Script to find network interface name from IPv6 address

Experts,

Please help me to write a script to find the network interface name from the given IPv6 address.

For example:

if "ifconfig" gives the output like:

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:90440 errors:0 dropped:0 overruns:0 frame:0
          TX packets:90440 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:10181289 (10.1 MB)  TX bytes:10181289 (10.1 MB)

eth0      Link encap:Ethernet  HWaddr 00:50:56:bb:9f:9d
          inet6 addr: fe80::250:56ff:febb:9f9d/64 Scope:Link
          inet6 addr: 2001:111:1111:1111:1000::41/64 Scope:Global
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:138859 errors:0 dropped:10 overruns:0 frame:0
          TX packets:69332 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:46310896 (46.3 MB)  TX bytes:18119186 (18.1 MB)

eth1      Link encap:Ethernet  HWaddr 00:50:56:bb:9f:9d
          inet6 addr: fe80::250:56ff:febb:9f9d/64 Scope:Link
          inet6 addr: 2001:222:2222:2222:1000::41/64 Scope:Global
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:138859 errors:0 dropped:10 overruns:0 frame:0
          TX packets:69332 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:46310896 (46.3 MB)  TX bytes:18119186 (18.1 MB)

and the given IPv6 address is: 2001:111:1111:1111:1000::41 then the output should be "eth0"

Appreciate your help in advance.

Thanks.

Solution

Why make things complicated? I like simple. And this is about as simple as it gets. (And you shouldn't be using ifconfig as it's deprecated and not installed by default on modern Linux distributions.)

ip a s to fda8:75f3:eca7:100::1 | awk -F ": " 'NF > 1 {print $2}'

Let's go over it step by step.

First the ip output.

$ ip address show to fda8:75f3:eca7:100::1
12: virbr2: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 1000
    inet6 fda8:75f3:eca7:100::1/64 scope global 
       valid_lft forever preferred_lft forever

This tells us the interface the IP is on, and omits any other addresses that might be on the interface.

So we'll parse it out with awk. We use ": " as a field separator, print the second field, and only print matching lines.

$ ip address show to fda8:75f3:eca7:100::1 | awk -F ": " 'NF > 1 {print $2}'
virbr2

Finally we'll abbreviate address show to the minimum.

$ ip a s to fda8:75f3:eca7:100::1 | awk -F ": " 'NF > 1 {print $2}'
virbr2

This will also work with IPv4 addresses, if you want to locate one of those.