: Interface Serial0/0/0, changed state to down
*Dec 11 18:41:55.847: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.1.103.1 (Serial0/0/0) is down: interface down
*Dec 11 18:41:56.843: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0/0, changed state to down
.!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!
Success rate is 99 percent (374/376), round-trip min/avg/max = 28/39/96 ms R3#
How many packets were dropped?
_______________________________________________________________________________
When examining the EIGRP reconvergence speed after deactivating the serial link between R1 and R3, the focus should not be on the count of lost ping packets but rather on the duration of connectivity loss or how long it took to perform a successful cutover. The router waits for up to two seconds for each sent ICMP ECHO request to receive a reply and only then does it send another ECHO request. If the router did not wait for the reply, the count of lost packets would be much higher. Because two packets were lost, the cutover took approximately 4 seconds.
Another factor to consider is that an interface deliberately delays the information about loss of connectivity for 2 seconds to prevent transient link flaps (link going up and down) from introducing instability into the network. If the real speed of EIGRP is to be observed, this delay can be made as short as possible using the command carrier-delay msec 0 on all serial interfaces.
g. Issue the no shutdown command on the R1 Serial0/0/1 interface before continuing to the next step.
Step 6: Observe unequal-cost load balancing.
Review the composite metrics advertised by EIGRP using the show ip eigrp topology 10.1.2.0/30 command,.
R3# show ip eigrp topology 10.1.2.0/30
IP-EIGRP (AS 100): Topology entry for 10.1.2.0/30
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 40640000 Routing Descriptor Blocks:
10.1.203.2 (Serial0/0/1), from 10.1.203.2, Send flag is 0x0 Composite metric is (40640000/128256), Route is Internal Vector metric:
Minimum bandwidth is 64 Kbit Total delay is 25000 microseconds Reliability is 255/255
Load is 1/255 Minimum MTU is 1500 Hop count is 1
10.1.103.1 (Serial0/0/0), from 10.1.103.1, Send flag is 0x0 Composite metric is (41152000/40640000), Route is Internal Vector metric:
Minimum bandwidth is 64 Kbit Total delay is 45000 microseconds Reliability is 255/255
Load is 1/255 Minimum MTU is 1500 Hop count is 2
The reported distance for a loopback network is higher than the feasible distance, so DUAL does not consider it a feasible successor route.
To demonstrate unequal-cost load balancing in your internetwork, upgrade the path to the destination network through R1 with a higher bandwidth. Change the clock rate and bandwidth on the R1, R2, and R3 serial interfaces to 128 kb/s.
R1(config)# interface serial 0/0/0
R1(config-if)# bandwidth 128
R1(config-if)# clock rate 128000 R1(config-if)# interface serial 0/0/1
R1(config-if)# bandwidth 128
R2(config)# interface serial 0/0/0
R2(config-if)# bandwidth 128
.
R3(config)# interface serial 0/0/0
R3(config-if)# clock rate 128000
R3(config-if)# bandwidth 128
Issue the show ip eigrp topology 10.1.2.0/30 command again on R3 to see what has changed.
R3# show ip eigrp topology 10.1.2.0/30
IP-EIGRP (AS 100): Topology entry for 10.1.2.0/30
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 21152000 Routing Descriptor Blocks:
10.1.103.1 (Serial0/0/0), from 10.1.103.1, Send flag is 0x0 Composite metric is (21152000/20640000), Route is Internal Vector metric:
Minimum bandwidth is 128 Kbit Total delay is 45000 microseconds Reliability is 255/255
Load is 1/255 Minimum MTU is 1500 Hop count is 2
10.1.203.2 (Serial0/0/1), from 10.1.203.2, Send flag is 0x0 Composite metric is (40640000/128256), Route is Internal Vector metric:
Minimum bandwidth is 64 Kbit Total delay is 25000 microseconds Reliability is 255/255
Load is 1/255 Minimum MTU is 1500 Hop count is 1
After manipulating the bandwidth parameter, the preferred path for R3 to the loopback interfaces of R2 is now through R1. Even though the hop count is two and the delay through R1 is nearly twice that of the R2 path, the higher bandwidth and lower FD results in this being the preferred route.
Issue the show ip route command to verify that the preferred route to network 10.1.2.0 is through R1 via Serial0/0/0 to next hop 10.1.103.1. There is only one route to this network due to the difference in bandwidth.
R3# show ip route eigrp
10.0.0.0/8 is variably subnetted, 12 subnets, 2 masks
D 10.1.2.8/30 [90/21152000] via 10.1.103.1, 00:16:52, Serial0/0/0 D 10.1.1.8/30 [90/20640000] via 10.1.103.1, 00:16:52, Serial0/0/0 D 10.1.2.0/30 [90/21152000] via 10.1.103.1, 00:16:52, Serial0/0/0 D 10.1.1.0/30 [90/20640000] via 10.1.103.1, 00:16:52, Serial0/0/0 D 10.1.2.4/30 [90/21152000] via 10.1.103.1, 00:16:52, Serial0/0/0 D 10.1.1.4/30 [90/20640000] via 10.1.103.1, 00:16:52, Serial0/0/0 D 10.1.102.0/29 [90/21024000] via 10.1.103.1, 00:16:52, Serial0/0/0
Issue the debug ip eigrp 100 command on R3 to show route events changing in real time. Then, under the EIGRP router configuration on R3, issue the variance 2 command, which allows unequal-cost load balancing bounded by a maximum distance of (2) × (FD), where FD represents the feasible distance for each route in the routing table.
R3# debug ip eigrp 100
IP-EIGRP Route Events debugging is on
R3# conf t
Enter configuration commands, one per line. End with CNTL/Z.
.
R3(config)# router eigrp 100
R3(config-router)# variance 2 R3(config-router)#
*Feb 5 15:11:45.195: IP- EIGRP(Default-IP-Routing-Table:100): 10.1.3.8/30 routing table not updated thru 10.1.203.2
*Feb 5 15:11:45.195: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.2.8 ()
*Feb 5 15:11:45.199: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.2.8 ()
*Feb 5 15:11:45.199: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.1.8 ()
*Feb 5 15:11:45.199: IP- EIGRP(Default-IP-Routing-Table:100): 10.1.1.8/30 routing table not updated thru 10.1.203.2
*Feb 5 15:11:45.199: IP- EIGRP(Default-IP-Routing-Table:100): 10.1.3.0/30 routing table not updated thru 10.1.203.2
*Feb 5 15:11:45.199: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.2.0 ()
*Feb 5 15:11:45.199: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.2.0 ()
*Feb 5 15:11:45.199: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.1.0 ()
*Feb 5 15:11:45.199: IP- EIGRP(Default-IP-Routing-Table:100): 10.1.1.0/30 routing table not updated thru 10.1.203.2
*Feb 5 15:11:45.199: IP- EIGRP(Default-IP-Routing-Table:100): 10.1.3.4/30 routing table not updated thru 10.1.203.2
*Feb 5 15:11:45.199: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.2.4 ()
*Feb 5 15:11:45.199: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.2.4 ()
*Feb 5 15:11:45.199: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.1.4 ()
*Feb 5 15:11:45.199: IP- EIGRP(Default-IP-Routing-Table:100): 10.1.1.4/30 routing table not updated thru 10.1.203.2
*Feb 5 15:11:45.199: IP- EIGRP(Default-IP-Routing-Table:100): 10.1.103.0/29 routing table not updated thru 10.1.203.2
*Feb 5 15:11:45.199: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.102.0 ()
*Feb 5 15:11:45.203: IP-EIGRP(Default-IP-Routing-Table:100): route installed for 10.1.102.0 ()
Issue the show ip route command again to verify that there are now two routes to network 10.1.2.0.
R3# show ip route eigrp
10.0.0.0/8 is variably subnetted, 12 subnets, 2 masks
D 10.1.2.8/30 [90/40640000] via 10.1.203.2, 00:02:27, Serial0/0/1 [90/21152000] via 10.1.103.1, 00:02:27, Serial0/0/0 D 10.1.1.8/30 [90/20640000] via 10.1.103.1, 00:02:27, Serial0/0/0
D 10.1.2.0/30 [90/40640000] via 10.1.203.2, 00:02:27, Serial0/0/1 [90/21152000] via 10.1.103.1, 00:02:27, Serial0/0/0 D 10.1.1.0/30 [90/20640000] via 10.1.103.1, 00:02:27, Serial0/0/0
D 10.1.2.4/30 [90/40640000] via 10.1.203.2, 00:02:27, Serial0/0/1 [90/21152000] via 10.1.103.1, 00:02:27, Serial0/0/0 D 10.1.1.4/30 [90/20640000] via 10.1.103.1, 00:02:27, Serial0/0/0
D 10.1.102.0/29 [90/41024000] via 10.1.203.2, 00:02:27, Serial0/0/1 [90/21024000] via 10.1.103.1, 00:02:27, Serial0/0/0
.
These unequal-cost routes also show up in the EIGRP topology table, even though they are not considered feasible successor routes. Use the show ip eigrp topology command to verify this.
R3# show ip eigrp topology
IP-EIGRP Topology Table for AS(100)/ID(10.1.3.9)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - reply Status, s - sia Status
P 10.1.3.8/30, 1 successors, FD is 128256 via Connected, Loopback39
P 10.1.2.8/30, 1 successors, FD is 21152000
via 10.1.103.1 (21152000/20640000), Serial0/0/0 via 10.1.203.2 (40640000/128256), Serial0/0/1
P 10.1.1.8/30, 1 successors, FD is 20640000
via 10.1.103.1 (20640000/128256), Serial0/0/0 P 10.1.3.0/30, 1 successors, FD is 128256
via Connected, Loopback31
P 10.1.2.0/30, 1 successors, FD is 21152000
via 10.1.103.1 (21152000/20640000), Serial0/0/0 via 10.1.203.2 (40640000/128256), Serial0/0/1
P 10.1.1.0/30, 1 successors, FD is 20640000
via 10.1.103.1 (20640000/128256), Serial0/0/0 P 10.1.3.4/30, 1 successors, FD is 128256
via Connected, Loopback35
P 10.1.2.4/30, 1 successors, FD is 21152000
via 10.1.103.1 (21152000/20640000), Serial0/0/0 via 10.1.203.2 (40640000/128256), Serial0/0/1
P 10.1.1.4/30, 1 successors, FD is 20640000
via 10.1.103.1 (20640000/128256), Serial0/0/0 P 10.1.103.0/29, 1 successors, FD is 20512000
via Connected, Serial0/0/0
P 10.1.102.0/29, 1 successors, FD is 21024000
via 10.1.103.1 (21024000/20512000), Serial0/0/0 via 10.1.203.2 (41024000/20512000), Serial0/0/1
P 10.1.203.0/29, 1 successors, FD is 40512000 via Connected, Serial0/0/1
Load balancing over serial links occurs in blocks of packets, the number of which are recorded in the routing table’s detailed routing information. Use the show ip route 10.1.2.0 command to get a detailed view of how traffic is shared between the two links.
R3# show ip route 10.1.2.0
Routing entry for 10.1.2.0/30
Known via "eigrp 100", distance 90, metric 21152000, type internal Redistributing via eigrp 100
Last update from 10.1.203.2 on Serial0/0/1, 00:05:41 ago Routing Descriptor Blocks:
10.1.203.2, from 10.1.203.2, 00:05:41 ago, via Serial0/0/1 Route metric is 40640000, traffic share count is 25
Total delay is 25000 microseconds, minimum bandwidth is 64 Kbit Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
* 10.1.103.1, from 10.1.103.1, 00:05:41 ago, via Serial0/0/0 Route metric is 21152000, traffic share count is 48
Total delay is 45000 microseconds, minimum bandwidth is 128 Kbit Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 2
.
Check the actual load balancing using the debug ip packet command. Ping from R3 to 10.1.2.1 with a high enough repeat count to view the load balancing over both paths. In the case above, the traffic share is 25 packets routed to R2 to every 48 packets routed to R1.
To filter the debug output to make it more useful, use the following extended access list.
R3(config)# access-list 100 permit icmp any any echo
R3(config)# end
R3# debug ip packet 100
IP packet debugging is on for access list 100 R3# ping 10.1.2.1 repeat 50
Type escape sequence to abort.
Sending 50, 100-byte ICMP Echos to 10.1.2.1, timeout is 2 seconds:
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
*Feb 5 15:20:54.215: IP: tableid=0, s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), routed via RIB
*Feb 5 15:20:54.215: IP: s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), len 100, sending
*Feb 5 15:20:54.231: IP: tableid=0, s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), routed via RIB
*Feb 5 15:20:54.231: IP: s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), len 100, sending
*Feb 5 15:20:54.247: IP: tableid=0, s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), routed via RIB
*Feb 5 15:20:54.247: IP: s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), len 100, sending
*Feb 5 15:20:54.263: IP: tableid=0, s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), routed via RIB
*Feb 5 15:20:54.263: IP: s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), len 100, sending
*Feb 5 15:20:54.279: IP: tableid=0, s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), routed via RIB
*Feb 5 15:20:54.279: IP: s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), len 100, sending
*Feb 5 15:20:54.295: IP: tableid=0, s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), routed via RIB
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
*Feb 5 15:20:54.295: IP: s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), len 100, sending
*Feb 5 15:20:54.311: IP: tableid=0, s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), routed via RIB
*Feb 5 15:20:54.311: IP: s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), len 100, sending
!
!
*Feb 5 15:20:55.395: IP: tableid=0, s=10.1.203.3 (local), d=10.1.2.1 (Serial0/0/1), routed via RIB
!
R3 just switched to load-share the outbound ICMP packets to Serial0/0/1.
!
*Feb 5 15:20:55.395: IP: s=10.1.203.3 (local), d=10.1.2.1 (Serial0/0/1), len 100, sending
.
*Feb 5 15:20:55.423: IP: tableid=0, s=10.1.203.3 (local), d=10.1.2.1 (Serial0/0/1), routed via RIB
*Feb 5 15:20:55.423: IP: s=10.1.203.3 (local), d=10.1.2.1 (Serial0/0/1), len 100, sending
*Feb 5 15:20:55.451: IP: tableid=0, s=10.1.203.3 (local), d=10.1.2.1 (Serial0/0/1), routed via RIB
*Feb 5 15:20:55.451: IP: s=10.1.203.3 (local), d=10.1.2.1 (Serial0/0/1), len 100, sending
*Feb 5 15:20:55.483: IP: tableid=0, s=10.1.203.3 (local), d=10.1.2.1 (Serial0/0/1), routed via RIB
*Feb 5 15:20:55.483: IP: s=10.1.203.3 (local), d=10.1.2.1 (Serial0/0/1), len 100, sending
If a deliberate metric manipulation is necessary on a router to force it to prefer one interface over another for EIGRP-discovered routes, it is recommended to use the interface-level command "delay" for these purposes. While the "bandwidth" command can also be used to influence the metrics of EIGRP-discovered routes through a particular interface, it is discouraged because the "bandwidth" will also influence the amount of bandwidth reserved for EIGRP packets and other IOS subsystems as well. The "delay" parameter specifies the value of the interface delay that is used exclusively by EIGRP to perform metric calculations and does not influence any other area of IOS operation.
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