[c-nsp] 7500 queue question

[Rik Koenig]

Hello all,

 

Last week we were playing around with output queue depths and packet loss.
Running a 7507 with RSP4, and VIP2-50 (128/8), and PA-FE-TX and PA-4E. Using
the 100Mb Ethernet as input and the 10Mb as output. CEF is running, but not
dCEF. 

 

We would burst a given number of 224B frames into the 100Mb port, to exit
the 10Mb port. Given the 40-deep FIFO exit queue, we needed to burst 170
packets before any were dropped! When we dropped the queue down to 5 or 1,
we needed 40 or so. 

 

Now, to my thinking, if a 100Mb link is receiving 41 packets, a 10Mb link
that reports it can hold 40 packets should back up and tail-drop. But this
didn't happen. What am I missing?

 

Thanks,

~Rik