RE: [Xen-devel] Xen Networking query

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Pradeep Singh, TLS-Chennai
> Sent: 13 April 2007 09:33
> To: xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-devel] Xen Networking query
> 
> Hi All,
> 
> Assume ,I create a connection from remote host to a Xen 
> machine using sockets.
> 
> AFAIK xen hypervisor doesnot have a network stack but uses 
> dom0's tcp/ip stack for networking.Right?

Correct, Dom0 has all the networking protocols, Xen's Hypervisor doesn't
even know what a network card is, nor has any idea of what happens on
the network in general [of course, the Hypervisor receives the interrupt
from the hardware, but the interrupt is just forwarded to the guest
owning the hardware, and xen doesn't actually know (or care) what the
reason/purpose of the interrupt is]. 
> 
> This mean, the very first time a conncetion is made the 
> packet is recieved by the NIC which is handled by the driver 
> and the TCP/IP stack in the dom0. Am i right?

This is a good question. From what I understand, and this page
http://linux-net.osdl.org/index.php/Bridge agrees, the networking to
forward packets from Dom0 to DomU is done at "ethernet level", e.g. the
TCP/IP stack (or any other protocol stack above Ethernet) is not used in
Dom0 to determine the destination or purpose of the DomU packet.

> 
> Subsequent data transfer to this connection(to the domU) 
> doesnot goes through dom0 TCP/IP stack but goes through the 
> domU's tcp/ip stack. Is my understanding of the Xen 
> networking correct?

All packets received by DomU goes through the DomU TCP/IP stack,
regardless of whether it was necessary for Dom0 to parse them too, or
not. [But if the above is correct, Dom0 doesn't even look at the packet
aside from the Ethernet address].

--
Mats
> 
> Thank you
> 
> ~psr
> 
> 
> -----------------------
> Pradeep Singh
> Member Technical Staff
> Server and Storage Group
> 51, Greams Road.
> HCL Technologies, Chennai
> 
> 
> 
> 



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