[ovs-discuss] IPv6 dadfailed

[Gurucharan Shetty]

On Fri, Dec 12, 2014 at 5:08 AM, Tobias Brunner <tobias.brunner at vshn.ch> wrote:
> Hi list
>
> I'm trying to get IPv6 traffic to flow over the Open vSwitch, but it always
> fails at assigning an IPv6 address (this is a VM, connected to Open vSwitch):
>
> 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qlen 1000
>     inet6 fe80::5054:ff:fed6:46a3/64 scope link tentative dadfailed
>        valid_lft forever preferred_lft forever
>
> When disabling dad, IPv6 communication works:
>
> sysctl -w net.ipv6.conf.eth0.accept_dad=0
>
> 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qlen 1000
>     inet6 fe80::5054:ff:fed6:46a3/64 scope link
>        valid_lft forever preferred_lft forever
>
> ping6 google.ch
> PING google.ch(mil01s19-in-x1f.1e100.net) 56 data bytes
> 64 bytes from mil01s19-in-x1f.1e100.net: icmp_seq=1 ttl=58 time=6.22 ms
> 64 bytes from mil01s19-in-x1f.1e100.net: icmp_seq=2 ttl=58 time=5.16 ms
>
> The VM and the host are both running Ubuntu Server 14.04.1 LTS. Open vSwitch
> is at version 2.0.2. On the host only libvirt and kvm is used, nothing more...
>
> Any ideas why dad does not work or how I can debug this thing?
I don't use IPv6, so I don't know the specifics, but here are some
details on how you can debug it.

* Assuming you have just one VM, on your hypervisor, a 'ovs-vsctl
show' will show you the name of the virtual interface name (vif). So
the first thing to do is put a tcpump on that interface to see if any
traffic is coming through. (If there are many VMs, you will have to
look at libvirt's xml file to get hints on vif name.)

* Assuming, you see some traffic on vif, next thing to do is, run
'ovs-dpctl -m dump-flows'. This will show all the flows in the kernel.
If it is a lot of flows, it may be a better idea, to limit OVS use to
just that one VM, so that you know that all the flows being shown is
just that VM. If there is no bug, you may see that there is some flow
which shows as 'drop'. Then you know that there is some problem there.

* If there is a bug, it is also likely that there is some log message
in '/var/log/openvswitch/ovs-vswitchd.log' which shows an entry for
every packet loss.





>
> Cheers,
> Tobias
> _______________________________________________
> discuss mailing list
> discuss at openvswitch.org
> http://openvswitch.org/mailman/listinfo/discuss