[ovs-discuss] skipping output to input port

Nicolas Bouliane nbouliane at digitalocean.com
Tue Nov 12 21:27:19 UTC 2019


Sometimes, icmpv6 neighbor advertisement packets are being sent out of the
hypervisor without their VLAN tag. It seems to only happens when the icmpv6
is sent to a multicast address. That doesn't happen to every VMs, and not
all the time. Can't reproduce the problem on demand yet.

I'm trying to better understand what the log message "skipping output to
input port" really means. Because every time a packet is sent without a
VLAN tag, we also see this printed in the log. Normally, these packets are
being VLAN tagged, and when we  ofproto/trace, we see that the packet
should be tagged.

2019-11-12T21:06:13.838Z|01842|ofproto_dpif_xlate(handler148)|INFO|skipping
output to input port on bridge br0 while processing
recirc_id=0x5a4de60,ct_state=inv|trk,eth,icmp6,in_port=10227,vlan_tci=0x0000,dl_src=6a:5e:dd:34:f9:be,dl_dst=33:33:ff:25:80:0b,ipv6_src=fe80::685e:ddff:fe34:f9be,ipv6_dst=ff02::1:ff25:800b,ipv6_label=0x00000,nw_tos=0,nw_ecn=0,nw_ttl=255,icmp_type=135,icmp_code=0,nd_target=2604:xxxx:x:xx::xx:xxxx,nd_sll=6a:5e:dd:34:f9:be,nd_tll=00:00:00:00:00:00

I read
https://github.com/openvswitch/ovs/blob/master/ofproto/ofproto-dpif-xlate.c but
yet I'm not sure I fully grasp what it means. Also, since it's
intermittent, seems like there is something dynamic. Looked at the
connection tracking, and also at the ovs/show/route cache... but haven't
figured yet.

thanks !
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