Sep 22nd, 2008

Hi All,

Trying to load share on two paths to a destination from a router on a serial and fast ethernet interfaces.

both interfaces have minimun bandwidth of 1544Kbp/s and 25100 microsecond of total delay, hence the metric becomes 2300416.

Now i want the serial interface to carry twice as much load as the fast ethernet interface.

To achieve this the author says,

OLD METRIC: 2,300,416 = (6476 + 2510)

NEW METRIC :4,600,832 = 256(6476 + 510 + X).

Following this equation,to find the new delay = 6476 (old min bandwidth + 510 "the sum of the delay without the delay on the serial interface" and this is exactly what i have problem with and will appreciate a thorough explanations of how that is achieved, knowing well that EIGRP uses 50% of interface bandwidth by default, why is that 510 not halve the 1544?.

Thank you all

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Replies

Giuseppe Larosa Mon, 09/22/2008 - 04:32
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Hello New,

actually EIGRP metric is :

256 * [ (sum of delays in 10s of microsec) + 10^7/min_BW_in_path in kbps ]

the BW contribute is actually the first number 6476 : 10^7/1544 = 6476,684 so the 510 +x is a delay contribute.

you need to configure this X delay on the last preferred interface in your case the FE.

second note:

when is said that EIGRP uses half of bandwidth is not meant for metric calculation is referred to how bandwidth is used by EIGRP for sending its own packets including hello, queries, and so on.

EIGRP "shapes" its own traffic to 50% of bandwidth

Hope to help

Giuseppe

newnetman Mon, 09/22/2008 - 05:26

Hello Sir,

I'm most grateful for your prompt response. To further clarify my main area that is unclear, could you please demonstrate in your calculation how 510 was achieved?.

"the BW contribute is actually the first number 6476 : 10^7/1544 = 6476,684 so the 510 +x is a delay contribute."

Giuseppe Larosa Mon, 09/22/2008 - 08:32
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Hello New,

look at all the path to the destination prefix.

510 is here for 5100 microseconds. this is the meaning of

examples of delay:

1000 microseconds = default delay on FE / eth interface.

5000 microseconds : typical delay of a loopback interface

I don't know how the 5100 microseconds comes in your network but the 6476 comes from the BW part of the metric as I explained in the previuos post.

Hope to help

Giuseppe