Supported format for Client Identifier.

sthaug at sthaug at
Tue Jun 16 21:01:13 UTC 2009

> > Since RFC4361 supersedes RFC2132, is it safe to ask Redback to  
> > implement it using the format specified in RFC 4361?
> Nothing is ever perfectly safe, but the RFC4361 client identifier  
> format is backwards-compatible with RFC2132, so it would take a very,  
> very broken implementation to choke on it.

It is backwards compatible *except* for the fact that the "standard"
DHCPv4 format of hardware type (1) followed by the 6 byte MAC address
is no longer permitted, as far as I can see.

As has been discussed on this list, see for instance the threads

"host-identifier with IPv6"

"DHCPv6 host-identifier, the Never Ending Thread: A Summary"

some people *really* want to be able to get the MAC address of the
client, and the RFC 4161 format removed this possibility.

Steinar Haug, Nethelp consulting, sthaug at

More information about the dhcp-users mailing list