[PLUG] UDP/ICMP packet loss question on RH

[John Todd]

Thanks, that's actually useful for other applications and I'll store 
that away, but I don't think it does anything for me in this 
particular question - these are very low speed streams - 1kbps or 
less.  I shouldn't be overrunning any buffers here.  Plus, with 
multiple tests, each end station gets the same packet loss to the 
target no matter how many testers there are (I tried with four) which 
leads me to think that this is a per-stream issue.

JT


>I don't know if this is relevant, but we had problems with systems receiving
>heavy (>50Mbit/sec) multicast (i.e. UDP) streams. Problem solved by increasing
>the following buffer size(s) [Thanks, Galen!]
>
># ----------------------------------------------------------------------
># SVS-3500
># -- UDP working buffer sized to accept heavy incoming multicast
># streams without discarding packets
>net.core.rmem_default = 524288
>net.core.rmem_max = 524288
>
>(The above lines were added to /etc/sysctl.conf on RedHat 7.3 systems.)
>
>- Don
>
>
>Stafford A. Rau wrote:
>
>>* John Todd <jtodd at loligo.com> [030723 01:08]:
>>
>>>Now, I have been unable to answer my first question about VoIP 
>>>badness (which I think may be software related elsewhere) but my 
>>>investigation makes me wonder why something is dropping these 
>>>packets, either inbound UDP or outbound ICMP.  No other OS I 
>>>tested against showed the same symptoms.  Is this some kind of 
>>>rate-limiting feature in Linux?  I know that IOS will not process 
>>>more than a certain %age of packets that are ICMP outbound from 
>>>the router itself; perhaps someone thought that was a good idea to 
>>>include in the Linux TCP/IP stack.
>>>   
>>>
>>
>>I haven't found any answer in just a minute or two of Googling, but I do
>>seem to recall that FreeBSD by default does some kind of rate limiting
>>on icmp packets. Perhaps certain Linux kernels do as well?
>>
>>I would suspect you're seeing missed icmp ttl expired messages, rather
>>than missing udp source packets.
>>
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