s390x OSA bridging causes network issues

[Phoenyx Cameron]

Enabling linux bridging, via netplan, whilst using an OSA card on the s390x architecture causes large amounts of packets to be received on the sending interface. This behaviour is not seen while using other types of network card on a Z, and is also not seen on any other server architecture (x86 / ppc64).

When performing a ping test, the following can be seen:

- Pings that are unsuccessful (Around 60% of packets sent) are not received by the network switches
- These unsuccessful pings will trigger the following message in a dmesg output: "received packet on vlan2011 with own address as source address"
- tcpdump will also display the packet twice, confirming the dmesg output.

The behaviour is not seen during connections to other addresses on the same VLAN.
Successful pings occur directly after an ARP request is made, however permanently setting the ARP entry results in 100% of packets failing to send

We are using Ubuntu 22.04.4 LTS.

I've attached a zipped folder containing the outputs of the dmesg and tcpdumps - As well as the outputs of a dbginfo command

[Ubuntu Foundations Team Bug Bot (crichton)]

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[bugproxy (bugproxy)]

------- Comment From <email address hidden> 2024-04-15 02:52 EDT-------
A reply I sent via email to Phoenix Cameron and others:

I had an look at the data attached to the bugzilla.
I don?t really understand the setup. Why do have 30 bridges on top of 30 VLAN interfaces all connected to the same OSA interface?
Why not 1 bridge with 30 vlan-bridgeports ?

I am wondering whether this could be related to the infamous arp flux issue.
Maybe you want to try setting
net.ipv4.conf.all.arp_ignore=1
net.ipv4.conf.all.arp_announce=2

[bugproxy (bugproxy)]

------- Comment From <email address hidden> 2024-04-29 05:15 EDT-------
I got the reply from Phoenyx:
Hi Sandy,

We?ve made the suggested changes to arp_ignore and arp_announce, but this does not seem to have had any effect on the issue unfortunately ? There has been no reduction in the number of packets that giving the ?received packet on vlan2011 with own address as source address? error.

We could certainly look at setting up 1 bridge with multiple bridgeports to test that configuration, it was set up this way to replicate our working Z14 environment. I?m not sure what the original decision was that led to that setup though.

Kind regards,
Phoenyx