EIGRP calculation

[Andy White]

Hello,

When calculating the Feasibility Distance between 2 routers how do I get the delay value, obviously I know the bandwidth as I can get this from the interface on router config, but I need the delay value so I can complete the FS calculation?

Many thanks

[Giuseppe Larosa]

Hello Andy,

you need to sum all delays of all interfaces on the path (counted only one side per link in the direction to the network ) and to divide by ten.

The result needs to be multiplied by 256

256 * (sum of delays [tens of microseconds]) + 256 * 10000000 /BW*

BW* = min BW on path [ kbps]

sh interface provides you delay in microseconds, EIGRP formula uses tens of microseconds

example:

sh int f0/0

FastEthernet0/0 is up, line protocol is up

  Hardware is AmdFE, address is 0012.8056.ec00 (bia 0012.8056.ec00)

  Description: link XXXX

  Internet address is x.y.128.218/30

  MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec, => 10 tens of microseconds

     reliability 255/255, txload 1/255, rxload 1/255

  Encapsulation ARPA, loopback not set

  Keepalive set (10 sec)

the bandwidth to be considered is the lowest on the path, not necessarily the bandwidth of the last interface

Hope to help

Giuseppe

[Andy White]

Thanks,

Between 2 routers the FD is [90/21024000] and both interfaces look like this (R1 to R2's WAN serial interfaces):

R1:

Serial0/1/0 is up, line protocol is up (connected)
  Hardware is HD64570
  Internet address is 200.0.0.2/30
  MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,

R2:

Serial0/1/0 is up, line protocol is up (connected)
  Hardware is HD64570
  Internet address is 200.0.0.1/30
  MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,

How do they get to the FD of 21024000?  I tried use the foumla but I get no where near this?

[Andy White]

Ah got it:

I did:

10^7/128 = 78125

(20000 + 20000)/10=4000

78125 = 4000 = 82125

82125 x 256 = 21024000

[Andy White]

How is the DLY calculated on an interface?  Is it a default value based on it's speed?

Thanks

[Giuseppe Larosa]

Hello Andy,

>> How is the DLY calculated on an interface?  Is it a default value based on it's speed?

yes it is an administrative parameter you can change it using delay command in interface mode

it does not mean it is the effective delay on the interface it is an administrative parameter

Hope to help

Giuseppe

[Andy White]

Thanks, so is there a table that shows these default delay values?