Re: [lisp] looking for clarifications on rfc 6830

Yes. Agreed. 

With yours and Dino's explanation, I understand why LISP needs those "more specific" prefixes. The original wording just doesn't seem straightforward enough. 

OK. I'll keep track of them for your future revision.

Thanks,

Richard

-----Original Message-----
From: Joel Halpern Direct [mailto:jmh.direct@joelhalpern.com] 
Sent: Wednesday, October 21, 2015 3:41 PM
To: Richard Li; LISP mailing list list
Subject: Re: [lisp] looking for clarifications on rfc 6830

Looking at the text, there are two different references.  The first part talks about "a Map-Request with n EID that best matches any EID-prefix MUST be returned."
This is correct.  The Map-Reply must include the EID-prefix which best-matches the EID from the request.
The grammar is a bit awkward in trying to say that if any other prefixes need to be returned along with that, they need to go in the same Map-Reply message.  But the text is not incorrect.

And the later text makes it clear that the prefixes that must be included are the more-specific prefixes within the best-match. The current structure is important in part because conceptually there may be other reasons why a set of prefixes need to be sent.

Still, I would ask that you help us keep track of the fact that thsi third paragraph of 5.3 could be worded better.

Yours,
Joel

On 10/21/15 6:16 PM, Richard Li wrote:
> Thanks for your answers.
>
> Speaking about the Best-Match Prefixes, the RFC asks for returning all 
> best-matched prefixes. For the example in the RFC, The prefix 
> 10.1.2.0/24, for example, is NOT a best-match prefix, but the RFC 
> still wants to return it. This is exactly where the confusion comes 
> from.
>
> After reading your explanation, it comes to my mind that it is better 
> off to introduce a concept like "more specific" and "less-specific".
>
> 10.1.2.0/24 is "more specific" than 10.1.0.0/16, and 10.0.0.0/8 is 
> "less-specific" than 10.1.0.0/16.
>
> Using "more specific", the RFC could be rephrased as something like
> this: It will return the best-match prefix and all prefixes that are 
> more specific than the best-match prefix.
>
> For the example in the spec, a Map-Request for EID 10.1.5.5 would 
> cause a Map-Reply with a record count of 3 to be returned with mapping 
> records for EID-Prefixes 10.1.0.0/16, 10.1.1.0/24, and 10.1.2.0/24, 
> since 10.1.0.0/16 is the best-match prefix and the other two are more 
> specific than the best-match prefix.
>
> Does the above make sense?
>
> Richard
>
>
> -----Original Message----- From: Joel M. Halpern 
> [mailto:jmh@joelhalpern.com] Sent: Monday, October 19, 2015 12:02 PM
> To: Richard Li; LISP mailing list list Subject: Re: [lisp] looking for 
> clarifications on rfc 6830
>
> Thank you for reading RFC 6830 carefully. My understanding of the 
> answers to your questions is in line below. Yours, Joel
>
> On 10/19/15 2:43 PM, Richard Li wrote:
>> Hi Folks,
>>
>> I have read RFC 6830. I have a few points I could not figure them out 
>> by myself. Appreciated if you could clarify them.
>>
...
>> 3.Best-Match Prefixes
>>
>> Page 35, Section 6.1.5:
>>
>> A Map-Request for EID 10.1.5.5 would cause a Map-Reply with a record 
>> count of 3 to be returned with mapping records for EID-Prefixes 
>> 10.1.0.0/16, 10.1.1.0/24, and 10.1.2.0/24.
>>
>> Take a look at the EID prefixes in binary:
>>
>> 00001010.00000000.00000000.00000000 (10.0.0.0/8)
>>
>> 00001010.00000001.00000000.00000000 (10.1.0.0/16)
>>
>> 00001010.00000001.00000001.00000000 (10.1.1.0/24)
>>
>> 00001010.00000001.00000010.00000000 (10.1.2.0/24)
>>
>> 00001010.00000001.00000101.00000101 (10.1.5.5/32)
>>
>> Performing the best match of 10.1.5.5/32 against the EID prefix 
>> database, we will have only 10.1.0.0/16.
>
> I am not sure what your question is here.  The reason the extra 
> entries (beyond 10.1.0.0/16 have to be returned is not that one of 
> them matches the request.  Youa re correct, and the text agrees, that 
> there is only one entry matching 10.1.5.5/32.  The reason the extra 
> entries need to be returned is that in the absence of those entries, 
> later packets which match those other entries will be misdirected. Is 
> the text insufficiently clear about the reason for sending the 
> additional entries? If so, can you suggest text improvement for us to 
> use in the next revision?
>
>>
>> Thanks,
>>
>> Richard
>>
>>
>>
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