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New Member

Calculating percent of collisions for switch catalyst 5000

Hi all.

We need to calculate the percent of collisions in a catalyst 5000 switch port.

We've being studying a very interesting cisco document, 'Troubleshooting Cisco Catalyst Switches to Network Interface Card (NIC) Compatibility Issues', at At 'Understanding Data Link Errors' we can read 'a 1 percent ratio of errors to total traffic is acceptable for half duplex connections. If the ratio ... is greater than two...performance degradation may be noticed'. After that there is a description for the output of commands 'sh mac' and 'sh port', useful for troubleshooting. But what are the output items we have to take for making the collisions calculation?

Thanks in advance.

Jose Luis De Diego.


Re: Calculating percent of collisions for switch catalyst 5000

Here is an answer right off one of cisco Q&A forums .

How Do I Determine Collision Percentage?

Question: How do I determine collision percentage?


Divide the number of packets output by the number of collisions

on the show int command.

That will only tell you the collision rate as seen by that interface alone.

To get the collision rate of the actual wire, you should get an analyzer on

the wire.

If your next question is "What is an acceptable collision rate?"... there isn''t

a single answer to that. It depends on how much delay traffic can bear due

to having to retransmit so much and how expensive it is if the source of those

packets is over a serial link.

A very general rule of thumb is that collisions may be okay up to around 20%

of traffic. The collision rate at that point starts to geometrically grow due

to more retransmissions, causing more collisions.

New Member

Re: Calculating percent of collisions for switch catalyst 5000

Hi Glen.

First of all thanks for your reply.

The matter is that the 'sh int' does not give that output info, but this one:

Catalyst5000# (enable) sh int

sl0: flags=51

slip dest

sc0: flags=63

vlan 12 inet netmask broadcast

I suppose it's because that's for IOS CLI, and not for CatOS which is our CLI.

Do you know the command for calculating that with CatOS?

Thanks again in advance.

New Member

Re: Calculating percent of collisions for switch catalyst 5000

You might want to try the following command on every port of interest.



missw04> (enable) sh counters 8/1

0 rxUnicastPacketCount = 299734514

1 txUnicastPacketCount = 303820221

2 rxMulticastPacketCount = 163288

3 txMulticastPacketCount = 4262129

4 rxBroadcastPacketCount = 1101597

5 txBroadcastPacketCount = 3063148

6 rxByteCount = 65940549643

7 txByteCount = 54706955393

8 pkts64 = 228273

9 pkts65to127 = 135390514

10 pkts128to255 = 443984595

11 pkts256to511 = 4892573

12 pkts512to1023 = 3984201

13 pkts1024to1522 = 23664741

14 rxNoPacketBufferCount = 0

15 rxCRCAlignErrorPacketCount = 0

16 rxUndersizedPacketCount = 0

17 rxOversizedPacketCount = 0

18 rxFragmentPacketCount = 0

19 rxJabberPacketCount = 0

20 pauseControlFramesRx = 0

21 pauseControlFramesTx = 0

22 unsupportedOpcodesRx = 0

23 txQueueNotAvailable = 0

24 totalCollisionCount = 0

25 lateCollisionCount = 0

26 singleCollisionFrames = 0

27 multipleCollisionFrames = 0

28 excessiveCollisionFrames = 0

29 deferredTransmissions = 0

30 carrierSenseErrors = 0

31 falseCarrierDuringIdle = 0

32 symbolErrorDuringCarrier = 0

33 sequenceErrorDuringCarrier = 0

missw04> (enable)

New Member

Re: Calculating percent of collisions for switch catalyst 5000

Thanks a lot Neil.

Amazing amount of info from that command! Very useful.

Bye and regards.

José Luis.