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Boris
Asked: 2024-10-30 16:21:50 +0800 CST

How to get global IPv6 address of the current machine?

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I a bash script, I want to obtain the global IPv6 address of my machine for a given network adapter (on my case 'ens18'). To get started, I issued the following command:

ip -6 addr

This gives me the followig output, which contains the address I'm looking for:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 state UNKNOWN qlen 1000
    inet6 ::1/128 scope host noprefixroute 
       valid_lft forever preferred_lft forever
2: ens18: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 fd00::3170:4ff:eff4:a4ab/64 scope global dynamic mngtmpaddr noprefixroute 
       valid_lft 6736sec preferred_lft 3136sec
    inet6 2a02:8070:2982:4300:3170:4ff:eff4:a4ab/64 scope global dynamic mngtmpaddr noprefixroute 
       valid_lft 6736sec preferred_lft 3136sec
    inet6 af60::3170:4ff:eff4:a4ab/64 scope link 
       valid_lft forever preferred_lft forever
3: br-7ac197bd041e: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP 
    inet6 af60::42:80ff:fe52:3481/64 scope link 
       valid_lft forever preferred_lft forever
4: docker0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP 
    inet6 af60::42:6eff:fecf:5e6/64 scope link 
       valid_lft forever preferred_lft forever
6: veth074f8b0@if5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP 
    inet6 af60::7073:40ff:fe59:aad0/64 scope link 
       valid_lft forever preferred_lft forever
8: vethe85ed67@if7: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP 
    inet6 af60::5c09:65ff:fe34:34f4/64 scope link 
       valid_lft forever preferred_lft forever

So the global IPv6 address is "2a02:8070:2982:4300:3170:4ff:eff4:a4ab".

How can retrieve this value reliably from my bash script?

bash

2 Answers

  1. Best Answer

    I would start with

    ip -6 addr ls -deprecated primary dev ens18 scope global | awk '/inet6/{print $2}'

    where

    • dev ens18 tell ip to query only for ens18
    • -deprecated (to be put after ls or show) filter out temporary outgoing IP
    • primary select primary (e.g. first IP given to interface)
    • scope global print only global adress (won't print link level address like fe80:: )
    • /inet6/ tell awk to filter line with inet6
    • { print $2} print value

    Note that ipv6 like fe80:: and fd00:: are local and site address (thoses are filtered out by scope global flag).

    a more XXI-th century solution would be

    ip --json addr ${OTHER_ARGS} |
  jq -r '.[].addr_info[] |
         select(.scope == "global") |
         select(.family == "inet6") |
         .local'

    (with ${OTHER_ARGS} from awk's solution above)

    • 2

  2. I would say that instead of parsing ip output or relying on tools like js (which needs to be installed), you may start off the hostname -I output which simply presents a list of all IP addresses assigned to the machine. Like this:

    for i in `hostname -I`; do if echo ${i} | grep -qv \\. ; then echo ${i}; break; fi done

    This will show the first IPv6 address appeared in the list, even if it's link-local or site-local. You can grep them away too:

    for i in `hostname -I`; do if echo ${i} | grep -qvP "\.|^fe80:|^fd00:" ; then echo ${i}; break; fi done
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