[ovs-discuss] How GRE traffic finds way after arrive GRE remote end points (in open vswitch)?

[Jesse Gross]

On Thu, Jul 18, 2013 at 11:03 PM, JinHwan Hwang <calanchue at gmail.com> wrote:
> I'm quite new to both network and open vswitch, I'm not sure whether this
> question is more relevant to open vswitch or gre.
>
> belows are my ovs setting commands. There are two hosts. Each host has two
> bridge br1 and br2. br2 has the gre tunnel interface which has ip of br1 as
> its remote end point.
>
> host A
>
> sudo ifconfig eth1 0
> sudo ovs-vsctl add-br br1
> sudo ovs-vsctl add-br br2
> sudo ovs-vsctl add-port br1 eth0
> sudo ifconfig br1 192.168.1.155 netmask 255.255.255.0
> sudo ifconfig br2 10.1.1.1 netmask 255.255.255.0
> sudo ovs-vsctl add-port br2 gre0 -- set interface gre0 type=gre
> options:remote_ip=192.168.1.152
>
> hostB
>
> sudo ifconfig eth1 0
> sudo ovs-vsctl add-br br1
> sudo ovs-vsctl add-br br2
> sudo ovs-vsctl add-port br1 eth0
> sudo ifconfig br1 192.168.1.152 netmask 255.255.255.0
> sudo ifconfig br2 10.1.1.2 netmask 255.255.255.0
> sudo ovs-vsctl add-port br2 gre0 -- set interface gre0 type=gre
> options:remote_ip=192.168.1.155
>
>
> How does GRE traffic find their way after arrive its remote end point?. It
> looks like that there are no connection between br1 and br2 at the same
> host. I could understand how traffic from br2 at host A go through br1 at
> host B. But I couldn't understand traffic finds way to br2 at host B from
> br1 at host B(gre destination). Are there any implicit connection between
> bridges at same host? I thought they would be isolated. if there are no
> rules are specified.

The connection is the host IP stack. On receive, the packet will
egress from the local port (which causes the stack to receive the
packet) and ingress from GRE protocol handler.
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