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No traffic on br-tun

asked 2014-03-02 20:20:56 -0500

xionglingfeng gravatar image

updated 2014-03-02 20:21:55 -0500

I configured one network node and one compute node on a Xen based server. When a VM is bring up, it cannot get a IP address from DHCP. I tried to set its IP address manually and ping the gateway, of course, all packets are timed out.

In computer node, I run tcpdump to capture packets. For br-int, I do captured packets from client

xxxx@os-compute:~$ sudo tcpdump -i br-int

tcpdump: WARNING: br-int: no IPv4 address assigned

tcpdump: verbose output suppressed, use -v or -vv for full protocol decode

listening on br-int, link-type EN10MB (Ethernet), capture size 65535 bytes

22:48:56.730834 ARP, Request who-has tell , length 28

However, in br-tun, there is no traffic.

Anyone can help me on this? Thanks.

The configuration of OpenVSwitch is listed below:

xxxx@os-compute:~$ sudo ovs-vsctl show


Bridge br-int

    Port br-int

        Interface br-int

            type: internal

    Port "eth3"

        Interface "eth3"

    Port patch-tun

        Interface patch-tun

            type: patch

            options: {peer=patch-int}

Bridge br-tun

    Port "vxlan-1"

        Interface "vxlan-1"

            type: vxlan

            options: {in_key=flow, local_ip="", out_key=flow, remote_ip=""}

    Port br-tun

        Interface br-tun

            type: internal

    Port patch-int

        Interface patch-int

            type: patch

            options: {peer=patch-tun}

ovs_version: "1.10.2"
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Are you using VXLan ? Just run 'sudo udhcpc' from vm and till which point packets are coming ? Run tcpdump -n -i <interface> command. See whether DHCP requests are coming at every interface point.

dheeru gravatar imagedheeru ( 2014-03-02 23:04:06 -0500 )edit

I too have the same problem it is reaching hust br-int not br-tun. please help

fresher gravatar imagefresher ( 2015-01-01 01:28:30 -0500 )edit

check ovs-ofctl dump-flows br-tun to check if the amount of packets being accepted is increasing or not. Tcpdump -i br-tun might not work for several reasons.

rever gravatar imagerever ( 2015-02-04 09:44:14 -0500 )edit

1 answer

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answered 2019-07-23 12:58:22 -0500

gsm.asad gravatar image

The TAP devices and veth devices are normal Linux network devices and may be inspected with the usual tools, such as ip and tcpdump. Open vSwitch internal devices, such as patch-tun, are only visible within the Open vSwitch environment. If you try to run tcpdump -i patch-tun, it will raise an error, saying that the device does not exist.

It is possible to watch packets on internal interfaces, but it does take a little bit of networking gymnastics. First you need to create a dummy network device that normal Linux tools can see. Then you need to add it to the bridge containing the internal interface you want to snoop on. Finally, you need to tell Open vSwitch to mirror all traffic to or from the internal port onto this dummy port. After all this, you can then run tcpdump on the dummy interface and see the traffic on the internal port.

All this is mentioned in the Openstack network troubleshooting guide

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Asked: 2014-03-02 20:20:56 -0500

Seen: 1,205 times

Last updated: Mar 02 '14