Re: [DNA] IMPORTANT: Combined DNA Solution draft

[Christian Vogt <chvogt@tm.uka.de>]

Hi Syam.

> I think it is good to mandate the routers to support Landmark option 
> and it is optional for hosts to use it. This will ease the 
> implemention on host side.

Yes, compliance to DNA should require routers to support both.  Then
hosts can choose what to use.  Jari brought this up initially.

Besides, support of LinkID on routers will help CPL-only nodes, because
false positives will no longer occur.  (If routers do not use Link ID,
CPL may give you false positives.)  Note that CPL-only nodes will not
know about the use of LinkID, but that doesn't matter.

- Christian

-- 
Christian Vogt, Institute of Telematics, University of Karlsruhe
www.tm.uka.de/~chvogt/pubkey/



Syam Madanapalli wrote:
> On 11/6/05, Christian Vogt <chvogt@tm.uka.de> wrote:
> 
>>>>> [...]
>>>>> 
>>>>> - If the RS has a landmark and the router recognizes it a 
>>>>> short RA is possible. - If the RS has a landmark but the 
>>>>> router doesn't understand it, the landmark is ignored and a 
>>>>> complete RA is sent that the host can use to make an 
>>>>> immediate decision. - If the RS has no landmark, then the 
>>>>> router sends a complete RA that the host can again make use 
>>>>> of immediately.
>>>> 
>>>> 
>>>> Its agreed that if complete RAs can be used then there's really
>>>>  no issue (other than perhaps loss of a little bit of
>>>> bandwidth, but I wouldn't worry about that). However, in your
>>>> second case above, what happens if the RS has a landmark, the
>>>> router doesn't implement them, and it can't fit all the
>>>> prefixes in the complete RA? It seems that the router will make
>>>> a "random" decision of what prefixes to include, and since it
>>>> doesn't recognize the landmark option, it may not include the
>>>> host's prefix. Will this cause a problem?
>>> 
>>> 
>>> I don't think so.  The choice of prefixes to include is not quite
>>>  random, because the router is required to include the "LinkID" 
>>> prefix. That may not be the prefix that the host picked as a 
>>> landmark, but it will have been received by the host in any 
>>> earlier RAs if movement has not taken place.  Note that I removed
>>>  the word optional in the suggested text for the previous comment
>>>  because the the language in section 6 does not make the LinkID 
>>> inclusion optional.
>> 
>> 
>> I thought you agreed earlier during your discussion that Landmark 
>> and LinkID are optional for hosts only, but both mandatory for 
>> routers.
>> 
>> If you change the draft in this regard, a router not understanding 
>> the Landmark option would consequently not support the DNA Protocol
>>  3 at all.  But such a router would not support LinkID either, and 
>> the host would end up having to apply CPL logic anyway to arrive at
>>  a movement decision.
>> 
>> The host recognizes that it must use CPL because it sent a Landmark
>>  option with the RS, but the solicited RA neither includes a 
>> Landmark option nor has the C flag set.
>> 
>> This said, I don't see a reason why "case 2" (i.e., the RS has a 
>> landmark but the router doesn't understand it) need to be 
>> considered for this protocol at all.
>> 
> 
> 
> I think it is good to mandate the routers to support Landmark option 
> and it is optional for hosts to use it. This will ease the 
> implemention on host side.
> 
> Regards, Syam