Subject: [dhcwg] *THIRD TRY* Re: Review of draft-ietf-netlmm-pmip6-ipv4-support

From: Ralph Droms <[email-masked]>
Date: Mon, 2 Feb 2009 13:54:01 -0500

Here's my review of http://tools.ietf.org/html/draft-ietf-netlmm-pmip6-ipv4-support-09 
  ; Jari could use any additional comments in addition to my input.

The idea behind Proxy Mobile IPv6 is to provide "transparent" mobility  
support for hosts, allowing them to switch attachment points without  
invoking IPv6 mobility on the host.  This draft suggests extensions to  
to Proxy Mobile IPv6 to allow the same sort of mobility for IPv4 hosts  
using the Proxy Mobile IPv6 infrastructure.

Focusing on the use of DHCP in the draft ... unless I misunderstand  
the way in which change-of-attachment/handoff will work, I think the  
text labeled "IPv4 Home Address Renewal with a different DHCP server  
(After Handoff):" in section 3.4.1 needs to be revised and a new  
section needs to be added to section 3.4.2.

I don't think the scenario described under "IPv4 Home Address Renewal  
with a different DHCP server (After Handoff):" will ever occur, unless  
the mobile host can somehow switch attachment points without notifying  
the DHCP client to cause the client to go into INIT-REBOOT state.   
Therefor, I think the associated text should be replaced with text  
that describes the scenario in which the mobile host has switched  
attachment points and broadcasts a DHCPREQUEST in INIT-REBOOT state.   
Section 3.4.2 needs to be extended with similar text that describes  
the scenario in which the mobile host has switched attachment.

Unless I just missed the text, it would be good to clarify that the  
"IPv4 Default-Router Address" received from the LMA needs to be  
forwarded through DHCP to the mobile host.  How does the DHCP server  
determine the subnet mask to send to the mobile host?  Might be  
helpful to add a table with the required options and the sources of  
the values for those options.

Editorial aside - and it may be too late to change at this point - why  
bother with "alignment"?  Is there really an advantage to putting data  
values on 32-bit boundaries these days in a control protocol?

How does the MAG identify the LMA for the host?

Sections 3.4.1 and 3.4.2 (Figures 6 and 7) show different orders for  
the DHCPDISCOVER and Proxy Mobile IPv6 signaling events.  The text for  
the figures explains that these messages can occur in any order.  In  
what situation would the Proxy Mobile IPv6 signaling begin before the  
DHCPDISCOVER is received?  If, in section 3.4.1, the Proxy Mobile IPv6  
signaling can take place before the DHCPDISCOVER is received by the  
DHCP server, doesn't the DHCP server have to check to see if it  
already has an IPv4 address for the mobile host, as suggested in this  
text from section 3.4.2: "check if there is already an assigned IPv4  
home address for the mobile node from the local mobility anchor"?

How do DHCP address lease times and address assignments from LMAs  
interact?  Section 3.4.1 mentions the use of DHCPFORCERENEW, which is  
not universally implemented today.

Does the text about DHCPRELEASE in section 3.4.2 also apply to section  
3.4.1?

- Ralph

_______________________________________________
dhcwg mailing list
[email-masked]
https://www.ietf.org/mailman/listinfo/dhcwg