10 GB Interface RCV Discards

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Jun 4th, 2008
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I'm interested in what might cause RCV Discards on 10GB interfaces.

I'm speculating it may be related to buffer settings on the switch, but I'm looking into any and all possibilities to consider.

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Ryan Carretta Wed, 06/04/2008 - 22:34
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Can you get a 'show interface ' for the tengig intf you are talking about?

Discards can be because of buffer settings as you mentioned...this would have a lot to do with the traffic flow in your box. For example, if you have a steady stream of 9G in one port and out a 10G port, and then you burst some traffic in this interface, I would expect to see some discards. What will happen is the port-asic on the egress line card in this case may attempt to flow-control the ingress port asic over the fabric, which will cause it to buffer traffic until its buffers are full, at which point it will have no choice but to discard packets.

Ryan Carretta Thu, 06/05/2008 - 00:17
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What model of line card? There are plenty of 8 and 16 port modules. =)

Ryan Carretta Thu, 06/05/2008 - 00:20
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That was a dumb question. If you are doing 10gig they have to be either 6708 or 6716. Both of those cards are oversubscribed on the fabric. Each fabric channel supports half the ports on the line cards and is a 20gig pipe.

Ryan Carretta Thu, 06/05/2008 - 00:24
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You would potentially see lots of input drops, and possibly buffer overruns as shown by show interfaces. You might also want to look at the transmitting side to see if there are output drops there.

jrabener Thu, 06/05/2008 - 06:18
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Thanks for the replies. Here are more details.

WS-C6513 (R7000) processor (revision 1.0) with 458720K/65536K bytes of memory

CEF720 4 port 10-Gigabit Ethernet WS-X6704-10GE

TenGigabitEthernet11/4 is up

Input queue: 0/75/857/857 (size/max/drops/flushes); Total output drops: 0

AVG Transmit bps =20mbps Peaks to 40mbps

AVG Receive bps = 10mbps Peaks to 50mbps

Utilization on the 4 tengig ports remains well under 10%.


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