Re: [mpls] [Technical Errata Reported] RFC3107 (4499)

[Alexander Okonnikov <[e-mail]>]

Good. I know that at least three major vendors interwork correctly. One 
of them use 0x800000, and two others - 0x000000. No problems with 
interoperability were noticed. My point was to make label stack encoding 
consistent for both cases - when single and multiple routes are 
advertised. By the way, it is not clear for me why don't encode label 
from previously advertised route when this one is being withdrawn.

Thank you.

On 10/16/2015 11:16 PM, Eric C Rosen wrote:
> Nice bit of detective work figuring out where the 0x800000 value came 
> from.
>
> However, I don't think the erratum can be accepted, given its 
> potential for causing interoperability issues.
>
> To the best of my knowledge, section 4 ("Advertising Multiple Routes 
> to a Destination") is not widely implemented (to say the least), so 
> the issue of "which route to the prefix did you intend to withdraw?" 
> doesn't really come up.
>
> On 10/13/2015 6:05 PM, RFC Errata System wrote:
>> The following errata report has been submitted for RFC3107,
>> "Carrying Label Information in BGP-4".
>>
>> --------------------------------------
>> You may review the report below and at:
>> http://www.rfc-editor.org/errata_search.php?rfc=3107&eid=4499
>>
>> --------------------------------------
>> Type: Technical
>> Reported by: Alexander Okonnikov <[e-mail]>
>>
>> Section: 3
>>
>> Original Text
>> -------------
>>     A BGP speaker can withdraw a previously advertised route (as well as
>>     the binding between this route and a label) by either (a) 
>> advertising
>>     a new route (and a label) with the same NLRI as the previously
>>     advertised route, or (b) listing the NLRI of the previously
>>     advertised route in the Withdrawn Routes field of an Update message.
>>     The label information carried (as part of NLRI) in the Withdrawn
>>     Routes field should be set to 0x800000.  (Of course, terminating the
>>     BGP session also withdraws all the previously advertised routes.)
>>
>>
>> Corrected Text
>> --------------
>>     A BGP speaker can withdraw a previously advertised route (as well as
>>     the binding between this route and a label) by either (a) 
>> advertising
>>     a new route (and a label) with the same NLRI as the previously
>>     advertised route, or (b) listing the NLRI of the previously
>>     advertised route in the Withdrawn Routes field of
>>     an MR_UNREACH_NLRI attribute of an Update message.
>>     The label information carried (as part of NLRI) in the Withdrawn
>>     Routes field should be set to 0x000001.  (Of course, terminating the
>>     BGP session also withdraws all the previously advertised routes.)
>>
>>
>> Notes
>> -----
>> 1. Labeled routes are withdrawn by virtue of MR_UNREACH_NLRI attribute.
>> 2. Label value should be set to 0x00000 with BoS=1.  Value 0x800000 
>> was carried from draft, where BoS was high-order bit.
>>
>> Instructions:
>> -------------
>> This erratum is currently posted as "Reported". If necessary, please
>> use "Reply All" to discuss whether it should be verified or
>> rejected. When a decision is reached, the verifying party (IESG)
>> can log in to change the status and edit the report, if necessary.
>>
>> --------------------------------------
>> RFC3107 (draft-ietf-mpls-bgp4-mpls-04)
>> --------------------------------------
>> Title               : Carrying Label Information in BGP-4
>> Publication Date    : May 2001
>> Author(s)           : Y. Rekhter, E. Rosen
>> Category            : PROPOSED STANDARD
>> Source              : Multiprotocol Label Switching
>> Area                : Routing
>> Stream              : IETF
>> Verifying Party     : IESG
>>
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