Raspberry Pi 4 | Router on a stick | Gigabit WAN?

I am having gigabit WAN installed within the next few days.

My current setup is:

  • Raspberry Pi 4
  • OpenWrt 21.02.0-rc2 r16122-c2139eef27 / LuCI openwrt-21.02 branch git-21.148.49484-14511e5
  • Managed switch.
  • VLANs segmenting PPPoE and LAN traffic.

I was planning to keep using the inbuilt gigabit port, but some other posts have suggested that might be a bottleneck.

Is the gigabit port on the RP4 a known issue? Does in not run at full gigabit speeds both in and out?

I have SQM QoS running, so I was going to limit that to 800Mbps, if that's relevant.

I don't have a gigabit connection, so don't have any experience with it unfortunately, but I can't recall seeing any complaints about the built in port, the only problems I've seen reported have been with the asix drivers in the new tp-link adapter which seems to be limited to around 600mbps, maybe someone else can chime in.

Router on a stick means you have to use a single (onboard-) port for wan and lan, this works fine up to ~500 MBit/s (more like 750-800 MBit/s in practice, as you'll rarely experience fully symmetric up- and downstream usage scenarios), but to achieve the full 1 GBit/s up and down, you need dedicated interfaces for wan and lan (so not router on a stick).

To explain it simply, your (onboard-) 1 GBit/s ethernet card is fully symmetric - it can do 1 GBit/s up and 1 GBit/s down at the same time. For routing to work, the data passes through this single link twice - once in, once out, but the hardware can only do 1+1 GBit/s, not 2+2 GBit/s, which you'd need for a symmetric load for a router on a stick. This is not specifically an issue of the RPi, but a rather physical limitation of 1000BASE-T - you'd need at least 2.5GBASE-T (or 5GBASE-T, 10GBASE-T) to escape this (for practical reasons, two dedicated 1000BASE-T cards are just much cheaper than busting the 1 GBit/s limit).

tl;dr: don't worry, it will still work (with a slight performance impact), but you'd still want to get a second ethernet card exclusively for WAN.


Thanks for taking the time to reply. That does make sense I was only considering the wan traffic in a single direction and wasn't seeing the issue.

Which models of usb adaptor are recommended for full 1gbps speeds?

Anything based on RealTek RTL8152/3 works fine

TP-Link UE300 is a popular cheap choice - I use one, and am very happy with it

From personal experience, avoid anything with AX88179 chipset

I've ordered one for delivery tomorrow.

With regards to openwrt config, is it easy to move config to the new wan link - e.g. adblock, DNS redirections, wireguard, etc?

Would it all need reconfiguring or can I just add the interface to the wan zone?

just change the "Device" used by WAN/WAN6 from eth0 to eth1

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