Shortcut Forwarding Engine?

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Wildlion
DD-WRT Guru


Joined: 24 May 2016
Posts: 1407

PostPosted: Thu Nov 12, 2020 14:51    Post subject: Reply with quote
SFE is essentially the same as CTF since I do not feel like going into all of the technical details just read:

https://en.wikipedia.org/wiki/Cut-through_switching

or in short summary, the packet header is only partially processed and forwarding starts before full packet is processed.

This is why there are conflicts with QoS, because QoS depends on having the packet and being able to delay it or give it priority.
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MonarchX
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Joined: 26 Sep 2009
Posts: 119

PostPosted: Thu Nov 12, 2020 21:13    Post subject: Reply with quote
I switched to K2.6 from 3.X SFE became identical to non-SFE speeds. I think 85Mbps throughput on 100Mbps device is as good as it is going to get.

I do appreciate the prompt reply though!
Bib
DD-WRT Guru


Joined: 07 Jul 2008
Posts: 629
Location: France

PostPosted: Thu Apr 22, 2021 22:23    Post subject: Reply with quote
Hi
Coming from a whr-g54s I duplicate the working mode to a R7800, that is WAP, i.e. routing mode set to Router plus WAN, firewall and routing disabled, WAN port assigned to LAN.
Then is there any benefit to keep SFE enabled?

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Last edited by Bib on Sun Apr 25, 2021 14:43; edited 1 time in total
mac913
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Joined: 02 May 2008
Posts: 1848
Location: Canada

PostPosted: Fri Apr 23, 2021 1:19    Post subject: Reply with quote
Bib wrote:
Hi
Coming from a whr-g54s I duplicate the working mode to a R7800, that is WAP, i.e. routing mode set to Router plus WAN, firewall and routing disabled, WAN port assigned to LAN.
Then is there any benefit to keep FSE enabled?


I have YaMON running on my R7800 and SFE has to be disabled to work correctly. I also have custom Firewall rules. So I prefer to leave SFE disabled, since the R7800 is fast enough.

Anyone who has a complex Firewall setup will need to test their rules if SFE is enabled too make sure nothing is broken.

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Bib
DD-WRT Guru


Joined: 07 Jul 2008
Posts: 629
Location: France

PostPosted: Sun Apr 25, 2021 14:55    Post subject: Reply with quote
mac913 wrote:
...Anyone who has a complex Firewall setup will need to test their rules if SFE is enabled too make sure nothing is broken.

Thanks for advice man. But now you explained, like you I won't use it as I'm not hunting the µs with my R7800 and have ~complex~ firewall rules. Please, could you update my quote above as I mistyped SFE in my first post (2 first letters swapped = web pollution. Souvenir From Earth, I'll remember Wink)
Kind thanks

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piticu21
DD-WRT Novice


Joined: 25 May 2023
Posts: 1

PostPosted: Tue Jun 06, 2023 10:20    Post subject: Reply with quote
I read the whole thread. It's a pity how you guys are testing this feature on lower connections than 4G mobile.

It's like developing DD-WRT infrastructure for the 2010s when there it was no internet.

Shortcut Forwarding Engine enabled on my router - NETGEAR R7800 - is ruining my VPN connection, as a result I can't forward anything over VPN.
Also with Shortcut Forwarding Engine enabled, I have 1Gbps speed through the router. With it disabled I have VPN of 100mbps, but the internet connection drops to 300 - 400 mbps and the temperature of the router becomes very high. Which is bad.
On original NETGEAR firmware I have 1Gpbs internet connections, 30 mbps VPN connections, but I have issues accessing Tinder, Instagram stories and other services that are using some special internet. I did not have time to debug this. If I have had time I wouldn't be here.

It's also a pity that being a phpbb here, there is no proper search and indexing of threads and routers with their problems, but Google doesn't help either.

Questions:
- how do you configure the VPN to work with Shortcut Forwarding Engine enabled?
- why is there this huge difference in transfer speeds between Shortcut Forwarding Engine enabled and disabled?
- which is the best option, considering the first question?
blkt
DD-WRT Guru


Joined: 20 Jan 2019
Posts: 5660

PostPosted: Tue Jun 06, 2023 10:53    Post subject: Reply with quote
1.) In general do not configure or use VPN with SFE enabled, unless your set up config is simple.
2.) SFE is a software hack to bypass kernel performance limitation, but has its own set of issues.
3.) Use x86 platform 1 Gbps or greater. R7800 cannot handle both Gbps and VPN all in software.

Search for all terms, display results as posts, return all available characters of posts. "VPN SFE"
hw112
DD-WRT Novice


Joined: 27 May 2023
Posts: 16

PostPosted: Tue Jun 06, 2023 14:14    Post subject: Reply with quote
On my R7800 I did not see much difference between WAN <> LAN throughput with or without SFE both gave me over 850 Mb/s.

But the router is lightly taxed only providing Wifi to a three person household and no VPN (WireGuard runs on an other router)

I am not running the latest build but 52242

I also have an R7800 running OpenWRT but to get comparable speeds as with DDWRT you have to use the NSS build which has some stability issues.

For VPN you better use WireGuard which is much easier to setup and has three times the speed of OpenVPN
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