On 10/02/2012 12:03 AM, Eric A Louie wrote:
I'm inheriting a problem that I could use some ideas to troubleshoot.
Speedtesting from within my core to other locations within the core give me
"asymmetrical" performance. I've traced the routes and the path is the same
download and upload, but I'll get very good download speeds (30Mbps) and
terrible upload speeds (3Mbps, 6Mbps)
Good compared to what? You haven't really given us any idea of what kind
of network it is, and what you're expecting - and what that's reasonable.
I've looked at MTU and it doesn't appear that there's a lot of packet
fragmentation/reassembly
There really shouldn't be *any*.
I've looked at total bandwidth utilization during the test times across the
backhaul and I'm not saturating the bandwidth in either direction
I've looked at the interfaces through which the packets are traveling, and there
are no CRC errors, no drops, no retransmissions
The physical layer radio transmissions seem to be good both directions with the
performance testing at that level.
Ugh. Radio.
This kind of problem is super-hard to troubleshoot on any network. My
usual technique is to jump straight to getting a tcpdump of the packets
at ingress to the network, and egress to the machine, and using
wireshark or (preferably) tcptrace to analyse them. If you're getting
slow downloads and have respectable loss and RTT in ping, odds are the
congestion control algorithms think there's a problem.
iperf and such like are your friend in this situation. But you'll need a
known-good machine upstream to source/sink traffic from/to.
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