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Re: [mpls] Last Call: <draft-ietf-mpls-ldp-ipv6-14.txt> (Updates to LDP for IPv6) to Proposed Standard

2015-01-09 21:28:13
Hi Mustapha, 

Thanks for the clarity.

1. You have a fair point. While it is implicit that section 2.5.5 of RFC
5036 (maintaining hello adj) would apply, it is reasonable to make it
explicit. We can add the below text -

//A Dual-stack LSR MUST still follow section 2.5.5 of RFC5036 and check
for matching Hello
messages from the peer (either all Hellos also include the Dual-stack
capability (with same TR value) or none do).//



2. This is already covered in both 3a and 3b by the following verbiage
"However, if IPv6 hellos are also received at any time from that
neighbor..” in the beginning of 2nd para. Note "at any time” here.

The text is sufficient, IMHO.

3. Closed. 

4.5. Ok. The following "(even if IP capability negotiation for IPv6
address family was done)” is appended to make it explicit. And Thanks for
catching the copy-paste error. :) Fixed.

Closed.


-- 
Cheers,
Rajiv Asati
Distinguished Engineer, Cisco





-----Original Message-----
From: <Aissaoui>, Mustapha Aissaoui 
<mustapha(_dot_)aissaoui(_at_)alcatel-lucent(_dot_)com>
Date: Friday, January 9, 2015 at 6:19 PM
To: Rajiv Asati <rajiva(_at_)cisco(_dot_)com>, IETF Discussion 
<ietf(_at_)ietf(_dot_)org>,
IETF-Announce <ietf-announce(_at_)ietf(_dot_)org>
Cc: "mpls(_at_)ietf(_dot_)org" <mpls(_at_)ietf(_dot_)org>
Subject: RE: [mpls] Last Call: <draft-ietf-mpls-ldp-ipv6-14.txt> (Updates
to LDP for IPv6) to Proposed Standard

Hi Rajiv,
Thanks for the reply. I added some follow-up inline below.

Regards,
Mustapha.

-----Original Message-----
From: Rajiv Asati (rajiva) [mailto:rajiva(_at_)cisco(_dot_)com]
Sent: Tuesday, January 06, 2015 6:03 PM
To: Aissaoui, Mustapha (Mustapha); ietf(_at_)ietf(_dot_)org; IETF-Announce
Cc: mpls(_at_)ietf(_dot_)org
Subject: Re: [mpls] Last Call: <draft-ietf-mpls-ldp-ipv6-14.txt>
(Updates to LDP for
IPv6) to Proposed Standard

Hi Mustapha,

Having said that, I want to keep the spirit of cooperation and make
sure we get this  draft published. To that effect, I am not opposed to
its publication as long as the  following points are clarified in the
draft since now FEC capability of the LSR peer is  determined by a
check a both adjacency and session levels:

Thanks for pointing out the below scenarios. We think that all but one
are either
covered or require editorial changes.


1. This scenario (sending hellos with DS capability on fewer interfaces
for a peer)
does NOT look realistic, since hitless upgrading a router would result
in sending
v4+v6 hellos either with DS capability or without DS capability (for a
DS peer,
assuming the peer was enabled for DS LDP, default or not, in an
implementation).

Perhaps, you had a different scenario in mind.
MA> This could occur during a hitless upgrade for Hello adjacencies from
different line cards during a transient time. I will not insist on this
point but I found the draft lacks what action to take if the Hello
messages received on parallel links from the same LSR are not consistent,
meaning they have different TR values or the message on one link do not
have the DS capability. The only thing I found is this paragraph in
Section 6.1.1 but it does not say what to do if an LSR receives
inconsistent Hello messages:
"
An LSR MUST convey the same transport connection preference ("TR"
  field value) in all (link and targeted) Hellos that advertise the
  same label space to the same peer and/or on same interface.  This
  ensures that two LSRs linked by multiple Hello adjacencies using the
  same label spaces play the same connection establishment role for
  each adjacency.
"

2. Yes. This scenario is well covered in section 6.1.1 point#3.


//
     3. If "Dual-stack capability" TLV is NOT present, and

Š
             resulting in any established LDPoIPv4 session being reset
             and a fatal Notification message being sent (with status

Š

//
MA> What I was talking about is a transition from state 2a to state 3a or
from state 2b to state 3b in Section 6.1.1. Perhaps one way to explicitly
state that the session is bounced would be to add something like this to
items 2a and 2b of Section 6..1.1:
"
2. If "Dual-stack capability" TLV is present, and remote
       preference matches with the local preference, then:

         a) If TR=0100 (LDPoIPv4), then determine the active/passive
            roles for TCP connection using IPv4 transport address as
            defined in section 2.5.2 of RFC 5036.

         b) If TR=0110 (LDPoIPv6), then determine the active/passive
            roles for TCP connection by using IPv6 transport address
            as defined in section 2.5.2 of RFC 5036.
  *If subsequently to establishing the LDP session, the Hello messages
from the peer
  do not include the Dual-stack capability TLV, the session is
terminated and a fatal Notification message is sent with     status code
of 'Dual-Stack Non-Compliance' (IANA allocation TBD).*
"



3. Yes (to the expected behavior). This is somewhat covered in bullet
#1 in section
6.1.1, but we can make it explicit by adding "or does not get
recognized² as below:


OLD:
If "Dual-stack capability" TLV is present and remote preference does
not match
with the local preference,..


NEW:
If "Dual-stack capability" TLV is present and remote preference does
not match
with the local preference (or does not get recognized),..
MA> Your proposed modification does address this comment. Thank you.


4 and 5. Yes (to the expected behavior). It is implicit in section 7.2
para 4.

//..
 An LSR MAY further constrain the advertisement of FEC-label bindings
for a
particular address family by negotiating the IP Capability...//

Are you suggesting to make it explicit?
MA> Yes I wanted something more explicit. This section certainly says the
IPv6 prefix FEC capability can further constrain a particular FEC type
which is allowed by the check of the DS capability TLV. It however does
not discuss the negative case, i.e., the DS capability TLV did not allow
a FEC type but the IP capability allowed it.
I believe the following addition to an earlier paragraph in Section 7.2
would help clarify this:
"
If an LSR enabled with Dual-stack LDP for a peer and

    1. Is NOT able to find the Dual-stack capability TLV in the
       incoming IPv4 LDP hello messages from that peer, then the LSR
       MUST NOT advertise IPv6 FEC-label bindings to the peer *even if
it received an IP capability
       from the peer indicating the enabling of the IPv6 FEC type*.
"
BTW, there is a "copy & paste" mistake in the following paragraph in the
same Section 7.2. The "via ADDRESS message" is not correct here since
this is about FEC distribution, hence Label Mapping message, and not
address distribution.
"
If an LSR is enabled with Single-stack LDP for any peer, then it
  MUST advertise (via ADDRESS message) FEC-Label bindings for the
  enabled address family, and accept FEC-Label bindings for the
  enabled address family.
"

--
Cheers,
Rajiv Asati
Distinguished Engineer, Cisco





-----Original Message-----
From: <Aissaoui>, Mustapha Aissaoui
<mustapha(_dot_)aissaoui(_at_)alcatel-lucent(_dot_)com>
Date: Tuesday, December 16, 2014 at 12:21 PM
To: IETF Discussion <ietf(_at_)ietf(_dot_)org>, IETF-Announce
<ietf-announce(_at_)ietf(_dot_)org>
Cc: "mpls(_at_)ietf(_dot_)org" <mpls(_at_)ietf(_dot_)org>
Subject: Re: [mpls] Last Call: <draft-ietf-mpls-ldp-ipv6-14.txt>
(Updates
to LDP for IPv6) to Proposed Standard

Hi Adrian and all,
I was the one who raised the interop issues we found while testing our
implementation of LDP IPv6 against existing and deployed
implementations.
I proposed a simple method of using the existing FEC advertisement
capability at the session level as a way for an LSR to detect if an
implementation support LDP IPv6 FECs and IPv6 addresses. This existing
FEC advertisement capability at session level is defined in
draft-ietf-mpls-ldp-ip-pw-capability-08 but with the limitation that it
can be used only to disable support of IPv6 FECs in LDP Initialization
Message; we proposed to generalize the method to also indicate explicit
support for IPv6 FECs and IPv6 Addresses in LDP Initialization Message.
This method is safe and was also used with mLDP P2MP and MP2MP FECs
when
they were introduced. The intent here is that all session level
capabilities in LDP should follow RFC 5561 approach.

There was an individual contributor which supported the proposal on the
mailing list but the authors chose to ignore it and went with a
proposal
which overloaded the meaning of the dual-stack capability TLV.
Regardless
of the merit of either method, the discussion on the MPLS mailing list
was not closed properly from my perspective.

Now here is the concern I raised with using the dual-stack capability.
Not only this TLV is an adjacency level feature which is has nothing to
do with FEC capability advertisement, but it is introducing complexity
in
the implementation which now has to check dual-stack capability for
*each* adjacency to the peer *and* the session level FEC capability to
decide what the peer is capable of at the *session level*.

Having said that, I want to keep the spirit of cooperation and make
sure
we get this draft published. To that effect, I am not opposed to its
publication as long as the following points are clarified in the draft
since now FEC capability of the LSR peer is determined by a check a
both
adjacency and session levels:

1. The draft is missing the behavior when multiple adjacencies exist to
the same LSR and the peer LSR advertised the dual-stack capability only
over a subset of these Hello adjacencies.
I assume here the peer LSR is considered to be dual-stack capable as
soon
as any of the Hello adjacencies includes the dual-stack capability.
This
would allow a hitless upgrade scenario from an older implementation to
one which complies to this draft

2. Similarly, what would be the behavior if a hello adjacency changes
from sending the dual-stack capability to not sending it? This would be
for example in a hitless downgrade to a version of LDP which does not
comply to this draft.
I assume here that the session must be bounced since the LSRs need a
clean state to not send IPv6 addresses and IPv6 FECs.

3. The document defines 2 values for the dual-stack capability TR. It
does not mention the behavior when an unknown value is received.
Will that be considered a fatal error?

4. The draft is missing the behavior of when the peer LSR does not
advertise the dual-stack capability in all the Hello adjacencies but it
advertised the enabling or disabling of the IPv6 prefix FEC capability
in
the session initialization message.
I assume here that the absence of the dual-stack capability overrides
any
session level IPv6 FEC prefix capability advertisement.

5. The draft is missing the behavior of when the peer LSR does not
advertise the dual-stack capability in all the Hello adjacencies but it
advertised the enabling of the IPv6 prefix FEC capability in the
session
Capability message.
I assume the same behavior as in (4) applies here.

Regards,
Mustapha.

-----Original Message-----
From: mpls [mailto:mpls-bounces(_at_)ietf(_dot_)org] On Behalf Of The IESG
Sent: Thursday, December 04, 2014 2:37 PM
To: IETF-Announce
Cc: mpls(_at_)ietf(_dot_)org
Subject: [mpls] Last Call: <draft-ietf-mpls-ldp-ipv6-14.txt> (Updates
to LDP for IPv6)
to Proposed Standard


The IESG has received a request from the Multiprotocol Label
Switching
WG
(mpls) to consider the following document:
- 'Updates to LDP for IPv6'
  <draft-ietf-mpls-ldp-ipv6-14.txt> as Proposed Standard

The IESG plans to make a decision in the next few weeks, and solicits
final
comments on this action. Please send substantive comments to the
ietf(_at_)ietf(_dot_)org
mailing lists by 2014-12-18. Exceptionally, comments may be sent to
iesg(_at_)ietf(_dot_)org
instead. In either case, please retain the beginning of the Subject
line to allow
automated sorting.

Abstract

   The Label Distribution Protocol (LDP) specification defines
   procedures to exchange label bindings over either IPv4, or IPv6 or
   both networks. This document corrects and clarifies the LDP
behavior
   when IPv6 network is used (with or without IPv4). This document
   updates RFC 5036 and RFC 6720.

The file can be obtained via
http://datatracker.ietf.org/doc/draft-ietf-mpls-ldp-ipv6/

IESG discussion can be tracked via
http://datatracker.ietf.org/doc/draft-ietf-mpls-ldp-ipv6/ballot/


No IPR declarations have been submitted directly on this I-D.

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