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linux bridge eth0 and cifx0 - carmel85 - August-11th-2020


I'm trying to setup a linux bridge (brctl) between eth0 and cifx0 using the following setup:

brctl addbr br0

brctl addif br0 eth0
brctl addif br0 cfix0

PCs connected to eth0 and cfix0 are able to communicate with the netPI - but traffic across the bridge does not seem to be forwarded correctly (in either direction).

Is the cifx0 capable of being part of a linux bridge?
Are there and specific settings need to be applied to the cfix0 device for the bridge to be operational?


RE: linux bridge eth0 and cifx0 - Armin@netPI - August-11th-2020

My first question is which OS are you using? Are you using netPI OS that comes preinstalled on netPI or are you using any other OS like Raspbian?

The second thing I have to say is that I personally have not worked with bridged functionality yet independent if it is netPI or Raspberry Pi or any x86 platform and Ubuntu da da da... My personal expectation is that bridging and forwarding telegrams between the two networks is a software and logical thing only and handled by Linux core functions and it is not a hardware thing where the two Ethernet chips are briged with a direct acccess method. Does that also meet your expectation?


RE: linux bridge eth0 and cifx0 - Armin@netPI - August-11th-2020

Another question is how is you basic setup of the two networks are in terms of IP addresses, subnet masks and gateways of the devices connected to eth0, cifx0 are and which IP setting you have configured for br0? Can you state it please here.

And how do you detect that the specifically bridging is not working correctly? Is there for example a ping command you send from the network connected to the cifx0 interface not passing the bridge and does not reach the network connected eth0 side?

RE: linux bridge eth0 and cifx0 - Armin@netPI - August-13th-2020

I got in touch with our development team and ask for bridging support of cifx0 interface. I received the following response:

As in this article mentioned at https://iomem.com/archives/4-Ethernet-Bridges-under-Linux.html an interface supporting bridge mode needs to support promiscuous mode among others. The cifx0 interface and the underlying netX controller firmware does not support the promiscuous mode. This means any try to let cifx0 be part of a Linux bridge will fail.

I am sorry to have no better news for you. Supporting promiscuous mode is not possible with Hilscher's netX network controller.