[Bloat] Testing Offer - Comcast L4S Trials

[Sebastian Moeller]

While I have no test that I can volunteer, let alone a test that supports L4S.

I want to take the opportunity to share my tcpdump invocations that can show ECN in action on the IP-level:

# ECN: IPv4
tcpdump -i pppoe-wan -v -n 'ip and (ip[1] & 0x3) != 0' # NOT Not-ECT
tcpdump -i pppoe-wan -v -n 'ip and (ip[1] & 0x3) == 0' # Not-ECT
tcpdump -i pppoe-wan -v -n 'ip and (ip[1] & 0x3) == 1' # ECT(1)
tcpdump -i pppoe-wan -v -n 'ip and (ip[1] & 0x3) == 2' # ECT(0)
tcpdump -i pppoe-wan -v -n 'ip and (ip[1] & 0x3) == 3' # CE


# ECN: IPv6
tcpdump -i pppoe-wan -v -n 'ip6 and (ip6[0:2] & 0x30) >> 4  != 0' # NOT Not-ECT
tcpdump -i pppoe-wan -v -n 'ip6 and (ip6[0:2] & 0x30) >> 4  == 0' # Not-ECT
tcpdump -i pppoe-wan -v -n 'ip6 and (ip6[0:2] & 0x30) >> 4  == 1' # ECT(1)
tcpdump -i pppoe-wan -v -n 'ip6 and (ip6[0:2] & 0x30) >> 4  == 2' # ECT(0)
tcpdump -i pppoe-wan -v -n 'ip6 and (ip6[0:2] & 0x30) >> 4  == 3' # CE


# ECN IPv4/6
tcpdump -i pppoe-wan -v -n '(ip6 and (ip6[0:2] & 0x30) >> 4  != 0)' or '(ip and (ip[1] & 0x3) != 0)' # NOT Not-ECT
tcpdump -i pppoe-wan -v -n '(ip6 and (ip6[0:2] & 0x30) >> 4  == 1)' or '(ip and (ip[1] & 0x3) == 1)' # ECT(1)
tcpdump -i pppoe-wan -v -n '(ip6 and (ip6[0:2] & 0x30) >> 4  == 2)' or '(ip and (ip[1] & 0x3) == 2)' # ECT(0)
tcpdump -i pppoe-wan -v -n '(ip6 and (ip6[0:2] & 0x30) >> 4  == 3)' or '(ip and (ip[1] & 0x3) == 3)' # CE


Just replace "-i pppoe-wan" with your own network interface of interest, this seems to work on both recent inux and older macos (12.6.7).
Before L4S roll-out the test for ECT(1) can be helpful to confirm that there is no background ECT(1) usage that might (or might not) cause issues with L4S.



> On Jun 29, 2023, at 16:12, Livingood, Jason via Bloat <bloat at lists.bufferbloat.net> wrote:
> 
> As noted recently, we (Comcast) will soon begin L4S testing with customers. We’re working on our test plans now. So my offer here is to let me know if:
> 1 – You have test probes you’d like us to deploy. We are working on a plan to send out (1) University of Chicago NetMicroscope probes and (2) RIPE Atlas probes.
> 2 – You have web-based tests you’d like people to run, or have one-click install client for Mac or Windows. (Most testers will not be technical enough to run CLI-based tests, the the exception of the Apple network responsiveness test.) 
>  
> Thx! If this is of interest, please ping me 1:1 off-list.
> Jason
>  
> Current list
> (1.a) Ookla web-based
> (1.b) Ookla client
> (1.c) M-Labs NDT
> (1.d) Fastly web-based
> (1.e) Netflix web-based
> (1.f) Waveform web-based
> (1.g) DSL Reports web-based 
> (1.h) Apple Network Responsiveness test

	[SM] Not mine to offer, but I think speed.cloudflare.com also might be interesting as it seems to follow the modern "let's not ignore latency under load" paradigm as well as the translate the results into terms suitable for casual users, while also reporting the hard numbers for those interested. 
	What seems not available right now is a public test that can selectively exercise both L4S queues independently.

Regards
	Sebastian

>  
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