View page 20 at https://www.hastexo.com/system/files/...

1.The packet leaves the VM and hits the hypervisor node on br-int
2.From there,it is forwarded to br-tun,which adds the GRE encapsulation to it
3.It leaves the hypervisor on eth2 into the GRE network
4.It reaches eth2 on the network node
5.It gets sent through br-tun,which removes the GRE Headers
6.It is then forwarded to br-int(br-int on the network node is connected to the
qROUTERnamespace--that is why we defined our external network as router for
the admin tenant network earlier)
7.From br-int,the packet hits the external bridge(br-ex) and finally leaves the
network node into the internet

You can replace "GRE" by "VXLAN" in text above and it will have the same sense.
Eth3 is OVS port of external OVS bridge br-ex ( having IP belongs to external network ). That's why it doesn't have IP. It's IP got moved to external OVS bridge br-ex ( Network Node).
On RH systems corresponding ifcfg-* files look like :-

[root@juno1 network-scripts(keystone_admin)]# cat ifcfg-br-ex
DEVICE="br-ex"
BOOTPROTO="static"
IPADDR="192.168.1.127"
NETMASK="255.255.255.0"
DNS1="83.221.202.254"
BROADCAST="192.168.1.255"
GATEWAY="192.168.1.1"
NM_CONTROLLED="no"
DEFROUTE="yes"
IPV4_FAILURE_FATAL="yes"
IPV6INIT=no
ONBOOT="yes"
TYPE="OVSIntPort"
OVS_BRIDGE=br-ex
DEVICETYPE="ovs"

[root@juno1 network-scripts(keystone_admin)]# cat ifcfg-enp2s0
DEVICE="enp2s0"
# HWADDR=00:22:15:63:E4:E2
ONBOOT="yes"
TYPE="OVSPort"
DEVICETYPE="ovs"
OVS_BRIDGE=br-ex
NM_CONTROLLED=no
IPV6INIT=no

and ovs-vsctl show report on Network Node looks as follows

. . . . . . . . . . . . . . . . . . . . 
 Bridge br-ex
        Port br-ex
            Interface br-ex
                type: internal
        Port "enp2s0"
            Interface "enp2s0"
        Port phy-br-ex
            Interface phy-br-ex
                type: patch
                options: {peer=int-br-ex}
        Port "qg-a632b464-07"
            Interface "qg-a632b464-07"
                type: internal
    ovs_version: "2.3.1"