Re: Cat6500 oversubscription

Hi Antonio,

I ran into this earlier this year. You should see drops on all the ports
within an asic. Eight ports at a time will show drops. You'll notice a
pattern with the ports that are dropping traffic vs the ports that are not.

Try something like sh int | in drops to quickly identify a pattern and check
all the ports for a few days.

The switching module has 48 oversubscribed ports in six groups of eight
ports each:

   -

   Ports 1, 2, 3, 4, 5, 6, 7, 8
   -

   Ports 9, 10, 11, 12, 13, 14, 15, 16
   -

   Ports 17, 18, 19, 20, 21, 22, 23, 24
   -

   Ports 25, 26, 27, 28, 29, 30, 31, 32
   -

   Ports 33, 34, 35, 36, 37, 38, 39, 40
   -

   Ports 41, 42, 43, 44, 45, 46, 47, 48

The eight ports within each group use common circuitry that effectively
multiplexes the group into a single, nonblocking, full-duplex Gigabit
Ethernet connection to the internal switch fabric. For each group of eight
ports, the frames that are received are buffered and sent to the common
Gigabit Ethernet link to the internal switch fabric. If the amount of data
received for a port begins to exceed buffer capacity, flow control sends
pause frames to the remote port to temporarily stop traffic and prevent
frame loss.

If the frames received on any group exceeds the bandwidth of 1 Gbps, the
device starts to drop the frames. These drops are not obvious as they are
dropped at the internal ASIC rather than the actual interfaces. This can
lead to slow throughput of packets across the device

If more throughput is required, either use ports from a line module that
does not use oversubscription, or use ports from different port-groupings on
oversubscribed line modules. For example, if the line module has 48 ports in
groups of eight, you can select ports 1, 9, 17, 25, 33, and 41 for the same
port channel.
HTH

-- 
Regards,
Peter Kurdziel
CCIE# 25418
On Fri, Sep 17, 2010 at 7:00 AM, Antonio Saez <
antonio.saez.jimenez_at_gmail.com> wrote:
> Hi all,
>
> I am trying to indentify if there are loss of frames due oversubscription
> in
> a 6500 with ws-x6548-ge-tx linecards. I have found some documents talking
> about "overruns" counter, some other talking about "qos3Outlost" counter.
>
> what is the right counter I have to check?
>
>
> Regards
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
Blogs and organic groups at http://www.ccie.net