Seeing the same issue with Fedora KDE from Fedora Cosmic. Firewall ports are opened using the firewall-cmd --zone=myzone --add-service=steam-lan-transfer --permanent and reloading firewalld (or rebooting).
The blue banner appears to say transfering but the download rate never climbs above my internet connection speed and then after a short time the banner goes and it continues to download over internet connection.
Pause/resume will once more bring the banner up but it does not appear to actually perform a lan transfer.
The firewall service above opens the ports:
<port protocol="tcp" port="27040" />
<port protocol="udp" port="27031-27036" />
Which matches the steam support document
It mentions big picture clients cannot transfer, so I placed both clients in non big picture mode, made no difference.
Edit: Scratch the above, it's PEBCAK. I installed the game and forgot to first force proton compatibility, so it downloaded/installed the linux version and not the Windows version, realised after launching as the linux version isn't supported for network play anymore. Uninstalled and installed with proton forced and now it's transferring at gigabit lan speeds as expected.
I'll leave this post though as it includes the firewall rules that were needed on the transfer host for Fedora.
Nothing extracted yet.
Steam gives up on LAN peers during "Game Transfer over Local Network" far too easily and too often.
It happens on Steam-for-LINUX and also Steam-for-Windows.
It happens no matter the partners, like so:
LINUX -> LINUX
LINUX -> Windows
Windows -> LINUX
Windows -> Windows
I am reporting it here for the LINUX client even though it affects both LINUX and Windows.
Anyway, the quick summary is that during any Local Network Transfer, the Steam client will often quit using the peer host on the LAN and then start downloading from the Steam servers on the internet. If I immediately pause the download, then restart it, it will then start downloading from the peer host across the LAN again, until it quits again a little while later. The end result is that I have to tend to the transfer, sitting there in front of the downloading peer, pausing and then restarting the download whenever it switches from the LAN to the internet.
I have a slow internet connection and would strongly prefer transfers across the LAN. Once one computer gets the update, it should be used to propagate the update to all the other computers in the house.
My internet connection is not particularly unreliable. I can play MMOs and other multiplayer games fine. Also, note that when it switches to the Steam servers on the internet, it does so just fine, and that itself is proof that the internet is reliable enough.
In short, I think that the algorithm used to determine whether a peer is available on the LAN is either outright buggy (drops the local peer even though it is available) or far too sensitive (decides that a small/short disconnect is worth switching to the Steam servers for).
Let's say the Local Network Transfers uses the ICMP ping latency to tell if a peer is available or not, and it drops the peer connection when it sees a latency over 10ms. I'd like that threshold increased or even user-configurable.
I don't actually know the mechanism or algorithm by which Steam determines whether to give up on a peer host on the LAN; I'm just giving this hypothetical example as an illustration of the intended goal.
Thanks in advance!