How to find a Linux namespace by network adapter?

Question

I have a Linux server with multiple network namespaces defined:

# ip netns list
qdhcp-7dedbd4e-2265-4aa2-baac-add4e341dd18
qdhcp-851379ba-1d51-4e45-8e50-b756e81c0949
qdhcp-a19927c5-83b4-4bb4-a8b8-f21fdb5e004b
qdhcp-b94605ff-b0e2-4cfe-a95e-3dd10208a5fb
... ...

Each namespace contains one or more virtual network adapters - in this case, it's a TAP device:

# ip netns exec qdhcp-7dedbd4e-2265-4aa2-baac-add4e341dd18 ip route
192.168.168.0/24 dev tapda4018ab-b7  proto kernel  scope link  src 192.168.168.2
169.254.0.0/16 dev tapda4018ab-b7  proto kernel  scope link  src 169.254.169.254
default via 192.168.168.1 dev tapda4018ab-b7

Now let's say I know the name of the adapter - tapda4018ab-b7 - but I don't know the namespace it belongs to. Is there a way to look it up without checking namespaces one by one? Is there a generic Linux command to do this? Or at least OpenStack Neutron-specific command?

Answer 1

According to this man page http://man7.org/linux/man-pages/man8/ip-netns.8.html you could run the exec command on all namespaces but I tested it on an ubuntu trusty servers and it will not accept "-all" as an argument. So the only way I know to get such an information is via a small bash script. I made one that could certainly be improved as my scripting skills are rather basic, but it will do the work:

#!/bin/bash
i=$(ip netns list | wc -l)
counter=1
while [ $counter -le $i ]; do
    ns=$(ip netns | head -$counter | tail -1)
    ip netns exec $ns ip route | grep $1 | grep proto
    let counter=counter+1
done

You can then launch the script using as sole argument your tap device as in the example bellow:

root@columbo:~# ./list_all_namespace tap8164117b-e3
5.5.5.0/25 dev tap8164117b-e3  proto kernel  scope link  src 5.5.5.3

If you do not provide an argument it will give you an error.

Answer 2

If I understand Neutron correctly (which is a big if - my only experience is with a fairly limited toy installation of Kilo/2015.1.2), you should be able to track through neutron's database to figure out the netns you're looking for

I believe your tap interface would be named using the first 5 octets (10 characters) of the port uuid that it's associated with, and the qdhcp netns uses the uuid of it's network, so you should be able to use the neutron CLI to track down the correct namespace.

You should be able to find the neutron port for your tap interface with:

$ neutron port-list | grep "da4018ab-b7"
| da4018ab-b7xx-xxxx-xxxx-xxxxxxxxxxxx |   | fa:16:xx:xx:xx:xx | {"subnet_id": ...

where "da4018ab-b7" was pulled out of "tapda4018ab-b7". You can then use the full port uuid:

$ neutron port-show da4018ab-b7xx-xxxx-xxxx-xxxxxxxxxxxx

The network_id in the result from port-show should let you figure out the netns (qdhcp-network_id) containing tapda4018ab-b7.

You should be able to use similar logic to track down qg interfaces (which will probably show up on bridges in the default netns), but in that case it's the device_id that owns the port that gives you the qrouter-device_id netns you want.

Answer 3

You can use this script. Save this as get_dhcp_namespace.sh :-

ubuntu@ubuntu$ cat get_dhcp_namespace.sh

#!/bin/bash

interface=$1
id=${interface:3}

port_id=$(neutron port-list | grep $id | awk -F'|' '{print $2}' | tr -d ' ')
net_id=$(neutron port-show $port_id | grep network_id | awk -F'|' '{print $3}' | tr -d ' ')
echo "DHCP namespace is: qdhcp-$net_id"

Run this with the tap interface provided as argument. Don't forget to source the keystonerc/openstackrc/credentials file.

ubuntu@ubuntu$ ./get_dhcp_namespace.sh tapda4018ab-b7
qdhcp-bd39f45d-b45c-4e08-ab74-85c0b1180aea