TEAS Working Group X. Zhang, Ed.
Internet-Draft Huawei Technologies
Intended status: Standards Track V. Beeram, Ed.
Expires: September 12, 2017 Juniper Networks
I. Bryskin
Huawei Technologies
D. Ceccarelli
Ericsson
O. Gonzalez de Dios
Telefonica
March 11, 2017
Network Assigned Upstream-Label
draft-ietf-teas-network-assigned-upstream-label-04
Abstract
This document discusses a Generalized Multi-Protocol Label Switching
(GMPLS) Resource reSerVation Protocol with Traffic Engineering (RSVP-
TE) mechanism that enables the network to assign an upstream label
for a bidirectional LSP. This is useful in scenarios where a given
node does not have sufficient information to assign the correct
upstream label on its own and needs to rely on the downstream node to
pick an appropriate label.
Status of This Memo
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This Internet-Draft will expire on September 12, 2017.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Use-Case: Wavelength Setup for IP over Optical Networks . . . 3
3. The "Crankback Signaling" Approach . . . . . . . . . . . . . 3
4. Symmetric Labels . . . . . . . . . . . . . . . . . . . . . . 5
5. Unassigned Upstream Label . . . . . . . . . . . . . . . . . . 5
5.1. Processing Rules . . . . . . . . . . . . . . . . . . . . 6
5.2. Backwards Compatibility . . . . . . . . . . . . . . . . . 6
6. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Initial Setup . . . . . . . . . . . . . . . . . . . . . . 7
6.2. Wavelength Change . . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
10. Security Considerations . . . . . . . . . . . . . . . . . . . 9
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
11.1. Normative References . . . . . . . . . . . . . . . . . . 9
11.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
The Generalized Multi-Protocol Label Switching (GMPLS) Resource
reSerVation Protocol with Traffic Engineering (RSVP-TE) extensions
for setting up a bidirectional LSP are specified in RFC 3473
[RFC3473]. The bidirectional LSP setup is indicated by the presence
of an UPSTREAM_LABEL Object in the PATH message. As per the existing
setup procedure outlined for a bidirectional LSP, each upstream node
must allocate a valid upstream label on the outgoing interface before
sending the initial PATH message downstream. However, there are
certain scenarios where it is not desirable or possible for a given
node to pick the upstream label on its own. This document defines
the protocol mechanism to be used in such scenarios. This mechanism
enables a given node to offload the task of assigning the upstream
label for a given bidirectional LSP onto the network.
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1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Use-Case: Wavelength Setup for IP over Optical Networks
Consider the network topology depicted in Figure 1. Nodes A and B
are client IP routers that are connected to an optical WDM transport
network. F, H and I represent WDM nodes. The transponder sits on
the router and is directly connected to the add-drop port on a WDM
node.
The optical signal originating on "Router A" is tuned to a particular
wavelength. On "WDM-Node F", it gets multiplexed with optical
signals at other wavelengths. Depending on the implementation of
this multiplexing function, it may not be acceptable to have the
router send signal into the optical network unless it is at the
appropriate wavelength. In other words, having the router send
signal with a wrong wavelength may adversely impact existing optical
trails. If the clients do not have full visibility into the optical
network, they are not in a position to pick the correct wavelength
up-front.
|
| +---+ /-\
| | | Router ( ) WDM
| +---+ Node \-/ node
|________________________________
+---+ /-\ /-\ /-\ +---+
| A |---------( F )---------( H )---------( I )---------| B |
+---+ \-/ \-/ \-/ +---+
Sample Topology
Figure 1
3. The "Crankback Signaling" Approach
There are currently no GMPLS RSVP-TE protocol mechanisms that an
upstream node can use for indicating that it does not know what
upstream label to use and that it needs the downstream node to pick
the label on its behalf.
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The "Crankback Signaling" RFC 4920 [RFC4920] approach can be applied
to address the above use-case as shown in the following setup
sequence:
+---+ /-\ /-\ +---+
| A |----------------( F ) ~~~~~~~~~ ( I )----------------| B |
+---+ \-/ \-/ +---+
PATH
Upstream Label (any available value)
--------------------->
PATH-ERR
Routing problem/Unacceptable Label Value
Acceptable Label Set (L1, L2 .. Ln)
<---------------------
PATH
Upstream Label (L2)
--------------------->
-- ~~ -- ~~ -->
PATH
-------------------->
RESV
<--------------------
<-- ~~ -- ~~ --
RESV
Label (Assigned)
<---------------------
Setup Sequence - Crank-back Approach
Figure 2
The above approach does work, but there are a few obvious concerns:
o Since "Router-A" does not know which upstream label to use, it
picks some random label and signals it without programming its
data-plane (this is a deviation from the UPSTREAM_LABEL processing
procedures outlined in RFC 3473 [RFC3473]). As a result, the
outgoing PATH message has no indication of whether the upstream
label has been installed along the data-path or not.
o Even if "Router-A" somehow correctly guesses an acceptable
upstream label upfront, the network may end up finding a path
which is suboptimal (there could be a different acceptable
upstream label which corresponds to a better path in the network)
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o The "PATH-ERR with Acceptable Label Set" retry approach is usually
used for exception handling. The above solution uses it for
almost every single setup request (except in the rare scenario
where the appropriate upstream label is guessed correctly).
o There is an awkward window between the time the network sends out
the PATH-ERR message (with the ACCEPTABLE_LABEL_SET) and receives
the corresponding PATH message (with the selected UPSTREAM_LABEL);
this window opens up the possibility of the selected
UPSTREAM_LABEL to be stale by the time the network receives the
retry PATH.
o The above solution assumes the use of "symmetric labels" by
default.
The rest of the sections in this draft present a solution proposal
that is devoid of any of the above concerns.
4. Symmetric Labels
As per RFC 3471 [RFC3471], the upstream label and the downstream
label for an LSP at a given hop need not be the same. The use-case
discussed in this document pertains to Lambda Switch Capable (LSC)
LSPs and it is an undocumented fact that in practice, LSC LSPs always
have symmetric labels at each hop along the path of the LSP.
The use of the protocol mechanism discussed in this document mandates
"Label Symmetry". This mechanism is meant to be used only for
bidirectional LSPs that assign symmetric labels at each hop along the
path of the LSP.
5. Unassigned Upstream Label
This document proposes the use of a special label value -
"0xFFFFFFFF" (for a 4-byte label) - to indicate an Unassigned
Upstream Label. Similar "all-ones" patterns are expected to be used
for labels of other sizes. The presence of this value in the
UPSTREAM_LABEL object of a PATH message indicates that the upstream
node has not assigned an upstream label on its own and has requested
the downstream node to provide a label that it can use in both
forward and reverse directions. The presence of this value in the
UPSTREAM_LABEL object of a PATH message MUST also be interpreted by
the receiving node as a request to mandate "symmetric labels" for the
LSP.
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5.1. Processing Rules
The Unassigned Upstream Label is used by an upstream node when it is
not in a position to pick the upstream label on its own. In such a
scenario, the upstream node sends a PATH message downstream with an
Unassigned Upstream Label and requests the downstream node to provide
a symmetric label. If the upstream node desires to make the
downstream node aware of its limitations with respect to label
selection, it MUST specify a list of valid labels via the LABEL_SET
object as specified in RFC 3473 [RFC3473].
In response, the downstream node picks an appropriate symmetric label
and sends it via the LABEL object in the RESV message. The upstream
node would then start using this symmetric label for both directions
of the LSP. If the downstream node cannot pick the symmetric label,
it MUST issue a PATH-ERR message with a "Routing Problem/Unacceptable
Label Value" indication.
The upstream node will continue to signal the Unassigned Upstream
Label in the PATH message even after it receives an appropriate
symmetric label in the RESV message. This is done to make sure that
the downstream node would pick a different symmetric label if and
when it needs to change the label at a later point in time.
+----------+ +------------+
---| Upstream |--------------------| Downstream |---
+----------+ +------------+
PATH
Upstream Label (Unassigned)
Label-Set (L1, L2 ... Ln)
------------------->
RESV
Label (Assigned - L2)
<-------------------
Unassigned UPSTREAM_LABEL
Figure 3
5.2. Backwards Compatibility
If the downstream node is running an older implementation and doesn't
understand the semantics of an Unassigned UPSTREAM LABEL, it will
either (a) reject the special label value and generate an error as
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specified in Section 3.1 of RFC 3473 [RFC3473] or (b) accept it and
treat it as a valid label.
If the behavior that is exhibited is (a), then there are obviously no
backwards compatibility concerns. If there is some existing
implementation that exhibits the behavior in (b), then there could be
some potential issues. However, at the time of publication, there is
no documented evidence of any existing implementation that uses the
"all-ones" bit pattern as a valid label. Thus, it is safe to assume
that the behavior in (b) will never be exhibited.
6. Applicability
The use-case discussed in Section 2 is revisited to examine how the
mechanism proposed in this document allows the optical network to
select and communicate the correct wavelength to its clients.
6.1. Initial Setup
+---+ /-\ /-\ +---+
| A |----------------( F ) ~~~~~~~~~ ( I )----------------| B |
+---+ \-/ \-/ +---+
PATH
Upstream Label (Unassigned/0xFFFFFFFF)
--------------------->
-- ~~ -- ~~ -->
PATH
-------------------->
RESV
<--------------------
<-- ~~ -- ~~ --
RESV
Label (Assigned)
<---------------------
Initial Setup Sequence
Figure 4
Steps:
o "Router A" does not have enough information to pick an appropriate
client wavelength. It sends a PATH message downstream requesting
the network to assign an appropriate symmetric label for its use.
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Since the client wavelength is unknown, the laser is off at the
ingress client.
o The downstream node (Node F) receives the PATH message, chooses
the appropriate wavelength values and forwards them in appropriate
label fields to the egress client ("Router B")
o "Router B" receives the PATH message, turns the laser ON and tunes
it to the appropriate wavelength (received in the UPSTREAM_LABEL/
LABEL_SET of the PATH) and sends out a RESV message upstream.
o The RESV message received by the ingress client carries a valid
symmetric label in the LABEL object. "Router A" turns on the
laser and tunes it to the wavelength specified in the network
assigned symmetric LABEL.
For cases where the egress-node relies on RSVP signaling to determine
exactly when to start using the LSP, this draft recommends
integrating the above sequence with any of the existing graceful
setup procedures:
o "RESV-CONF" setup procedure (or)
o 2-step "ADMIN STATUS" based setup procedure ("A" bit set in the
first step; "A" bit cleared when the LSP is ready for use).
6.2. Wavelength Change
After the LSP is set up, the network MAY decide to change the
wavelength for the given LSP. This could be for a variety of reasons
- policy reasons, restoration within the core, preemption etc.
In such a scenario, if the ingress client receives a changed label
via the LABEL object in a RESV modify, it MUST retune the laser at
the ingress to the new wavelength. Similarly, if the egress client
receives a changed label via UPSTREAM_LABEL/LABEL_SET in a PATH
modify, it MUST retune the laser at the egress to the new wavelength.
If the node receiving the changed label in a PATH/RESV message does
not find the label acceptable, then the corresponding error
procedures defined in RFC 3473 [RFC3473] MUST be followed.
7. Acknowledgements
The authors would like to thank Adrian Farrel and Chris Bowers for
their inputs.
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8. Contributors
John Drake
Juniper Networks
Email: jdrake@juniper.net
Gert Grammel
Juniper Networks
Email: ggrammel@juniper.net
Pawel Brzozowski
ADVA Optical Networking
Email: pbrzozowski@advaoptical.com
Zafar Ali
Cisco Systems, Inc.
Email: zali@cisco.com
9. IANA Considerations
This document makes no requests for IANA action.
10. Security Considerations
This document defines a special label value to be carried in the
UPSTREAM_LABEL object of a PATH message. This special label value is
used to enable the function of requesting network assignment of an
upstream label. The changes proposed in this document pertain to the
semantics of a specific field in an existing RSVP object and the
corresponding procedures. Thus, there are no new security
implications raised by this document and the security considerations
put together by RFC 3473 [RFC3473] still applies.
For a general discussion on MPLS and GMPLS related security issues,
see the MPLS/GMPLS security framework RFC 5920 [RFC5920].
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
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[RFC3471] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Functional Description",
RFC 3471, DOI 10.17487/RFC3471, January 2003,
<http://www.rfc-editor.org/info/rfc3471>.
[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
DOI 10.17487/RFC3473, January 2003,
<http://www.rfc-editor.org/info/rfc3473>.
[RFC4920] Farrel, A., Ed., Satyanarayana, A., Iwata, A., Fujita, N.,
and G. Ash, "Crankback Signaling Extensions for MPLS and
GMPLS RSVP-TE", RFC 4920, DOI 10.17487/RFC4920, July 2007,
<http://www.rfc-editor.org/info/rfc4920>.
11.2. Informative References
[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
<http://www.rfc-editor.org/info/rfc5920>.
Authors' Addresses
Xian Zhang (editor)
Huawei Technologies
Email: zhang.xian@huawei.com
Vishnu Pavan Beeram (editor)
Juniper Networks
Email: vbeeram@juniper.net
Igor Bryskin
Huawei Technologies
Email: igor.bryskin@huawei.com
Daniele Ceccarelli
Ericsson
Email: daniele.ceccarelli@ericsson.com
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Oscar Gonzalez de Dios
Telefonica
Email: ogondio@tid.es
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