How to determine the actual BW on a WAN Link

Unanswered Question
Oct 2nd, 2008

with out contacting the ISP is there any way to know the actual BW on a LINK

if I do a SH INT SERIAL it may show me the BW that may not be the true BW ?

I have this problem too.
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tcordier Thu, 10/02/2008 - 08:35

There is no way to determine from the router the amount of bandwidth your provider has actually provisioned to you.

The bandwidth statement is a configurable amount which does not reflect the actual bandwith, and this is what you see in the output of the "sh int serial".

Ethernet interfaces determine the bandwith from auto-negotiation (unless set to a fixed speed), but even this amount does not need to be the actual bandwidth provisioned. Your Ethernet provider could provision only 20MB while your interface shows still 100MB bandwidth.

The only way to determine the actual bandwidth is to fill the link with traffic and monitor the amount of interface utilization. For this exercise select traffic types which are not affected by latency or packet loss (e.g. UDP). By approximation, you can use various speedtests available on the Internet (e.g.

HTH Thomas

jonathanbarrett1976 Thu, 10/02/2008 - 08:46

What about P2P connections? Is there a way to go from router to router to measure Bandwidth and Throughput?

tcordier Mon, 10/06/2008 - 22:57

From my experience you can verify very little about BW and throughput on the router itself.

Essentially you can only issue ICMP packets (ping) and check the interface utilization

and drops. But this is a very crude measure, and Cisco only allows 18K byte ICMP

packets which allows to test a 128K line at best. The idea is that a router is just that and not a network management device.

If you want to check available bandwidth, the only means is to generate traffic

(using a traffic generator or applications such as ftp) and check the interface

utilization you can reach by either checking on the router or using a network

management tool which collects the data from the interface.

HTH, Thomas

satish_zanjurne Tue, 10/07/2008 - 00:29

Search for the utility "iperf" & "jperf"

Easy to run, GUI is Jperf, it uses iperf in background.

HTH..rate if helpful..

jay77jay77 Tue, 10/07/2008 - 02:22

i have seen in 7200VXR model, can list out clock rate under the "sh controllers serial" command.

Probably cisco can import such codes in ISR routers too!


tcordier Tue, 10/07/2008 - 04:44

The clock rate is a configurable setting. More generally, controller information will give you at best information on the bitrate at which you can send traffic. The available end-to-end bandwidth however can still be limited by provider equipment down the line, or the simple fact that your traffic enters a shared network with contention (this is also the case for point-to-point links). Information on the bandwithh you really can use end-to-end needs network utilization measurements, using tools as suggested in one of the earlier posts.

Regards, Thomas


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