Subject: [mobile-ip] 10.6 List of Home Network Prefixes

From: Joe Lau <[email-masked]>
Date: Mon, 5 May 2003 16:37:15 -0700 (PDT)

Jari,

Regarding the new text on section 10.6.1 List of Home Network Prefixes

  "If there are multiple home agents, differences in the advertisements
   sent by different home agents can lead to an inability to use a
   particular home address when changing to another home agent.  In
   order to ensure that the mobile nodes get the same information from
   different home agents, it is desired that all the home agents on the
   same link be configured in the same manner.

   To support this, the home agent monitors prefixes advertised by
   itself and other home agents routers on the home link.  Observed
   differences SHOULD be logged."

I believe the "Observed differences SHOULD be logged" is more than what
RFC 2467 has already specified in 6.2.7 Router Advertisement Consistency.

Can we make the text more specific or is that the text really meant 
"any difference" on the prefixes SHOULD be logged.

Joe

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From: Vijay Devarapalli <[email-masked]>
Date: Mon, 05 May 2003 17:01:16 -0700

hi Joe,

> RFC 2467 has already specified in 6.2.7 Router Advertisement Consistency.

I guess you meant 2461. I think RFC 2461 talks about differences 
in advertisements sent out by two routers regarding the same 
prefix. for example one router could advertise the prefix with 
lifetime 100 seconds. another router could advertise the same 
prefix with lifetime 120 seconds. such differences should be 
logged.

> "any difference" on the prefixes SHOULD be logged.

MIPv6 talks about logging differences in the sets of prefixes
advertised by different home agents on the same home link. the
current MIPv6 spec recommends that the all Home Agents advertise
the same set of prefixes.

Vijay

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From: Joe Lau <[email-masked]>
Date: Mon, 5 May 2003 17:08:32 -0700 (PDT)

Hi Vijay,

> I guess you meant 2461. I think RFC 2461 talks about differences 

Ooops!  Typo.

> the same set of prefixes.

Adding your "text" to the spec will be helpful.  Is it too late?

Joe

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From: Jari Arkko <[email-masked]>
Date: Tue, 06 May 2003 09:58:09 +0300

I'm not quite sure what text change you two agreed on, but here's
how I think the text should be changed:

    To support this, the home agent monitors prefixes advertised by
    itself and other home agents routers on the home link.  Observed
    differences SHOULD be logged.

=>

    To support this, the home agent monitors prefixes advertised by itself
    and other home agents on the home link. In addition to the consistency
    checks specified in Section 6.2.7 of RFC 2461 [ref], home
    agents SHOULD log differences in the sets of prefixes advertised by
    the different home agents.

--Jari

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From: Erik Nordmark <[email-masked]>
Date: Tue, 6 May 2003 10:54:28 +0200 (CEST)

> RFC 2467 has already specified in 6.2.7 Router Advertisement Consistency.

The intent is that the set of prefixes (and their A and O bit?) match,
whereas RFC 2462 doesn't log anything when two routers advertise different
prefixes.
So it makes sense to be more specific about what to compare.
For example,
if HA1 announces P1 and P2, and HA2 only announces P1 then this should be
logged.

> "any difference" on the prefixes SHOULD be logged.

Careful. The actual lifetime values might be different because the
router advertisements are sent at different times.
If both HA1 and HA2 are configured to advertise P1 with a valid lifetime 
that decrements in real time, then the two advertisements could
differ in their lifetime. RFC 2461 covers the issues in comparing
the lifetimes.

  Erik

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From: Erik Nordmark <[email-masked]>
Date: Tue, 6 May 2003 11:28:18 +0200 (CEST)

>     the different home agents.

How about adding something like this:
	In RFC 2461 it is acceptable for two routers to advertise different
	sets of prefixes on the same link. For Home Agents such differences 
	should be detected since a mobile node only communicates with
	one home agent at a time and the mobile node needs to know the
	full set of prefixes assigned to the home link.
	All other comparisons of router advertisements are as specified
	in RFC 2461.

  Erik

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From: Jari Arkko <[email-masked]>
Date: Tue, 06 May 2003 12:45:31 +0300

> 	All other comparisons of router advertisements are as specified

The text that I crafted had the same intent, I think, but I have
now take in your text...

--Jari

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From: Markku Savela <[email-masked]>
Date: Tue, 6 May 2003 12:49:23 +0300

> From: Erik Nordmark <[email-masked]>

> 	one home agent at a time and the mobile ...

I would prefer that "single home agent at time" limitation is not
"hard coded" into the specification. I accept that support may be
optional.

I believe it would be quite sensible configuration to have multiple
home agents at same time.

Say, for example

 - I have fixed connection and domain name for my home network. I run
   home agent at home and while travelling I want connections to
   certain home address there to be redirected to my mobile unit.

 - at same time, I may have similar arrangement with my office
   network,

 - and even maybe, the network operator is offering same service.

Thus, while away, I may suddenly get connections via any of those home
agents, so I need to be prepared to handle multiple home agents at
same time.

---

From: Jari Arkko <[email-masked]>
Date: Tue, 06 May 2003 13:08:49 +0300

> "hard coded" into the specification. I accept that support may be

Right, it shouldn't be hardcoded. You can indeed have multiple home agents,
on different networks.

I fixed the proposed text to "... one home agent on a given home
link at a time ..."

--Jari

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From: Erik Nordmark <[email-masked]>
Date: Wed, 7 May 2003 15:05:54 +0200 (CEST)

> home agents at same time.

For different Home Address, which I think is your example,
I fully agree.

For a single home address the MN needs to communicate with the set of HAs
on the corresponding home link. And the protocol as specified says to
do this using optional home agent discovery and then communicating with
a single HA; anything else will cause confusion in the area of DAD.

So do you see a need to allow communication with multiple home agents
for a single home address?

If not, how about 
	should be detected since a given home address a mobile node only 
	communicates with a single home agent at a time and the mobile ...

  Erik

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From: Erik Nordmark <[email-masked]>
Date: Tue, 6 May 2003 10:54:28 +0200 (CEST)

Erik

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From: Erik Nordmark <[email-masked]>
Date: Tue, 6 May 2003 11:28:18 +0200 (CEST)

Erik

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From: Vijay Devarapalli <[email-masked]>
Date: Mon, 05 May 2003 18:11:45 -0700

and congratulations!! you brought up the 300th issue ;-)

Vijay

ps: Jari, this will be added to the issues list, right?