As suggested by David, document a somewhat unexpected behavior that results from net.ipv4.tcp_l3mdev_accept=1. This behavior was encountered while debugging FRR, a VRF-aware application, on a system which used net.ipv4.tcp_l3mdev_accept=1 and where TCP connections for BGP with MD5 keys were failing to establish. Cc: David Ahern <dsahern@xxxxxxxxx> Signed-off-by: Benjamin Poirier <bpoirier@xxxxxxxxxx> --- Documentation/networking/vrf.rst | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/Documentation/networking/vrf.rst b/Documentation/networking/vrf.rst index 0dde145043bc..0a9a6f968cb9 100644 --- a/Documentation/networking/vrf.rst +++ b/Documentation/networking/vrf.rst @@ -144,6 +144,19 @@ default VRF are only handled by a socket not bound to any VRF:: netfilter rules on the VRF device can be used to limit access to services running in the default VRF context as well. +Using VRF-aware applications (applications which simultaneously create sockets +outside and inside VRFs) in conjunction with ``net.ipv4.tcp_l3mdev_accept=1`` +is possible but may lead to problems in some situations. With that sysctl +value, it is unspecified which listening socket will be selected to handle +connections for VRF traffic; ie. either a socket bound to the VRF or an unbound +socket may be used to accept new connections from a VRF. This somewhat +unexpected behavior can lead to problems if sockets are configured with extra +options (ex. TCP MD5 keys) with the expectation that VRF traffic will +exclusively be handled by sockets bound to VRFs, as would be the case with +``net.ipv4.tcp_l3mdev_accept=0``. Finally and as a reminder, regardless of +which listening socket is selected, established sockets will be created in the +VRF based on the ingress interface, as documented earlier. + -------------------------------------------------------------------------------- Using iproute2 for VRFs -- 2.32.0
