BRIDGE STP MODE VALUES(9)

👑 NAME

Bridge STP mode values — the three constants that decide who runs STP on your bridge: userspace or the kernel, bestie 💅

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🎀 DESCRIPTION

okay so picture this: your bridge has STP turned on, and the kernel needs to know who's actually driving — a userspace daemon or the kernel itself. These are the values that answer that question. There are exactly three, and they are iconic ✨

💖 BR_STP_MODE_AUTO

This one's the default, no cap. The kernel goes and invokes the /sbin/bridge-stp helper so it can hand the bridge over to a userspace STP daemon (think mstpd and friends 🧚).

🫶 tiny little caveat: this is only attempted in the initial network namespace. In any other network namespace it falls back to kernel STP. iykyk

💜 BR_STP_MODE_USER

Directly enable userspace STP (BR_USER_STP) without invoking the /sbin/bridge-stp helper. Snip snip, no middleman 🔥

This one works in any network namespace, which is lowkey the whole point.

⚠️ heads up bestie: userspace is responsible for making sure an STP daemon is actually managing the bridge. Nobody's gonna do it for you.

🦋 BR_STP_MODE_KERNEL

Directly enable kernel STP (BR_KERNEL_STP) without invoking the helper. Just you and the kernel, no daemons, no drama 💀

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🌸 the vibe check on all three

The mode controls how the bridge selects between userspace and kernel STP when STP is enabled via IFLA_BR_STP_STATE.

🚨 but listen — it can only be changed while STP is disabled, so IFLA_BR_STP_STATE == 0. Try it any other time and it returns -EBUSY. periodt.

And yeah, the default value is BR_STP_MODE_AUTO (we said that already but it bears repeating okay 😭).

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👀 SEE ALSO

• Kernel file ./include/uapi/linux/if_link.h struct rtnl_link_stats64(9)
• Bridge enum definition(9)
• Bridge mode enum definition(9)
• Bridge port enum definition(9)

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that's the whole page, bestie — go forth and bridge responsibly 🫶

this gem lives at ./include/uapi/linux, dated October 2026. mwah 💋