Take the 2-minute tour ×
Server Fault is a question and answer site for system and network administrators. It's 100% free, no registration required.

I'm trying to test UDP multicast throughput via iperf but it seems like it's not sending more than 10Mbit/s from my dev machine:

C:\> iperf -c 224.0.166.111 -u -T 1 -t 100 -i 1 -b 1000000000
------------------------------------------------------------
Client connecting to 224.0.166.111, UDP port 5001
Sending 1470 byte datagrams
Setting multicast TTL to 1
UDP buffer size: 8.00 KByte (default)
------------------------------------------------------------
[156] local 192.168.1.99 port 49693 connected with 224.0.166.111 port 5001
[ ID] Interval       Transfer     Bandwidth
[156]  0.0- 1.0 sec  1.22 MBytes  10.2 Mbits/sec
[156]  1.0- 2.0 sec  1.14 MBytes  9.57 Mbits/sec
[156]  2.0- 3.0 sec  1.14 MBytes  9.55 Mbits/sec
[156]  3.0- 4.0 sec  1.14 MBytes  9.56 Mbits/sec
[156]  4.0- 5.0 sec  1.14 MBytes  9.56 Mbits/sec
[156]  5.0- 6.0 sec  1.15 MBytes  9.62 Mbits/sec
[156]  6.0- 7.0 sec  1.14 MBytes  9.53 Mbits/sec

When I run it on another server, I'm getting ~80Mbit/s which is quite a bit better but still not anywhere near the 1Gbps limits that I should be getting?

C:\> iperf -c 224.0.166.111 -u -T 1 -t 100 -i 1 -b 1000000000
------------------------------------------------------------
Client connecting to 224.0.166.111, UDP port 5001
Sending 1470 byte datagrams
Setting multicast TTL to 1
UDP buffer size: 8.00 KByte (default)
------------------------------------------------------------
[180] local 10.0.101.102 port 51559 connected with 224.0.166.111 port 5001
[ ID] Interval       Transfer     Bandwidth
[180]  0.0- 1.0 sec  8.60 MBytes  72.1 Mbits/sec
[180]  1.0- 2.0 sec  8.73 MBytes  73.2 Mbits/sec
[180]  2.0- 3.0 sec  8.76 MBytes  73.5 Mbits/sec
[180]  3.0- 4.0 sec  9.58 MBytes  80.3 Mbits/sec
[180]  4.0- 5.0 sec  9.95 MBytes  83.4 Mbits/sec
[180]  5.0- 6.0 sec  10.5 MBytes  87.9 Mbits/sec
[180]  6.0- 7.0 sec  10.9 MBytes  91.1 Mbits/sec
[180]  7.0- 8.0 sec  11.2 MBytes  94.0 Mbits/sec

Anybody has any idea why this is not achieving close to link limits (1Gbps)?

Thanks,

Tom

share|improve this question
    
Multicast would be the first place to look, do you get the same limits for unicast TCP testing? –  polynomial Oct 5 '11 at 1:09
2  
Are you connected to a switch that supports pause frames? If so, broadcast and multicast will be limited to the speed of the slowest port. –  David Schwartz Oct 5 '11 at 2:10
    
hm, I do have an IP Phone plugged into the same switch on the same subnet which is probably running at 10MBit - could that be the limiting factor? However, the switch on the server is a Cisco 3750G, fully running at 1Gbit on all links, why wouldn't I manage to achieve more then 10% of link capacity there? –  Tom Frey Oct 5 '11 at 2:36
    
I turned off Flow Control on the NIC of my dev machine and am now getting ~10MBytes/sec, same as on the server. So that definitely helped but is still only 10% of link capacity, any idea why? I tried adjusting the UDP send buffer which didn't seem to have any effect –  Tom Frey Oct 5 '11 at 13:53
2  
are the any multicast or broadcast storm protections enabled on the switch. –  The Unix Janitor Feb 1 '12 at 11:10

1 Answer 1

Check if your switch (your network cards should already support it) is accidentally not set to auto-mdix or if there is fixed value and you got a mismatch. This can cause the problems you describe, I've seen the exact same behaviour in our own network with a mismatch. Sometimes auto-mdix might not work and you should also try setting it to the same value on both sides manually.

http://en.wikipedia.org/wiki/Mdix#MDIX

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.