PPPoE + SQM + Gigabit

So, we all know that PPPoE is polarising. Opinions seem to range from it being almost harmless, to it being awful.

It sounds like high end routers, either with hardware offload or beefy CPUs can handle the processing overhead of PPPoE. Can they simultaneously handle SQM, the anti-bufferbloat measure?

I know that SQM is incompatible with software/hardware offload, so for Gigabit speeds will require a beefy CPU. What's not clear to me is if the processing overhead is essentially doubled by doing both PPPoE and SQM, or whether it's more “two for the price of one”?

What I would ask is how many simultaneous heavy users are you really expecting to justify the need for SQM.

The problem with PPPoE is that just about all open source implementations of it are single threaded and suck. FreeBSD's sucks and that is the basis of PFsense etc.

Even Ubiquiti have issues with it.

Which wouldn't be so bad, except that it brings no benefit to the end user, and ISPs seem to use it mostly out of habit.

But yes, if you are using PPPoE, you by definition have less CPU power left over for other things than if you didn't use PPPoE. I would also like it to die off, but it probably won't any time soon.

Mikrotik seem to have a much better implementation, since moving from UDM Pro to CCR2004-1g-12s+2xs I have had no issues at all, despite both devices using the same CPU.

Fair question. One and a half? I think it'd be nice if large file downloads (e.g. Steam) don't interfere with video conferencing latency.

I am on 4G at the moment, and the bufferbloat is horrendous. It causes ping times of 30-50ms to easily double. That said, I probably shouldn't assume that bufferbloat on FTTP is anywhere near as bad

Thanks for explaining the single threaded nature of existing open source PPPoE implementations. That's relevant to me, because I like OpenWRT.

Thanks also for confirming that the CPU requirements are cumulative. I am fortunate enough that some of my local CityFibre ISPs use IPoE/DHCP. That said, they don't support IPv6. So I guess I just have to decide which feature I find more important.

I am probably overthinking it, and neither (perhaps unfortunately) is actually important

Post deleted by _iain_

Edited by _iain_ (Fri 23-Dec-22 23:33:46)

In reply to a post by _iain_:

Fair question. One and a half? I think it'd be nice if large file downloads (e.g. Steam) don't interfere with video conferencing latency.

I am on 4G at the moment, and the bufferbloat is horrendous. It causes ping times of 30-50ms to easily double. That said, I probably shouldn't assume that bufferbloat on FTTP is anywhere near as bad

Experiment with it, but temper your expectations. The various implementations of SQM are all very CPU bound (and particularly single threaded) so you need a (relatively) meaty processor in the router to be able to perform the function adequately at the higher but rates. As they say you mileage may vary.

Bufferbloat in any event will be undoubtedly superior on FTTP/TC than any wireless solution. Just the nature of the beast.

In reply to a post by Pheasant:

Experiment with it, but temper your expectations. [...]

Bufferbloat in any event will be undoubtedly superior on FTTP/TC than any wireless solution. Just the nature of the beast.

Rodger that, I will temper my expectations. But even without SQM, as you say, I should be much happier once I can get FTTx.

In reply to a post by _iain_:

Thanks for explaining the single threaded nature of existing open source PPPoE implementations. That's relevant to me, because I like OpenWRT.

Thanks also for confirming that the CPU requirements are cumulative. I am fortunate enough that some of my local CityFibre ISPs use IPoE/DHCP. That said, they don't support IPv6. So I guess I just have to decide which feature I find more important.

I am probably overthinking it, and neither (perhaps unfortunately) is actually important

I have a Zotac ZBOX CI660 (i7 Quad Core 1.8Ghz Quad Core) that I picked up for a bargain and repurposed as a OpenWRT router. My current topology is a Virgin Router in bridge mode connected to my Zotac router which in turn is then connected to a DUMB WiFi AP (also running on OpenWRT). Handles the Gigabit throughput with SQM (Cake) enabled on wired connections wonderfully at 800MBbps. My average latency under load only increases by around 5ms. Should I expect more CPU demand than what I have currently when I move to Giganet with PPPoE or is the extra CPU strain confined to the SQM implementation rather than the PPPoE protocol?