Re: dhcpleased with option dhcp-client-identifier

On Wed, Aug 18, 2021 at 07:48:10PM +0200, florian@openbsd.org wrote:
> > It seems dhcpleased is automatically adding the hostname of the machine
> > in the DHCP message. That's the first instance of "browser" seen above.
> >
> > dhcpd(8) doesn't seem to catch correctly the client identifier. Is it
> > supposed to work like that ?
>
> They both send the hostname, that's not the problem. Opinions differ on how
> the client ID should be encoded.
>
> > Aug 13 18:10:11.599556 fe:e1:bb:d1:b2:92 ff:ff:ff:ff:ff:ff 0800 342:
> > 0.0.0.0.68 > 255.255.255.255.67: [udp sum ok] xid:0xba962e2
> > vend-rfc1048 DHCP:REQUEST HN:"browser"
> ^^^^ hostname
>
> > CID:0.98.114.111.119.115.101.114 PR:SM+DG+NS+HN+DN+BR+119+121
> ^^^ client id
>
> > RQ:192.168.1.98 [tos 0x10] (ttl 128, id 0, len 328)
>
> > Aug 13 18:12:13.530188 fe:e1:bb:d1:c2:c4 fe:e1:ba:d0:b7:ec 0800 342:
> > 192.168.1.219.68 > 192.168.1.12.67: [udp sum ok] xid:0xfbdfb850
> > secs:4188 C:192.168.1.219 vend-rfc1048 DHCP:REQUEST HN:"rex"
> ^^^ hostname
> > PR:SM+BR+TZ+121+DG+DN+119+NS+HN+BF+TFTP CID:114.101.120 [tos 0x10]
> ^^^ client id
> > (ttl 128, id 38490, len 328)
>
> dhclient sends this as client id:
> CID:114.101.120
>
> Which is hardware type 114 and hardware address 101.120 (in decimal)
> Interpreted as ascii this is of course "rex".
>
> RFC 2132 has this:
> The client identifier MAY consist of type-value pairs similar to the
> 'htype'/'chaddr' fields defined in [3]. For instance, it MAY consist
> of a hardware type and hardware address. In this case the type field
> SHOULD be one of the ARP hardware types defined in STD2 [22]. A
> hardware type of 0 (zero) should be used when the value field
> contains an identifier other than a hardware address (e.g. a fully
> qualified domain name).
>
> dhcpleased sends this:
> CID:0.98.114.111.119.115.101.114
>
> Which is hardware type 0 + "browser"
>
> dhcpleased.conf has this:
> send client id client-id
> Send the dhcp client identifier option with a value of client-id.
> If client-id consists of a series of octets of two-digit
> hexadecimal numbers separated by colons, the first octet is used
> as the type and the rest as value. The MAC address
> 00:53:FF:AA:BB:CC would be configured as
>
> send client id "01:00:53:FF:AA:BB:CC"
>
> Otherwise the string client-id is sent verbatim with type zero.
> The default is to send the interface's MAC address as client
> identifier.
>
> now, what will probably work for you is:
>
> send client id "00:62:72:6f:77:73:65:72"
>
> So in short, everything is terrible.
>
> Should dhcpleased do what dhclient does?
> People who actually use this please speak up.
>


Thanks you Florian for the detailed explanation. Appreciated.
Best.

--
Olivier Cherrier
Phone: +352691570680
mailto:oc@symacx.com