Finding out the veth# interface of a docker container

Question

I have hundreds of containers in various software virtual switches. I would like to know if its possible to find out which vnet# belongs to which docker container. Right now, I am detecting that by watching syslog as each container gets created. In KVM, there is a command "virsh domiflist ", which is exactly what i'm looking for.

Answer 1

The iflink of the container is the same as the ifindex of the veth#.

You can get the iflink of the container as follows:

docker exec -it <container-name> bash -c 'cat /sys/class/net/eth0/iflink'

Say, that results in 12, then grep for that:

grep -l 12 /sys/class/net/veth*/ifindex

That will give a unique result, on my system:

/sys/class/net/veth11d4238/ifindex

Combine that in a script:

#!/bin/bash

for container in $(docker ps -q); do
    iflink=`docker exec -it $container bash -c 'cat /sys/class/net/eth0/iflink'`
    iflink=`echo $iflink|tr -d '\r'`
    veth=`grep -l $iflink /sys/class/net/veth*/ifindex`
    veth=`echo $veth|sed -e 's;^.*net/\(.*\)/ifindex$;\1;'`
    echo $container:$veth
done

The script was written to be easy to follow.

Sample run:

$ docker ps -q
c4d8096eff43
34ac6e9f1e6e
d5a2aa5f3de3

$ sudo ./vethfinder
c4d8096eff43:veth11d4238
34ac6e9f1e6e:veth7d52cd1
d5a2aa5f3de3:vethe46073d

Reference: https://forums.docker.com/t/relationship-between-interface-vethxxxxx-and-container/12872/20

Answer 2

searches for all interfaces in containers.

#!/bin/bash

for container in $(docker ps --format '{{.Names}}'); do
    iflink=`docker exec -it $container bash -c 'cat /sys/class/net/eth*/iflink'`
    for net in $iflink;do
        net=`echo $net|tr -d '\r'`
        veth=`grep -l $net /sys/class/net/veth*/ifindex`
        veth=`echo $veth|sed -e 's;^.*net/\(.*\)/ifindex$;\1;'`
        echo $container:$veth
    done
done

Answer 3

I am using a different method, which seem to work just fine:

[root@kh1 ~]# docker inspect 6d48e279c5b8 --format '{{.State.Pid}}'                                                                                                                                                                                                              
56316
[root@kh1 ~]# 
[root@kh1 ~]# ip netns identify 56316
ns-56316
[root@kh1 ~]# 
[root@kh1 ~]# ip netns list | grep ns-56316
ns-56316 (id: 6)
[root@kh1 ~]# 
[root@kh1 ~]# ip link show | grep -B1 "link-netnsid 6"
330: veth1ce76e2b@if3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master cni0 state UP mode DEFAULT group default 
    link/ether de:f8:ce:a2:85:f9 brd ff:ff:ff:ff:ff:ff link-netnsid 6

Answer 4

Have a look here: https://stackoverflow.com/questions/37860936/find-out-which-network-interface-belongs-to-docker-container

There are examples of how one can fetch veth names for running docker containers without root access.

An example shell script can be found here: https://github.com/dicho-usp/dockerveth

#!/bin/bash

NAME=$1
PID=$(docker inspect $NAME --format "{{.State.Pid}}")
while read iface id; do
    [[ "$iface" == lo ]] && continue
    veth=$(ip -br addr | sed -nre "s/(veth.*)@if$id.*/\1/p")
    echo -e "$NAME\t$iface\t$veth"
done < <(</proc/$PID/net/igmp awk '/^[0-9]+/{print $2 " " $1;}')