[PATCH iproute-mptcp 0/6] mptcp: new endpoint type and info flags

[PATCH iproute-mptcp 0/6] mptcp: new endpoint type and info flags

[Matthieu Baerts (NGI0)]

Here is a series for iproute2 I'm planning to send to netdev. If nobody
has time to check them, I'm sure it is fine if I send them directly.

- Patch 1: add an entry in the MAINTAINERS file for MPTCP.
  Note: There is usually one person and one ML per entry, but I can add
  more if preferred.

- Patch 2: fix two minor typos in the man page.

- Patch 3: add laminar endpoint support

- Patches 4-6: display missing attributes and flags in the 'monitor'.

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Matthieu Baerts (NGI0) (6):
      MAINTAINERS: add entry for mptcp
      man: mptcp: fix minor typos
      mptcp: add 'laminar' endpoint support
      mptcp: monitor: add 'server side' info
      mptcp: monitor: add 'deny join id0' info
      mptcp: monitor: support 'server side' as a flag

 MAINTAINERS         |  7 +++++++
 ip/ipmptcp.c        | 20 +++++++++++++++++---
 man/man8/ip-mptcp.8 | 17 +++++++++++++++--
 misc/ss.c           |  2 ++
 4 files changed, 41 insertions(+), 5 deletions(-)
---
base-commit: ca756f36a0c6d24ab60657f8d14312c17443e5f0
change-id: 20251022-laminar-a8f8719ff4f6

Best regards,
-- 
Matthieu Baerts (NGI0) <matttbe@kernel.org>

[PATCH iproute-mptcp 1/6] MAINTAINERS: add entry for mptcp

[Matthieu Baerts (NGI0)]

Add Matthieu as main maintainer, but also the MPTCP Linux mailing list
to reach more people interested by MPTCP when submitting patches on this
subject.

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 MAINTAINERS | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 51833ec1..2d13c752 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -42,6 +42,13 @@ devlink
 M: Jiri Pirko <jiri@resnulli.us>
 F: devlink/*
 
+Multipath TCP - mptcp
+M: Matthieu Baerts <matttbe@kernel.org>
+L: mptcp@lists.linux.dev
+F: ip/ipmptcp.c
+F: man/man8/ip-mptcp.8
+K: mptcp
+
 netkit
 M: Daniel Borkmann <daniel@iogearbox.net>
 M: Nikolay Aleksandrov <razor@blackwall.org>

-- 
2.51.0

[PATCH iproute-mptcp 2/6] man: mptcp: fix minor typos

[Matthieu Baerts (NGI0)]

- 'signaled' -> 'signalled'

- 'a implicit' -> 'an implicit'

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 man/man8/ip-mptcp.8 | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/man/man8/ip-mptcp.8 b/man/man8/ip-mptcp.8
index e4a55f6c..500dc671 100644
--- a/man/man8/ip-mptcp.8
+++ b/man/man8/ip-mptcp.8
@@ -156,7 +156,7 @@ ID.
 
 .TP
 .BR signal
-The endpoint will be announced/signaled to each peer via an MPTCP ADD_ADDR
+The endpoint will be announced/signalled to each peer via an MPTCP ADD_ADDR
 sub-option. Typically, a server would be responsible for this. Upon reception of
 an ADD_ADDR sub-option, the other peer, typically the client side, can try to
 create additional subflows, see
@@ -207,7 +207,7 @@ is then optional.
 .BR implicit
 In some scenarios, an MPTCP
 .BR subflow
-can use a local address mapped by a implicit endpoint created by the
+can use a local address mapped by an implicit endpoint created by the
 in-kernel path manager. Once set, the implicit flag cannot be removed, but
 other flags can be added to the endpoint. Implicit endpoints cannot be
 created from user-space.

-- 
2.51.0

[PATCH iproute-mptcp 3/6] mptcp: add 'laminar' endpoint support

[Matthieu Baerts (NGI0)]

This new endpoint type has been recently added to the kernel in v6.18
[1]. It will be used to create new subflows from the associated address
to additional addresses announced by the other peer. This will be done
if allowed by the MPTCP limits, and if the associated address is not
already being used by another subflow from the same MPTCP connection.
Note that the fullmesh flag takes precedence over the laminar one.

The support of the new flag is easy: simply by adding it in the
mptcp_addr_flag_names array.

The usage menu and the manual now references the new endpoint type. The
new corresponding counter has also been added in ss.

Link: https://git.kernel.org/torvalds/c/539f6b9de39e [1]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 ip/ipmptcp.c        |  3 ++-
 man/man8/ip-mptcp.8 | 13 +++++++++++++
 misc/ss.c           |  2 ++
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/ip/ipmptcp.c b/ip/ipmptcp.c
index 2415cac8..2908b69e 100644
--- a/ip/ipmptcp.c
+++ b/ip/ipmptcp.c
@@ -32,7 +32,7 @@ static void usage(void)
 		"	ip mptcp limits show\n"
 		"	ip mptcp monitor\n"
 		"FLAG-LIST := [ FLAG-LIST ] FLAG\n"
-		"FLAG  := [ signal | subflow | backup | fullmesh ]\n"
+		"FLAG  := [ signal | subflow | laminar | backup | fullmesh ]\n"
 		"CHANGE-OPT := [ backup | nobackup | fullmesh | nofullmesh ]\n");
 
 	exit(-1);
@@ -59,6 +59,7 @@ static const struct {
 	{ "backup",		MPTCP_PM_ADDR_FLAG_BACKUP },
 	{ "fullmesh",		MPTCP_PM_ADDR_FLAG_FULLMESH },
 	{ "implicit",		MPTCP_PM_ADDR_FLAG_IMPLICIT },
+	{ "laminar",		MPTCP_PM_ADDR_FLAG_LAMINAR },
 	{ "nobackup",		MPTCP_PM_ADDR_FLAG_NONE },
 	{ "nofullmesh",		MPTCP_PM_ADDR_FLAG_NONE }
 };
diff --git a/man/man8/ip-mptcp.8 b/man/man8/ip-mptcp.8
index 500dc671..d821f714 100644
--- a/man/man8/ip-mptcp.8
+++ b/man/man8/ip-mptcp.8
@@ -66,6 +66,8 @@ ip-mptcp \- MPTCP path manager configuration
 .RB "|"
 .B subflow
 .RB "|"
+.B laminar
+.RB "|"
 .B backup
 .RB "|"
 .B fullmesh
@@ -169,6 +171,17 @@ path manager will try to create an additional subflow using this endpoint
 as the source address after the MPTCP connection is established. A client would
 typically do this.
 
+.TP
+.BR laminar
+The endpoint will be used to create new subflows from the associated address to
+additional addresses announced by the other peer. This will be done if allowed
+by the MPTCP limits, and if the associated address is not already being used by
+another subflow from the same MPTCP connection. Note that the
+.BR fullmesh
+flag takes precedence over the
+.BR laminar
+one.
+
 .TP
 .BR backup
 If this is a
diff --git a/misc/ss.c b/misc/ss.c
index 989e168a..b3566f6b 100644
--- a/misc/ss.c
+++ b/misc/ss.c
@@ -3308,6 +3308,8 @@ static void mptcp_stats_print(struct mptcp_info *s)
 		out(" bytes_acked:%llu", s->mptcpi_bytes_acked);
 	if (s->mptcpi_subflows_total)
 		out(" subflows_total:%u", s->mptcpi_subflows_total);
+	if (s->mptcpi_endp_laminar_max)
+		out(" endp_laminar_max:%u", s->mptcpi_endp_laminar_max);
 	if (s->mptcpi_last_data_sent)
 		out(" last_data_sent:%u", s->mptcpi_last_data_sent);
 	if (s->mptcpi_last_data_recv)

-- 
2.51.0

Re: [PATCH iproute-mptcp 3/6] mptcp: add 'laminar' endpoint support

[Matthieu Baerts]

Hello,

On 12/11/2025 17:24, Matthieu Baerts (NGI0) wrote:
> This new endpoint type has been recently added to the kernel in v6.18
> [1]. It will be used to create new subflows from the associated address
> to additional addresses announced by the other peer. This will be done
> if allowed by the MPTCP limits, and if the associated address is not
> already being used by another subflow from the same MPTCP connection.
> Note that the fullmesh flag takes precedence over the laminar one.
> 
> The support of the new flag is easy: simply by adding it in the
> mptcp_addr_flag_names array.
> 
> The usage menu and the manual now references the new endpoint type. The
> new corresponding counter has also been added in ss.

(...)

> diff --git a/man/man8/ip-mptcp.8 b/man/man8/ip-mptcp.8
> index 500dc671..d821f714 100644
> --- a/man/man8/ip-mptcp.8
> +++ b/man/man8/ip-mptcp.8
> @@ -66,6 +66,8 @@ ip-mptcp \- MPTCP path manager configuration
>  .RB "|"
>  .B subflow
>  .RB "|"
> +.B laminar
> +.RB "|"
>  .B backup
>  .RB "|"
>  .B fullmesh
> @@ -169,6 +171,17 @@ path manager will try to create an additional subflow using this endpoint
>  as the source address after the MPTCP connection is established. A client would
>  typically do this.
>  
> +.TP
> +.BR laminar
> +The endpoint will be used to create new subflows from the associated address to
> +additional addresses announced by the other peer. This will be done if allowed
> +by the MPTCP limits, and if the associated address is not already being used by
> +another subflow from the same MPTCP connection. Note that the
> +.BR fullmesh
> +flag takes precedence over the
> +.BR laminar
> +one.

I suggest adding here:

> .... Without any of these two flags, the path-manager will create new subflows
> to additional addresses announced by the other peer by selecting the source   
> address from the routing tables, which is harder to configure if the announced
> address is not known in advance.                                              

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.

[PATCH iproute-mptcp 4/6] mptcp: monitor: add 'server side' info

[Matthieu Baerts (NGI0)]

This info has been added a while ago in the kernel [1], but it was not
displayed in 'ip monitor'.

Now, 'server_side' is displayed if the attribute is defined and set to
true. It looks better to do that instead of showing server_side=0. Note
that from v6.18 [2], this attribute is only defined if it is set to
true.

Link: https://git.kernel.org/torvalds/c/41b3c69bf941 [1]
Link: https://git.kernel.org/torvalds/c/c9809f03c158 [2]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 ip/ipmptcp.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/ip/ipmptcp.c b/ip/ipmptcp.c
index 2908b69e..aaacc0a5 100644
--- a/ip/ipmptcp.c
+++ b/ip/ipmptcp.c
@@ -536,6 +536,8 @@ static int mptcp_monitor_msg(struct rtnl_ctrl_data *ctrl,
 		printf(" reset_reason=%u", rta_getattr_u32(tb[MPTCP_ATTR_RESET_REASON]));
 	if (tb[MPTCP_ATTR_RESET_FLAGS])
 		printf(" reset_flags=0x%x", rta_getattr_u32(tb[MPTCP_ATTR_RESET_FLAGS]));
+	if (tb[MPTCP_ATTR_SERVER_SIDE] && rta_getattr_u8(tb[MPTCP_ATTR_SERVER_SIDE]))
+		printf(" server_side");
 
 	puts("");
 out:

-- 
2.51.0

[PATCH iproute-mptcp 5/6] mptcp: monitor: add 'deny join id0' info

[Matthieu Baerts (NGI0)]

Until recently, the 'flags' attribute was not used. This has recently
been changed with the introduction of the 'deny_join_id0' flag [1].

This flag is set when a connection is created and the other peer set the
'C' flag in the MP_CAPABLE packets [2]. This flag can be set to tell the
other side that the peer will not accept extra subflows requests sent to
its initial IP address and port: typically set by a server behind a
legacy Layer 4 load balancer.

Now, when this flag is set, "deny_join_id0" will be printed instead of
"flags=1". Unknown remaining flags will be printed in hexadecimal at the
end, e.g. "flags=0x2".

Link: https://git.kernel.org/torvalds/c/2293c57484ae [1]
Link: https://datatracker.ietf.org/doc/html/rfc8684#section-3.1-20.6 [2]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 ip/ipmptcp.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/ip/ipmptcp.c b/ip/ipmptcp.c
index aaacc0a5..01f6906f 100644
--- a/ip/ipmptcp.c
+++ b/ip/ipmptcp.c
@@ -477,6 +477,7 @@ static int mptcp_monitor_msg(struct rtnl_ctrl_data *ctrl,
 	const struct genlmsghdr *ghdr = NLMSG_DATA(n);
 	struct rtattr *tb[MPTCP_ATTR_MAX + 1];
 	int len = n->nlmsg_len;
+	__u16 flags = 0;
 
 	len -= NLMSG_LENGTH(GENL_HDRLEN);
 	if (len < 0)
@@ -526,8 +527,6 @@ static int mptcp_monitor_msg(struct rtnl_ctrl_data *ctrl,
 		printf(" backup=%u", rta_getattr_u8(tb[MPTCP_ATTR_BACKUP]));
 	if (tb[MPTCP_ATTR_ERROR])
 		printf(" error=%u", rta_getattr_u8(tb[MPTCP_ATTR_ERROR]));
-	if (tb[MPTCP_ATTR_FLAGS])
-		printf(" flags=%x", rta_getattr_u16(tb[MPTCP_ATTR_FLAGS]));
 	if (tb[MPTCP_ATTR_TIMEOUT])
 		printf(" timeout=%u", rta_getattr_u32(tb[MPTCP_ATTR_TIMEOUT]));
 	if (tb[MPTCP_ATTR_IF_IDX])
@@ -539,6 +538,15 @@ static int mptcp_monitor_msg(struct rtnl_ctrl_data *ctrl,
 	if (tb[MPTCP_ATTR_SERVER_SIDE] && rta_getattr_u8(tb[MPTCP_ATTR_SERVER_SIDE]))
 		printf(" server_side");
 
+	if (tb[MPTCP_ATTR_FLAGS])
+		flags = rta_getattr_u16(tb[MPTCP_ATTR_FLAGS]);
+	if (flags & MPTCP_PM_EV_FLAG_DENY_JOIN_ID0) {
+		flags &= ~MPTCP_PM_EV_FLAG_DENY_JOIN_ID0;
+		printf(" deny_join_id0");
+	}
+	if (flags) /* remaining bits */
+		printf(" flags=0x%x", flags);
+
 	puts("");
 out:
 	fflush(stdout);

-- 
2.51.0

[PATCH iproute-mptcp 6/6] mptcp: monitor: support 'server side' as a flag

[Matthieu Baerts (NGI0)]

In the v6.18 kernel, the 'server side' attribute has been deprecated [1]
in favour of the 'server side' flag [2].

Support both: first checking the new flag, then the old attribute to
continue supporting older kernels.

Link: https://git.kernel.org/torvalds/c/c8bc168f5f3d [1]
Link: https://git.kernel.org/torvalds/c/3d7ae91107b8 [2]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 ip/ipmptcp.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/ip/ipmptcp.c b/ip/ipmptcp.c
index 01f6906f..acd008f3 100644
--- a/ip/ipmptcp.c
+++ b/ip/ipmptcp.c
@@ -535,11 +535,14 @@ static int mptcp_monitor_msg(struct rtnl_ctrl_data *ctrl,
 		printf(" reset_reason=%u", rta_getattr_u32(tb[MPTCP_ATTR_RESET_REASON]));
 	if (tb[MPTCP_ATTR_RESET_FLAGS])
 		printf(" reset_flags=0x%x", rta_getattr_u32(tb[MPTCP_ATTR_RESET_FLAGS]));
-	if (tb[MPTCP_ATTR_SERVER_SIDE] && rta_getattr_u8(tb[MPTCP_ATTR_SERVER_SIDE]))
-		printf(" server_side");
 
 	if (tb[MPTCP_ATTR_FLAGS])
 		flags = rta_getattr_u16(tb[MPTCP_ATTR_FLAGS]);
+	if ((flags & MPTCP_PM_EV_FLAG_SERVER_SIDE) ||
+	    (tb[MPTCP_ATTR_SERVER_SIDE] && rta_getattr_u8(tb[MPTCP_ATTR_SERVER_SIDE]))) {
+		flags &= ~MPTCP_PM_EV_FLAG_SERVER_SIDE;
+		printf(" server_side");
+	}
 	if (flags & MPTCP_PM_EV_FLAG_DENY_JOIN_ID0) {
 		flags &= ~MPTCP_PM_EV_FLAG_DENY_JOIN_ID0;
 		printf(" deny_join_id0");

-- 
2.51.0