Re: [PATCH] selftests: net: local_termination: test link-local protocols

[Vladimir Oltean]

On Mon, Mar 09, 2026 at 04:03:57PM +0000, Daniel Golle wrote:
> Add tests to local_termination.sh to verify that link-local frames
> arrive. On some switches the DSA driver uses bridges to connect the
> user ports to their CPU ports. More "intelligent" switches typically
> don't forward link-local frames, but may trap them to an internal
> microcontroller. The driver may have to change trapping rules, so
> link-local frames end up on the DSA CPU ports instead of being
> silently dropped or trapped to the internal microcontroller of the
> switch.
> 
> Add two tests which help to validate this has been done correctly:
>  - Link-local STP BPDU should always arrive at the Linux netdev

I don't really like the "always" comment here. The only reason why STP
is part of the forwarding plane and not the control plane is because the
bridge has stp_state=0. See br_handle_frame():

	if (unlikely(is_link_local_ether_addr(dest))) {
		u16 fwd_mask = p->br->group_fwd_mask_required;

		/*
		 * See IEEE 802.1D Table 7-10 Reserved addresses
		 *
		 * Assignment		 		Value
		 * Bridge Group Address		01-80-C2-00-00-00
		 * (MAC Control) 802.3		01-80-C2-00-00-01
		 * (Link Aggregation) 802.3	01-80-C2-00-00-02
		 * 802.1X PAE address		01-80-C2-00-00-03
		 *
		 * 802.1AB LLDP 		01-80-C2-00-00-0E
		 *
		 * Others reserved for future standardization
		 */
		fwd_mask |= p->group_fwd_mask;
		switch (dest[5]) {
		case 0x00:	/* Bridge Group Address */
			/* If STP is turned off,
			   then must forward to keep loop detection */
			if (p->br->stp_enabled == BR_NO_STP ||
			    fwd_mask & (1u << dest[5]))
				goto forward;
			*pskb = skb;
			__br_handle_local_finish(skb);
			return RX_HANDLER_PASS;

perhaps this can be part of the commit message somehow.

>  - Link-local LLDP should arrive at standalone ports (and the test
>    should be skipped on bridged ports similar to how it is done
>    for the IEEE1588v2/PTP tests)
> 
> Signed-off-by: Daniel Golle <daniel@xxxxxxxxxxxxxx>
> ---

With that addressed:

Reviewed-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
Tested-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>