Configuring EIGRP

The objectives of the lab are as follows:
■ Configuring basic EIGRP
■ Disabling autosummarization
■ Load-balancing across unequal paths
■ Configuring a default route
■ Verifying EIGRP configuration


Step 1: Configure and Verify Basic EIGRP Connectivity—Initial  Configurations

Initial Configuration for R1

hostname R1
interface FastEthernet0/0
ip address 10.1.1.1 255.255.255.0
duplex auto
speed auto
!
interface Serial0/0
bandwidth 2000
ip address 192.168.11.1 255.255.255.0
encapsulation ppp
!
interface FastEthernet0/1
ip address 192.168.1.1 255.255.255.0
duplex auto
speed 10

Initial Configuration for R2
hostname R2
!
interface Ethernet0
ip address 192.168.1.2 255.255.255.0
!
interface Serial0
bandwidth 2000
ip address 192.168.11.2 255.255.255.0
encapsulation ppp
clock rate 2000000
!
interface Serial1
ip address 192.168.2.2 255.255.255.0
encapsulation ppp
clock rate 2000000


Initial Configuration for R3hostname R3
!
interface Ethernet0
ip address 10.1.2.3 255.255.255.0
!
interface Serial0
bandwidth 2000
ip address 192.168.2.3 255.255.255.0
encapsulation ppp

Step 1: Configure and Verify Basic EIGRP Connectivity—Ending Configurations


Basic EIGRP Configuration for R1
router eigrp 1
network 10.1.1.0 0.0.0.255
network 192.168.1.0
network 192.168.11.0

Basic EIGRP Configuration for R2
router eigrp 1
network 192.168.1.0
network 192.168.2.0
network 192.168.11.0

Basic EIGRP Configuration for R3
router eigrp 1
network 10.1.2.0 0.0.0.255
network 192.168.2.0

Step 2: Disable Autosummarization


After the initial EIGRP configuration, the lab shows that, by default, EIGRP advertises networks at
their classful boundary. Specifically, in this lab, the 10.1.1.0/24 network on router R1 and the
10.1.2.0/24 network on router R3 are both advertised to router R2 as network 10.0.0.0/8. This is
because a Class A IP address has an 8-bit classful subnet mask.

Therefore, given the Ethernet link’s more favorable EIGRP metric router, R2 always uses the
Ethernet connection to R1 when trying to send packets to the 10.0.0.0/8 network. As a result, network
10.1.2.0/24 becomes unreachable from routers R1 and R2.

To overcome this default behavior, and to advertise a network’s subnet mask along with the network
addresses, this lab disables EIGRP’s autosummarization behavior on all routers in the topology.

Disabling Autosummarization on R1
router eigrp 1
no auto-summary

Disabling Autosummarization on R2

router eigrp 1
no auto-summary

Disabling Autosummarization on R3

router eigrp 1
no auto-summary

Step 3: Load-Balance Across Unequal-Cost Paths
One link is a serial interface running at 2 Mbps, and the other link is a 10-Mbps Ethernet interface. By default, EIGRP uses the link withthe most attractive metric, which, by default, is based on bandwidth and delay. Therefore, as traffic passes between routers R1 and R2, the serial link is not used.

To increase throughput between those routers, you should enable EIGRP’s variance feature. The
variance feature allows EIGRP to load-balance across unequal-cost paths. However, the cost (that
is, the metric) must vary by no more than a specific factor, as specified by the variance command.
This lab uses a variance of 10. The variance parameter is a multiplier applied to the best metric to
create a range of metrics. EIGRP then load-balances across all available paths that have metrics in
that range.
Configuring the Variance Feature on R1
router eigrp 1
variance 10

Configuring the Variance Feature on R2
router eigrp 1
variance 10

Step 4: Advertise a Default Route

 When end-to-end connectivity is established in the lab topology and all links are used, because of
the variance configuration, this lab discusses how to point the routers to a default route. The
default route is statically configured to point out the Ethernet 0 interface of router R3. This static
route is then advertised via EIGRP to routers R1 and R2.

Configuring a Static Default Route on R3
ip route 0.0.0.0 0.0.0.0 Ethernet0

Advertising a Static Default Route on R3 
router eigrp 1
network 0.0.0.0

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