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

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.