On Fri, Jul 17, 2026 at 06:45:16AM +0000, Jack Ma wrote:
> Commit 1274e1cc4226 ("vxlan: ecmp support for mac fdb entries") lets a
> single inner MAC be reached through a group of remote VTEPs, with the
> kernel flow-hashing across the group members. Each member carries its
> own remote IP, but the UDP destination port is always taken from the
> VXLAN device (vxlan->cfg.dst_port) and cannot be set per member.
>
> Some deployments pack several receivers behind one underlay IP and tell
> them apart by UDP port, so they need a per-nexthop destination port to
> spread flows across (IP, port) tuples rather than IP alone.
>
> Add a netlink attribute NHA_FDB_PORT (__be16, mirroring NDA_PORT) that
> carries an optional UDP destination port on an fdb nexthop. It is only
> accepted together with NHA_FDB and NHA_GATEWAY; it is stored in struct
> nh_info and echoed back on dump. This patch is control-plane plumbing
> only; the VXLAN datapath is wired up in a follow-up patch, so behaviour
> is unchanged for now.
>
> Signed-off-by: Jack Ma <[email protected]>
> ---
> include/net/nexthop.h | 2 ++
> include/uapi/linux/nexthop.h | 3 +++
> net/ipv4/nexthop.c | 20 +++++++++++++++++++-
> 3 files changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/include/net/nexthop.h b/include/net/nexthop.h
> index 572e69cda..9c8227996 100644
> --- a/include/net/nexthop.h
> +++ b/include/net/nexthop.h
> @@ -28,6 +28,7 @@ struct nh_config {
> u8 nh_protocol;
> u8 nh_blackhole;
> u8 nh_fdb;
> + __be16 nh_fdb_port;
> u32 nh_flags;
>
> int nh_ifindex;
> @@ -63,6 +64,7 @@ struct nh_info {
> u8 family;
> bool reject_nh;
> bool fdb_nh;
> + __be16 fdb_port;
>
> union {
> struct fib_nh_common fib_nhc;
> diff --git a/include/uapi/linux/nexthop.h b/include/uapi/linux/nexthop.h
> index bc49baf4a..e587bbf3b 100644
> --- a/include/uapi/linux/nexthop.h
> +++ b/include/uapi/linux/nexthop.h
> @@ -83,6 +83,9 @@ enum {
> /* u32; read-only; whether any driver collects HW stats */
> NHA_HW_STATS_USED,
>
> + /* be16; UDP destination port for an fdb nexthop (e.g. VXLAN) */
> + NHA_FDB_PORT,
> +
> __NHA_MAX,
> };
>
> diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c
> index 6205bd57a..5b27cc9a9 100644
> --- a/net/ipv4/nexthop.c
> +++ b/net/ipv4/nexthop.c
> @@ -39,6 +39,7 @@ static const struct nla_policy rtm_nh_policy_new[] = {
> [NHA_ENCAP_TYPE] = { .type = NLA_U16 },
> [NHA_ENCAP] = { .type = NLA_NESTED },
> [NHA_FDB] = { .type = NLA_FLAG },
> + [NHA_FDB_PORT] = { .type = NLA_U16 },
Maybe NLA_POLICY_MIN(NLA_BE16, 1) given that it's BE16 and that we don't
dump / use a destination port of 0?
> [NHA_RES_GROUP] = { .type = NLA_NESTED },
> [NHA_HW_STATS_ENABLE] = NLA_POLICY_MAX(NLA_U32, true),
> };
> @@ -956,6 +957,9 @@ static int nh_fill_node(struct sk_buff *skb, struct
> nexthop *nh,
> } else if (nhi->fdb_nh) {
> if (nla_put_flag(skb, NHA_FDB))
> goto nla_put_failure;
> + if (nhi->fdb_port &&
> + nla_put_be16(skb, NHA_FDB_PORT, nhi->fdb_port))
> + goto nla_put_failure;
> } else {
> const struct net_device *dev;
>
> @@ -1055,6 +1059,9 @@ static size_t nh_nlmsg_size_single(struct nexthop *nh)
> break;
> }
>
> + if (nhi->fdb_nh)
Why not nhi->fdb_port ?
> + sz += nla_total_size(2); /* NHA_FDB_PORT */
> +
> if (nhi->fib_nhc.nhc_lwtstate) {
> sz += lwtunnel_get_encap_size(nhi->fib_nhc.nhc_lwtstate);
> sz += nla_total_size(2); /* NHA_ENCAP_TYPE */
> @@ -2956,8 +2963,10 @@ static struct nexthop *nexthop_create(struct net *net,
> struct nh_config *cfg,
> nhi->family = cfg->nh_family;
> nhi->fib_nhc.nhc_scope = RT_SCOPE_LINK;
>
> - if (cfg->nh_fdb)
> + if (cfg->nh_fdb) {
> nhi->fdb_nh = 1;
> + nhi->fdb_port = cfg->nh_fdb_port;
> + }
>
> if (cfg->nh_blackhole) {
> nhi->reject_nh = 1;
> @@ -3147,6 +3156,15 @@ static int rtm_to_nh_config(struct net *net, struct
> sk_buff *skb,
> cfg->nh_fdb = nla_get_flag(tb[NHA_FDB]);
> }
>
> + if (tb[NHA_FDB_PORT]) {
> + if (!tb[NHA_FDB] || !tb[NHA_GATEWAY]) {
> + NL_SET_ERR_MSG(extack,
> + "FDB port can only be set on fdb
> nexthops that have a gateway");
> + goto out;
> + }
> + cfg->nh_fdb_port = nla_get_be16(tb[NHA_FDB_PORT]);
> + }
> +
> if (tb[NHA_GROUP]) {
> if (nhm->nh_family != AF_UNSPEC) {
> NL_SET_ERR_MSG(extack, "Invalid family for group");
>
> --
> 2.43.0
>
