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
 - 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@makrotopia.org>
---
 .../net/forwarding/local_termination.sh       | 25 +++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/tools/testing/selftests/net/forwarding/local_termination.sh b/tools/testing/selftests/net/forwarding/local_termination.sh
index 1f2bf6e818477..9bc9d25e71368 100755
--- a/tools/testing/selftests/net/forwarding/local_termination.sh
+++ b/tools/testing/selftests/net/forwarding/local_termination.sh
@@ -100,6 +100,15 @@ PTP_1588_IPV6_PDELAY_REQ=" \
 00 00 3e 37 63 ff fe cf 17 0e 00 01 00 01 05 7f \
 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 \
 00 00 00 00 00 00"
+LINK_LOCAL_STP_BPDU=" \
+01:80:c2:00:00:00 00:00:de:ad:be:ef 00 26 42 42 03 \
+00 00 00 00 00 80 00 aa bb cc dd ee ff 00 00 00 00 \
+80 00 aa bb cc dd ee ff 80 01 00 00 14 00 02 00 \
+0f 00"
+LINK_LOCAL_LLDP=" \
+01:80:c2:00:00:0e 00:00:de:ad:be:ef 88:cc 02 07 04 \
+00 11 22 33 44 55 04 05 05 65 74 68 30 06 02 00 \
+78 00 00"
 
 # Disable promisc to ensure we don't receive unknown MAC DA packets
 export TCPDUMP_EXTRA_FLAGS="-pl"
@@ -213,7 +222,15 @@ run_test()
 	mc_route_destroy $rcv_if_name
 	mc_route_destroy $send_if_name
 
+	ip maddress add 01:80:c2:00:00:00 dev $rcv_if_name
+	send_raw $send_if_name "$LINK_LOCAL_STP_BPDU"
+	ip maddress del 01:80:c2:00:00:00 dev $rcv_if_name
+
 	if [ $skip_ptp = false ]; then
+		ip maddress add 01:80:c2:00:00:0e dev $rcv_if_name
+		send_raw $send_if_name "$LINK_LOCAL_LLDP"
+		ip maddress del 01:80:c2:00:00:0e dev $rcv_if_name
+
 		ip maddress add 01:1b:19:00:00:00 dev $rcv_if_name
 		send_raw $send_if_name "$PTP_1588_L2_SYNC"
 		send_raw $send_if_name "$PTP_1588_L2_FOLLOW_UP"
@@ -304,7 +321,15 @@ run_test()
 		"$smac > $UNKNOWN_MACV6_MC_ADDR3, ethertype IPv6 (0x86dd)" \
 		true "$test_name"
 
+	check_rcv $rcv_if_name "Link-local STP BPDU" \
+		"> 01:80:c2:00:00:00" \
+		true "$test_name"
+
 	if [ $skip_ptp = false ]; then
+		check_rcv $rcv_if_name "Link-local LLDP" \
+			"> 01:80:c2:00:00:0e" \
+			true "$test_name"
+
 		check_rcv $rcv_if_name "1588v2 over L2 transport, Sync" \
 			"ethertype PTP (0x88f7).* PTPv2.* msg type *: sync msg" \
 			true "$test_name"
-- 
2.53.0

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@makrotopia.org>
> ---

With that addressed:

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