This is not a question, but more an oddity and simple solution. I was bringing some old network monitoring code up-to-date, I attempted to install both Net::Pcap and Net::PcapUtils on my Ubuntu 10.04 Virtualbox. Both installs failed, hanging in a test 01-loop.t. I was creating plenty of traffic on my only Ethernet interface, which is needed to finish this test.

Since the interface was eth3, I thought there might be some assumptions that were failing or other defaults in selecting the device. I had installed Net::Pcap through apt-get because it had hung in the very same test. So I used the sample code from the Net::Pcap manual page and added printouts of all of the possible devices: 

use Net::Pcap;

my $err = '';# storsge string fille by sub error
my %devinfo;

my @devs  = Net::Pcap::pcap_findalldevs(\%devinfo, \$err);
for my $dev (@devs) {
  print "$dev : $devinfo{$dev}\n";
}
exit;

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The surprising result was: 
tuser@desktop:~/Pcap$ sudo perl testNetPcap-2.pl
usbmon1 : USB bus number 1
usbmon2 : USB bus number 2
eth3 : No description available
any : Pseudo-device that captures on all interfaces
lo : Loopback device
tuser@desktop:~/Pcap$

[download]
The '01-loop' test program simply does: 
my $result = Net::PcapUtils::loop(\&process_pkt);

if (!$result eq "") {
    print("$result\n");
}

[download]
Net::PcapUtils::loop calls Net::Pcap::lookupdev, which, in the absence of a specific device returns the first entry in the list ('usbmon1'). If This means it was reading the 'Uusbon1' interface, and not the Ethernet interface.

This may be a reason that both of these packages install failed. They weren't accessing the correct interface. Why the USB interfaces are on the list is a deeper problem that I can handle. I am dropping PcapUtils because it won't pass it's test, and have installed Pcap through the 'apt-get' packages. Then I modified the test program: 


my $eth;

my @devs  = Net::Pcap::pcap_findalldevs(\%devinfo, \$err);
for my $dev (@devs) {
  print "$dev : $devinfo{$dev}\n";
  if ( ! $eth && $dev=~/eth/){ $eth=$dev;}
}
print " eth=<$eth>\n";

[download]
And it ran fine.

It is always better to have seen your target for yourself, rather than depend upon someone else's description.

In reply to pcap_findalldevs picks .... by Wiggins

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