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https://issues.apache.org/jira/browse/VCL-909?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14969759#comment-14969759
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Andy Kurth commented on VCL-909:
--------------------------------
Are you certain get_random_mac_address() selected the same MACs? It gets
called from libvirt.pm without any arguments, meaning it generates a MAC
starting with '52:54' and randomly selects the last 4 octets.
Perl's _rand_ function isn't perfect, but there are still 4,294,967,296 (256 ^
4) combinations. I ran a test where I called get_random_mac_address() until a
duplicate occurred, and repeated this 100 times:
{code}
ROUND: for (my $round=1; $round<=100; $round++) {
my $macs = {};
my $iteration = 0;
while(1) {
$iteration++;
my $mac = get_random_mac_address();
if (defined($macs->{$mac})) {
print "duplicate found on iteration $iteration\n";
next ROUND;
}
else {
$macs->{$mac} = $iteration;
}
}
}
{code}
On average, it took 82,063 iterations before a duplicate MAC address was
selected.
> get_random_mac_address in utils.pm may generate the same mac for VMs
> --------------------------------------------------------------------
>
> Key: VCL-909
> URL: https://issues.apache.org/jira/browse/VCL-909
> Project: VCL
> Issue Type: Bug
> Components: vcld (backend)
> Affects Versions: 2.4.2
> Reporter: Xianqing Yu
>
> We use get_random_mac_address() in libvirt.pm to generate random mac address
> for VMs. However, we observe some of our reservations failed because some of
> VMs have exactly the same mac (for both eth0 and eth1). Since reservations
> are made by multiple users simultaneously, current design of
> get_random_mac_address may return the same mac to multiple requests.
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