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Beginner

EIGRP - influencing routes

Hi networkers!

Here is an scenario example...

metro_example.jpg

The problem is with EIGRP route decision.

EIGRP always looks at the outgoing interface speed of a router for selection of the best route.

In my case, R1 goes directly to R3 because of 50 Mbit outgoing bandwith on R1 and does not "see" 6 Mbit on R3 side.

Logicaly I would like it to go R1 --> R2 --> R3 because of higer speed via R2.

From R3, the route is OK, R3 --> R2 --> R1.

I know about some methods like OFFSET LISTS, ROUTE MAPS ...

The question is, which method is the best concidering this is only an example, in reality there are many more Routers and ME links on my network?

Is there an option to configure on R3 only and propagate to the whole network via EIGRP?

Thanks in adwice...

Everyone's tags (5)
1 ACCEPTED SOLUTION

Accepted Solutions
Rising star

Re: EIGRP - influencing routes

Hi,

You have only three options to modify the metric calculation of Eigrp.

1- Modifying the Bandwidth Of the Interface.

2- Modifying the Delay Value of the Interface.

3- Configuring Offset-list.

I would suggest you set an Offest-list Value on R3 to higer the delay towards R1, this way R1 would believe R2 is the best path to reach R3.

Follow the below link for more info about Setting Offset_list:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800c2d96.shtml

Regards,

Mohamed

6 REPLIES 6
Rising star

Re: EIGRP - influencing routes

Hi,

Who told you Eigrp doesnt see The whole Path Bandwidth, For the Metric Calculation in Eigrp, it caLCULATE THE TOTAL BANDWITH of the path to the destination along with the delay value, and it considers the  path of  (Minimum Bandwidth & accumulative delay) as its metric.

The lowest metric is indeed prefered, and the path would be selected as ( Successor ). Every router in the Eigrp Topology adverises its current Bandwidth and delay to the neighboring router via update message.

Every Eigrp router has three tables, Topolgy Table, Neighbor Table and IP routing table. in the end , the router would have full topolgy overview.

If for any reason you need to influence Eigrp Metric calculation, then Its higly recommended to modify the Delay value of the interface rsather then the bandwidth value, since the bandwidth value could have affect on other routing protocol decisions.

HTH

Mohamed

Beginner

Re: EIGRP - influencing routes

Thank you for your answer.

I know this, had a try to leave on it's defaults but there were no results.

Tryed also to change the delay values, still no luck.

Every interface on my routers has the bandwith xxxx command, there is no problem with this because all this values are thrue and it's not causing any problems to qos or anithing else...

My opinion is that the problem is caused my ME, because the metrics can not be calculated as it should be.

For example, R1 has an outgoing interface to the ME at 50Mbit and has no clue that the R3's same interface is limited to 4 Mbit, or R2's to 10Mbit, for him this links have a bandwith of 50Mbit.

Like i sad before, this is only an example for easier understanding of the problem, in reality I have a more complex situation, with aprox 30 routers, 15 ME links, FC-s, Wifi bridges ecc. with different speeds. Everything else works like a charm exept ME...

Thanks!

Hall of Fame Guru

Re: EIGRP - influencing routes

The problem is not really R3. EIGRP uses the outgoing interface value for bandwidth and so R3 HAS 1Gbps, same as R2.

So what is in between R3 and R1 ?? If there is nothing but switches then you need to modify the bandwidth or preferably the delay on the R3 interface that connects to SW2.

Jon

Beginner

Re: EIGRP - influencing routes

Correct!


But the problem is not R3, R3's routing table is ok!

R1 doesn't know that the route to R3 is beter via R2, because he has the same cost values to both R2 & R3.

Is there a command or something I could issue on R3 that will be propagated to the whole network (via EIGRP)?

Already tried to modify delay value with no results because the metrics difference between interfaces is bigger that delay could influence.

All I want to know, is there some other possibility appart from OFFSET LISTS or ROUTE MAPS?

Thanks in advice,

Rising star

Re: EIGRP - influencing routes

Hi,

You have only three options to modify the metric calculation of Eigrp.

1- Modifying the Bandwidth Of the Interface.

2- Modifying the Delay Value of the Interface.

3- Configuring Offset-list.

I would suggest you set an Offest-list Value on R3 to higer the delay towards R1, this way R1 would believe R2 is the best path to reach R3.

Follow the below link for more info about Setting Offset_list:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800c2d96.shtml

Regards,

Mohamed

Beginner

Re: EIGRP - influencing routes

Thank you for your answer.

For my situation, offset-list is the only method that works because of ME functionality.

Regards!

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