EIGRP FD & AD PROBLEM

From: marish shah (contactmarish@gmail.com)
Date: Tue Mar 10 2009 - 04:25:14 ARST


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

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             |Fa0/0
155.1.37.3
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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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