Re: [dhcwg] [v6ops] Fwd: New Version Notification for draft-link-dhc-v6only-01.txt

["Bernie Volz (volz)" <[e-mail]>]

That is a good find. I didn’t recall this.

On the surface, it looks like this document does a similar thing to the v6only option (stop DHCP). And, if yiaddr was 0, this would require checking both the autoconfigure and v6only to see how to proceed?

   DHCPOFFERs with a 'yiaddr' of 0x00000000 will only be sent by DHCP
   servers supporting the Auto-Configure option when the DHCPDISCOVER
   contained the Auto-Configure option.  Since the DHCPDISCOVER will
   only contain the Auto-Configure option when a DHCP client knows how
   to handle it, there will be no inter-operability problems.

It is likely something that the authors of draft-link-dhc-v6only will need to think about if a yiaddr of 0 is allowed for that case? Personally, another good argument not to use a yiaddr of 0 as it has a special semantic per RFC2563.

Note that this was also a question that was raised for draft-link-dhc-v6only – should it auto configure a link-local address. Perhaps they want to mention RFC2563 as one way to control this on the client side.

Thanks much for pointing out this document!! (Not sure how widely implemented this is as no one else mentioned it.)


  *   Bernie

From: David Farmer <[e-mail]>
Sent: Thursday, December 12, 2019 5:54 PM
To: Bernie Volz (volz) <[e-mail]>
Cc: Roy Marples <roy=[e-mail]>; Ted Lemon <[e-mail]>; [e-mail]
Subject: Re: [dhcwg] [v6ops] Fwd: New Version Notification for draft-link-dhc-v6only-01.txt



On Thu, Dec 12, 2019 at 3:03 PM Bernie Volz (volz) <[e-mail]<mailto:[e-mail]>> wrote:
> You can argue that said boxes are not RFC compliant, but that is the same as the argument here - nothing in the standard says that 0.0.0.0 cannot be offered.

Yes, there is no text that directly says 0.0.0.0 MUST NOT be offered. But it is pretty clear:

Field      DHCPOFFER            DHCPACK             DHCPNAK
-----      ---------            -------             -------
...
'yiaddr'   IP address offered   IP address          0
           to client            assigned to client

Offering 0.0.0.0 is not given the client an address it can use. There's plenty of documents that document 0.0.0.0 is not a destination address on the network. I can't see how in the absence of this use case, 0.0.0.0 would ever be a valid yiaddr in a DHCPOFFER.

Wait a sec, RFC2563 a standards-track document specifies that 0.0.0.0 is returned in yiaddr, many DHCP servers support this and option 116. Now I agree it is a very similar use case, but it's nothing new.

Many older DHCP clients support RFC2563, Win95, Win2000 are examples. I think many newer clients don't support it.

Nevertheless, using 0.0.0.0 may still be a bad idea, but it is standardized and therefore valid by definition.

Thanks
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