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I would like to assign a static IPv6 address to my machine running Ubuntu Server 15 using DHCPv6. To do so, I need to know the DUID used by the DHCP client so I can assign the static IP to it in my network's DHCP server.

How can I find out which DUID is being used?

ThiefMaster
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2 Answers2

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Ubuntu server calls dhclient with a few flags, but mostly default options, and it therefore defaults to a type 1 DUID-LLT DUID. Ubuntu desktop uses Network Manager which then calls dhclient with a type 4 DUID-UUID DUID.

For servers, it puts it in /var/lib/dhcp/dhclient6.......lease
For desktop, it puts it in /var/lib/NetworkManager/dhclient6.......lease

It's a weird string that looks like:
default-duid "\000\001\000\001\037\305\371\341\001\002\003\004\005\006"

Here's a short script you can use to convert it to a normal hex format duid.
Just run the script like:

./script '\000\001\000\001\037\305\371\341\001\002\003\004\005\006'

The script:

#!/bin/bash

printf $1 | hexdump -e '14/1 "%02x " "\n"' | sed 's/ /:/g'
Bryce Larson
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    my dhclient6..lease file has the following: "\000\004\354\352~\365\017\375\330\201!\230+<Oj\031\302" which returns an error with your script. Any ideas? – Arindrew Feb 21 '17 at 18:09
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    Replace the double quotes with single quotes because there are characters like ! in your duid lease file and change the 14/1 to 18/1 in the script to account for the longer length of type 4 duid's. I think the script originally came from some redhat documentation and only had type 1 and type 3 duid's in mind. – Bryce Larson Feb 22 '17 at 07:57
  • actually, I found even better was to add -s 2 to skip some of the pre-amble, e.g.:

    hexdump -s 2 -e '14/1 "%02x " "\n"' /var/lib/dhcpv6/dhcp6c_duid

     – Brian Redbeard Jul 09 '17 at 07:49
  • I also found a mix of ASCII and octal. This bash shell function decodes it: decode_lease_id () { local pat='^\\([0-9]{3})|.' input=$1; while [[ "$input" =~ $pat ]]; do if [[ "${BASH_REMATCH[1]}" ]]; then int=$(( 8#${BASH_REMATCH[1]} )); input=${input:4}; else int=\'${BASH_REMATCH[0]}; input=${input:1}; fi; printf '%02x' "$int"; if [[ "$input" ]]; then printf :; else printf '\n'; fi; done; } so decode_lease_id '\000\004\354\352~\365\017\375\330\201!\230+<Oj\031\302' produces 00:04:ec:ea:7e:f5:0f:fd:d8:81:21:98:2b:3c:4f:6a:19:c2. – Walf Feb 26 '25 at 07:46
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If you are using DHCP with ISC dhcpd look in:

/etc/dhcp/dhclient6.conf

If you are using dibbler as dhcp client check for the DUID in:

/var/lib/dibbler/client-duid

It might also be worth checking in /etc/dibbler/client.conf if any other bits are there.

kcrk
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