RE: Questions related to single-hop IP BFD over IPv6

[Alexander Vainshtein <[e-mail]>]

Dear colleagues,
This is a gentle reminder about questions I've asked exactly 1 week ago.
Your help would be highly appreciated.

Regards,
Sasha

Office: [phone]
Cell:      [phone]
Email:   [e-mail]

From: Alexander Vainshtein
Sent: Thursday, May 18, 2017 5:14 PM
To: '[e-mail]' <[e-mail]>; David Ward <[e-mail]>
Cc: Michael Gorokhovsky <[e-mail]>; Alexander Ferdman <[e-mail]>; Shigang Wang <[e-mail]>; Natalie Rogozovsky ([e-mail]) <[e-mail]>; James Lian <[e-mail]>; BFD WG <[e-mail]>
Subject: Questions related to single-hop IP BFD over IPv6

Dear colleagues,
I have several questions dealing with single-hop IP BFD sessions over IPv6. So far I have failed to find clear answers to these questions in RFC 5881<https://tools.ietf.org/html/rfc5881>.


1.       Is it possible to use link-local source and destination IPv6 addresses in encapsulation of single-hop IP BFD Control packets? For the reference:

a.       Section 4 of RFC 5881 explicitly states that link-local addresses SHOULD NOT be used in encapsulation of BFD Echo packets, but it does not say anything about BFD Control packets

b.      OSPFv3 for IPv6 always uses link-local IPv6 addresses as the Next Hop addresses of the routes it computes (see RFC 5340<https://tools.ietf.org/html/rfc5340>, Section 4.8.2). Therefore it looks reasonable to me to use single-hop IPv6 BFD sessions with link-local addresses at least for monitoring OSPFv3 adjacencies

2.       Section 3 of RFC 5881 states that "there will be only a single BFD session between  two systems over a given interface (logical or physical) for a particular protocol". I would like to understand how this requirement can be addressed in the following scenario:

a.       Let us assume that the answer to the question 1 above is positive.

b.      Let's further assume that:

                                                               i.      Router A and Router B are connected across a single IPv6 hop (an IPv6 link)

                                                             ii.      A single-hop IPv6 BFD session using link-local addresses of the corresponding interfaces has been successfully established

                                                            iii.      Globally unique IPv6 addresses have been configured on the interfaces terminating this link in Router A and Router B and have successfully passed the DAD check, i.e., these addresses are assigned and preferred addresses in the terminology of RFC 4862<https://tools.ietf.org/html/rfc4862>

                                                           iv.      The user (or some application) now tries to set up a single-hop IPv6 BFD session bound to the same interfaces but using globally unique IPv6 addresses assigned to these interfaces

c.       Should, under the assumptions above,  the implementation prevent formation of an additional single-hop IPv6 BFD session between A and B running across the same link but using assigned globally unique IPv6 addresses of the corresponding interfaces? If yes, how can this be achieved?

d.      Similar to above, but:

                                                               i.      The interfaces connecting Router A and Router B have been assigned with multiple globally unique IPv6 addresses

                                                             ii.      A single-hop IPv6 BFD session using one pair of assigned IP addresses of these interfaces has been successfully established

                                                            iii.      Should the implementation prevent formation of an additional single-hop IPv6 BFD session between A and B running on the same link but using a different pair of assigned globally unique IP addresses? If yes, how can this be achieved?

Your inputs would be highly appreciated.

Regards, and lots of thanks in advance,
Sasha

Office: [phone]
Cell:      [phone]
Email:   [e-mail]<mailto:[e-mail]>


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