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How can I debug network-related issues?

asked 2013-03-27 16:44:03 -0500

iainbuc gravatar image

updated 2013-06-11 10:27:44 -0500

fifieldt gravatar image

I'm having real trouble setting up networking with OpenStack. I had it partly working a while ago, but now I don't even get an IP address. I followed the main guide, but found it difficult to understand why things were being done - a list of instructions is all very well, but without explanations/background it makes debugging tough.

I've got a few questions I hope someone can help me with:

  • responsibility for networking has mainly moved from nova to quantum. So the new way of doing things is solely in quantum - I can ignore anything network related in nova EXCEPT for metadata?

  • is there a problem with rebooting - the bridges created in the guide don't come up automatically?

If I manually start the bridges and restart all the services I can bring up a virtual machine in the web GUI and see messages in /var/log/syslog - pairs of DHCPDISCOVER/DHCPOFFER. This goes on for some time until the VM gives up:

cloud-init-nonet waiting 120 seconds for a network device.
cloud-init-nonet gave up waiting for a network device.
ci-info: lo    : 1       .
ci-info: eth0  : 1 .               .               fa:16:3e:14:5a:69
route_info failed

The bridge setup (ovs-vsctrl show):

   Bridge br-tun
       Port br-tun
           Interface br-tun
               type: internal
       Port patch-int
           Interface patch-int
               type: patch
               options: {peer=patch-tun}
   Bridge br-int
       Port "qr-03033815-f4"
           tag: 1
           Interface "qr-03033815-f4"
               type: internal
       Port br-int
           Interface br-int
               type: internal
       Port patch-tun
           Interface patch-tun
               type: patch
               options: {peer=patch-int}
       Port "qvocd51bf09-06"
           tag: 1
           Interface "qvocd51bf09-06"
       Port "tap5ec829c5-74"
           tag: 1
           Interface "tap5ec829c5-74"
               type: internal
   Bridge br-ex
       Port br-ex
           Interface br-ex
               type: internal
       Port "eth1"
           Interface "eth1"
   ovs_version: "1.4.0+build0"
  • Interfaces: the "tap" interface seems to be the network node, while the "qr" interface is the controller. (Is this always the case? I'm just matching IP addresses when I do "ifconfig <interface>") The "qvoc" interface is the VM - I think - it has no IP address?

  • Connectivity: all three of them are on the br-int bridge, so presumably they should all be able to talk to each other? (This is the same as if they were all plugged into a switch, right?)

  • Is there a way to see where things are going wrong? It looks like the DHCPOFFER is never reaching the VM, which if they're all connected seems odd. Can I get a trace of packets being dropped or similar?

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answered 2013-03-29 17:25:55 -0500

smaffulli gravatar image

It's very hard to debug network-related issues. I can give a pointer to a post that explains more about debugging and logging OpenStack. By Victoria Martínez de la Cruz Logging and debugging in OpenStack. If you're still stuck probably the best thing to do is to hop on IRC and get some real-time help there.

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Asked: 2013-03-27 16:44:03 -0500

Seen: 1,284 times

Last updated: Mar 29 '13