Quick EIGRP Question

[Abdullah Net]

Hello there,

R5(config)#do show ip eigrp topology

IP-EIGRP Topology Table for AS(1)/ID(20.0.0.1)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,

       r - reply Status, s - sia Status

P 10.0.0.0/29, 1 successors, FD is 307200

        via 20.0.0.1 (307200/281600), FastEthernet0/1

P 20.0.0.0/29, 1 successors, FD is 281600

        via Connected, FastEthernet0/1

P 192.168.50.1/32, 1 successors, FD is 128256

        via Connected, Loopback50

P 192.168.30.1/32, 1 successors, FD is 409600

        via 20.0.0.1 (409600/128256), FastEthernet0/1

P 192.168.20.1/32, 1 successors, FD is 435200

        via 20.0.0.1 (435200/409600), FastEthernet0/1

R5(config)#

from where did FD values of 307200, first line, and 435200, last line, came from?

How did the router calculated those values?

Thanks in advance,

Abdy,

[Sandeep Choudhary]

HI Abdullah,

Yes. There is a calculation. It is a bit complex and convoluted. A lot of the values have to be calculated prior to them being fed through the calculation. For example, delay is in 10's of microseconds. More about the calculation can be found at the link below.

http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094cb7.shtml#eigrpmetrics

Regards

Dont forget to rate helpful posts.

[Peter Paluch]

Hi Sandeep,

I seem to be invading your posts Sorry, it is not intentional - it's just we both answer at the same time.

Best regards,

Peter

[Peter Paluch]

Hi Abdullah,

The highlighted values are not FD values; they just match the FD value in the line above (FD is ...). Values you have highlighted are total distances (sometimes called Computed Distances) to the particular network through the particular neighbor. They have been computed using the distance the particular neighbor reported (the value after the slash sign), plus the metric of the interface between this router and the particular neighbor. We would need to see a more detailed output from the show ip eigrp topology to actually see the metric components that were used to compute the resulting metric.

The FD is a concept deserving special mention: it is the lowest known distance to a particular network since the last time the network went from Active to Passive state. It is not the current distance to the destination, it just may match it if the current distance is lowest since the Active/Passive transition. Most textbooks say that the FD is the current distance; this is wrong.

Best regards,

Peter

[Sandeep Choudhary]

Hi Peter,

I can understand

It also happens with me and I am also learning form your posts.YOU are the champ.

Regards