Steam downloads capped at ~115 Mb/s on gigabit connection (Nobara/Fedora, Akamai/Fastly peers) #12291
Description
System Information:
Distro: Nobara 42 (Fedora-based)
Kernel: (insert uname -r output)
Steam version: (insert steam --version output)
ISP: Origin Broadband Ultrafast (NBN, Superloop backhaul)
Connection: Gigabit (confirmed ~900 Mb/s via speedtest/wget)
Download region tested: Adelaide, Melbourne, Sydney, NZ
Issue Description
On Linux (Nobara 42, Fedora-based) with a gigabit connection (Origin Broadband Ultrafast / Superloop), Steam downloads are consistently capped at ~11.5 MB/s (~115 Mb/s).
This limit persists across:
Steam GUI and SteamCMD
Multiple download regions (Adelaide, Melbourne, Sydney, NZ)
IPv4 and IPv6 CDN peers (Akamai, Fastly, i3D)
Different runtime builds (native RPM vs Flatpak)
Meanwhile, non-Steam downloads (speedtest.net, wget, Final Fantasy XIV patcher via XIVLauncher) saturate the full line at ~900 Mb/s on the same machine, same connection, same moment.
This suggests the bottleneck lies with Steam’s client runtime or CDN peering on Linux, not the ISP or system configuration.
Expected Behavior
Steam should be able to use available bandwidth and saturate the line (hundreds of Mb/s up to gigabit speeds), similar to other applications.
Actual Behavior
Steam caps at ~11.5 MB/s regardless of:
IPv4 vs IPv6
Download region
SteamCMD vs GUI
Cache cleared / client reinstalled
This cap coincidentally matches speeds of my previous 100/40 plan, but I am now on gigabit and have confirmed line rate elsewhere.
Steps to Reproduce
On Linux (Fedora/Nobara, but reports suggest it affects other distros too).
Connect to a gigabit ISP (in this case, Origin Broadband via Superloop, Australia).
Download a large game or mod (e.g., Arma 3, AppID 107410) via Steam GUI or SteamCMD:
./steamcmd.sh +login anonymous +force_install_dir ./test +app_update 90 validate +quit
Monitor throughput with nload or a logging script (example attached).
Observe Steam stuck at ~11.5 MB/s while other apps (wget/FFXIV patcher) hit ~900 Mb/s.
Evidence
Steam log snippet (Arma 3 mods):
2025-08-24T17:07:10+09:30,wlp4s0,11.46,
"23.11.170.102:443 23.60.149.116:443 146.75.103.52:443 202.130.202.*:443"
FFXIV log snippet (same machine, same line):
2025-08-24T18:12:05+09:30,wlp4s0,92.53,
"patch-dl.ffxiv.com (Akamai CDN)"
Speedtest / wget results: ~900 Mb/s.
Steam (GUI + SteamCMD): ~115 Mb/s.
Notes
Disabling IPv6 (sysctl -w net.ipv6.conf.all.disable_ipv6=1) → Steam switches to IPv4 peers but still capped.
SteamCMD logs confirm identical limit.
Likely causes:
Steam Linux client runtime mishandling multiple CDN sockets, OR
Steam’s CDN peers (Akamai/Fastly/i3D) capped for certain ISPs (Superloop/AU).
Attachments:
steam_log.txt → Per-second throughput + peers during Steam download.
steam_log.txt
Steps to Reproduce
Prepare the environment
Run on a Linux system (tested on Nobara 42 / Fedora, but likely affects others).
Confirm a high-speed internet connection (≥500 Mb/s, gigabit in this case).
Verify line rate with wget or a speed test (expect ~900 Mb/s).
Start a large Steam download
Option A – SteamCMD (minimal variables):
./steamcmd.sh +login anonymous +force_install_dir ./test +app_update 90 validate +quit
(Any large app or depot works; Arma 3 mods used here.)
Option B – Steam GUI:
Open Steam → Settings → Downloads.
Select a nearby region (Sydney, Adelaide, Melbourne, NZ tested).
Download or repair a large game / Workshop collection.
Monitor throughput during the download
Run nload or use the attached logger script:
./net_log.sh 1 steam | tee ~/steam_log.txt
Replace with your network interface (e.g., enp3s0 for Ethernet, wlp4s0 for Wi-Fi).
Log for at least 2–3 minutes while the download is active.
Observe the behavior
Steam throughput is capped around 11–12 MB/s (~115 Mb/s).
Multiple peers (Akamai/Fastly/i3D) are visible in the log.
The cap persists regardless of:
SteamCMD vs GUI
IPv4 vs IPv6 (tested with IPv6 disabled via sysctl)
Different download regions
Control test (non-Steam)
Download a large file via wget or patch a game like Final Fantasy XIV:
wget -O /dev/null http://speedtest.tele2.net/10GB.zip
Observe throughput saturating the line (~500–900 Mb/s).
Compare results
Steam: ~115 Mb/s cap (matches old 100/40 NBN speeds).
Non-Steam: near full gigabit line rate.