Re: RFC: PTP Boundary Clock over UDPv4/UDPv6 on Linux bridge

[Vladimir Oltean <vladimir.oltean@nxp.com>]

On Tue, Nov 16, 2021 at 11:19:24AM +0100, Kurt Kanzenbach wrote:
> Hi all,
> 
> I'm currently trying to setup a PTP Boundary Clock over UDPv4 or UDPv6
> on top of a switch using a Linux bridge. It works fine using PTP Layer 2
> transport, but not for UDP. I'm wondering whether this is supported
> using Linux or if I'm doing something wrong.
> 
> My setup looks like this:
> 
> Bridge (DSA):
> 
> |$ ip link set eth0 up
> |$ ip link set lan0 up
> |$ ip link set lan1 up
> |$ ip link add name br0 type bridge
> |$ ip link set dev lan0 master br0
> |$ ip link set dev lan1 master br0
> |$ ip link set br0 up
> |$ dhclient br0
> 
> PTP:
> 
> |$ ptp4l -4 -i lan0 -i lan1 --tx_timestamp_timeout=40 -m
> 
> It seems like ptp4l cannot receive any PTP messages. Tx works fine.
> 
> The following hack solves the problem for me. However, I'm not sure
> whether that's the correct approach or not. Any opinions, ideas,
> comments?
> 
> Thanks,
> Kurt
> 
> |From 2e8b429b3ebabda8e81693b9704dbe5e5205ab09 Mon Sep 17 00:00:00 2001
> |From: Kurt Kanzenbach <kurt@linutronix.de>
> |Date: Wed, 4 Aug 2021 09:33:12 +0200
> |Subject: [PATCH] net: bridge: input: Handle PTP over UDPv4 and UDPv6
> |
> |PTP is considered management traffic. A time aware switch should intercept all
> |PTP messages and handle them accordingly. The corresponding Linux setup is like
> |this:
> |
> |         +-- br0 --+
> |        / /   |     \
> |       / /    |      \
> |      /  |    |     / \
> |     /   |    |    /   \
> |   swp0 swp1 swp2 swp3 swp4
> |
> |ptp4l runs on all individual switch ports and needs full control over sending
> |and receiving messages on these ports.
> |
> |However, the bridge code treats PTP messages over UDP transport as regular IP
> |messages and forwards them to br0. This way, the running ptp4l instances cannot
> |receive these frames on the individual switch port interfaces.
> |
> |Fix it by intercepting PTP UDP traffic in the bridge code and pass them to the
> |regular network processing.
> |
> |Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
> |---
> | net/bridge/br_input.c | 13 +++++++++++++
> | 1 file changed, 13 insertions(+)
> |
> |diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
> |index b50382f957c1..4e12be70a003 100644
> |--- a/net/bridge/br_input.c
> |+++ b/net/bridge/br_input.c
> |@@ -271,6 +271,13 @@ static int br_process_frame_type(struct net_bridge_port *p,
> | 	return 0;
> | }
> | 
> |+static const unsigned char ptp_ip_destinations[][ETH_ALEN] = {
> |+	{ 0x01, 0x00, 0x5e, 0x00, 0x01, 0x81 }, /* IPv4 PTP */
> |+	{ 0x01, 0x00, 0x5e, 0x00, 0x00, 0x6b }, /* IPv4 P2P */
> |+	{ 0x33, 0x33, 0x00, 0x00, 0x01, 0x81 }, /* IPv6 PTP */
> |+	{ 0x33, 0x33, 0x00, 0x00, 0x00, 0x6b }, /* IPv6 P2P */
> |+};
> |+
> | /*
> |  * Return NULL if skb is handled
> |  * note: already called with rcu_read_lock
> |@@ -280,6 +287,7 @@ static rx_handler_result_t br_handle_frame(struct sk_buff **pskb)
> | 	struct net_bridge_port *p;
> | 	struct sk_buff *skb = *pskb;
> | 	const unsigned char *dest = eth_hdr(skb)->h_dest;
> |+	int i;
> | 
> | 	if (unlikely(skb->pkt_type == PACKET_LOOPBACK))
> | 		return RX_HANDLER_PASS;
> |@@ -360,6 +368,11 @@ static rx_handler_result_t br_handle_frame(struct sk_buff **pskb)
> | 	if (unlikely(br_process_frame_type(p, skb)))
> | 		return RX_HANDLER_PASS;
> | 
> |+	/* Check for PTP over UDPv4 or UDPv6. */
> |+	for (i = 0; i < ARRAY_SIZE(ptp_ip_destinations); ++i)
> |+		if (ether_addr_equal(ptp_ip_destinations[i], dest))
> |+			return RX_HANDLER_PASS;
> |+
> | forward:
> | 	switch (p->state) {
> | 	case BR_STATE_FORWARDING:
> |-- 
> |2.30.2
>

This should do the trick as well?

/sbin/ebtables --table broute --append BROUTING --protocol 0x88F7 --jump DROP

/sbin/ebtables --table broute --append BROUTING --protocol 0x0800 --ip-protocol udp --ip-destination-port 320 --jump DROP
/sbin/ebtables --table broute --append BROUTING --protocol 0x0800 --ip-protocol udp --ip-destination-port 319 --jump DROP

/sbin/ebtables --table broute --append BROUTING --protocol 0x86DD --ip6-protocol udp --ip6-destination-port 320 --jump DROP
/sbin/ebtables --table broute --append BROUTING --protocol 0x86DD --ip6-protocol udp --ip6-destination-port 319 --jump DROP