[Users] strange problem with nagios nrpe server

[Kirill Korotaev]

Steve Wray wrote:
> Just one other possible data point.
> 
> I may have just dismissed these problems as some kind of creeping 
> senility but I've seen some other bizarre issues with VMs migrated into 
> OpenVZ.
> 
> One of these is to do with Samba filesharing.
> 
> When the VM is migrated into OpenVZ from Xen, samba fileshares on the VM 
> can be accessed from Windows *only* by FQDN not by bare hostname.
> 
> Note that this broke *existing* mapped network drives for Windows users.
> 
> Also note that this did *not* affect Linux nor OSX clients; only Windows.
> 
> Since I've verified that this wierdness is *only* apparent when the VM 
> was running under OpenVZ not under Xen I'm not inclined to believe that 
> I am going insane when I find that NRPE under Debian Sarge has a problem 
> when running under OpenVZ and not under Xen.
>
>
> It starts to seem that OpenVZ can produce all *kinds* of unpredictable 
> behavior... either that or I really am going mad complete with 
> hallucinations :-/ Not discounting that possibility out of hand...

Oh, don't say so. Everything should have a logical explanation.
And I guess I know the answer to this one.

First of all, plz check that you don't have any kind of firewall
rules in host system and VE with 'iptables -L'.

But the real suspect is broadcast network messages from NetBIOS protocol.
Working FQDN means that host can be found via DNS and by IP.
Non-working short hostnames mean that your hosts are not setup
in default domain in DNS and that name resolution via netbios failed.

You need to connect your VE to ethX adapter using veth (virtual ethernet)
adapter and Linux bridge. This will allow use of network broadcasts.
The default venet networking is a secure IP-level networking which filters
out broadcasts.

http://wiki.openvz.org/Virtual_Ethernet_device
http://wiki.openvz.org/Differences_between_venet_and_veth
http://forum.openvz.org/index.php?t=msg&goto=7295&&srch=samba#msg_7295
http://en.wikipedia.org/wiki/NetBIOS

Forseeing your question about why venet is used as default networking type:
1. venet is more secure (see wiki).
2. venet is more scalable up to hundrends and thousands of VEs,
   while veth/ethernet/bridge broadcasts/multicasts will simply kill (DoS) the node
   in case of many VEs.

Thanks,
Kirill