Subject: Re: [DNA] Issue 6: DNAHostLinkIDList

From: Sathya Narayanan <[email-masked]>
Date: Fri, 26 Jan 2007 15:04:16 -0500

This is the last email on this subject I can find on the list.

I am going to close this issue, removing LinkID from the solution while
making sure that the points raised by JinHyeock are covered in the text.

I still haven't closed Issue 2:, changes to support Stateful
autoconfiguration scenario. The current text depends on DHCP CONFIRM to
address this scenario. I am still uncomfortable requiring configuration
of each router on the link with the smallest prefix - a sysadmin then
becomes responsible for keeping track of the smallest prefix and
updating the configuration each time. Depending on DHCP CONFIRM is a
more dynamic solution, imho. I will close this later on, after I do
one-on-one discussion with a few people.

Hopefully, I will submit a new version before the end of next week.

Thanks,
Sathya

Sathya Narayanan wrote:

> Dear JinHyeock:
>
> You are right. The DNA bit in the RA should be enough to take care of
> non-DNA router messages. If the host doesn't find a prefix in a DNA-RA
> that is already in the DNAHostPrefixList, it can conclude that it has
> changed link - and it would be correct. If it is a non-DNA-RA, it
> should fall back on CPL or wait for another DNA-RA. I will make sure
> that the text is written accordingly.
>
> - Sathya
>
>> Dear Sathya
>>
>>> Since I didn't hear any other objections, I am going start closing the
>>> issues using the suggested changes, except for this issue on
>>> DNAHostLinkIDList.
>>>
>>> My proposal for removing DNAHostLinkIDList is as follows:
>>> We remove the concept of identifying a particular prefix as LinkID
>>> prefix and mandate the inclusion of the smallest prefix in all RA
>>> messages. On the host side, we only need to check if there is a prefix
>>> included in the RA that is in the DNAHostPrefixList. This will work if
>>> we make sure that when there is a change in the smallest prefix, the RA
>>> includes the previous smallest and the current smallest (similar to
>>> what
>>> is done when the LinkID changes now). So, the algorithm will be:
>>>
>>> For non-landmark RA or a NO landmark response:
>>> Router SHOULD try to send a completeRA.
>>> If the completeRA is not possible due size restriction, the RA MUST
>>> include the smallest prefix.
>>> If the smallest prefix was first seen within 1.5 hours ago, then the
>>> second smallest prefix MUST be included in the RA.
>>> If the second smallest prefix was first seen within 1.5 hours ago, then
>>> the third smallest prefix MUST be included in the RA.
>>> And so on... (I don't like that this is open ended, but thats how
>>> things
>>> are right now with including LinkIDs)
>>>
>>> For unsolicited RA:
>>> MAY be a completeRA.
>>>
>>> If not a completeRA, same rules as above to include the smallest
>>> prefix(es).
>>>
>>> What I am trying to do here should be obvious. The functionality is
>>> exactly the same as the LinkID component of the current draft, but
>>> there
>>> is no explicit marking as such and more importantly no explicit LinkID
>>> check at the host. The overlapping prefix check covers that for us,
>>> removes the need for a DNAHostLinkIDList, thus simplifying the
>>> operation
>>> significantly on the host side.
>>>
>>> For future non-prefix linkIDs, they can be included in the LPO and they
>>> MUST be 128 bits long. Since LPO cannot be used to configure addresses
>>> this won't cause any trouble and cannot overlap with other prefixes
>>> since they are 128 bits.
>>>
>>> I would like to know if people think this is workable - am I
>>> overlooking
>>> something?
>>
>>
>> I think the above is workable but have a few concerns.
>>
>> 1.
>>
>>>                                                     This will work if
>>> we make sure that when there is a change in the smallest prefix, the RA
>>> includes the previous smallest and the current smallest (similar to
>>> what
>>> is done when the LinkID changes now). So, the algorithm will be:
>>
>>
>> For the above, DNA routers should manage "the smallest prefix list"
>> which it recently advertised.
>>
>> 2. RA should include the indication that this RA includes the
>> smallest prefix.
>>
>> A DNA router and a non-DNA router may co-exist on a link. If the
>> non-DNA router advertises an RA without the smallest prefix, that may
>> cause a host to make a mistake.
>>
>> The inclusion of the smallest prefix can be indicated with
>> either 1) DNA router bit in RA or 2) a new bit in PIO.
>>
>> For the first, a host assumes that the RA from the DNA router includes
>> the smallest prefix automatically.
>>
>> For the second, a host assumes that the RA includes the smallest
>> prefix only when there is a smallest prefix bit in PIO/ or LPIO.
>>
>> Thanks for your kind consideration.
>>
>> Best Regards
>>
>> JinHyeock
>
>

---

From: JinHyeock Choi <[email-masked]>
Date: Mon, 29 Jan 2007 11:41:04 +0900

Dear Sathya

Thanks for your trouble advancing the work.

> updating the configuration each time.

Sysamin doesn't have to keep track of the smallest prefix and
configure it to each router manually.

Sysamin only have to configure a router to advertise at least one
prefix. Then, after a while, the routers on the same link, upon
hearing the prefixes from each other, will pick the smallest prefix
and advertise it in either PIO or LPIO.

Best Regards

JinHyeock

---

From: Greg Daley <[email-masked]>
Date: Tue, 30 Jan 2007 14:36:24 +1100

Hi JinHyeock, 

If the router has an address prefix configured for routing (local delivery),
even if it is not configured for stateless address autoconfiguration, it
can advertise it as a learned prefix.

This could be an automatic process.

If the router doesn't have any prefixes configured for routing, then
I would prefer not requiring it to have a prefix configured just for the
purpose
of link identification.

How about we say:

"...
In some circumstances, such as when DHCPv6 is used, a router may not be
configured
to advertise prefixes in Prefix Information Options [RFC3315].  If a router
interface is configured with a non link-local prefix and does not send
Prefix Information Options, each Router Advertisement it sends MUST
contain at
least one prefix in a Learned Prefix Option for the purposes of Link
Identification.

If the router has not learnt any valid Prefix Information Options this
prefix MUST
be one of its own locally configured non link-local prefixes, and the
"Complete"
flag MUST NOT be set in the RA.

If this router learns valid prefixes from a Prefix Information Option,
it SHOULD
advertise this instead, advertising the "Complete" flag if all of the
link's PIO
advertised prefixes are readvertised in LPOs.
..."

Of course, learned prefixes aren't readvertised, and multiple non
PIO-advertising
routers may advertise disjoint LPOs.

In that case, the Complete Flag isn't set, and the routers provide the
prefix only
to assist CPL hosts in determining link change.

The system reverts to nromal operation if even one router advertises
with a PIO.

Greg

----- Original Message -----
From: JinHyeock Choi <[email-masked]>
Date: Monday, January 29, 2007 1:44 pm
Subject: Re: [DNA] Issue 6: DNAHostLinkIDList
To: Sathya Narayanan <[email-masked]>
Cc: Dna <[email-masked]>

> > address this scenario. I am still uncomfortable requiring 
> configuration> of each router on the link with the smallest prefix -
> a sysadmin then

---

From: Sathya Narayanan <[email-masked]>
Date: Tue, 30 Jan 2007 10:26:14 -0500

JinHyeock  -

You are right. I didn't realize that before. Thanks for correcting me. I
feel a lot more comfortable now.

Now, is it ok the REQUIRE the sysadmin to configure the routers with
atleast one prefix even if stateful address configuration is used. I
guess it is ok. I don't know what others think.

Greg -

Your idea to use the configured non-link local prefix is a good one, but
it still leaves the scenario where the router is configured only with
link-local addresses on it local interface. AFAIK, thats going to be the
most common scenario. So, if we require the routers to advertise atleast
one prefix, it MUST be configured on the router even when stateful
address configuration is used.

Sathya

---

From: JinHyeock Choi <[email-masked]>
Date: Wed, 31 Jan 2007 19:21:46 +0900

Dear Greg

glad to hear from you after a while. :-)

> This could be an automatic process.

ok. If a router receives traffic through prefix based routing, (i.e
other routers forward packets to the router with the longest prefix
match), I guess some prefix need to be configured to the router.

> I would prefer not requiring it to have a prefix configured just for the

It's my opinion that would be simpler and, may say, better. Also I
think the above case (router with some prefix being configured) holds
for the most occasions. If I miss something, kindly let me know.

Best Regards

JinHyeock

---

From: JinHyeock Choi <[email-masked]>
Date: Wed, 31 Jan 2007 19:22:02 +0900

Dear Sathya

glad to hear that now you feel more comfortable. :-)

> guess it is ok. I don't know what others think.

It's ok for me.

Best Regards

JinHyeock