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New Member

Load balancing EIGRP not working

Please take a look at this and explain why the variance command is not adding the serial connection path to the routing table along with the fast ethernet interface. A variance of 10 should be all that is needed, and I have tried 100 just to be safe, but the routing table still just adds the fast ethernet route via EIGRP. I have cleared the EIGRP neighbors also.

Here is the sequence.

RA#sh ip eigrp topology 155.155.0.0

IP-EIGRP (AS 10): Topology entry for 155.155.0.0/16

  State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2221056

  Routing Descriptor Blocks:

  185.185.10.26 (FastEthernet0/0), from 185.185.10.26, Send flag is 0x0

      Composite metric is (2221056/2195456), Route is Internal

      Vector metric:

        Minimum bandwidth is 1544 Kbit

        Total delay is 22000 microseconds

        Reliability is 255/255

        Load is 1/255

        Minimum MTU is 1500

        Hop count is 2

  170.170.10.4 (Serial1/0), from 170.170.10.4, Send flag is 0x0

      Composite metric is (21049600/20537600), Route is Internal

      Vector metric:

        Minimum bandwidth is 128 Kbit

        Total delay is 41000 microseconds

        Reliability is 255/255

        Load is 1/255

        Minimum MTU is 1500

        Hop count is 2

RA#sh 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

C    170.170.0.0/16 is directly connected, Serial1/0

C    185.185.0.0/16 is directly connected, FastEthernet0/0

D    155.155.0.0/16 [90/2221056] via 185.185.10.26, 00:07:51, FastEthernet0/0

D    190.190.0.0/16 [90/2195456] via 185.185.10.26, 00:07:51, FastEthernet0/0

D    160.160.0.0/16 [90/2707456] via 185.185.10.26, 00:07:51, FastEthernet0/0

RA#config t

Enter configuration commands, one per line.  End with CNTL/Z.

RA(config)#router eigrp 10

RA(config-router)#variance 10

RA(config-router)#^Z

RA#clear ip eigrp neighbors

RA#

*Mar  1 15:21:00.799: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 170.170.10.4 (

Serial1/0) is down: manually cleared

*Mar  1 15:21:00.799: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 185.185.10.26

(FastEthernet0/0) is down: manually cleared

*Mar  1 15:21:01.024: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 170.170.10.4 (

Serial1/0) is up: new adjacency

*Mar  1 15:21:01.737: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 185.185.10.26

(FastEthernet0/0) is up: new adjacency

RA#sh 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

C    170.170.0.0/16 is directly connected, Serial1/0

C    185.185.0.0/16 is directly connected, FastEthernet0/0

D    155.155.0.0/16 [90/2221056] via 185.185.10.26, 00:00:11, FastEthernet0/0

D    190.190.0.0/16 [90/2195456] via 185.185.10.26, 00:00:11, FastEthernet0/0

D    160.160.0.0/16 [90/2707456] via 185.185.10.26, 00:00:11, FastEthernet0/0

RA#

4 ACCEPTED SOLUTIONS

Accepted Solutions

Re: Load balancing EIGRP not working

Steve,

I hope you checked the reported distance via s1/0.

Shouldnt that be less than the FD over Fa0/0 at first place ?

Try manipulating the metrics on the Serial intf to influence RD so that it will be less than the FD which is learned on the other link.

This should solve.

HTH,

Hall of Fame Super Blue

Re: Load balancing EIGRP not working

Steve

The variance command will load-balance over unequal cost link but it can only use routes that have a lower reported metric that the FD (Feasible distance) on the local router.

From your output -

IP-EIGRP (AS 10): Topology entry for 155.155.0.0/16

  State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2221056

  Routing Descriptor Blocks:

185.185.10.26 (FastEthernet0/0), from 185.185.10.26, Send flag is 0x0

      Composite metric is (2221056/2195456), Route is Internal

so the FD = 2221056

  170.170.10.4 (Serial1/0), from 170.170.10.4, Send flag is 0x0

      Composite metric is (21049600/20537600), Route is Internal

the reported metric is 20537600 which is much greater than the FD of the route. So it cannot be used. You must get the reported metric to be below the FD.


Jon

Hall of Fame Super Silver

Re: Load balancing EIGRP not working

Hello Steve,

EIGRP metric with default k values is proportional to cumulative delay on path and inversely proportional to lowest BW on path

EIGRP metric =  256 * (cumulative delay [tens of microseconds] + 256 * (10^7/ min BW [kbps])

so path1 gives:

256*2200 + 256 * (10^7/1544) = 2221231,0880829015544041450777202

on path2:  256* 4100 + 256 * (10^7 / 128) = 21049600

it gives a 9,47 ratio.

However, as noted by Ibrahim the reported distance from neighbor on serial interface has to satisfy the feasibility condition in order for the path to be considered.

the conditions for unequal load balancing are:

RDx < FD

LDx < V* FD

where LDx is metric on path x calculated on local node as it has been done above

in your case we see that  the line in sh ip eigrp topology says:

State is Passive, Query origin  flag is 1, 1 Successor(s), FD is 2221056

no feasible successor is reported so path2 does not satisfy to feasibility condition.

Hope to help

Giuseppe

Re: Load balancing EIGRP not working

The feasability condition is sometimes a bit confusing, and I prefer to put it in simpler terms.

Looking at your ip eigrp topology, your best route is via F0/0, and has a composite metric of 2,221,056.

Your second best route vie S1/0 has a metric of 21,049,600, almost 10 times as much.  That would be OK, were it not for the fact that the next hop for that route has a metric 20,537,600, which is even further away from the destination than you are already if you go via F0/0.  EIGRP will never send its traffic to someone who is even further away from the destination than it is already.  EIGRP doesn't like cycling uphill.  So the route S1/0 is not feasible.

Kevin Dorrell

Luxembourg

6 REPLIES

Re: Load balancing EIGRP not working

Steve,

I hope you checked the reported distance via s1/0.

Shouldnt that be less than the FD over Fa0/0 at first place ?

Try manipulating the metrics on the Serial intf to influence RD so that it will be less than the FD which is learned on the other link.

This should solve.

HTH,

New Member

Re: Load balancing EIGRP not working

This is probably related to why, when I went the other end of the network to RD, I was able to load balance there back to the 170.170.0.0 network -- I'll check the FD and reported metrics there. Thanks all for the great posts and very helpful explanations. I understand the concepts but will have to work with the FD and metrics to see how I can alter them.

Hall of Fame Super Blue

Re: Load balancing EIGRP not working

Steve

The variance command will load-balance over unequal cost link but it can only use routes that have a lower reported metric that the FD (Feasible distance) on the local router.

From your output -

IP-EIGRP (AS 10): Topology entry for 155.155.0.0/16

  State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2221056

  Routing Descriptor Blocks:

185.185.10.26 (FastEthernet0/0), from 185.185.10.26, Send flag is 0x0

      Composite metric is (2221056/2195456), Route is Internal

so the FD = 2221056

  170.170.10.4 (Serial1/0), from 170.170.10.4, Send flag is 0x0

      Composite metric is (21049600/20537600), Route is Internal

the reported metric is 20537600 which is much greater than the FD of the route. So it cannot be used. You must get the reported metric to be below the FD.


Jon

New Member

Re: Load balancing EIGRP not working

Now I completely understand, thanks for using the concepts with the output.

Hall of Fame Super Silver

Re: Load balancing EIGRP not working

Hello Steve,

EIGRP metric with default k values is proportional to cumulative delay on path and inversely proportional to lowest BW on path

EIGRP metric =  256 * (cumulative delay [tens of microseconds] + 256 * (10^7/ min BW [kbps])

so path1 gives:

256*2200 + 256 * (10^7/1544) = 2221231,0880829015544041450777202

on path2:  256* 4100 + 256 * (10^7 / 128) = 21049600

it gives a 9,47 ratio.

However, as noted by Ibrahim the reported distance from neighbor on serial interface has to satisfy the feasibility condition in order for the path to be considered.

the conditions for unequal load balancing are:

RDx < FD

LDx < V* FD

where LDx is metric on path x calculated on local node as it has been done above

in your case we see that  the line in sh ip eigrp topology says:

State is Passive, Query origin  flag is 1, 1 Successor(s), FD is 2221056

no feasible successor is reported so path2 does not satisfy to feasibility condition.

Hope to help

Giuseppe

Re: Load balancing EIGRP not working

The feasability condition is sometimes a bit confusing, and I prefer to put it in simpler terms.

Looking at your ip eigrp topology, your best route is via F0/0, and has a composite metric of 2,221,056.

Your second best route vie S1/0 has a metric of 21,049,600, almost 10 times as much.  That would be OK, were it not for the fact that the next hop for that route has a metric 20,537,600, which is even further away from the destination than you are already if you go via F0/0.  EIGRP will never send its traffic to someone who is even further away from the destination than it is already.  EIGRP doesn't like cycling uphill.  So the route S1/0 is not feasible.

Kevin Dorrell

Luxembourg

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