Xen users - Oct 2005 - network in general, when routed when bridged?

On Sun, 16 Oct 2005 14:24:19 +0200, Sueveges Gyoergy wrote:
>   I''m now a little bit confused with networking. When should be
bridging
> used? And When should be the routed network used? When I have one public
> IP address, and for the domU-s I would have private ones (192.168....)
> then can I use bridged network? Unfortunetly in docu I cannot see enough
> info for the routed network settings (probably they assume that one is
> familiar with networking :))
Well, yes -- to set this all up and understand how it works, you *need* to
be familiar with networking. There are a lot of resources you can use to
learn, though, ranging from public documentation and published books to
University courses on the subject, and I strongly advise that you
look into them -- this is one of those topics that one really must know to
be a good sysadmin.

To give a very brief overview, though:

Bridging two devices acts like connecting them with an ethernet cable. If
you bridge your virtual instances to your outside network connection,
that''s just like plugging your physical machine, your XenU instances
and
your outside net connection all into the same Ethernet switch. Doing
firewalling on a bridge is possible (with ebtables) but is certainly
not beginners'' functionality.

Routing puts a machine in the middle that can act like... well, a router.
It can do tricks like IP masquerading, (easier, iptables-based)
firewalling and whatnot. IP masquerading is probably what you want if you
wouldn''t plug multiple machines directly into your outside network.

That''s not to say you can''t do routing *and* have a bridge! If
you''re
going to have multiple Xen instances and be starting or shutting them
down, I find it easiest to put them all on a bridge and then route between
that bridge and the outside world.


None of this is in any way Xen-specific, and so arguably this is the wrong
forum for both the question and its answers.


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Hi all

  I''m now a little bit confused with networking. When should be
bridging
used? And When should be the routed network used?
When I have one public IP address, and for the domU-s I would have private  
ones (192.168....) then can I use bridged network?
Unfortunetly in docu I cannot see enough info for the routed network  
settings (probably they assume that one is familiar with networking :))
Thnx for the answers

George


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On Sun, 2005-10-16 at 14:24 +0200, Sueveges Gyoergy
wrote:
> Hi all
> 
>   I''m now a little bit confused with networking. When should be
bridging
> used? And When should be the routed network used?
> When I have one public IP address, and for the domU-s I would have private
> ones (192.168....) then can I use bridged network?
> Unfortunetly in docu I cannot see enough info for the routed network  
> settings (probably they assume that one is familiar with networking :))
> Thnx for the answers
> 
> George
>From what I can piece together of your issue you probably want a
scenario like this.

		
		--------------- non rfc 1918 - Internet Address
			|
			| eth0
			|
		      dom0 
			|
			| eth1
			|
		---------------- rfc 1918 - Non Internet Routable
                 | | | | | | |
 		domU,s network

dom0 configured for ip forwarding, iptables PREROUTING chain to forward
traffic from Internet DA to domU. 

This would be used for access to the domU''s via the Internet Address
used for the dom0.

dom0 configured for ip forwarding, iptables POSTROUTING chain to forward
traffic from domU to Internet.

This would be used when the domU''s need to access the Internet.



In your case you should diagram your traffic flow, setting things up
properly requires an understanding of the flow of packets and how you
want to manipulate those packets. Big difference in how one sets up a
client side app, versus a server.




Regards,
Ted



Regards,
Ted 



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