[ovs-discuss] User space tunneling doesn't support setting tunnel key (e.g. tunnel id for VxLAN) by flow

Li, Ricky ricky.li at intel.com
Wed Mar 25 02:23:52 UTC 2015


I tried to test user space tunneling according to this guide:

Everything works in this guide, but when I tried to specify the tunnel ID with flow as below, there is a problem:
ovs-vsctl add-port int-br vxlan0 -- set interface vxlan0 type=vxlan  options:remote_ip= options:out_key=flow

I try to add an option: out_key=flow to make OVS specify the tunnel ID by flow as below:
ovs-ofctl add-flow int-br "in_port=LOCAL, icmp, actions=set_tunnel:3, output:1"     (1 is the port# of vxlan0)

But this setup doesn't work, because the output tunnel ID is still 0 (the default tunnel ID) but not 3.
I also tried the same flow with kernel space Datapath and it works, the tunnel ID will be changed by flow.

Then I looked up the source code related to user space tunneling and I can find when OVS tries to encapsulate the tunnel header, it will firstly try to build the tunnel header:

In ofproto-dpif-xlate.c: compose_output_action__()
            if (tnl_push_pop_send) {
                build_tunnel_send(ctx, xport, flow, odp_port);
                flow->tunnel = flow_tnl; /* Restore tunnel metadata */
tnl_push_pop_send is the flag for user space tunneling, and it will try to build tunnel header in lib/tunnel.c:

In tunnel.c: tnl_port_build_header()

tnl_port_build_header(const struct ofport_dpif *ofport,
                      const struct flow *tnl_flow,
                      uint8_t dmac[ETH_ADDR_LEN],
                      uint8_t smac[ETH_ADDR_LEN],
                      ovs_be32 ip_src, struct ovs_action_push_tnl *data)
res = netdev_build_header(tnl_port->netdev, data);

We can find it calls the Netdev API "netdev_build_header" to build the tunnel header. If the tunnel ID is set by flow, it should be saved in the object "tnl_flow" (tnl_flow->tunnel->tun_id), but it's not passed into the Netdev API.

In netdev-vport.c: netdev_vxlan_build_header()
put_16aligned_be32(&vxh->vx_vni, htonl(ntohll(tnl_cfg->out_key) << 8));

The tunnel id (VNI) is directly set by tunnel port configuration (tnl_cfg), then I think the "options:out_key=flow" will never works because of this? The tunnel ID will always set with the tunnel configuration when we initiate it.

One suggestion is to add one more input for the Netdev API:
Int netdev_build_header(const struct netdev *netdev, struct ovs_action_push_tnl *data, const struct flow *tnl_flow)

The new input "const struct flow *tnl_flow" can be passed to the callback for building tunnel header, e.g. for VxLAN:
put_16aligned_be32(&vxh->vx_vni, htonl(ntohll(tnl_flow->tunnel.tun_id) << 8));

Similar changes can be made for other tunnel ports like GRE. This patch can work on my side with some simple experiments. I want to check if my understanding is right, and hope for any advices and inputs.


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