Subject: [Mip6] Multiple Simultaneous Bindings / Ambiguities in mipv6-24 draft

From: "Donald W. Gillies" <[email-masked]>
Date: Thu, 22 Apr 2004 13:52:12 -0700

RE: http://www.ietf.org/internet-drafts/draft-ietf-mobileip-ipv6-24.txt

1.  The terminology :

         Primary care-of address
         Non-Primary care-of address

         should be defined formally with its own bullet item in the 
terminology section #3.1.
         How is a primary care-of address identified at the Home Agent 
??  How is a non-primary
         care-of address identified at the home agent, if at all ??  For 
example, could one specify
         non-primary care-of address by sending a binding update to the 
home agent without the
         "H" bit set ??  This is never spelled out clearly, and a new 
reader of the spec has to guess.

         If MIPv4 supports simultaneous bindings with the home agent, as 
ambiguously suggested
         in 11.5.3, does MIPv6 really support this feature ??  I shouldn't 
have to look for other internet
         drafts to figure this out.  If support for multiple simultaneous 
bindings with the home agent
         has been dropped, why is this not mentioned in Section 2, the 
comparison to MIPv4 ??
         This is a pretty major change, to drop this feature.  If support 
for this feature is retained :

         What is done with a packet that contains 2 Alternate Care-of 
Addresses in it ?
         If such a packet is accept, what would the expiry time mean when a 
packet
         of this type is received ?

2.  In section 11.7.1, page 130, bullet 4, it says that in a binding update,

    o  The care-of address for the binding MUST be used as the Source
       Address in the packet's IPv6 header, unless an Alternate Care-of
       Address mobility option is included in the Binding Update.  This
       option MUST be included in all home registrations, as the ESP
       protocol will not be able to protect care-of addresses in the IPv6
       header.  (Mobile IPv6 implementations that know they are using
       IPsec AH to protect a particular message might avoid this option.
       For brevity the usage of AH is not discussed in this document.)

This is inconsistent with the following sections of the specification.

         5.2.6, top of page 29.
         6.2.5, page 49, throughout
         9.5.1, page 82

that say that care-of address is the source IPv6 address or the alternate 
care-of address - no restrictions.  In general, the spec and implementation 
would be a lot simpler if the alternate care-of address attribute was 
always used everywhere in all binding updates, and the source IP address 
was ignored.

- Don Gillies

---

From: Brian Haley <[email-masked]>
Date: Mon, 26 Apr 2004 17:24:28 -0400

> reader of the spec has to guess.

I think you mis-read that section.  A care-of address is simply an 
address that isn't your home address - you might have many of them 
depending on the type and number of interfaces you have.  One of these 
addresses is your primary care-of address, the one you register with 
your HA and use as the tunnel endpoint.  When you determine that address 
is no longer usable, or for some other reason you prefer to use another 
address, you should pick another address to use as the primary and 
update your HA.  You should continue to receive packets sent to the old 
address for some period of time to account for in-flight packets and 
such.  The Home Agent has only one mapping of home address to care-of 
address.

>         in 11.5.3, does MIPv6 really support this feature ??  I 
> shouldn't have to look for other internet

There is no support for multiple Home bindings with the same home 
address in the base specification.

>         What is done with a packet that contains 2 Alternate Care-of 

Implementation-specific, although I would assume the last one wins.

>         If such a packet is accept, what would the expiry time mean when 
> a packet

How does having multiple Alt-coa's change the expiration time?  That's 
determined by the lifetime field in the Binding Update.

> that say that care-of address is the source IPv6 address or the 
> alternate care-of address - no restrictions.  In general, the spec and 
> implementation would be a lot simpler if the alternate care-of address 
> attribute was always used everywhere in all binding updates, and the 
> source IP address was ignored.

I think you're mixing-up BUs sent to the HA (which MUST have an Alt-coa 
w/ESP) as opposed to those sent to a CN (which MAY have an Alt-coa).

-Brian

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