IGRP Bandwidth and Delay

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Todd Lammle's CCNA routing and switching study guide Chapter 19 page 823

In the troubleshooting steps for routers that don't have adjacency it has you change serial interfaces Delay and bandwidth metrics to the default.

Is this implying that if 2 serial interfaces that have different bandwidth and Delay they wont' form neighbor relationships?
IN the book it doesn't solve the problem and he moves on to the next step.
Or is he showing that it doesn't matter if they are mismatched.

In packet tracer they can differ and still be neighbors.
thanks for the help!

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Comments

Simrid

In order to form an EIGRP adjacency, neighbors must agree on a couple of things; K values, authentication and AS numbers. The K values consist of Bandwidth, Delay, Reliability, Load and MTU. I believe what you are explaining referring to the bandwidth and delay metrics within the K values. Please correct me if I am wrong.

To see your configured K values, you can use the "show ip protocols" command.

I hope this helps.

minerbob

Yes I agree K values must match, but in the book the example had mismatched values on the interface it self. "show int serial" show show the values. for bandwidth and delay.

They were mismatched and the book for troubleshooting had us return them to the default values. In the book the processes didn't resolve the issue, and had us continue on checking K values ect.

was this to point out it doesn't matter or would it matter?

DragonNOA1

I think the book is just going through different steps you could try in troubleshooting, even though the first step of changing BW or DLY wouldn't ever fix the problem because two neighbors can have different bandwidth and delay statements (added manually to the interface) and still form an adjacency, as long as the K values match.

K values just say what the router will use in the calculation of routes. If all routers calculate FD differently, then routes wouldn't be accurate between routers. So saying that all neighbors/routers use only bandwidth and delay in their calculations, then they can be trusted when calculating and sharing routes, since all routers calculate routes using the same math.