On Mon, Oct 25, 2010 at 4:15 AM, Daniel Lezcano <daniel.lezc...@free.fr> wrote: > On 10/25/2010 07:24 AM, Nirmal Guhan wrote: >> >> On Sun, Oct 24, 2010 at 3:07 PM, Daniel Lezcano<dlezc...@fr.ibm.com> >> wrote: >> > > [ snip ] >> >> How does it work when I have eth0 in lxc attached to br0? I still >> assign IP to eth0 in this case as part of lxc config. Is this a >> special case where IP is required for interface attached to the >> bridge? >> > > I assume you are talking about a veth + bridge, right ? > > The network stacks are separated between the host and the container and the > veth is a pass-through network device, > it is a pair device (vethA - vethB). When the packets are injected to vethA, > they are received by vethB and when they are injected to vethB, they are > received by vethA. > > Practically, when the container is created, the vethA is attached to the > bridge and vethB is moved inside the container and renamed eth0 for > convenience. No IP address is assigned to vethA but it is assigned to vethB. > > Assuming you have an IP address 1.2.3.4 on vethB and another host with the > IP 1.2.3.5, if you ping from the container to the host, here is what > happens: > > (container) : search the route for dest address 1.2.3.5 > (container) : found the dev where to send packet is eth0 (aka vethB) > (container) : send the packet to this device > (host) : the packet arrives from vethA > (host) : the bridge hooks the packet > (host) : lookup the destination with the mac @ > (host) : send the packet on all the ports > (host) : the packet goes through the real device eth0 > (peer) : the packet arrives to the peer and this one answers > (host) : the packet arrives on the real device eth0 > (host) : the packet is hooked by the bridge code > (host) : the bridge look for the dest mac @ and find vethA > (host) : the bridge send the packet to vethA > (container) : the packet arrives to eth0 (aka vethB) > Thanks for the detailed explanation. So, if I have multiple interfaces (eth, tap) attached to bridge, I will assign IP to bridge. As I tested, I was also able to assign IP to tap interface attached to bridge (so there are two IPs and still ping both of them. Only missing piece is - bridge is a layer 2 device that can take an L3 IP too :-) This helps me, though!! ~Nirmal
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