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

From: Josh Blum
Subject: Re: [Discuss-gnuradio] UHD: cannot find usrp2.
Date: Sat, 18 Dec 2010 00:34:28 -0800
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20101208 Lightning/1.0b2 Thunderbird/3.1.7

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

You should just need 49152 to be open. The broadcasts only occur on the
control port.

> Appears  to allow uhd_find_devices to do its thing.

Glad to hear it!

> Any protocol that does "discovery" using a UDP broadcast, followed by
> a unicast reply will run into trouble with iptables, which is why

Basically the firewall lets devices talk back through port that
initiated the conversation. Because of this, UHD sends an data packet
into the USRP2 even for receive only applications. :-)

However, this simple firewall rule will not, in the case of a broadcast
open a reply hole for every device talking through that port.

I guess its just another one of those things you do to prepare a host
system for use. Just like setting up udev, or sysctl limits.


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