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Re: [Discuss-gnuradio] UHD: cannot find usrp2.

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] UHD: cannot find usrp2.
Date: Sat, 18 Dec 2010 01:13:45 -0500
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20101027 Fedora/3.0.10-1.fc12 Thunderbird/3.0.10

On 12/17/2010 09:56 PM, Josh Blum wrote:
> Disabling the firewall entirely seems to fix it. Thats using a
> sledgehammer when you need a chisel. :-)
> -josh
> _______________________________________________
The "most elegant" way to solve this is with a "conntrack" module for
the kernel, a la the conntrack
  module for netbios-ns and snmp.  But in lieu of that, the following
line in /etc/sysconfig/iptables
  (on Fedoren):

-A INPUT -m state --state NEW -m udp -p udp --sport 49152:49153 --dport
1024:65535 -j ACCEPT

Appears  to allow uhd_find_devices to do its thing.

Any protocol that does "discovery" using a UDP broadcast, followed by a
unicast reply will run
  into trouble with iptables, which is why "conntrack" modules were
invented to handle
  specific protocols that use a broadcast "discovery" phase. While there
appears to have been
  discussion of a "generic" conntrack module to cover this case, it
doesn't appear to have been
  worked on.

The problem with the iptables config line above is that it doesn't
*quite* provide the required security
  semantic that would be provided by a conntrack module.  But it will
suffice for now.

Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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