Well "common knowledge" assumes everybody has it. Just like "common sense" for that matter. Turns out it's not a thing

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Jokes aside,for installing OpenWRT there is the official wiki as well as my "tutorial" (2 Posts) mentioned here:
What are "Channels" exactly for Ethernet ?
VLANs should work as expected. LACP I don't believe it works at all, I didn't try it. And I don't know if with stock Firmware it works either.
Not sure what these really implements:
If ports of a RTL93xx switch are not added to a port matrix then they are not used for the link aggregation. As result, communication will then just break on non-primary interfaces. This can be rep...
github.com
If link aggregation with LACP is activated, we must send out the LACP packets on the physical port and not on a logic port. Otherwise, the per port packets might be (re-balanced) between the differ...
github.com
This mentions jumbo frames, but it's a very old kernel mixing rtl93xx PR with mentions about rtl83xx:
Fix VLAN behaviour support jumbo frames by default enable 2.5 gig for rtl930x Fix led behaviour Fix detection of current port status Expose register and phy_mmd register r/w in sysfs to aid develop...
github.com
I'd say there is basically ZERO (or close to) support for LACP or LAGG
This repository is a mirror of https://git.openwrt.org/openwrt/openwrt.git It is for reference only and is not active for check-ins. We will continue to accept Pull Requests here. They will be mer...
github.com
This repository is a mirror of https://git.openwrt.org/openwrt/openwrt.git It is for reference only and is not active for check-ins. We will continue to accept Pull Requests here. They will be mer...
github.com
Not sure about what of these is true link aggregation (probably not much):
This repository is a mirror of https://git.openwrt.org/openwrt/openwrt.git It is for reference only and is not active for check-ins. We will continue to accept Pull Requests here. They will be mer...
github.com
Xikestor SKS8300-8X stock Chinese Firmware claims to support LACP, according to Manufacturer Website.
Whether that's true or not is another Matter.
I'm not entirely sure why OpenWRT would be so far behind. On one hand, there is probably some NDA / confidential information. On the other IIRC the "stock firmware" that these were running was basically just the manufacturer reference design / example code, so it shouldn't be so hard to implement.
About SFP+ Modules I think one of the most knowleageable people around here is
@blunden.
I think I bought 3pcs of the 30m Variant here:
I cannot remember however if this was mostly targeted towards 2,5gbps (and maybe 5gbps) or if it could also do 10gbps without glowing bright red, due to the power consumption of the module.
However, if you want higher bandwidth, I wonder if going with a used Mellanox SX6036 or similar would be a better Idea. With the Fans tuned down I think the Idle Power Consumption would be around 35W-40W or something like that. That is more than the 10W or so of the Xikestor, but it's also many more Ports (40gbe or 56gbe with some special mellanox cables), with possibility for breakout to 4x10gbe on some ports. I don't know if the SX6036 supports LACP either though. It would have at least a 40gbe upstream connection though ...
EDIT 1: price wise the ONTI 8 port x 10gbe (85-90 EUR - ish to Europe) should be approximatively the same as a used Mellanox SX6036 off eBay if bought from the US (approx. 100 USD plus shipping to Europe), possibly a bit less for the ONTI, but you get 8x10gbe instead of 36x40gbe/56gbps infiniband.