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Does the input/output rate of the interface take into account the Interframe Gap and preamble?

mrisler.ig
Level 1
Level 1

Hi Team,

 

So that is my question. When i run a "show interface Gi x/x", does the below ouput consider the Interframe gap and preamble, or just start counting the bits from the layer 2? 

 

5 minute input rate 47000 bits/sec, 90 packets/sec
  5 minute output rate 44000 bits/sec, 91 packets/sec

 

Thanks for your help! 

3 Replies 3

Peter Paluch
Cisco Employee
Cisco Employee

Hi,

In my best belief, these counters do not count Inter Frame Gap and preambles. If I may ask, what would be the purpose of taking these values into account?

Best regards,
Peter

eter,

 

Thanks very much for your reply! You are correct, it does not count inter frame gap and preamble. I just did a quick test with a JDSU Tester, a cisco switch ( WS-C3560G ) and a hard loop. When i configured CIR of 9.87 Mbps, on my loop i was receiving 10 Mbps of bandwidth ( Line speed Layer 1 ) and 9.87 Mbps of IR ( Layer 2). Then, i checked my interface`s input/output rate and saw the same result:

MIA-SW5#sh int gigabitEthernet 0/14 | i 30
  30 second input rate 9870000 bits/sec, 813 packets/sec
  30 second output rate 9870000 bits/sec, 813 packets/sec  

I was trying to understand the tool iPerf and the bandwidth command on it. I actually think they may refer bandwidth to throughput ( Layer 3), because when i configured 2Mbps with MTU of 1500, i was expecting to see 2 Mbps on my switch`s interface, but i saw 2.15 Mbps aprox. 

I will keep learning on how to use this tool.  

Thanks for your reply! 

 

 

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You might also find, L2 framing overhead isn't counted either.