Hello there. In this post, I will explain how to configure EIGRP with load balancing. I made this post because I want to educate myself on writing skills, and share my knowledge with readers.
You can use either physical devices or packet tracer to demonstrate the following configuration. I assume you have configured all the routers with the following IP. At the end of this post, I included the configuration that I used in this post. The configuration at the end of this post is still not configured to have a load balance since I will explain it.
Let's get started
If you notice from the topology above, there are multiple connections from R1 to R5.
For the first path, the connection is R1 -> R2 -> R5. This path is using gigabit connections all the way from R1 to R5.
For the second path, the connection is R1 -> R3 -> R5. This path is using a serial connection from R1 to R3, and then using gigabit connection from R3 to R5.
For the third path, the connection is R1 -> R4 -> R5. This path is using serial connections all the way from R1 to R5.
Determine the current best route to the destination
Now, check on R1 which path is the best route for the connection. We will check the route from R1 to the R5, and the IP for R5 is 10.5.5.5. Use the following command to check the route.
sh ip route 10.5.5.5
Result:
Router-ONE#sh ip route 10.5.5.5
Routing entry for 10.5.5.5/32
Known via "eigrp 99", distance 90, metric 131072, type internal
Redistributing via eigrp 99
Last update from 10.12.12.2 on GigabitEthernet0/0, 00:05:12 ago
Routing Descriptor Blocks:
* 10.12.12.2, from 10.12.12.2, 00:05:12 ago, via GigabitEthernet0/0
Route metric is 131072, traffic share count is 1
Total delay is 5020 microseconds, minimum bandwidth is 1000000 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 2
You can see that R1 is going to R5 through IP 10.12.12.2, which is IP on R2. What is the important value of this information? We can see the route metric. What is the significance of this route metric?
Identify EIGRP Feasible Successor (FS) route
Next, try to check EIGRP Feasible Successor (FS) routes. What is Feasible Successor? Feasible Successor or FS is a backup route that can be used in case the successor route is broke or down. To determine the feasible successor, use the following command.
sh ip eigrp topology
Result:
Router-ONE#sh ip eigrp topology
IP-EIGRP Topology Table for AS 99/ID(10.1.1.1)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - Reply status
P 10.1.1.1/32, 1 successors, FD is 128256
via Connected, Loopback0
P 10.2.2.2/32, 1 successors, FD is 130816
via 10.12.12.2 (130816/128256), GigabitEthernet0/0
P 10.3.3.3/32, 1 successors, FD is 131328
via 10.12.12.2 (131328/131072), GigabitEthernet0/0
via 10.13.13.3 (2297856/128256), Serial0/0/0
P 10.4.4.4/32, 1 successors, FD is 2297856
via 10.14.14.4 (2297856/128256), Serial0/0/1
P 10.5.5.5/32, 1 successors, FD is 131072
via 10.12.12.2 (131072/130816), GigabitEthernet0/0
via 10.13.13.3 (2298112/130816), Serial0/0/0
P 10.12.12.0/24, 1 successors, FD is 2816
via Connected, GigabitEthernet0/0
P 10.13.13.0/24, 1 successors, FD is 2169856
via Connected, Serial0/0/0
P 10.14.14.0/24, 1 successors, FD is 2169856
via Connected, Serial0/0/1
P 10.25.25.0/24, 1 successors, FD is 3072
via 10.12.12.2 (3072/2816), GigabitEthernet0/0
P 10.35.35.0/24, 1 successors, FD is 3328
via 10.12.12.2 (3328/3072), GigabitEthernet0/0
via 10.13.13.3 (2170112/2816), Serial0/0/0
P 10.45.45.0/24, 1 successors, FD is 2170368
via 10.12.12.2 (2170368/2170112), GigabitEthernet0/0
via 10.14.14.4 (2681856/2169856), Serial0/0/1
via 10.13.13.3 (2682112/2170112), Serial0/0/0
We can see all the EIGRP topology here. But let's focus on the route to the 10.5.5.5.
P 10.5.5.5/32, 1 successors, FD is 131072
via 10.12.12.2 (131072/130816), GigabitEthernet0/0
via 10.13.13.3 (2298112/130816), Serial0/0/0
What is this? Let me explain.
via 10.12.12.2 (131072/130816), GigabitEthernet0/0
The first one is the successor, which means it is the first route that R1 use to go to R5 through R2. Now, what is value 131072 and 130816 for?
131072 is the value for Feasible Distance (FD), and 130816 is the value for Advertised Distance (AD).
Now let see Feasible Successor, which is the second one. Feasible Successor is a backup route for R1 to go to R5.
via 10.13.13.3 (2298112/130816), Serial0/0/0
2298112 is the value for Feasible Distance (FD), and 130816 is the value for Advertised Distance (AD).
Feasible successor looks like going through R3. And the value of FD and AD here is different. The route from R1 to R5 through R3 meets the feasibility requirement because the AD for route R3 is less than FD on route R2.
We will use this FS which is 10.13.13.3 to configure load balancing on EIGRP routing.
Configure the variance value
Variance value is a value multiplier that multiplied the value of the Feasible Distance of Successor. If the multiplied value of the Feasible Distance of Successor is bigger than Feasible Distance of Feasible Successor, it will install a Feasible Successor route into routing table. Let's do some calculations to determine what value of variance we need in order to install the Feasible Successor route into routing table.
Current Feasible Distance for Successor is 131072.
So we need to multiply Feasible Distance with a number that produces a value that bigger than Feasible Distance for Feasible Successor, which is 2298112. The variance value would be 18, because 131072 times with 18, is 2359296, and 2359296 is bigger than 2298112. Next is to configure the variance. Use following command to configure variance.
router eigrp 99
variance 18 Router-ONE#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Router-ONE(config)#router eigrp 99
Router-ONE(config-router)#variance 18
Now you should be able to see the changes happened.
Router-ONE(config-router)#
%DUAL-5-NBRCHANGE: IP-EIGRP 99: Neighbor 10.13.13.3 (Serial0/0/0) is up: new adjacency
Router-ONE(config-router)#
%DUAL-5-NBRCHANGE: IP-EIGRP 99: Neighbor 10.14.14.4 (Serial0/0/1) is up: new adjacency
Router-ONE(config-router)#
%DUAL-5-NBRCHANGE: IP-EIGRP 99: Neighbor 10.12.12.2 (GigabitEthernet0/0) is up: new adjacency
Router-ONE(config-router)#config-router)#variance 18
Use the following command to check the route to R5.
sh ip route 10.5.5.5
You should see there are 2 routes to go to R5.
Router-ONE#sh ip route 10.5.5.5
Routing entry for 10.5.5.5/32
Known via "eigrp 99", distance 90, metric 131072, type internal
Redistributing via eigrp 99
Last update from 10.12.12.2 on GigabitEthernet0/0, 00:02:39 ago
Routing Descriptor Blocks:
* 10.12.12.2, from 10.12.12.2, 00:02:39 ago, via GigabitEthernet0/0
Route metric is 131072, traffic share count is 1
Total delay is 5020 microseconds, minimum bandwidth is 1000000 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 2
10.13.13.3, from 10.13.13.3, 00:02:40 ago, via Serial0/0/0
Route metric is 2298112, traffic share count is 1
Total delay is 25010 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 2
Even though the route metric which is Feasible Distance is different on both router, it still will be used to load balance.
Configuration
R1 config:
en
conf t
hostname Router-ONE
no ip domain-lookup
line con 0
logging synchro
exit
int lo0
ip addr 10.1.1.1 255.255.255.255
no shut
exit
int g0/0
ip addr 10.12.12.1 255.255.255.0
no shut
exit
int s0/0/0
ip addr 10.13.13.1 255.255.255.0
clock rate 128000
no shut
exit
int s0/0/1
ip addr 10.14.14.1 255.255.255.0
clock rate 128000
no shut
exit
router eigrp 99
no auto-summary
network 10.1.0.0
network 10.12.0.0
network 10.13.0.0
network 10.14.0.0
end
R2 config:
en
conf t
hostname Router-TWO
no ip domain-lookup
line con 0
logging synchro
exit
int lo0
ip addr 10.2.2.2 255.255.255.255
no shut
exit
int g0/0
ip addr 10.12.12.2 255.255.255.0
no shut
exit
int g0/1
ip addr 10.25.25.2 255.255.255.0
no shut
exit
router eigrp 99
no auto-summary
network 10.2.0.0
network 10.12.0.0
network 10.25.0.0
end
R3 config:
en
conf t
hostname Router-THREE
no ip domain-lookup
line con 0
logging synchro
exit
int lo0
ip addr 10.3.3.3 255.255.255.255
no shut
exit
int s0/0/0
ip addr 10.13.13.3 255.255.255.0
no shut
exit
int g0/0
ip addr 10.35.35.3 255.255.255.0
no shut
exit
router eigrp 99
no auto-summary
network 10.30.0.0
network 10.13.0.0
network 10.35.0.0
end
R4 config:
en
conf t
hostname Router-FOUR
no ip domain-lookup
line con 0
logging synchro
exit
int lo0
ip addr 10.4.4.4 255.255.255.255
no shut
exit
int s0/0/0
ip addr 10.14.14.4 255.255.255.0
no shut
exit
int s0/0/1
ip addr 10.45.45.4 255.255.255.0
clock rate 128000
no shut
exit
router eigrp 99
no auto-summary
network 10.4.0.0
network 10.14.0.0
network 10.45.0.0
end
R5 config:
en
conf t
hostname Router-FIVE
no ip domain-lookup
line con 0
logging synchro
exit
int lo0
ip addr 10.5.5.5 255.255.255.255
no shut
exit
int g0/0
ip addr 10.25.25.5 255.255.255.0
no shut
exit
int g0/1
ip addr 10.35.35.5 255.255.255.0
no shut
exit
int s0/0/0
ip addr 10.45.45.5 255.255.255.0
no shut
exit
router eigrp 99
no auto-summary
network 10.5.0.0
network 10.25.0.0
network 10.35.0.0
network 10.45.0.0
end
In this post, I use the following resources to learn and share it back here.
https://www.mustbegeek.com/configure-load-balancing-on-cisco-eigrp/
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