High and Low Buffer Ports

Hi All,

I have a basic question on understanding on how buffer works in the Cisco devices.

- When does the Packets go into the Buffer? Which means there is some packets that is going to come to the port and been send out without even going to the Buffer space?

- Is port buffer and the input/output queue the same?

- in what scenario does a normal buffer port gets full and how does a high buffer port help. Lets say if we have 1 gig port, it should be able to throughput 1 gig of data right, it should not have any buffern overruns in the port.

- When does a buffer overrun happens and how do we prevent it?

Would be great if you all can share some knowledge on understanding the buffers. Because we have a client who is very concerned on the buffer overruns they are seeing on there 1gig ports on the 6509 switches.

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Buffers are physical memory used by the switch to carry different size packets. If a switch is extremely busy, you can get buffer overflows. Input and output queues are on each interface. These house the data until it can be transmitted across the backbone of the switch. These are not the same as buffers.

 You can fix buffer overflows by increasing the buffer space for the appropriate buffer.

buffers small min-free 125
This sets  the buffer count for small buffers to the minimum being free set at 125.

buffers small permanent 200
This sets the maximum buffers to 200.
By using the command "show buffers" on the switch, you can figure out where you're having problems and increase the buffer that is having problems. Keep in mind not to set it very high to start and work your way up. If you set it too high, you can crash the switch because the memory is used up buffering packets.

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kamalgopiAuthor Commented:
Thanks a lot. Your solutions pointed me to the right direction.
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