I've been helping to troubleshoot an interesting problem with variable latency through a 4948. I haven't run into this before. I usually have seen really low latency through 4948s, but this particular application requires consistent low latency and they've been noticing that latency goes up on average as load goes up. It didn't seem to be a problem on their servers, but communication through busy interfaces seemed to dramatically increase the latency. They were used to <1ms latency and it was bouncing up to 20+ ms at times. I'm starting to think this is due to the shared output buffer in the 4948 causing the output buffer on the uplink to dynamically get bigger.
I've been trying to find more details on how the 4948 handles its shared output queue space, but I haven't been able to find anything. Do any of you know more about how this works and what commands I could use to troubleshoot? I can't find anything that might show how much buffer space a particular interface is using at any given time, or if it even makes sense to think of it that way. If I knew the size of the buffer at any given moment, I could calculate the expected latency and prove whether or not that was the problem. Thanks! John _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
