Simulating bandwidth tools?

Simulating bandwidth tools?

Post by Bria » Thu, 10 Jul 2003 07:35:14



Hello,

I have been searching Google for a while, and I think I'm just not
searching for the right thing.

I am having some problems with our network, but not all the time.  I am
seeing some packet loss when there is a lot of network traffic
(sustained 5-7Mb/s), but not so much when it's lower.  The problem seems
very transient, so I am look for tools to help me figure out what's wrong.

The main thing I was hoping to find is a bandwidth simulator, something
I can say "push X Mb/s", with the goal of gettings a reliable packet
loss number.

What brought this up is we have MRTG running, and when the server is
pushing 6Mb/s, MRTG is reporting ~8Mb/s.  We think it's due to packet
loss, but it is very hard to pin down.

Any suggestions would be appreciated.

- Brian

 
 
 

Simulating bandwidth tools?

Post by Hansang Ba » Thu, 10 Jul 2003 13:15:49




Quote:> Hello,

> I have been searching Google for a while, and I think I'm just not
> searching for the right thing.

> I am having some problems with our network, but not all the time.  I am
> seeing some packet loss when there is a lot of network traffic
> (sustained 5-7Mb/s), but not so much when it's lower.  The problem seems
> very transient, so I am look for tools to help me figure out what's wrong.

> The main thing I was hoping to find is a bandwidth simulator, something
> I can say "push X Mb/s", with the goal of gettings a reliable packet
> loss number.

> What brought this up is we have MRTG running, and when the server is
> pushing 6Mb/s, MRTG is reporting ~8Mb/s.  We think it's due to packet
> loss, but it is very hard to pin down.

> Any suggestions would be appreciated.

IF you want to simulate bandwidth and packet loss, search for NISTNet.

If you want to generate packets, you'll have to look elsewhere (like
smartbits, exia (sp?) etc.)

--

hsb

"Somehow I imagined this experience would be more rewarding"  Calvin
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Simulating bandwidth tools?

Post by Paul Tich » Thu, 10 Jul 2003 15:22:31


It is unlikely the difference is due to lost packets,
particularly as you do not complain of the performance.

It is likely that the difference is due to the server
and MRTG measuring throughput at different layers. The
server is likely measuring application layer performance,
and MRTG is likely including protocol and link layer
overhead (using a simple metric such as SNMP octets-out)
that the server does not count.

If you want to generate traffic, protocol analyzers can
usually do this and have fine granularity (protocols,
bandwidth, etc.)

If you want to verify you are not really seeing packet
loss, and want a benchmark throughput program for your
server, look at IPerf.

http://dast.nlanr.net/Projects/Iperf/

------------------------

  Subject: Simulating bandwidth tools?
  Date: Tue, 08 Jul 2003 22:35:14 GMT


Hello,

I have been searching Google for a while, and I think I'm just not
searching for the right thing.

I am having some problems with our network, but not all the time.  I am
seeing some packet loss when there is a lot of network traffic
(sustained 5-7Mb/s), but not so much when it's lower.  The problem seems
very transient, so I am look for tools to help me figure out what's wrong.

The main thing I was hoping to find is a bandwidth simulator, something
I can say "push X Mb/s", with the goal of gettings a reliable packet
loss number.

What brought this up is we have MRTG running, and when the server is
pushing 6Mb/s, MRTG is reporting ~8Mb/s.  We think it's due to packet
loss, but it is very hard to pin down.

Any suggestions would be appreciated.

- Brian

 
 
 

Simulating bandwidth tools?

Post by Stuart Robins » Thu, 10 Jul 2003 17:09:00


Quote:> What brought this up is we have MRTG running, and when the server is
> pushing 6Mb/s, MRTG is reporting ~8Mb/s.  We think it's due to packet
> loss, but it is very hard to pin down.

I would initially doubt the measurements.

Even a fraction of a percent of packet loss is going to cause significant
delays since (unlike with collided packets) the lost packets are detected
by the protocols in use and retransmission may not occur until 10s or 100s
of milli seconds later.

If the packet loss were really 33% network performance is going to be very
Sloooooooooooooooooooooooooooooow.

Yours is one of the dilemmas of using network monitors, you need to be
able to trust the information it provides and understand why in some
circumstances it might be wrong.

Stuart.

 
 
 

Simulating bandwidth tools?

Post by mat » Thu, 10 Jul 2003 17:21:13



> Hello,

> I have been searching Google for a while, and I think I'm just not
> searching for the right thing.

> I am having some problems with our network, but not all the time.  I am
> seeing some packet loss when there is a lot of network traffic
> (sustained 5-7Mb/s), but not so much when it's lower.  The problem seems
> very transient, so I am look for tools to help me figure out what's wrong.

> The main thing I was hoping to find is a bandwidth simulator, something
> I can say "push X Mb/s", with the goal of gettings a reliable packet
> loss number.

> What brought this up is we have MRTG running, and when the server is
> pushing 6Mb/s, MRTG is reporting ~8Mb/s.  We think it's due to packet
> loss, but it is very hard to pin down.

> Any suggestions would be appreciated.

> - Brian

Have a look at Iperf http://dast.nlanr.net/Projects/Iperf/
and Qcheck by Netiq http://www.netiq.com/qcheck/default.asp

Iperf is a tool to measure maximum TCP bandwidth, allowing the tuning
of various parameters and UDP characteristics. Iperf reports
bandwidth, delay jitter, datagram loss.

Qcheck, the new network troubleshooting utility from NetIQ, slices,
dices, and checks network response time, throughput, and streaming
performance.

Hope this will help ,

Matthias

 
 
 

Simulating bandwidth tools?

Post by Matthew Salkel » Sat, 19 Jul 2003 20:18:09


Go to www.spirentcom.com. They have both the SmartBits and Adtech test
units. On the SmartBits side they have a application called SmartFlow that
will assist you in your needs.


Quote:> Hello,

> I have been searching Google for a while, and I think I'm just not
> searching for the right thing.

> I am having some problems with our network, but not all the time.  I am
> seeing some packet loss when there is a lot of network traffic
> (sustained 5-7Mb/s), but not so much when it's lower.  The problem seems
> very transient, so I am look for tools to help me figure out what's wrong.

> The main thing I was hoping to find is a bandwidth simulator, something
> I can say "push X Mb/s", with the goal of gettings a reliable packet
> loss number.

> What brought this up is we have MRTG running, and when the server is
> pushing 6Mb/s, MRTG is reporting ~8Mb/s.  We think it's due to packet
> loss, but it is very hard to pin down.

> Any suggestions would be appreciated.

> - Brian

 
 
 

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