Configuring EIGRP Maximum Paths

EIGRP by default load balances using 4 routes with identical metrics however you may need to change this for whatever reason. This lab will discuss and demonstrate the configuration and verification of EIGRP Maximum Paths

Real World Application & Core Knowledge

Now that your understanding of EIGRP has evolved lets touch on a few of the more advanced features of the routing protocol. EIGRP by default will load sharing over a maximum of 4 routes if they all have the same metric as shown by the show ip protocols command under “Maximum Paths”.

This number can be an integer value between 1 and 32. While load sharing over 32 routes is unheard of, there are some scenarios out there that would require such network configuration.

It is common practice to load share over multiple WAN links to some degree rather it be using load balanced routes in the routing table or some other technology such as ether-channel or ppp multi-link.

When the router load balances over multiple paths using the routing table, the default load balancing behavior is per-destination load sharing. Some platforms support different algorithms such as per-packet and per source port/per destination port or both layer4 ports.

In this lab you will learn how to statically set the maximum paths that EIGRP can use for ip route based load sharing.

If you’ve completed Lab 8-5 – Configuring EIGRP Timers, then you’ll notice on R1 if you view the routing table that the router is load sharing to the 10.80.23.0/30 network via R2 and R3. This is because R1 has two routes to that destination network with the same metric.

To statically configure EIGRP’s maximum path’s value, you’ll need to use the maximum-paths command in EIGRP router configuration mode followed by the the number value of paths.

Familiarize yourself with the following new command(s);

Command Description
maximum-paths # This command is executed in EIGRP router configuration mode to statically configure the maximum paths value on a per router basis.

This lab will continue to build upon the topology previously used in Lab 8-5 and other labs found through out Section 8.

Lab Prerequisites

  • If you are using GNS3 than load the Free CCNA Workbook GNS3 topology than start devices; R1, R2, R3, R4 and R5.
  • Establish a console session with devices R1, R2, R3, R4 and R5 than load the initial configurations provided below by copying the config from the textbox and pasting it into the respected routers console.

 

Lab Objectives

  • On R1, view the routing table and verify that R1 is load-balancing to 10.80.23.0/30; afterward, specify the maximum paths for EIGRP Autonomous System 10 to use only 1 path.
  • Verify your configuration by using the show ip route command.

Lab Instruction

Objective 1. – On R1, view the routing table and verify that R1 is load-balancing to 10.80.23.0/30; afterward, specify the maximum paths for EIGRP Autonomous System 10 to use only 1 path.

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
       * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

     10.80.0.0/8 is variably subnetted, 11 subnets, 4 masks
D       10.80.50.0/24 [90/2809856] via 10.80.234.4, 01:13:17, Serial00
D       10.80.40.0/24 [90/640256] via 10.80.234.4, 01:13:17, Serial00
D       10.80.23.1/32 [90/2681856] via 10.80.234.3, 01:13:17, Serial00
D       10.80.23.0/30 [90/2681856] via 10.80.234.3, 01:13:17, Serial00
                     [90/2681856] via 10.80.234.2, 01:13:17, Serial00
D       10.80.23.2/32 [90/2681856] via 10.80.234.2, 01:13:17, Serial00
D       10.80.30.0/24 [90/640256] via 10.80.234.3, 01:13:17, Serial00
D       10.80.45.2/32 [90/2681856] via 10.80.234.4, 01:13:17, Serial00
D       10.80.45.0/30 [90/2681856] via 10.80.234.4, 01:13:17, Serial00
D       10.80.20.0/24 [90/512512] via 10.80.234.2, 01:13:17, Serial00
C       10.80.10.0/24 is directly connected, Loopback0
C       10.80.234.0/29 is directly connected, Serial00
R1>enable
R1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
R1(config)#router eigrp 10
R1(config-router)#maximum-paths 1
R1(config-router)#end
R1#

Objective 2. – Verify your configuration by using 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
       * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

     10.80.0.0/8 is variably subnetted, 11 subnets, 4 masks
D       10.80.50.0/24 [90/2809856] via 10.80.234.4, 00:01:23, Serial00
D       10.80.40.0/24 [90/640256] via 10.80.234.4, 00:01:23, Serial00
D       10.80.23.1/32 [90/2681856] via 10.80.234.3, 00:01:23, Serial00
D       10.80.23.0/30 [90/2681856] via 10.80.234.2, 00:01:23, Serial00
D       10.80.23.2/32 [90/2681856] via 10.80.234.2, 00:01:23, Serial00
D       10.80.30.0/24 [90/640256] via 10.80.234.3, 00:01:23, Serial00
D       10.80.45.2/32 [90/2681856] via 10.80.234.4, 00:01:23, Serial00
D       10.80.45.0/30 [90/2681856] via 10.80.234.4, 00:01:23, Serial00
D       10.80.20.0/24 [90/512512] via 10.80.234.2, 00:01:23, Serial00
C       10.80.10.0/24 is directly connected, Loopback0
C       10.80.234.0/29 is directly connected, Serial00
R1#

As you can see from the routing table on R1 shown above that R1 is no longer load balancing traffic to 10.80.23.0/30 via R2 and R3 but using only R3 as the next hop.

You can view the EIGRP topology and the route to 10.80.23.0/30 via R2 will become the feasible successor (backup route) as shown below;

R1#show ip eigrp topology
IP-EIGRP Topology Table for AS(10)/ID(10.80.10.1)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status 

P 10.80.50.0/24, 1 successors, FD is 2298112
        via 10.80.234.4 (2809856/2297856), Serial00
P 10.80.40.0/24, 1 successors, FD is 128512
        via 10.80.234.4 (640256/128256), Serial00
P 10.80.23.1/32, 1 successors, FD is 2170112
        via 10.80.234.3 (2681856/2169856), Serial00
P 10.80.23.0/30, 1 successors, FD is 2170112
        via 10.80.234.2 (2681856/2169856), Serial00
        via 10.80.234.3 (2681856/2169856), Serial00
P 10.80.23.2/32, 1 successors, FD is 2170112
        via 10.80.234.2 (2681856/2169856), Serial00
P 10.80.30.0/24, 1 successors, FD is 128512
        via 10.80.234.3 (640256/128256), Serial00
P 10.80.45.2/32, 1 successors, FD is 2170112
        via 10.80.234.4 (2681856/2169856), Serial00
P 10.80.45.0/30, 1 successors, FD is 2170112
        via 10.80.234.4 (2681856/2169856), Serial00
P 10.80.20.0/24, 1 successors, FD is 768
        via 10.80.234.2 (512512/512), Serial00
P 10.80.10.0/24, 1 successors, FD is 128256
        via Connected, Loopback0
P 10.80.234.0/29, 1 successors, FD is 512256
        via Connected, Serial00
R1#
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