02-18-2007 06:22 AM - edited 03-03-2019 03:48 PM
Hi expert,
As showed below, the FD(metric) is 5511936 and I try to calculate it by formula and get "10120000" . What's wrong ? why they are different ?
2620#sh ip eigrp topology 172.20.1.4 255.255.255.252
IP-EIGRP (AS 1): Topology entry for 172.20.1.4/30
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 5511936
Routing Descriptor Blocks:
0.0.0.0 (Serial0/0), from Connected, Send flag is 0x0
Composite metric is (5511936/0), Route is Internal
Vector metric:
Minimum bandwidth is 512 Kbit
Total delay is 20000 microseconds
Reliability is 255/255
Load is 1/255
Minimum MTU is 1500
Hop count is 0
FD(Metric) =[10000000 / bw (kbps) + delay(microsec) ] *256
FD(Metric) = [10000000 / 512 + 20000 ] *256
FD(Metric) = 39531.25 * 256 = 10120000
Solved! Go to Solution.
02-18-2007 08:18 AM
The bandwidth term is correct, but remember that the delay value in the formula is expressed in 10s of microseconds. So the correct value is [10000000 / 512 + 2000 ] *256 = 5512000. Pretty close to the value the router calculated.
I've always assumed the slight variation that you get is due to 1kbps=1024 bits rather than 1000 bits, but I don't know if I've ever validated that theory.
Hope this helps,
John Sayer
02-18-2007 09:08 AM
Hello Jsayer,
FD = 256 * ((10000000/512) + (20000/10))
= 256 * (19531.25 + 2000)
= 256 * 21531
= 5511936
Cisco IOS? rounded bandwidth calculation to 19531 so it give's exact mentioned FD.
02-18-2007 08:18 AM
The bandwidth term is correct, but remember that the delay value in the formula is expressed in 10s of microseconds. So the correct value is [10000000 / 512 + 2000 ] *256 = 5512000. Pretty close to the value the router calculated.
I've always assumed the slight variation that you get is due to 1kbps=1024 bits rather than 1000 bits, but I don't know if I've ever validated that theory.
Hope this helps,
John Sayer
02-18-2007 09:08 AM
Hello Jsayer,
FD = 256 * ((10000000/512) + (20000/10))
= 256 * (19531.25 + 2000)
= 256 * 21531
= 5511936
Cisco IOS? rounded bandwidth calculation to 19531 so it give's exact mentioned FD.
02-19-2007 05:00 AM
See...here the calculation shows that you are calculating the advertised distance
but the FD = Advertised Distance + the cost to reach the advertising neighbour
FD(Metric) = [10000000 / 512 + 20000 ] *256
FD(Metric) = 39531.25 * 256 = 10120000
This is not the right way. This should be rather...
10000000/512 + 20000/10*256
this will give u a diatance of 5512000
Regards
Kunal P.
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