MBIM Interface in Bridge Mode

Sassy Natan sassyn at gmail.com
Mon Sep 21 19:51:53 UTC 2020

Hi All,

First thank you for the great support in this project and mailing group.
I'm trying for a few days to make my setup working, but unfortunately I'm
still stuck without any success. So maybe someone here can give me feedback.

In my setup I'm using VPP <https://wiki.fd.io/view/VPP> to create a high
end linux router using DPDK .
Up until now my setup was working with wire network interface only, meaning
all the interfaces running in my system were dpdk compiable network

Now my goal is to enable in my router a LTE device.
So first thing first, I decided to leave out the DPDK and VPP parts at the
first step, and try doing it with linux stack only.

*One thing to note here is that my requirements must set the LTE device
inside a linux bridge. *

Obviously the default mode where I enable ip-forwarding and setup NAT using
IPtables work right out of the box.
However, once I try to add the interface into a linux bride using the brcl
- things start to break out.

I followed this link
also this
didn't manage to get any good results from it.
The method explained in the second link, by using the veth method didn't
work for me and based on my understanding I'm not even sure it can work.

In my test I did manage to get to a point where I managed to add the MBIM
interface to a bridge br0, where the br0 was set with the ifconfig -arp
setup so it will be considered as a raw-ip without ethernet.
Then I have set the IP address on the br0 with the IP I got from the LTE
provider, and also set it up with a subnet mask of /32 -

For the default gateway I have setup the gateway using
ip route add dev br0

Note no IP in the gateway, just tell it to push all traffic from this
interface (I also used the wwan0 with the same results).

When doing ping -I wwan0 and running TCPDUMP I can see the ICMP do
get a replay, after masquerade the IP address using IPtables (the source
I also needed to set the rp_filer off, to enable ip spoofing.

Using arptables and ebtables didn't provide me with any good results (not
sure how to use them in this kind of topology).

I understand that that MAC is sent back with zero null (00:00:00:00:00:00)
which looks like it comes from the localhost (lo), but doing tcpdump on lo
interface didn't show any traffic going in or out.

To keep it simple for now, maybe someone can guide me how to set this in a
bride mode?

Based on the answer, I will provide a much more detailed explanation about
my setup, but for now maybe there is a simple solution?

Thank You


Sassy Natan
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