OC3 cannot reach maximun bandwitdth

Unanswered Question
Apr 13th, 2009

We have a c7206XVR with a npe 400 and a c7609 with sup720. These routers are connected with an OC3 circuit which suppose to has a maximum throughput of 155Mb/s. The 7206 is using a PA-POS-1OC3 and the 7609 is using a PA-POS-2OC3. But for some reason the circuit can only reach maximum of 80mb/s, even when we use a traffic generator to test it. At 80mb/s the 7206xvr cpu has reached around 89%, and the 7609 has just only reached around 15%.

These router both have GigEhternets to connect to their LAN core switches.

We did talk to the telco and they checked and found no issue on the circuit.

Any idea?

Thank you.

I have this problem too.
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Paolo Bevilacqua Mon, 04/13/2009 - 13:55

Is traffic bidirectional ?

What packet size are you using ?

7200 config ?

Beside that, the number seems about right. An NPE-400 is not really a fiber-class routing engine.

benjaminyu Mon, 04/13/2009 - 14:34

I used a generator to send UDP (source port 7 to destination port 7) packets from the 7609 side to 7206xvr side. I used a public domain 'Nsasoft Network Traffic Emulator'. It did not show me what packet size it used. The 7200xvr config is attached.

If NPE400 is not a fiber-class routing engine, how come Cisco said it supports PA-POS-1OC3 oc3 card?

Your insight is highly appreciated.

Attachment: 
Paolo Bevilacqua Mon, 04/13/2009 - 14:41

Packet size is very important.

I see that you have policy routing and ip flow, that should be eliminated for best performances. Also, the router seems loaded with too many interfaces and functionalities to perform optimally on an high speed link. With an NPE-400 engine (now 8 years old), you want it to be almost dedicated to the task.

In cisco world, supporting a given interface, does not necessarily means at wire rate for any packet size.

Joseph W. Doherty Mon, 04/13/2009 - 16:57

The NPE400 is rated at 400 Kpps. For Ethernet, this should support about 269 Mbps @ 64 bytes. Effective bandwidth should increase with larger packets. This is likely why Cisco says it will support a OC3 although perhaps not for all traffic if minimum sized packets.

Routers are loaded down by services and how the services are configured. Things such as ACLs, fancy QoS, syslogging, etc., all add to the load especially for some as the traffic rate increases.

Your mention of the CPU on the NPE400 hitting 89% likely indicates the combination of traffic and configuration is just too much for NPE400 engine.

Futher, since you don't know exactly what's the structure of traffic is being generated by your traffic generator, nor did you mention whether any traffic was being directed to an IP address on the 7200, your simulated traffic might not be fully representive of production traffic performance (and isn't likely to be with UDP port 7).

At worst, you might need a more powerful engine for your 7206. However, for normal production traffic and perhaps with some function off-loading (if possible) and/or performance tuning, your 7206 might deliver acceptable OC3 performance in your situation. (E.g. of performance tuning, activation of compiled ACLs on the 7200.)

benjaminyu Mon, 04/13/2009 - 19:15

The test traffic is not directly targeted the 7206xvr router.

This was what I did for the testing:

The traffic generator was running on a laptop connected to one of the Gigabit interfaces on our 7609 router. The target of the traffic is a gigabit switch connected behind a catalyst 4507 which is connected to the 7206xvr router.

Joseph W. Doherty Tue, 04/14/2009 - 04:13

What you might also try, UDP traffic directed to a non-existant host that's on a network beyond the 7206. Ideally something other than char echo (perhaps port 9 for discard). Port 7, on at least Cisco devices, may be unable to fully load a link due to device performance limitations. Also, char echo, might generate all minimum size packets.

Even better would be another traffic generator, with a host peer, the could generate traffic a little closer to "normal".

I would expect at least some bandwidth improvement. Again, in other words, I doubt UDP port 7 traffic to a network host will accurately simulate obtainable performance for "normal" production traffic.

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