From: Ravi Singh (way2ccie@googlemail.com)
Date: Tue Mar 10 2009 - 14:56:32 ARST
Hi Marish,
You are getting confused in the calculation . Your formula is right but when
you are calculating the FD you have already taken into consideration the
path till R6 , so there is no need to add the calculated FD to the AD again.
What you are missing though in the calculations is the delay values. In
EIGRP metric calculation the bandwidth is the lowest configured bandwidth in
the path to the prefix while the delay is the sum of the delays on the links
towards the prefix.Therefore in your calculation the lowest calculated
bandwidth is correct i.e BW 10000 for R6. The delay would be the interface
delay at R1 which is 100 usec + delay at SW1 i.e 100 usec again + the delay
on R6 which is 1000 usec. Putting these values in the formula gives you
(10^7/10000 ) = 1000 (Bandwidth )
(100/10 + 100/10 + 1000/10 ) = ( 10+10+100) = 120 ( Delay)
Therefore your FD would be (1000 + 120 ) * 256 = 1120 *256 = 286720.
People have different ways of remembering how to calculate the metric . The
way I do it is to find the lowest bandwidth along the path and for the
delays , find the delay values of the outbound ports while going towards the
prefix in question. for example in your case when moving from R1 ( which is
where we are checking the FD ) towards R6 , what all routed interfaces are
encountered in the direction away from R1. and this includes the interface
of the prefix involved as well.
HTH,
Ravi
On Tue, Mar 10, 2009 at 1:24 PM, marish shah <contactmarish@gmail.com>wrote:
> Hi Ravi,
> Thanks, Actually I'm working on IE I version 5 .Plz check the
> attached file for diagram I run eigrp only on all devices in diagram.AS u
> can see in diagrame to reach SW1 IP 155.1.37.0 from R1.I have two paths one
> is going through R6 and other one is through R3 .As I mention before the FD
> calculation is corect But AD is giving problem .And u can see to SW1 from R1
> if I use R6 path so interface between R1 and R6 is fastethernet/ethernet .
> ON R1
>
> Rack1R1#sh interfaces fastEthernet 0/0
>
>
>
> BW 100000 Kbit, DLY 100 usec,
>
>
> ON R6
>
>
>
> Rack1R6# sh interfaces ethernet 0/0.67
>
>
>
> BW 10000 Kbit, DLY 1000 usec
>
>
> Rack1R1#sh ip eigrp topology
>
> P 155.1.37.0/24, 1 successors, FD is 286720
>
> *via 155.1.146.6 (286720/284160), FastEthernet0/0*
>
> via 155.1.13.3 (2195456/281600), Serial1/1
>
> So now my AD is *284160 as u see *sh ip eigrp topology and my FD is *
> 286720.*
>
> *SO onces again I remind you Q ?
> *
>
> *How I can calculate total FD 286720 ?*
>
> *
> *
>
> *So for this what I do I use this formula 10^7/BW + delay x 256*
>
>
> *10^7=10000000*
>
> *10000000/100000 = 100 ( BW 100000 I put here is R1 fastethernet link )*
>
> *100 + 10 = 110 ( here I plus my BW with delay )*
>
> *110 x 256 = 28160 ( this is my total distance between R1 and R6 link)*
>
> *NOw if I plus both my AD and my distance so result is *
>
> *284160** + **28160 = 312320*
>
>
> *OK this result is not correct may be I did'nt take lowest bandwidth
> between link which is R6 Ethernet *BW 10000 ok lets do it this one also.
>
>
> *10^7=10000000*
>
> *10000000/10000 = 1000 ( Now this time I take R6 ethernet link bandwidth
> )*
>
> *1000 + 100 = 1100 ( now delay also this time changed because we take R6
> delay which is 100)*
>
> *1100 x 256 = 281600*
>
>
> *Now try to plus AD & FD **284160 + **281600 = 565760 So Now u see this is
> also wrong FD should be **286720 as show in eigrp topology table .*
>
>
> *So now plz tell how can I calculate mY FD.
> *
>
> *
> *
>
> *
> *
>
> *
> *
>
>
>
> On Tue, Mar 10, 2009 at 3:57 AM, Ravi Singh <way2ccie@googlemail.com>wrote:
>
>> Hi Marish,
>>
>> Your diagram is not very clear. Is it some specific vendor lab you are
>> working on ? A better diagram would certainly help . Also remember the
>> bandwidth that you have to consider while calculating the metric from Router
>> A to Router B should be the lowest bandwidth value in the path from Router A
>> to Router B. Check your interfaces for any non default bandwidth values.
>> Look at the physical topology again carefully. I doubt, there is something
>> very basic that you are missing here.
>>
>> HTH,
>> Ravi
>>
>>
>>
>> On Tue, Mar 10, 2009 at 6:25 AM, marish shah <contactmarish@gmail.com>wrote:
>>
>>> Hi Experts,
>>>
>>> Yesterday I was facing problem with eigrp lab.problem is reladed
>>> to FD (fesible distance) AD (advertise distance)
>>>
>>> ok Here is my senario
>>>
>>>
>>> Serial 1/3 155.1.13.3 155.1.13.1 Serial 1/0
>>> Fa0/0 155.1.146.1 155.1.146.6
>>> Fa0/0.146
>>>
>>>
>>> R3------------------------------------------------------R1------------------------------------------------------------------------R6
>>>
>>> |
>>> |
>>> |Fa0/0
>>> 155.1.37.3
>>> |
>>>
>>> |
>>> 155.1.67.6 Fa0/0.67 |
>>>
>>> |
>>> |
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>>> |
>>> |
>>> | 155.1.37.7 Fa
>>> 1/3 155.1.67.7 Vlan
>>> 67 |
>>>
>>>
>>> |----------------------------------------------------------SW1---------------------------------------------------------------------|
>>>
>>> R1 fastethernet 0/0 is conectd with R6 Fastethernet 0/0.146
>>> R1 Serial 1/0 is conected with R3 Serial 1/3
>>> R3 fastethernet0/0 is conected with SW1 fastethernet 1/3
>>> R6 fastethernet 0/0.67 is conected with SW fastethernet 1/6
>>>
>>> Now I enable eigrp 100 on all routers.
>>>
>>> After runing eigrp 100 I try to calculate FD and AD my traget is
>>> interface
>>> between R3 & SW1 (155.1.37.0) I'm on router 1
>>>
>>> Here is sh ip eigrp topology on R1
>>>
>>> R1#sh ip eigrp topology
>>>
>>> P 155.1.37.0/24, 1 successors, FD is 286720
>>> via 155.1.146.6 (286720/284160), FastEthernet0/0 ------primary
>>> path
>>> via 155.1.13.3 (2195456/281600), Serial1/1 ------- Backup
>>> path
>>> here u see I have two paths to reach 155.1.37.0 so now decision on FD I'm
>>> get lowest FD ( 286720) from 155.1.146.6 so this my primary path.
>>> On this point every thing is OK I calculate my AD ( 281600) the result
>>> is
>>> same.But when I try to calculate my FD on router 1 my mind stuck.AS I
>>> know
>>> for FD first we take our AD , second we take our distance ( R1 to R6)
>>> then
>>> plus both and we get our FD.But its not work.
>>>
>>> On R1 MY FD is 286720 for calculate my distance to R6
>>>
>>>
>>> Rack1R1#sh interfaces fastEthernet 0/0
>>>
>>> BW 100000 Kbit, DLY 100 usec,
>>>
>>> 10^7/BW + DELAY x 256
>>>
>>> 10^7= 10000000
>>> 10000000/100000 = 100 + 10 = 110 X 256 = 28160 R1 distane to R6
>>>
>>> Now 28160 + 284160 = 312320 but as u see in topology table FD is 286720
>>> .................
>>> So how can I calculate my FD ?
>>>
>>>
>>> your suggestion is really helpful to me.
>>>
>>> Regards,
>>> Thanks.
>>>
>>>
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