EIGRP unequal cost balancing

Answered Question
Jan 11th, 2008

Hi.I am trying to do an unequal cost load balancing across 2 routers on a remote location(routers 3 and 4 in the picture).The link on router 3 is 2 Mbits and 1 Mbit on router 4.They have HSRP between them in case one of them fails(with router 3 being primary).

They are all in the same EIGRP AS.

Router 1 is propagating the default static towards the firewall and the networks beyond it.

The problem is that from router 4 I can see both paths with the default route(across router 2 and 1) but from router 3 I can see only the default route across router 1.Probably because reported distance across router 4 is greater than FD.

I was trying to raise variance on the route but to no success because I still can't see the route across router 4.

How can I make router 3 to see the default route across router 4 and achieve load balancing?

I included a rough picture of the topology below.

Attachment: 
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Correct Answer by s.arunkumar about 9 years 1 week ago

Hi,

As i said earlier ur Feasible condition is not met.So try to maniputate the delay or B/w (recommended delay component) for the route via R4 so that the metric is less than ur FD.Then try to load balance it if unequal metric with variance cmd..

((Edited:))say ur edited post now.yes i think it would work if u make hsrp primary as R4,as the routing table there have routes for both.But just remember failing of R4 would again cause u the same situation..

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s.arunkumar Fri, 01/11/2008 - 04:29

Can u just provide the output of eigrp topology table and routing table of R3 and R4..

u told that reported distance across router 4 is greater than FD,if so it doesnt meet Feasible condition,so just increasing varience may not work..

arun

IgorHamzic Fri, 01/11/2008 - 04:31

I'll just post the results from router 3 and 4 as I'm trying do do that on them.

Router 3:

D*EX 0.0.0.0/0 [170/1285120] via 10.200.1.33, 02:51:11, FastEthernet0/1

P 0.0.0.0/0, 1 successors, FD is 1285120

via 10.200.1.33 (1285120/1282560), FastEthernet0/1

Router 4:

D*EX 0.0.0.0/0 [170/1287680] via 10.200.1.65, 04:43:32, FastEthernet0/1

[170/1287680] via 10.65.24.2, 04:43:32, FastEthernet0/0

P 0.0.0.0/0, 2 successors, FD is 1287680

via 10.65.24.2 (1287680/1285120), FastEthernet0/0

via 10.200.1.65 (1287680/1285120), FastEthernet0/1

While pasting the output another thought hit me.If I make the router 4 the primary HSRP router he would get all the traffic first and he could do the load balancing without the need to influence the EIGRP metrics.Is my way of thinking on the right track?

Correct Answer
s.arunkumar Fri, 01/11/2008 - 04:44

Hi,

As i said earlier ur Feasible condition is not met.So try to maniputate the delay or B/w (recommended delay component) for the route via R4 so that the metric is less than ur FD.Then try to load balance it if unequal metric with variance cmd..

((Edited:))say ur edited post now.yes i think it would work if u make hsrp primary as R4,as the routing table there have routes for both.But just remember failing of R4 would again cause u the same situation..

IgorHamzic Fri, 01/11/2008 - 05:03

I was just browsing some Cisco documentation and read that delay is the recommended metric for manipulating and I was thinking to try this first.

Any recommendations on whether to modify metric on the interface itself with the delay command or to do it through metric weights command in EIGRP routing?

s.arunkumar Fri, 01/11/2008 - 05:15

metric weight cmd is used to change values of K-factor. By default is set 1 for K1 and K3 and for other 0.I suggest dont manipulate that.u may mess up for all the routes,as all the eigrp domain should have same K value,otherwise then as ur neighborship will be down .

Do it with delay interface cmd.

Just some tips for doing that..

u can use "sh ip eigrp topo all-link" at R3 to see what is the current metric of default route.(which have not met FC).

See the delay component at each router in path,here R4 and R2 using "sh ip route 0.0.0.0" ,so that u get an idea of how much is t be manipulated for meeting FC..

Hope this help..

IgorHamzic Fri, 01/11/2008 - 07:47

Thanks for your help. I played around with the metrics and managed to get the route across Router 4 into routing table of Router 3.

I'll just keep an eye on the traffic over the next several days and watch how the traffic is going over both routers and maybe adjust the metrics.

s.arunkumar Fri, 01/11/2008 - 21:40

Hi

Nice to know that it hepled.

Got another think in my mind ,let me share here..

Now u are doing unequal loadbalancing at R3 ,while R4 is doing equal cost.why dont u try for that in R3 also.Here is a tip to make R3 also equal cost ,so that u need not have to depend on varience and do unequal loadbalancing..

Now ur metric through R1 at R3 for the default route is 1285120..

ie,if ur metric via R4 is this value ,then will make it equal cost load balancing. for that calculate delay to be configured at R3 by,

256 x ( (10^7)/BW + DLY ) = 1285120.((assuming K factor is default values))

here BW is ur bandwidth from "sh ip int " towards R4.

DLY is delay in tens of microsecond,which need to be found,and configured.

After finding DLY,see what is the delay at R4 for 0.0.0.0 using "sh ip route 0.0.0.0".say that value is DLY1.

then the delay to be configured on R3 is = DLY-DLY1.((as delay is sum of all delay component through out the path))

Hope i make sense..

lets see what experts says...

arun :)

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