Solved: EIGRP Metric

Manu Shankar · ‎07-01-2016

R4 and R5 are directly connected routers and EIGRP neighbors. The metric to reach a route in R5 from R4 is bit confusing. Please find the attached topology and details in the attached file. Anybody have idea on this?

As per the calculation, the metric is - 128320

But R5 advertising to R4 is - 128256

Thanks,

Manu

Peter Paluch · ‎07-01-2016

Manu,

Don't forget that Cisco routers do not perform floating point arithmetics. The metric computation is performed in integer arithmetics, stripping the fractional part away. Also, the multiplication by 256 is performed as the last step of the computation.

So, with this in mind, the metric is:

BW_E = 10^7 DIV 8000000 = 1
Delay = 5000 DIV 10 = 500
Metric = (1 + 500) * 256 = 501 * 256 = 128256

Best regards,
Peter

View solution in original post

Manu Shankar · ‎07-01-2016

Ok, I found the answer. If the Loopback0 interface BW is 10000000 Kbit instead of 8000000 Kbit, then the metric - 128256 would be correct. But the Loopback 0 interface BW is showing 8000000 Kbit.

Peter Paluch · ‎07-01-2016

Manu,

Don't forget that Cisco routers do not perform floating point arithmetics. The metric computation is performed in integer arithmetics, stripping the fractional part away. Also, the multiplication by 256 is performed as the last step of the computation.

So, with this in mind, the metric is:

BW_E = 10^7 DIV 8000000 = 1
Delay = 5000 DIV 10 = 500
Metric = (1 + 500) * 256 = 501 * 256 = 128256

Best regards,
Peter

Manu Shankar · ‎07-02-2016

Thank you Peter.