DHCP over PPP - or how to use sockets instead of BPF?

Patrik Lahti plahti at qnx.com
Fri Apr 16 19:16:40 UTC 2010

On 16/04/10 02:04 PM, sthaug at nethelp.no wrote:
>> But it would be nice to allow DHCPv4 to "work" somehow. Otherwise, how
>> do people automatically get DNS servers on PPP links?
> Basic PPP negotiation can give you an IP address. And then DHCPINFORM
> can give you DNS servers and other interesting parameters. DHCPINFORM
> requires a working IP address.
> Steinar Haug, Nethelp consulting, sthaug at nethelp.no

That's a good idea. I haven't really dived into DHCPINFORM, I'm assuming 
it's a bit like stateless DHCPv6 (Information-Request)?

It's just that in order to form a proper DHCPv4 message one would need 
to fill the CHADDR field. And from a quick look through RFC 2131 it 
seems to require CHADDR for DHCPINFORM too. I realize that in most cases 
the CHADDR field wouldn't matter for DHCPINFORM. But it would be 
important to be interoperable, in case servers/relays expect something 
useful there (e.g. for matching the CHADDR to certain config parameters).

Are you suggesting faking this hardware address or do one of the options 
in in RFC 3456?

I noted: 
https://lists.isc.org/pipermail/dhcp-users/2009-June/009072.html which 
suggests at least one client implementation fakes it.


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