On Wed, May 25, 2011 at 11:49:21AM -0400, Russ Purinton wrote:
> I thought that even 127.0.0.0/8 traffic still went thru the NIC to loop. I
> can't seem to find anything on the net supporting this one way or the other,
> though I've seen multiple posts about pinging 127.0.0.1 to test and verify
> the NIC card and drivers working properly. Not sure what this means.
>
> Also, if it doesn't pass to the NIC, the NIC then the question arises how the
> IP and TCP checksums are being applied if offloading is enabled and it
> doesn't pass thru the NIC.
>
> I had thought that on a physical host, the loopback ping would hit the
> network card. I'm guessing with a virtual host, the loopback ping would only
> hit the Virtual NIC but likely not the physical NIC. If it goes to the
> virtual NIC, then it would be passing thru the PV drivers to the QEMU layer
> supporting the virtual networking right?
>
> The packets shouldn't be visible even from Dom0 because they should stay
> within the vNIC. Again, not finding any supporting documentation on the
> 'net, one way or the other, so feel free to prove me wrong.
>
Just check "ifconfig -a" output.
127.0.0.1 IP is on the 'lo' interface, not on 'ethX' interface.
lo-interface is provided by the loopback-driver.
Even if you don't have any nic drivers loaded, you still have 'lo' and pinging
localhost works.
Try it. rmmod your nic driver and ping localhost.
-- Pasi
> Thanks
>
> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Pasi Kärkkäinen
> Sent: Wednesday, May 25, 2011 10:08 AM
> To: Russ Purinton
> Cc: Carl Byström; xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-users] Bad TCP accept performance
>
>
> Using localhost (127.0.0.1) goes thru loopback device only, ie. interface
> 'lo',
> so it does NOT go through NIC card or xen/PV drivers..
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