tl;dr mpls_output expects skb->protocol to be set to correct ethertype, but it isn't
https://github.com/torvalds/linux/blob/ede2059dbaf9c6557a49d466c8c7778343b208ff/net/mpls/mpls_iptunnel.c#L64 Problem: I set up two interfaces pointed at each other, and added a static arp entry to minimise complexity ifconfig enp0s8 10.0.0.1/24 up ifconfig enp0s9 up arp -s 10.0.0.5 00:12:34:56:78:90 I then added an MPLS route ./dev/iproute2/ip/ip route add 192.168.2.0/24 encap mpls 100 via inet 10.0.0.5 dev enp0s8 I then tried to ping an IP in this route but got errors back ping 192.168.2.1 * PING 192.168.2.1 (192.168.2.1) 56(84) bytes of data. * ping: sendmsg: Invalid argument I then recorded calls to skb_kfree ./tools/perf/perf record -e skb:kfree_skb -g -a This gave me the following packet trace: 100.00% 100.00% ping [kernel.kallsyms] [k] kfree_skb | ---kfree_skb mpls_output lwtunnel_output ip_local_out_sk ip_send_skb ip_push_pending_frames raw_sendmsg inet_sendmsg sock_sendmsg ___sys_sendmsg __sys_sendmsg sys_sendmsg entry_SYSCALL_64_fastpath sendmsg 0 I then went through mpls_output.c and put printk() at every call to "goto drop" and found that this was being hit after failing to match skb->protocol https://github.com/torvalds/linux/blob/ede2059dbaf9c6557a49d466c8c7778343b208ff/net/mpls/mpls_iptunnel.c#L64 My understanding is that skb->protocol is normally set after dst_output. For example, a ping packet hitting a normal IPv4 route should follow something like: raw_sendmsg ip_push_pending_frames ip_send_skb ip_local_out_sk dst_output ip_output ip_output() is the first place where skb->protocol gets set https://github.com/torvalds/linux/blob/dbd3393c56a8794fe596e7dd20d0efa613b9cf61/net/ipv4/ip_output.c#L356 The path that a packet follows when hitting an MPLS route is as follows: raw_sendmsg ip_push_pending_frames ip_send_skb ip_local_out_sk dst_output lwtunnel_output mpls_output lwtunnel_output merely routes to the correct output function (mpls_output) mpls_output expects skb->protocol to be set, but nothing has set it yet, so it drops the packet! Any suggestions on how mpls_output should detect the protocol? Setup: Ubuntu 15.10 iproute2 built from head Kernel 4.3, both ubuntu mainline and home-built: make menuconfig, add lwtunnel, mpls-router, mpls-gso and mpls-iptunnel Running virtualbox on OSX -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
