Lets create another network in the same tenant, and create 3 more VMS.

Lets check where these VMs are running [you can also do nova show $uuid  and get the host where its running currently]


neutron net-list

neutron net-show c4520434-aea7-4263-b714-ac0b6fcdc57a

check segmentation_id — its 87

neutron net-show officeNet-2  [using name also works ]

check segmentation_id — its 15

lets take a closer look at these:

So I have vx-2 and vx-2-1 with the same IP address in the same host. (c24)


root@c14_utility_container-cc97b930:~# openstack server show 9f0fb1af-192b-4a30-a41b-8c8694ac9f05

root@c14_utility_container-cc97b930:~# openstack server show 82fcbddc-f10a-41d9-b628-c558994d5e8c

root@c14_utility_container-cc97b930:~# ssh c24 virsh dumpxml instance-0000002a


root@c14_utility_container-cc97b930:~# ssh c24 virsh dumpxml instance-00000033


root@c14_utility_container-cc97b930:~# ssh c24 brctl show

As you can see, vx-2 is vlan-87 and  vx2-1 is on vlan-15, so they are separated and treated differently.

If there are 2 instances of the same network (same vxlan), they would appear in the same brqXXX bridge.

root@c14_utility_container-cc97b930:~# ssh c25 brctl show

So there is also something on c25 that is on vxlan-15

ifconfig vxlan-15 or ip link show vxlan-15 is not going to show anything special 🙂

you need to do

ip -d link show vxlan-15

and its going to show the vxlan id – 15 , that its a part of the multicast group and uses dev-vxlan.

So as you see, there are a lot of interfaces 🙂

eth0 (inside the VM) <=> tapXXXX (outside the VM, on compute node) <=> brqXXX(bridge) <=> vxlan-XX (vtep) <=> br-vxlan <=>eth4 (physical interface) <=> switch <=>  [ the other side]

So when I ping between instances on different compute hosts and run tcpdump
I can  see the packets directly on tapXXX and on brqXXX  and also on vxlan-xx.

tcpdump on br-vxlan and eth4 shows the layer-3 br-vxlan ips on top.


When i ping  from (on c24),

inside the instance

$ arp -n

From outside the instance:

All learned mac addresses are in the bridge  (vxlan-87)


see that dst is which is the vxlan ip of c25.





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