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ipv6 only goes half-way

asked 2015-06-10 15:37:49 -0500

don gravatar image

updated 2015-06-13 18:41:08 -0500

juno, ubuntu 14.10

i have an instance which is sending IPv6. the UDP packets make it all the way, but TCP packets stop half way out of it. By this i mean these are the four interfaces involved (KVM, OVS). The tap interface and the qbr interface have ipv6 tcp on them, the qvb/qvo do not. But the udp goes there.

[edit: it appears this is incorrect. the first few packets after its been idle for a while work, and they are udp. This implies maybe some bridge learning issue].

Is there some checksum offload or something? this is on a compute node running just nova-compute+neutron ovs agent. There is no iptables rule preventing (in fact i have port-security = off).

qbr3cdf22f7-17 Link encap:Ethernet  HWaddr 26:bb:42:b0:66:42  
qvb3cdf22f7-17 Link encap:Ethernet  HWaddr 26:bb:42:b0:66:42  
qvo3cdf22f7-17 Link encap:Ethernet  HWaddr c6:c5:37:34:9e:72  
tap3cdf22f7-17 Link encap:Ethernet  HWaddr fe:16:3e:46:d6:59

so, uh, what could be eating the ipv6 tcp?

[on the topology, this is all within the compute node, so it has nothing to do w/ the rest of the system. it is the default setup of nova+neutron when using ovs plugin ml2. Those 4 tap interfaces should all have the same packets on them. 1 is bound to the instance port, 1 is bound to the ovs port, and the other two bridge between them somehow. If you have such a setup and you do ifconfig on the compute node you will see this tap/qvo/qvb/qbr ###### for each instance port]

the journey is: instance sends on 'tap' interface. There is a linux bridge from tap interface to qvb interface [using qbr]

brctl show qbr3cdf22f7-17
bridge name     bridge id               STP enabled     interfaces
qbr3cdf22f7-17          8000.26bb42b06642       no              qvb3cdf22f7-17
                                                        tap3cdf22f7-17

and that is where the packet ends. If i run tcpdump on 'tap' and on 'qbr', i see all packets. If i run tcpdump on 'qvb', the ipv6 packets are missing.

tap3cdf22f7-17 Link encap:Ethernet  HWaddr fe:16:3e:46:d6:59  
          UP BROADCAST RUNNING PROMISC MULTICAST  MTU:1500  Metric:1
          RX packets:248461 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1887 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:500 
          RX bytes:195112976 (195.1 MB)  TX bytes:316836 (316.8 KB)

qbr3cdf22f7-17 Link encap:Ethernet  HWaddr 26:bb:42:b0:66:42  
          UP BROADCAST RUNNING PROMISC MULTICAST  MTU:1500  Metric:1
          RX packets:4268 errors:0 dropped:0 overruns:0 frame:0
          TX packets:24 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:1493145 (1.4 MB)  TX bytes:2320 (2.3 KB)

qvo3cdf22f7-17 Link encap:Ethernet  HWaddr c6:c5:37:34:9e:72  
          UP BROADCAST RUNNING PROMISC MULTICAST  MTU:1500  Metric:1
          RX packets:3322 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1895 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen ...
(more)
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answered 2015-06-13 18:48:12 -0500

don gravatar image

updated 2015-06-13 19:33:37 -0500

It turns out if i run 'brctl setageing qbr3cdf22f7-17 0' then it works. This disables the bridge learning.

As to why, i don't know.

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answered 2015-06-12 10:10:03 -0500

Kannan Raman gravatar image

updated 2015-06-12 10:11:23 -0500

The topology part I could not understand it so make it clearly . I'll give you my best knowledge.

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Comments

i added a comment about the 'topology'. this is standard setup by nova+neutron when using ovs ml2, all within the compute node. https://github.com/lorin/openstack-ha... shows the path.

don gravatar imagedon ( 2015-06-13 09:34:55 -0500 )edit

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Asked: 2015-06-10 15:37:49 -0500

Seen: 290 times

Last updated: Jun 13 '15