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New Member

WAN link testing: ttcp ?

Hello

I have two remote routers - and i need to test WAN link between them. No access to other devices.

I've tried to use ttcp, but it does not allow to set TOS and i can not test my QOS policies.

Moreover ttcp seems to have so poor throughput, example (on receiver):

router#ttcp

transmit or receive [receive]:

perform tcp half close [n]:

receive buflen [8192]: 65000

bufalign [16384]: 65536

bufoffset [0]:

port [5001]:

sinkmode [y]:

rcvwndsize [4128]: 16384

delayed ACK [y]:

show tcp information at end [n]:

ttcp-r: buflen=65000, align=65536/0, port=5001

rcvwndsize=16384, delayedack=yes  tcp

ttcp-r: accept from x.x.x.x

ttcp-r: 122395000 bytes in 600508 ms (600.508 real seconds) (~198 kB/s) +++

But there should be 10Mbit/s....

Why ttcp has so poor performance ?

Is there any tool on router to test performance ? (extended ping is not enough for >10Mbit/s links)

Thanx

2 ACCEPTED SOLUTIONS

Accepted Solutions

Re: WAN link testing: ttcp ?

yes, sure in CEFswitching on the forwarding path, but TTCP doesn't use CEF, it's a CPU based process which generate packet stream, with CEF it has nothing to do.

Re: WAN link testing: ttcp ?

just to info, on a c7200 NPE-G1 I could reach with TTCP about 30-40 mbits/s but CPU was 100%

multiple ttcp's could be really helpful if CPU load doesn't reach 100%

13 REPLIES

WAN link testing: ttcp ?

don't forget that TTCP uses the routers CPU which is normally quite slow, if your router has some kind of hardware assistance.  You can check the CPU load during the TTCP session to see it.

and  try to activate "ip tcp path-mtu-discovery" on both sides.

New Member

WAN link testing: ttcp ?

I've enabled  "ip tcp path-mtu-discovery" and repeated test.

Receiver is cisco 2821, transmitter is cisco 3825.

Total CPU value was always below 15% on both devices.

Again it was very slow result ~200Kbit/s....

Re: WAN link testing: ttcp ?

try to repeat the test with  a tool  "iperf" on one of servers, if it's possible.

But cisco 2821 can process in CPU only about 6Mbit/s. Have you checked "sh proc cpu history"? did you see any peaks there?

Upd. try to use ttcp with default parameters first.

Hall of Fame Super Gold

Re: WAN link testing: ttcp ?

Konstantin Dunaev wrote:

But cisco 2821 can process in CPU only about 6Mbit/s. Have you checked "sh proc cpu history"? did you see any peaks there?

Incorrect. A 2821 can move 87 Mbit/s when normally configured in CEF switching. Attached reference.

Re: WAN link testing: ttcp ?

yes, sure in CEFswitching on the forwarding path, but TTCP doesn't use CEF, it's a CPU based process which generate packet stream, with CEF it has nothing to do.

New Member

WAN link testing: ttcp ?

You're right, for transit traffic there is no problem. It must have been CPU/control-plane.

Thanx

Hall of Fame Super Gold

WAN link testing: ttcp ?

Notwithstanding, packet sourced or destined for the CPU take a path thar is neither "process switched", or CEF. One cannot assume what is the performance for these packets.

That is also the reason why performance measurements should be done with external tools, not on the router.

Super Bronze

Re: WAN link testing: ttcp ?

Disclaimer

The    Author of this posting offers the information contained within this    posting without consideration and with the reader's understanding that    there's no implied or expressed suitability or fitness for any  purpose.   Information provided is for informational purposes only and  should not   be construed as rendering professional advice of any kind.  Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In    no event shall Author be liable for any damages whatsoever  (including,   without limitation, damages for loss of use, data or  profit) arising  out  of the use or inability to use the posting's  information even if  Author  has been advised of the possibility of such  damage.

Posting

Paolo Bevilacqua wrote:

Notwithstanding, packet sourced or destined for the CPU take a path thar is neither "process switched", or CEF. One cannot assume what is the performance for these packets.

That is also the reason why performance measurements should be done with external tools, not on the router.

Just to extend Paolo's point, Cisco routers and switches are optimized for their primary purpose.  Anything that uses ancillary or host like functions is a performance crapshoot.

New Member

To again further expand on

To again further expand on this issue..:  I did some testing with the embedded FTP client in a Cisco 1921 router.  At about 15 - 20 Mbits/sec the cpu was fully loaded and that was also the limit of the ftp transfer.

Both the line and ftp server capacity was *much* higher.

Edit:

I tested with a "copy ftp null:", so flash writing was not a bottleneck.  As far as i can see, it's purely the router's CPU that's limiting the ftp speed.

Super Bronze

If you're using the FTP

If you're using the FTP client, and copying to/from the router, bandwidth will be restricted both by the time is takes to read/write from the router's flash and the router is not optimized for being a FTP host.

Re: WAN link testing: ttcp ?

Hi,

200kB/s means 1,6Mb/s in fact.

I believe another increasing of the  rcvwndsize might bring you a little better throughput.

But possibly there is still some limit for a single TCP session due to the RTD?

What is the Ping time between those two routers?

Maybe running multiple TTCP sessions (different ports) at the same time could load the line more?

HTH,

Milan

Re: WAN link testing: ttcp ?

just to info, on a c7200 NPE-G1 I could reach with TTCP about 30-40 mbits/s but CPU was 100%

multiple ttcp's could be really helpful if CPU load doesn't reach 100%

Super Bronze

Re: WAN link testing: ttcp ?

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

Is there any tool on router to test performance ? (extended ping is not enough for >10Mbit/s links)

I use a freebie, pcattcp - use the UDP mode - set for continuous - set desired xmit rate.

I've tried to use ttcp, but it does not allow to set TOS and i can not test my QOS policies.

Set an inbound service policy to mark different test flows based on an ACL - for example, I've used different destination ports with the prior mentioned tool.

Why ttcp has so poor performance ?

As other poster mentioned, could be receiver's TCP isn't large enough for BDP.  Other issues include insufficient time allowed for TCP to ramp up, any packets drops, etc.

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