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EIGRP unequal cost load balance

gatlin007
Level 4
Level 4

‎07-05-2005 11:54 AM - edited ‎03-03-2019 09:58 AM

I’m attempting to configure unequal cost load balancing with EIGRP and haven had any luck. In the following output I’m attempting to load balance between fa0/3 and fa0/5 for the 5.5.5.5 host. If I make the metrics equal it does it no problem. As soon as I change the metric it only populates one route in the routing table.

-----------------------------

Switch#

Switch#show ip pro

*** IP Routing is NSF aware ***

Routing Protocol is "eigrp 100"

Outgoing update filter list for all interfaces is not set

Incoming update filter list for all interfaces is not set

Default networks flagged in outgoing updates

Default networks accepted from incoming updates

EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0

EIGRP maximum hopcount 100

EIGRP maximum metric variance 4

Redistributing: eigrp 100

EIGRP NSF-aware route hold timer is 240s

Automatic network summarization is not in effect

Maximum path: 4

Routing for Networks:

0.0.0.0

Routing Information Sources:

Gateway Distance Last Update

2.2.2.2 90 00:01:29

1.1.1.2 90 00:01:29

Distance: internal 90 external 170

Switch#

Switch#

Switch#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, E - EGP

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

1.0.0.0/24 is subnetted, 1 subnets

C 1.1.1.0 is directly connected, FastEthernet0/5

2.0.0.0/24 is subnetted, 1 subnets

C 2.2.2.0 is directly connected, FastEthernet0/3

5.0.0.0/32 is subnetted, 1 subnets

D 5.5.5.5 [90/156160] via 2.2.2.2, 00:01:39, FastEthernet0/3

10.0.0.0/32 is subnetted, 2 subnets

C 10.0.0.3 is directly connected, Loopback0

D 10.0.0.1 [90/156160] via 2.2.2.2, 00:01:55, FastEthernet0/3

Switch#

Switch#

Switch#

Switch#show ip ei top det

IP-EIGRP Topology Table for AS(100)/ID(10.0.0.3)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,

r - reply Status, s - sia Status

P 5.5.5.5/32, 1 successors, FD is 156160, serno 6

via 2.2.2.2 (156160/128256), FastEthernet0/3

via 1.1.1.2 (284160/256256), FastEthernet0/5

P 1.1.1.0/24, 1 successors, FD is 28160, serno 15

via Connected, FastEthernet0/5

P 2.2.2.0/24, 1 successors, FD is 28160, serno 4

via Connected, FastEthernet0/3

P 10.0.0.3/32, 1 successors, FD is 128256, serno 1

via Connected, Loopback0

P 10.0.0.1/32, 1 successors, FD is 156160, serno 5

via 2.2.2.2 (156160/128256), FastEthernet0/3

Switch#

Switch#show run | be router ei

router eigrp 100

variance 4

network 0.0.0.0

no auto-summary

!

Labels:
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3 Replies 3

Kevin Dorrell
Level 10
Level 10

‎07-05-2005 12:14 PM

You are being caught by the "feasible successor" rule. At first sight, it may look like the two routes for 5.5.5.5 should balance, but they do not. Look in the topology table, and you see that only one is a successor. This is because the next hop via 1.1.1.2 is 256256 away from the destination. But you are only 156160 from the destination via your best route. Therefore you are closer to the destination than 1.1.1.2 is. So 1.1.1.2 cannot be a successor, to avoid loops.

The only way you can fiddle this so that it works is to artificially make your best route worse than 256256. Then 256256 would become a feasible successor.

Kevin Dorrell

Luxembourg

0 Helpful

limtohsoon
Level 1
Level 1

‎07-05-2005 01:24 PM

Hi,

To qualify as a feasible successor, a next-hop router must have an advertised distance (AD) less than the feasible distance (FD) of the current successor route.

In your case, the AD of router 1.1.1.2 is 256256, which is NOT less than the FD of your current successor 2.2.2.2 (FD=156160).

Only paths that are feasible can be used for load balancing. The two feasibility conditions are as follows:

(1) The local best metric (the current FD) must be greater than the next router best metric (the AD) learned from the next router.

(2) The variance X the local best metric (the current FD) must be greater than the metric (the FD) through the next router.

If both of these conditions are met, the route is called feasible and can be added to the routing table.

In your case, the path via 1.1.1.2 is not considered for load-balancing because it does not satisfy condition (1), though it satisfies condition (2).

Hope this helps.

Thank you.

B.Rgds,

Lim TS

0 Helpful

gatlin007
Level 4
Level 4
In response to limtohsoon

‎07-05-2005 03:41 PM

Thanks guys!!!

I adjusted it as per your advice and it worked great.

Chris Gatlin

-------------------------------

Switch#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, E - EGP

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

1.0.0.0/24 is subnetted, 1 subnets

C 1.1.1.0 is directly connected, FastEthernet0/5

2.0.0.0/24 is subnetted, 1 subnets

C 2.2.2.0 is directly connected, FastEthernet0/3

5.0.0.0/32 is subnetted, 1 subnets

D 5.5.5.5 [90/276160] via 2.2.2.2, 00:02:55, FastEthernet0/3

[90/284160] via 1.1.1.2, 00:02:55, FastEthernet0/5

10.0.0.0/32 is subnetted, 2 subnets

C 10.0.0.3 is directly connected, Loopback0

D 10.0.0.1 [90/276160] via 2.2.2.2, 00:02:55, FastEthernet0/3

Switch#

Switch#

Switch#show ip ei top det

IP-EIGRP Topology Table for AS(100)/ID(10.0.0.3)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,

r - reply Status, s - sia Status

P 5.5.5.5/32, 1 successors, FD is 276160, serno 10, Stats m(17)M(17)A(17)c(1)

via 2.2.2.2 (276160/248256), FastEthernet0/3

via 1.1.1.2 (284160/256256), FastEthernet0/5

P 1.1.1.0/24, 1 successors, FD is 28160, serno 2

via Connected, FastEthernet0/5

P 2.2.2.0/24, 1 successors, FD is 28160, serno 5

via Connected, FastEthernet0/3

P 10.0.0.3/32, 1 successors, FD is 128256, serno 1

via Connected, Loopback0

P 10.0.0.1/32, 1 successors, FD is 276160, serno 9

via 2.2.2.2 (276160/248256), FastEthernet0/3

Switch#

Switch#show run | be router ei

router eigrp 100

variance 2

offset-list 0 in 120000 FastEthernet0/3

network 0.0.0.0

no auto-summary

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