[RFE] Specify the precedence of port routes if multiple ports attached to a VM

[Rodolfo Alonso]

The aim of this RFE is to be able to, in case of having multiple ports attached to a VM, define a port preference. This port preference could be used to:
* Define the port routes metric.
* Set the default route via the highest preference port.

This RFE comes from [1].

[1]https://etherpad.opendev.org/p/oct2022-ptg-operator-hour-nova#L146

[Rodolfo Alonso (rodolfo-alonso-hernandez)]

One option: in Linux, to set the dnsmasq "dhcp-option=option:router" [1]. This suggestion is related to [2].

[1]https://blog.abysm.org/2020/06/human-readable-dhcp-options-for-dnsmasq/
[2]https://bugs.launchpad.net/neutron/+bug/1717560

[sean mooney (sean-k-mooney)]

the alternitive options are to use cloud-init metadata to set the metric per route in nova

https://cloudinit.readthedocs.io/en/latest/topics/network-config-format-v2.html#examples

   # static routes
      routes:
        - to: 192.0.2.0/24
          via: 11.0.0.1
          metric: 3

and or leave the microsfot dhcp option extions

https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-dhcpe/5e35b683-7ef0-46e3-a0bb-bb93ff0d7df2

as far as i am aware there is not a standard option for this in DHCP only the Microsoft vendor extension.

and yes https://bugs.launchpad.net/neutron/+bug/1717560 is related

to disable the default route today you have to remove the gateway from the subnet
but that then complicates adding routers as you need to specify the router port to use the "gateway" IP if you want things to just work.

providing a way to turn off sending the default route without disabling the gateway would be another approach.

the current workaround is to use a user-data script to configure the networking when creating the VM. that works but required the end user to remember to pass it every time and format it correctly.

[sean mooney (sean-k-mooney)]

this is also kind of related https://bugs.launchpad.net/neutron/+bug/1718954

[Rodolfo Alonso (rodolfo-alonso-hernandez)]

Hello Jonathan:

We have presented this feature during the drivers meeting today. We need to clarify first what is the expected implementation of this feature, caveats and scope. With this information, we'll meet again in the next drivers meeting to discuss if we approve it.

Regards.

[Rodolfo Alonso (rodolfo-alonso-hernandez)]

This Neutron RFE is not going to be implemented (at least now).