I can confirm that MPLS packets are sent correctly if the conditional at mpls_iptunnel.c:57-65 is removed and just replaced with lines 58-59:
ttl = ip_hdr(skb)->ttl; rt = (struct rtable *)dst; Obviously this isn't sufficient for IPv6, but is a workaround that enables MPLS-encapsulated packets to be sent from Linux in the meantime On 6 December 2015 at 23:20, Sam Russell <sam.h.russ...@gmail.com> wrote: > 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
