[hobbit] strange result in fping by hobbit and fping by yourstruly

[Dennis Ortsen]

The testping tag solved my problem.

Strange however that with that large number of access points I didn't have
the same issue. Perhaps it's just the additional number of IP-addresses that
are not resolvable that made this visible?

Anyway, I now get the correct results, thanks guys.

Br.

Dennis 

> -----Oorspronkelijk bericht-----
> Van: Henrik Stoerner [mailto:henrik at hswn.dk] 
> Verzonden: vrijdag 2 november 2007 18:07
> Aan: hobbit at hswn.dk
> Onderwerp: Re: [hobbit] strange result in fping by hobbit and 
> fping by yourstruly
> 
> On Fri, Nov 02, 2007 at 01:46:44PM +0100, Dennis Ortsen wrote:
> > I only do a conn test on an ip-address. I use the full path 
> to fping 
> > in hobbitserver.cfg, without any extra parameters. When 
> hobbit starts 
> > testing the connection, only 14 terminals respond to a 
> ping, but when 
> > I execute a fping myself (as the hobbit user) in a shell to 
> the same 
> > amount of terminals, I get a totally different result, 
> instead of 14 
> > responding terminals, I get 95 responding terminals with 
> fping! It's 
> > not just a lucky shot, I can keep on trying these 
> terminals, the huge 
> > difference remains whether I fping them myself or when 
> hobbit fpings them.
> > 
> > I'm running hobbit 4.2.0. According to bbtest I have 806 hosts that 
> > are pinged, that takes about 26 seconds to complete. To 
> complete all 
> > tests (954), it takes about 47 seconds.
> > 
> > Does anyone have a clue why specifically these terminals 
> have such a 
> > difference in hobbit ping and a ping performed by myself?
> 
> What error does the failed ping tests show - DNS error, or 
> just ping failure ? If it's DNS errors, use the "testip" tag 
> to avoid doing DNS lookups - I understand from the other 
> mails in the thread that these systems are not in the DNS.
> 
> I suspect it might be an issue with the number of tests 
> running simultaneously. ICMP packets have lower priority in 
> most network equipment, and is therefore the first packets to 
> be discarded when there is a lot of traffic on the network. 
> Since you're referring to "terminals" they might not have a 
> lot of memory for network buffers and therefore they might 
> drop packets more often than "real" computers.
> 
> There is also a possibility that the number of hosts tested 
> is overflowing the ARP cache table on the Hobbit server, 
> which can lead to packets being lost.
> 
> I'd suggest starting with some extra options for bbtest-net (in
> hobbitlaunch.cfg): Add --concurrency=32 to the bbtest-net 
> command, and change the FPING setting in hobbitserver.cfg to 
> FPING="fping -i150", this will increase the time fping waits 
> between sending packets from 25 ms to 150 ms, so there is 
> less ICMP traffic on the network.
> 
> You can replicate how Hobbit performs the ping test by 
> putting the IP's of all your hosts into a text file (one IP 
> per line), then run
>     fping -Ae </tmp/IPlist.txt
> 
> 
> Regards,
> Henrik
> 
> 
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