Re: [mpls] [Technical Errata Reported] RFC5036 (4512)

You need to read the RFC more carefully. The advertised Transport
Address (implicity or explicity) is to be used only when opening a TCP
connection with the neighbor. Link hello packets are always sent with
a source address of the underlying interface.

2015-10-26 8:11 GMT-02:00 RFC Errata System <rfc-editor@rfc-editor.org>:
> The following errata report has been submitted for RFC5036,
> "LDP Specification".
>
> --------------------------------------
> You may review the report below and at:
> http://www.rfc-editor.org/errata_search.php?rfc=5036&eid=4512
>
> --------------------------------------
> Type: Technical
> Reported by: Jiessie <jiessie.xu@ericsson.com>
>
> Section: 2.5.2
>
> Original Text
> -------------
> 2.4.1.  Basic Discovery Mechanism
>
>    To engage in LDP Basic Discovery on an interface, an LSR periodically
>    sends LDP Link Hellos out the interface.  LDP Link Hellos are sent as
>    UDP packets addressed to the well-known LDP discovery port for the
>    \\"all routers on this subnet\\" group multicast address.
>
>
> 2.5.2.  Transport Connection Establishment
>
>    Note that when an LSR sends a Hello, it selects the transport address
>    for its end of the session connection and uses the Hello to advertise
>    the address, either explicitly by including it in an optional
>    Transport Address TLV or implicitly by omitting the TLV and using it
>    as the Hello source address.
>
> Corrected Text
> --------------
>
>
> Notes
> -----
> According to 2.4.1, an LSR send Hellos to \\"all routers on this subnet\\", the eligible reception LSR should be on this subnet.
>
> 2.5.2 states that one way for an LSR to advertise Transport Address is to uses it as Hello source address.
>
> On the topology below, LSRa uses 1.1.1.1 as Transport Address and sends Hello(source:1.1.1.1 destination:224.0.0.2) to LSRb.
> LSRb will ignore this packet which is not on its interface subnet.
>
> 1.1.1.1
> |LSRa|--------------|LSRb|
>       10.1.1.1             10.1.1.2
>
> My question is:
> What\\'s the scenario to use \\"implicitly\\" way to send Hello?
>
> Instructions:
> -------------
> This erratum is currently posted as "Reported". If necessary, please
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>
> --------------------------------------
> RFC5036 (draft-ietf-mpls-rfc3036bis-04)
> --------------------------------------
> Title               : LDP Specification
> Publication Date    : October 2007
> Author(s)           : L. Andersson, Ed., I. Minei, Ed., B. Thomas, Ed.
> Category            : DRAFT STANDARD
> Source              : Multiprotocol Label Switching
> Area                : Routing
> Stream              : IETF
> Verifying Party     : IESG
>
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-- 
Renato Westphal