Re: [Xen-users] DomU Bridged vs. Routed Networking?

[Nivedita Singhvi <nsnix@xxxxxxxxxxx>]

Ian Pratt wrote:

> > > Seems like most users opt for the bridged approach.  Perhaps it's 
> > > because it is easier to setup and it is the default setting.  For 
> > > route, I spent several days to learn that 
> > > /proc/sys/net/ipv4/conf/eth0/proxy_arp needs to be set to 0.  It is 
> > > not (Debian Sarge).  It should probably be added to 
> > > /etc/xen/scripts/network-route.
> > > I also modified scripts/vif-route (using iptables) to forward only 
> > > packets belonging to each domU's IP address, thereby 
> > preventing domU's 
> >
> > > from using IP addresses not assigned to them.  
> Please can you post diffs and we'll update the example scripts.
There are network-nat and vif-nat scripts, but they need
a little tweaking. Would be good to merge Andy's changes.

> > > With bridge, I'd need 
> > > to install etables - one extra program to install and learn.
> That's not actually true -- you can use iptables to do packet filtering
> in bridge mode. You only need ebtables if you want to do matches on MAC
> addrs. 
>
> > There is one other factor which some people have noticed and 
> > pointed out on this list: the interface is in promiscuous 
> > mode in the bridging scenario, which deteriorates performance.
> > Your mileage may vary.
> All modern Ethernet networks are switched rather than shared media.
> Putting the interface in promiscous mode will make NO difference to
> performance unless you have lots of *multicast* traffic on your network
> that this host isn't interested in.
Yep, mostly multicast traffic, since that's the only additional bucket
(unless you turn off icmp broadcast echo replies when not promiscuous)
but I measured this earlier this morning with a tcp netperf stream
and it was about 4% difference. Admittedly, today was an exception,
the network was getting hammered due to a misconfigured router,
congestion on the net due to the worm and some heavy multicast
traffic. I didn't see this till now but it was logging a bunch
of those, which exacerbated the load on the system.

thanks,
Nivedita


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