Get MAC from DUID

Tim Peiffer peiffer at
Wed May 20 11:25:53 UTC 2009

I saw a reply that says forget it and that the DUID can be manufactured.
For IPv6, Vista and other devices offer privacy extensions that hash the
IP address (even link local) every few hours, so relying on a table with
privacy fudge is no exactly helpful. RFC 3041 says the process is
supposed to be opaque to the outside.

What remains is OT.. so if you object, hit <delete>.

I would like to suggest that you turn to address tracking to find this
information. IPv6 provides the MAC address for every 'neighbor' in a
manner similar to the IPv4 ARP table.. Explicitly ask the devices (maybe
the router, maybe the DHCP server) on the wire with host for the
neighbor relationship. With vendor 'C', it is 'show ipv6 neighbor [ipv6
address]', With Unix, 'ip -f inet6 neigh', with XP, 'ipv6 nc' will show
you the neighbor cache. Filter out the link local addresses, the tunnel
addresses, and the stale entries, and you have the IPv6 to MAC binding.

Of course, the other part of the equation is physical location of
binding an address to switchport and room/jack.

Tim Peiffer
Network Support Engineer
Office of Information Technology
University of Minnesota/NorthernLights GigaPOP

Router# show ipv6 neighbor vlan787

IPv6 Address Age Link-layer Addr State Interface
2001:468:1910:201:1173:B0EB:3DC5:9278 56 000d.5693.205d STALE Vl787
FE80::212:3FFF:FEDC:A34D 75 0012.3fdc.a34d STALE Vl787

[peiffer at engineer8 ~]$ /sbin/ip -f inet6 neigh
fe80::20f:8fff:fee1:3740 dev eth0 lladdr 00:0f:8f:e1:37:40 router STALE
2001:468:1910:201::1 dev eth0 FAILED

H:\>ipv6 nc
8: fe80::205:9aff:fe3c:7800 00-05-9a-3c-78-00 permanent
6: fe80::ffff:ffff:fffd permanent
6: fe80::8000:f227:bec8:61af incomplete (router)
5: fe80::212:3fff:fed2:5a94 00-12-3f-d2-5a-94 permanent
5: fe80::20f:8fff:fee1:3740 00-0f-8f-e1-37-40 stale (router)
5: 2001:468:1910:201:212:3fff:fed2:5a94 00-12-3f-d2-5a-94 permanent
5: 2001:468:1910:201:bcb3:627f:9965:bd91 00-12-3f-d2-5a-94 permanent
5: 2001:468:1910:201:20f:1fff:fed4:3faf incomplete
4: fe80::213:ceff:fe1e:a136 00-13-ce-1e-a1-36 permanent
3: 2002:8065:e40c::8065:e40c permanent
3: 2002:8654:581b::8654:581b permanent
3: 2002:8654:8b::8654:8b permanent
3: 2002:c058:6301::c058:6301 permanent
3: 2002:8654:36::8654:36 permanent
3: 2001:468:1910:201:20f:1fff:fed4:3faf incomplete
2: fe80::5efe: permanent
2: fe80::5efe: permanent
2: fe80::5efe: permanent
2: fe80::5efe: permanent
1: fe80::1 permanent
1: ::1 permanent

roddy1986 wrote:
> dear all:
> I have a puzzle. I want to get the mac address from the DUID.
> It's my file:
> host 11 { host-identifier option dhcp6.client_id
> 00:01:00:01:11:a5:43:82:00:14:22:22:a1:1a; fixed-address6 feff::1; }
> I hope use the mac instead of DUID because the DUID will change in
> some situations.
> my boss asked maping ip to mac one-to-one for recording something
> SHOULD NOT i have all the client's ip and mac in DB.
> if anyone has ideas...
> Thanks~
> 2009-05-20
> roddy1986
> ------------------------------------------------------------------------
> _______________________________________________
> dhcp-users mailing list
> dhcp-users at

More information about the dhcp-users mailing list