[smokeping-users] Less smoke.

[Josh Luthman]

I want to say thank you very much for publishing this!  This is really
good information.

I do also want to comment that with the ARP cache populating and all
that noise on the first ping, I personally would like to have that in
my data.  This way I can judge if ARP is being way too slow upon new
connections.  Just personal preference at this point.

I do have to give you my compliments, though.  Great job!

On Fri, May 23, 2008 at 2:29 PM, Tobias Oetiker <tobi at oetiker.ch> wrote:
> Hi Ged,
>
> cool stuff ... thanks for the patch
>
> tobi
> Today G.W. Haywood wrote:
>
>> Hi there,
>>
>> It's very common for the RTT of the first ping in a series to be much
>> greater than those subsequent.  This is easily explained because there
>> may be much more work for the routers etc. along the way to do for the
>> first packet, they have to populate ARP caches for example.
>>
>> However this can give very misleading statistics in some cases.  I've
>> modified my copy of FPing.pm to send one more ping than requested, and
>> then to discard the first returned RTT value.
>>
>> 8<----------------------------------------------------------------------
>> *** FPing.pm.original 2008-05-23 15:02:39.000000000 +0100
>> --- FPing.pm  2008-05-23 15:08:15.000000000 +0100
>> ***************
>> *** 32,37 ****
>> --- 32,40 ----
>>
>>   The (optional) B<packetsize> option lets you configure the packetsize for the pings sent.
>>
>> + This version of FPing sends one more ping than requested, and discards
>> + the first RTT value returned as it's likely to be an outlier.
>> +
>>   The FPing manpage has the following to say on this topic:
>>
>>   Number of bytes of ping data to send.  The minimum size (normally 12) allows
>> ***************
>> *** 121,127 ****
>>
>>       my @cmd = (
>>                       $self->binary,
>> !                     '-C', $self->pings, '-q','-B1','-r1',
>>                   @params,
>>                       @{$self->addresses});
>>       $self->do_debug("Executing @cmd");
>> --- 124,130 ----
>>
>>       my @cmd = (
>>                       $self->binary,
>> !                     '-C', ($self->pings)+1, '-q','-B1','-r1',                                               # Add an extra ping
>>                   @params,
>>                       @{$self->addresses});
>>       $self->do_debug("Executing @cmd");
>> ***************
>> *** 134,140 ****
>>           my @times = split /\s+/;
>>           my $ip = shift @times;
>>           next unless ':' eq shift @times; #drop the colon
>> !
>>           @times = map {sprintf "%.10e", $_ / $self->{pingfactor}} sort {$a <=> $b} grep /^\d/, @times;
>>           map { $self->{rtts}{$_} = [@times] } @{$self->{addrlookup}{$ip}} ;
>>       }
>> --- 137,143 ----
>>           my @times = split /\s+/;
>>           my $ip = shift @times;
>>           next unless ':' eq shift @times; #drop the colon
>> !         shift @times;                                                                                       # Junk the first result.
>>           @times = map {sprintf "%.10e", $_ / $self->{pingfactor}} sort {$a <=> $b} grep /^\d/, @times;
>>           map { $self->{rtts}{$_} = [@times] } @{$self->{addrlookup}{$ip}} ;
>>       }
>>
>> 8<----------------------------------------------------------------------
>>
>> In some circumstances, the results can be striking:
>>
>> http://www.jubileegroup.co.uk/JOS/misc/less_smoke.png
>>
>> --
>>
>> 73,
>> Ged.
>>
>> _______________________________________________
>> smokeping-users mailing list
>> smokeping-users at lists.oetiker.ch
>> https://lists.oetiker.ch/cgi-bin/listinfo/smokeping-users
>>
>>
>
> --
> Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten
> http://it.oetiker.ch tobi at oetiker.ch ++41 62 213 9902
>
> _______________________________________________
> smokeping-users mailing list
> smokeping-users at lists.oetiker.ch
> https://lists.oetiker.ch/cgi-bin/listinfo/smokeping-users
>



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Josh Luthman
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