Re: Why are bridges required?

[krad <kraduk@xxxxxxxxx>]

Hi Lee

If you are to virtualize the network stack properly you need to do it all the way down to layer2. How do you connect multiple layer 2 devices together? Well a bridge, a switch being many bridges all in the one box. Hubs are not relevant here as there is no physical medium. As the llya said it totally possible to have a 1:1 relationship between the vms and host, ie a dedicated bridge per vm, with its own ip network on (/30 for ipv4, or /64 for ipv6). The host machine then does all the routing and/or natting for the guests

On 3 June 2014 04:06, Ilya Ponetayev <instenet@xxxxxxxxx> wrote:

You may create as many bridges as you want to have virtual interfaces, each bridge consisting only of connection to single VM, and handle traffic between bridges and between physical interfaces of host through iptables/iproute.

IHMO bridging is the most proper and popular technique because it provides the most flexible configuration. Your VM sees NIC as Ethernet card (so with all L2 features), so either you can terminate this L2 pipe with bridge in host, and perform L3/higher level handling, or you can use for example DHCP server on host binded to your bridge, or VLAN-handling config.

On 03.06.2014 06:25, lee wrote:

Hi,

all the descriptions of networking setups with VMs I`m seeing involve
bridges.  The only use I see for bridges is when I actually want to be
able to send network traffic to multiple arbitrary interfaces connected
to the bridge.  I do neither need, nor want bridges when I want to keep
the VMs separated, like when separating a VM in a DMZ from a VM in the
LAN.

The bridge acts like a hub.  Looking at [1] makes it seem that this is
undesirable --- otherwise there wouldn`t be need for a software switch
to prevent network traffic on a bridge from going to all of the
connected interfaces.

When there`s a bridge with multiple VMs connected to it, is a software
switch desirable to prevent network traffic on the bridge from going to
interfaces it doesn`t need to go to?  If so, isn`t it better not to use
a bridge to begin with?

Can`t we simply have virtual interfaces on the physical host which are
the "other end" of the interfaces showing up in the VMs, without
bridges?

[2] seems to suggest to leave all bridges "dangling", i. e. it says
you`re not supposed to connect an interface to the bridge.  What`s the
point of a bridge when only a single interface is connected to it?


[1]:
http://openvswitch.org/support/config-cookbooks/vlan-configuration-cookbook/

[2]: http://wiki.libvirt.org/page/Networking

--

Sincerely yours, Ilya Ponetayev <instenet@xxxxxxxxx>


_______________________________________________
CentOS-virt mailing list
CentOS-virt@xxxxxxxxxx
http://lists.centos.org/mailman/listinfo/centos-virt

_______________________________________________
CentOS-virt mailing list
CentOS-virt@xxxxxxxxxx
http://lists.centos.org/mailman/listinfo/centos-virt