[Bug]: Non-RSS packets distributed using RETA bucket 0 on ENA

[isliser]

Preliminary Actions

• I have searched the existing issues and didn't find a duplicate.
• I have followed the AWS official troubleshoot documentation.
• I have followed the driver readme and best practices.

Driver Type

DPDK PMD for Elastic Network Adapter (ENA)

Driver Tag/Commit

ena_linux_2.15.0

Custom Code

No

OS Platform and Distribution

Linux tk-md 6.16.0-arch1-1 #1 SMP PREEMPT_DYNAMIC Thu, 21 Aug 2025 06:32:32 +0000 x86_64 GNU/Linux

Bug description

Description:

When using DPDK 24.11.2-1 with the ENA 2.15.0g driver on Arch Linux (6.16 kernel), non-RSS packets such as ARP frames are not delivered to queue 0 (or a default queue).
Instead, they are directed to the queue specified in RETA entry 0.

For example, when RETA[0] → queue 1, ARP replies are received on queue 1 even though mbuf->hash.rss == 0, indicating that no RSS hash was computed.
This results in control-plane packets (ARP, LLDP, ICMP) being mixed with RSS traffic if RETA[0] is mapped away from queue 0.

Reproduction steps

* Enable RSS on an ENA port with multiple RX queues.
* Configure RETA[0] to point to a queue ≠ 0.
* Send an ARP request and observe the queue receiving the reply.
* Note that mbuf->hash.rss == 0, but the packet is steered to the queue mapped by RETA bucket 0.

Expected Behavior

Packets that do not have an RSS hash (e.g., ARP, LLDP, non-IP) should default to queue 0 or a configurable “default queue,” not follow RETA lookup.

Actual Behavior

Non-RSS packets are assigned to the queue corresponding to RETA index 0.
If RETA[0] ≠ 0, ARP and similar packets appear on that queue instead of queue 0.

Additional Data

m7i.4xlarge instance

Contact Details

sliser@nyrus.tech

[shaibran]

Thank you for reaching out to us.
Although this behavior differs from other PMDs, which bypass RETA for non-RSS traffic, we will verify it internally to determine whether it is intentional (e.g., skipping deep packet inspection) or should be classified as a bug.