[Spread-users] Problems with more than 2 hosts in a segment

[George Schlossnagle]

Just as a note 172.21.1.255 is not a classful broadcast address.  UNless
the netmask is specically set for this address, the broadcast by default
should be 172.21.255.255 (it's a class B address). 



Jonathan Stanton wrote:
> 
> Hi,
> 
>         It definitely sounds like something is wrong with your network's
> ability to broadcast.
> 
>         The 1 minute delay in Spread daemons finding each
> other is because the initial ('see if anyone answers my broadcast query')
> search for other daemons fails, and the daemons only find each other with
> the slower ('every minute try to contact other daemons in the config
> file') fallback technique. That would explain the 1 minute delay.
> 
>         To test the broadcast with r and s you run 'r' on several
> machines, and then run 's' from another machine giving the broadcast
> address instead of a unicast address. You should see something like this:
> 
> [jonathan at ice5 spread-src-3.15.0]$ ./r -p 8765
> Ready to receive on port 8765
> -------
> Report: total packets 100, total missed 1, total corrupted 0
> -------
> 
> [jonathan at ice8 spread-src-3.15.0]$ ./r -p 8765
> Ready to receive on port 8765
> -------
> Report: total packets 100, total missed 1, total corrupted 0
> -------
> 
> [jonathan at ice10 spread-src-3.15.0]$ ./s -p 8765 -n 100 -a 128.220.221.255
> Checking (128.220.221.255, 8765). Each burst has 100 packets, 1024 bytes
> each with 10 msec delay in between, for a total of 100 packets
> total time is (0,16453), with 0 problems
> [jonathan at ice10 spread-src-3.15.0]$
> 
> Where I ran it on ice5, ice8 and ice10 in our lab.
> 
> So here both ice5 and ice8 received the broadcast packets. If they don't
> all get them then something is preventing broadcast packets.
> 
> Possible networking problems (I don't know how relevant these are because
> I don't know your networking setup)
> 
> *) switch blocks broadcast
> *) firewall filters
> *) actual ethernet errors (check error counters on ethernet interfaces
> with 'ifconfig -a')
> 
> I'm not sure exactly why 2 machines work while 3 or more don't, but it
> might be because Spread sends retransmissions as unicast if only one other
> machine missed them, while as broadcast if several machines missed them.
> It might be that no broadcast packets work, but with only two machines the
> packets are retransmitted as unicast and they work. That might explain why
> it works with 2.
> 
> Hope this helps,
> 
> Jonathan
> 
> --
> -------------------------------------------------------
> Jonathan R. Stanton         jonathan at cs.jhu.edu
> Dept. of Computer Science
> Johns Hopkins University
> -------------------------------------------------------
> 
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