Interphase speed on X9124 module (FMS vs "show interphase")?

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Nov 21st, 2009
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We have MDS9509/9513 with X9124 modules with 4Gb ports.

We do notice that FMS reports a fix 400MB (shareable ofcource) for an interface speed, where as the "show interface" command shows the speed of the interface as 4Gbps (which translates to 512MB).

Which of this two is correct? Please find below an extract from the command line and FMS. The FMS shows the "I/F Speed" as "400.00MB", but the "Peak Tx/sec" is peaked to "416.419MB". The CLI shows the speed of the interface as "4 Gbps" which translates to 516MB.

fc10/8 is up

    Hardware is Fibre Channel, SFP is short wave laser w/o OFC (SN)

    Port WWN is 22:48:00:0d:ec:3c:2f:80

    Admin port mode is FX

    snmp link state traps are enabled

    Port mode is F, FCID is 0x680031

    Port vsan is 10

    Speed is 4 Gbps




I/F Speed

Avg. Rx/sec

Avg. Tx/sec


Peak Rx/sec

Peak Tx/sec



Last Updated











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pavanksharma Tue, 11/24/2009 - 06:51
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Anyone has an idea as to which of the two Interface speeds are correct the 400MB (as shown by FMS) or 512MB (4Gbps as shown in the CLI)?

stephen2615 Tue, 11/24/2009 - 23:42
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Thats a really interesting thing when you consider it. However, the maths just doesn't add up as 4000/8 = 500.

Many years ago I thought I saw a 2 Gpbs port recording over 200 MB/Sec and someone from Cisco said it must have been an error in the program that measured the throughput.  That makes you wonder about DWDM links that are 10 Gpbs normally devided into 4 links that say they are 2.5 Gpbs but the speed is only 2 Gpbs.  Same goes for some of the hardware cards I see that say 2.5 Gpbs.

I have never seen anything that pushes the 4 Gpbs performance.  The servers and the storage arrays just can't seem to do it so I can't comment on what you can expect.

What annoys me is that you can't cut and paste in this editing thing. I liked the old system..

iwallis Fri, 12/04/2009 - 12:41
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FC uses 10/8 bit convertion.  So the math is different than ethernet.  4000/10=400. 

pavanksharma Tue, 12/08/2009 - 14:42
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I am thinking that it uses 8 bit conversion on the CLI. From the output below the bits when divided by 8 gives the bytes as shown.

Now if you further divide the bytes by 1024 it is little over 400MB (400.19MB)


Unlike FMS, CLI claims the port speed to 4Gbps, if its base 2 and bit rate 8, then this figure 400.19MB is well under 512MBps. But, if it is base 10 and bit rate 10 then it is well over the max speed of 400MB, which is what seen in FMS.

I have opened ticket with Cisco and hoping to get some explanation on this. Let me know if you interpret differently.

chor1a# show interface  fc5/8

fc5/8 is up

     Hardware is Fibre Channel, SFP is short  wave laser w/o OFC (SN)

     Port WWN is  21:08:00:0d:ec:3c:2f:80

     Admin port mode is  FX

     snmp link state traps are  enabled

     Port mode is F, FCID is  0x6a0015

     Port vsan is  12

     Speed is 4  Gbps

     Rate mode is  shared

     Transmit B2B Credit is  31

     Receive B2B Credit is  16

     Receive data field Size is  2112

     Beacon is turned  off

     5 minutes input rate 30947672 bits/sec,  3868459 bytes/sec, 5337 frames/sec

     5 minutes output rate 3357059368 bits/sec, 419632421 bytes/sec,  204055 frame

Michael Brown Wed, 12/16/2009 - 09:31
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I believe that with Fibre Channel the design is to provide 400MB of user bandwidth over a 4 gig link.  Once you add in the headers and other FC control data, the raw though put would need to be a bit higher.  400.19 MB sounds about right.  Any bit or byte rate that is displayed on the CLI or FM should all be based on an 8 bit byte.  You would need to interogate the raw asic counters on the line card MAC (media access control) chips to see any form of throughput using the 10 bit conversion.



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