Masquerading VM works 99%

Derek O keeffe derekokeeffe85 at
Sat Feb 12 09:47:54 UTC 2022

Hi Laurent,

I will double check but I’m sure I’ve checked that. I forgot to mention that both vm’s can ping each other on the “private” interfaces.


> On 11 Feb 2022, at 19:33, Laurent Dumont <laurentfdumont at> wrote:
> You might want to look at port-security if you are using an Openstack VM as more of a router. By default, it will permit only it's own mac-address + ip-address from exiting the interface.
> You can fully disable it to see if it's the root cause.
> Remove allowed-address-pairs.
> Remove security-groups
> Disable port-security.
>> On Thu, Feb 10, 2022 at 11:17 AM Derek O keeffe <derekokeeffe85 at> wrote:
>> Hi all,
>> We have an openstack cluster with one controller and 4 computes (Victoria) we have set it up using vlan provider networks with linuxbridge agent, distributed routing & ml2 (I am only partly on the networking so there could be more to that which I can find out if needed)
>> So I was tasked with creating two Instances, one (lets call it the external vm) with an external interface and internal interface A second instance (lets call it the internal vm) would then be placed on the network.
>> I configured masquerading on the "external vm" and tried to ping the outside world from the "internal" vm as per something like this
>> Both VM's were instantiated on the same compute host (I've tried it with them on separate hosts as well).
>> I can see the ping leave using tcpdumps along the way and it makes it all the way back to the internal interface on the external machine. It just fails on the last hop to the internal machine. I've tried everything in my power to find why this won't work so I would be grateful for any advice at all. I have added the below to show how I followed the ping manually and where it went and when it failed. Thank you in advance.
>> Following the ping from source to destination and back:
>> Generated on the private VM
>> sent to the internal interface on the external vm
>> sent to the external interface on the external vm
>> sent to the tap interface on the compute
>> sent to the physical nic on the compute
>> sent to the nic on the network device out to the internet
>> received on nic on the network devicefrom the internet 
>> received on physical nic on the compute
>> received on tap interface on compute 
>> received on external interface on the external vm
>> received on the internal interface on the external vm
>> NEVER gets to last step on the internal vm 
>> Regards,
>> Derek
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