EIGRP K Values Formula

Lessons Discussion
21

Hi Rene!
K5 value is part of reliability and even though MTU is included K value configuration, Cisco router does not use it for composite metric calculation!

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22

doesn’t the speed command actually change the rate at which the interface transmits data? I know that the bandwidth command doesn’t.

23

Hi Rene

I am confused about the Feasible Distance and the Overall metric of a route. Are they the same thing?

Thanks

24

Hello Justin

Yes, the speed command will actually change the data rate of the interface in question. However, the speed command will only configure an interface to conform to a specific Ethernet technology that is supported by that interface. That is, 10Mbps, 100Mbps, 1000 Mbps, 10Gbps. Only these choices are available and only if that interface supports it.

Dynamic routing protocol metrics will also change according to the speed that is configured on specific interfaces.

I hope this has been helpful!

Laz

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25

Hello Quinton

The feasible distance is the overall metric of the best route to a specific destination from the point of view of a particular router.

Take a look at this Cisco documentation that explains feasible distance, reported distance and feasible successor quite well. You may find it useful.

I hope this has been helpful!

Laz

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26

Hi Lazaros,
Although the question was asked before but still it is not clear for me. the difference between feasible distance and metric.
And what is usec in Delay, is it millisecond or something else. please explain it in simple way.
Thanks in advance.

27

IS MTU parameter considered in EIGRP metric as we are not seeing Metric consideration in networklesson notes but seen in other documents
please clarify

28

Hello Kunal

There is a general confusion when it comes to the K5 value for EIGRP and the metric involved with it. The confusion has to do with the fact that it is part of the metric calculation formula.

Now the MTU metric component essentially is used to advertise the minimum MTU along the route to the particular destination. Even though this value is carried in the EIGRP message, MTU is not actually used in the best path selection process. It is not factored in to the composite metric nor is it used as any kind of tiebreaker. However, it is still part of the equation.

As a reminder, the equation is the following:

image

Remember!!! The K values are only flags, and have values of either 1 or 0!

Notice that K5 is the only value that has no associated coefficient with which it is multiplied directly. This means that the actual value of the maximum MTU in the path in question is not taken into account anywhere in the metric calculation. Also note that if K5 = 0, K4, which is reliability, even if it is 1 is not taken into account. In other words, in order for reliability to be taken into account, bot K4 and K5 must be set to 1. So in actual fact, K4 and K5 both deal with reliability (as far as the metric calculation goes) and not with MTU values.

I hope this has been helpful!

Laz

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29

Hello Muhammad

The metric is the term used to refer to the cost of a particular route. EIGRP uses a specific formula to calculate this metric. So the result of the formula calculation is called the metric. There may be many metrics to reach a particular destination, because there are multiple routes to get there. Each one has a metric of its own.

Now the feasible distance is the BEST metric to the destination, and it is the metric of the route that is ultimately installed in the routing table.

As for usec, this is actually microseconds. The “u” at the beginning is used to indicate the Greek letter mu or μ. It looks kind of the same, but not quite. In any case, u is used to substitute for μ so instead of getting μs you get usec.

I hope this has been helpful!

Laz

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30

Nice explanation Lazaros thank you very much.

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31

Hi, I have pasted the output below. I couldn’t compare the FD value and how its calculated. Please clarify.

R1# show int e0/0
Ethernet0/0 is up, line protocol is up
  Hardware is AmdP2, address is aabb.cc00.0100 (bia aabb.cc00.0100)
  Internet address is 12.0.0.1/24
  MTU 1500 bytes, BW 10000 Kbit/sec, DLY 1000 usec,
 reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:03, output 00:00:00, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
 2826 packets input, 280114 bytes, 0 no buffer
 Received 2811 broadcasts (0 IP multicasts)
 0 runts, 0 giants, 0 throttles
 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
 0 input packets with dribble condition detected
 4179 packets output, 360367 bytes, 0 underruns
 0 output errors, 0 collisions, 1 interface resets
 7 unknown protocol drops
 0 babbles, 0 late collision, 0 deferred
 0 lost carrier, 0 no carrier
 0 output buffer failures, 0 output buffers swapped out
R1#show ip eigrp topo
R1#show ip eigrp topology
EIGRP-IPv4 Topology Table for AS(100)/ID(13.0.0.1)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
   r - reply Status, s - sia Status

P 34.0.0.0/24, 1 successors, FD is 307200
    via 13.0.0.3 (307200/281600), Ethernet0/1
P 13.0.0.0/24, 1 successors, FD is 281600
    via Connected, Ethernet0/1
P 192.168.0.0/24, 1 successors, FD is 307200
    via 12.0.0.2 (307200/281600), Ethernet0/0
P 12.0.0.0/24, 1 successors, FD is 281600
    via Connected, Ethernet0/0

R1#
32

Hello Krishnendu

Assuming the default values are used, then only K1 and K3 are taken into account. This means we can use the following formula:

Metric = bandwidth (slowest link) + delay (sum of delays)

However, the information you provided in the above output is not enough to calculate the metric. This is because the bandwidth used is the slowest link in the path from R1 to the destination. We need information about the rest of the topology. Which is the slowest link? It may not be Ethernet0/0. Also, in order to determine the delay, we need a sum of all the delays involved for each hop between R1 and the destination. Only then can we calculate the metric and see if it is the same as that shown in the topology table you shared.

The routing table indicates that all routes that go via the Ethernet0/0 interface go to destinations that are not directly connected. This means that there are intervening routers for which the delay and the bandwidth must be known to calculate the metric.

I hope this has been helpful!

Laz

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33

Hi,

Delays should be diveded to 10 also. for example, It should be 76800 not 768000. could you check?

Delay = [sum of delays] * 256
Delay = [1000+1000+1000] * 256
Delay = 768,000

regards,

34

Hello Murat

Yes, the delay is measured in 10s of microseconds. The delay shown in the show ip eigrp topology or show interface commands is shown in microseconds, so you must divide by 10 before you use it in the formula. However, in the lesson, you can assume that the value being shown has already been divided by 10.

I hope this has been helpful.

Laz

35

@ReneMolenaar

It looks like the formatting on the first 2 code boxes of this lesson are misaligned.

-Bartley

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36

Hello Bartley,

Thanks for sharing this!

This was because of some theme updates we did. Just fixed it!

Rene

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37

Hi Guys - quick question - what does K stand for in EIGRP? In terms of K values?

38

Hello Gareth

That’s a good question. Doing a little bit of research, I was unable to find any indication of what K actually stands for. The K coefficients were originally introduced in the creation of the IGRP routing protocol, the precursor to EIGRP. I believe that it was just a letter that was chosen, as is often the case in physics and engineering, that doesn’t actually correspond to a word or alternate meaning. For example, in electronics, “I” is current and in physics “p” is momentum. That’s my feeling. It would be interesting to learn more about if there is another meaning behind the letter K.

Anyone else have any info on this?

Laz

39

Thanks Laz - just knowing that it doesn’t really relate to anything specific is good.

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40

“No need to do any manual calculations on the exam!”

Thank you ! <3

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