On 2/6/26 6:09 PM, Eric Dumazet wrote:

On Fri, Feb 6, 2026 at 5:28 PM Fernando Fernandez Mancera
[off-list ref] wrote:

quoted

It makes sense. I have tested this approach and we got a more even
distribution of source ports when having thousands of reserved ports. No
difference at all when not using reserved ports.

Please, you can find the distribution graph with the current algorithm
[1] and with the random step algorithm [2].

While I understand that this approach is introducing a call to
get_random_u32_below() on every connect, I am wondering if it makes
sense to replace the existing algorithm with this variant. What do you
think?

I would ask RFC 6056 experts like Fernando Gont what they think.

Note that if we use random at each connect(), we defeat one of the principles
of ephemeral port selection : try very hard to avoid 4-tuple collision.

Right. I will reach out to him and get his opinion. I have plenty of 
time before net-next open again. I am also collecting some metrics 
regarding the 4-tuple collision frequency.

quoted

Please, notice the implementation below. I plan to send an official v1
once net-next is open. In addition, I am rewriting the commit message as
I find the current one confusing.

[1] https://0xffsoftware.com/port_graph_current_alg.html

[2] https://0xffsoftware.com/port_graph_random_step_alg.html