Re: [dhcwg] What sorts of services does DHCP configure?

[Ted Lemon <[e-mail]>]

On Oct 14, 2013, at 10:33 PM, Sheng Jiang <[e-mail]> wrote:
> I guess I should not use IMAP configuration as the example for the definition of network-specific here. It mis-leaded you. I am not ready to discuss in deep regarding to IMAP configuration, yet. :P The clarification of myself should be: IMAP configuration may be configured through DHCP stateless model. It does not match my understanding of node-specific.

I chose IMAP deliberately, because it _is_ something that is a local network service, and that made some sense to configure using DHCP back in the olden days when we rode around in horse-drawn buggies and used computers that didn't fit in our pockets (and hence might roam to different networks).

> Regarding to your question of how node be able to distinguish a harmful configuration, unless there is another alternative mechanism can provide such function, it should not in the center of our concern.

To be clear, the question I am asking ought to be answered as if such a mechanism did exist.   People have talked about creating such a mechanism, and I think it's a good idea.   If there were a mechanism for delivering configuration information that ought not to vary as a device moves from network to network, what services would you still want to configure using DHCP?   What services would it no longer make sense to configure using DHCP.

It's important to note that _nobody_ uses DHCP to configure IMAP or POP or SMTP.   You can't buy a device that gets these configurations from DHCP automatically, even though DHCP provides the ability to configure these services.

Why not?   Because it doesn't work.   IMAP and POP are specific to the user.   You set up IMAP and POP manually.   Microsoft actually has a proprietary protocol for configuring Exchange based on your email address.

There are some services where it _sometimes_ works for DHCP to be what configures it.   There are some services where it _obviously_ works for DHCP to configure it.   There are some services where it _never_ makes sense for DHCP to configure it.   This is what I'm getting at.   I'd like to try to get some clarity on how we can predict which services, even if we added a DHCP option to support them, would never be configured by DHCP, which would be configured by DHCP only in restricted cases, and which would almost always be configured by DHCP.

I would also like us to discuss the security implications of configuring these services via DHCP.   E.g., if you configure SMTP via DHCP and start sending mail out the SMTP server you got from DHCP, isn't spam filtering going to cause your mail to bounce?   If you configure SIP using DHCP, aren't you going to wind up exposing yourself to eavesdropping when you use a SIP server without any secure mechanism for determining who operates it?