Can eth0 or eth1 be used as access or uplink ports

Hello, apologies for at least 3 things.

  1. My unfamiliarity with Cumulus
  2. My unfamiliarity with networking in general
  3. That I wasn’t able to find an answer to this by reading the documentation.

We have a 10/25G switch with SFP connections running cumulus 4.2. It is mostly to be used as an isolated network but we do need to bridge the physical servers on it to a 1G ethernet network. Most of the servers don’t have 1G ethernet interfaces, otherwise we could use some of those to bridge. It’s not possible to connect the 25G cumulus network to our 1G ethernet network via the 25G ports. (We could look to see if there is an adapter that could do it if necessary).

Is it possible to use either eth0 or eht1 (1G management interfaces) to act basically as a wan interface on the switch (apologies for the poor description), so that traffic can route to and from the switch via one of those interfaces to the 25G switch ports?

The research I have done suggests that isn’t possible but I want to double check that please.

Many thanks in advance.

Technically, yes. Practically, no.

The management interfaces are not connected to the ASIC and meant for oob management purposes. By default they are configured in the management VRF that prevents traffic passing from the front panel ports to the management ports (for security and management reasons). If you wouldn’t configure the oob ports in the management vrf, you can pass traffic between them, but that means traffic would pass over the CPU. Depending on the switch model, this would result in low speeds and affect the control plane as well.

As for the “adapter”, that would be a better solution, although that has affects as well (depending on the use-case). You can look at one of these: Universal Transceiver

The best solution though would be to look at the Nvidia SN2201 switch that provides you the necessary 1G connectivity.

Thanks very much for your responses attilla, I appreciate your time and effort. I think we will have to configure one of the 2 management ports to not be in the management VFT initially and live with passing traffic over the cpu. Then look at a universal transceiver or similar.

I assume removing a management port from the mngt VRF and adding it to the relevant vlan the swp’s are in should be enough or does the switch need to be configured to route via the management port too?

I agree with Attilla; I definitely recommend the adapter. They are very inexpensive and are a much better option. The use case of connecting Eth0 with the frontpanel ports is not supported officially these days and I would be hesistant to recommend it anywhere.

You would need to modify switchd.conf to set:
“# Ignore routes that point to non-swp interfaces
#ignore_non_swps = TRUE
ignore_non_swps = FALSE”

And restart the switchd service.
It may not work though as it’s not a recommended/tested configuration any longer.

Update to close out, went with the universal transceiver in one of the servers so not using a switch management port to route or bridge networks. Thanks for all your help, especially the transceiver pointer.