gigabit interface pause output

Unanswered Question
Jul 2nd, 2008

Hi,

We have a 6500 box and I'm seeing my pause output counter increment. Does that mean that the device connected to the port can't keep up with the data that it is receiving or that the port can't keep up with the data coming from the device that is connected? Can somebody please send me a link explaining what pause output counter is. THANKS!

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javickas1 Wed, 07/02/2008 - 08:14

Here's some data on pause.

It is a method of flow control which opperates at the MAC layer. Be aware there is a danger if using pause and TCP that the two methods of flow control running simultaneously can cause problems.

If a buffer on a Gigabit Ethernet port runs out of space, the port transmits a special packet that requests remote ports to delay sending packets for a period of time. This special packet is called a pause frame.

All Catalyst Gigabit Ethernet ports can receive and process pause frames from other devices. However, not all Catalyst Gigabit Ethernet ports can transmit pause frames to other devices.

802.3 Annex 31B

Method of temporarily stopping communication

The overwhelmed network element will send a PAUSE frame, which halts the transmission of the sender for a specified period of time.

PAUSE frames permit one end station to temporarily stop all traffic from the other end station

Works with full duplex only

PAUSE frame specifies how long pause should be expressed in units of 512 bit times

If an additional PAUSE frame arrives before the current PAUSE time has expired, its parameter replaces the current PAUSE time, so a PAUSE frame with parameter zero allows traffic to resume immediately.

New MAC control frame for the purpose of per priority or class based PAUSE

Used to control immediate link partner, not the connection partner

Support of PAUSE is optional

Destination Address 01-80-C2-00-00-01

CBFC class based flow control

It is valid to only support half the protocol (just send, or just receive PAUSE)

TX send and RX receive PAUSE parameters are negotiated separately

Other ends PAUSE capabilities negotiated with speed and duplex

Pause does not prioritize which protocols to refuse, it pauses ALL traffic

All Cisco Catalyst GbE ports can receive and process pause frames but not all can transmit them

Can cause head-of-line blocking, which messes with TCP flow control

Some Cisco switches are even permanently configured to receive pause frames but never emit them.

Endwigast Wed, 07/02/2008 - 08:34

Hi,

Thanks for the reply. If I understood your reply correctly a pause output counter incrementing means that the gigabit port can't keep up with the device? Is that correct? Can you give me the link where you got that? THANKS

Endwigast Wed, 07/02/2008 - 08:34

Hi,

Thanks for the reply. If I understood your reply correctly a pause output counter incrementing means that the gigabit port can't keep up with the device? Is that correct? Can you give me the link where you got that? THANKS

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