Internet DRAFT - draft-chandra-mpls-rsvp-shared-labels-np
draft-chandra-mpls-rsvp-shared-labels-np
MPLS Working Group C. Ramachandran
Internet-Draft V. Beeram
Intended status: Standards Track Juniper Networks
Expires: July 7, 2021 H. Sitaraman
Individual
January 3, 2021
Node Protection for RSVP-TE tunnels on a shared MPLS forwarding plane
draft-chandra-mpls-rsvp-shared-labels-np-05
Abstract
Segment Routed RSVP-TE tunnels provide the ability to use a shared
MPLS forwarding plane at every hop of the Label Switched Path (LSP).
The shared forwarding plane is realized with the use of 'Traffic
Engineering (TE) link labels' that get shared by LSPs traversing
these TE links. This paradigm helps significantly reduce the
forwarding plane state required to support a large number of LSPs on
a Label Switching Router (LSR). These tunnels require the ingress
Label Edge Router (LER) to impose a stack of labels. If the ingress
LER cannot impose the full label stack, it can use the assistance of
one or more delegation hops along the path of the LSP to impose parts
of the label stack.
The procedures for a Point of Local Repair (PLR) to provide local
protection against link failures using facility backup for Segment
Routed RSVP-TE tunnels are well defined and do not require specific
protocol extensions. This document defines the procedures for a PLR
to provide local protection against transit node failures using
facility backup for these tunnels. The procedures defined in this
document include protection against delegation hop failures.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 7, 2021.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Node Protection Specific Procedures . . . . . . . . . . . . . 4
3.1. Applicability of this Document . . . . . . . . . . . . . 4
3.2. PLR Procedures for Protecting Next-Hop Non-Delegation LSR 4
3.3. PLR Procedures for Protecting Next-Hop Delegation LSR . . 5
3.3.1. Label Allocation and Stacking . . . . . . . . . . . . 7
3.4. Backwards Compatibility . . . . . . . . . . . . . . . . . 7
3.4.1. LSR does not Support Node Protection for Shared
Labels . . . . . . . . . . . . . . . . . . . . . . . 7
3.4.2. Protected Hop does not Support Shared Labels . . . . 9
3.4.3. PLR does not Support Shared Labels . . . . . . . . . 9
4. Protocol Extensions . . . . . . . . . . . . . . . . . . . . . 9
4.1. DHLD Encoding in ETLD Attributes TLV . . . . . . . . . . 9
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
With the advent of Traffic Engineering (TE) link labels and Segment
Routed RSVP-TE Tunnels [RFC8577], a shared MPLS forwarding plane can
be realized by allowing the TE link label to be shared by MPLS RSVP-
TE Label Switched Paths (LSPs) traversing the link. The shared
forwarding plane behavior helps reduce the amount of forwarding plane
state required to support a large number of LSPs on a Label Switching
Router (LSR).
Segment Routed RSVP-TE tunnels request the use of a shared forwarding
plane at every hop of the LSP. The TE link label used at each hop is
recorded in the Record Route object (RRO) of the Resv message. The
ingress Label Edge Router (LER) uses this recorded information to
construct a stack of labels that can be imposed on the packets
steered on to the tunnel. In the scenario where the ingress LER
cannot impose the full label stack, it can use the assistance of one
or more delegation hops along the path of the LSP to impose parts of
the label stack.
Facility backup is a local repair method [RFC4090] in which a bypass
tunnel is used to provide protection against link or node failures
for MPLS RSVP-TE LSPs at the Point of Local Repair (PLR). The
facility backup procedures that provide protection against link
failures for Segment Routed RSVP-TE LSPs are defined in [RFC8577].
This document defines the facility backup procedures that provide
protection against node failures for these LSPs. These procedures
include protection against delegation hop failures. The document
also discusses the procedures for handling backwards compatibility
scenarios where a node along the path of the LSP does not support the
procedures defined in this document.
The procedures discussed in this document do not cover protection
against ingress/egress node failures. They also do not apply to
Point to Multipoint (P2MP) RSVP-TE Tunnels.
2. Terminology
The reader is expected to be familiar with the terminology specified
in [RFC3209], [RFC4090] and [RFC8577]. Unless otherwise stated, the
term LSPs in this document refer to Segment Routed RSVP-TE LSPs. The
following additional terms are used in this document:
Primary forwarding action: The outbound label forwarding action
performed at a PLR for a protected LSP before the occurrence of
local failure.
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Backup forwarding action: The outbound label forwarding action
performed at a PLR for a protected LSP after the occurrence of
local failure.
3. Node Protection Specific Procedures
A set of Segment Routed RSVP-TE LSPs can share a TE link label on an
LSR only if all the LSPs in the set share the same outbound label
forwarding action. For protected LSPs, having the same outbound
label forwarding action means having the same primary forwarding
action and the same backup forwarding action. In the case of LSPs
that do not request local protection or LSPs that request only link
protection, they can use the same outbound label forwarding action if
they reach a common next-hop LSR via a common outgoing TE link.
However, in the case of LSPs that request node protection, they can
use the same outbound label forwarding action only if they reach a
common next-next-hop LSR via a common outgoing TE link and a common
next-hop LSR.
3.1. Applicability of this Document
The label allocation and signaling procedures defined in [RFC8577]
can sufficiently cater to the following scenarios on an LSR:
(a) Offer no protection to LSPs that do not request local protection
(b) Offer no protection or link protection to LSPs that request link
protection
(c) Offer no protection or link protection to LSPs that request node
protection
The label allocation and signaling procedures defined in this
document are meant to enable LSRs to offer node protection to LSPs
that request node protection.
3.2. PLR Procedures for Protecting Next-Hop Non-Delegation LSR
If the protected next-hop LSR signals a TE link label for the LSP but
does not set the Delegation Label flag in the RRO Label Subobject
carried in Resv message, then the PLR SHOULD allocate multiple shared
labels for the same TE link such that a unique label is allocated for
every unique next-next-hop LSR that is reachable via the protected
next-hop LSR.
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326 348
+---+ +---+ 321+---+345 +---+ +---+
| A |-----| B |-----| C |-----| D |-----| E |
+---+ +---+ +---+ +---+ +---+
| | |376 | |
| | |378 | |
| | | | |
| +---+ +---+ +---+ +---+
+-------| F |-----|G |-----|H |-----|I |
+---+ +---+ +---+ +---+
Figure 1: Per-nhop-nnhop label allocation
In the example shown in Figure 1, LSR C has allocated the following
TE link labels:
321 for the TE link C-B to reach the next-next-hop LSR A
326 for the TE link C-B to reach the next-next-hop LSR F
345 for the TE link C-D to reach the next-next-hop LSR E
348 for the TE link C-D to reach the next-next-hop LSR H
376 for the TE link C-G to reach the next-next-hop LSR F
378 for the TE link C-G to reach the next-next-hop LSR H
If a LSP requesting node protection transits PLR C and if the
protected next-hop LSR after C along the LSP path is not a delegation
hop, then LSR C signals the respective TE link label depending on the
next-next-hop LSR on the LSP path.
LSP path: A -> B -> C -> D -> E : Label = 345
LSP path: A -> B -> C -> D -> H : Label = 348
LSP path: A -> B -> C -> G -> H : Label = 378
In all LSP paths above, at PLR C, the protected next-hop LSRs D and G
along the LSP paths signal TE link labels but are not delegation
hops.
If the primary TE link is operational, LSR C will pop the TE link
label and forward the packet to the corresponding next-hop LSR over
that TE link. During local repair, LSR C will pop the TE link label
and also the label beneath the top label, and forward the packet over
the node protecting bypass tunnel to the appropriate next-next-hop
LSR, which is the Merge Point (MP).
3.3. PLR Procedures for Protecting Next-Hop Delegation LSR
The outgoing backup label forwarding action corresponding to a label
shared by LSPs requesting node protection MUST bypass the protected
next-hop LSR. The PLR MUST push the label stack on behalf of the
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next-hop delegation LSR. Hence, the number of labels that a
delegation hop chooses to push also depends on the number of labels
that the upstream hop (acting as PLR) along the primary LSP can push.
This section extends the Effective Transport Label-Stack Depth (ETLD)
signaling procedure specified in [RFC8577] for LSPs requesting node
protection.
Considering Figure 2, assume LER A and LSR B can push a maximum of 3
labels on an MPLS packet while the remaining nodes can push a maximum
of 5 labels. LER A originates a Path message with an ETLD of 2 after
reserving space for the bypass tunnel label that should be pushed for
backup forwarding action. In addition to setting the ETLD, LER A
also sets the Delegation Helper Label Depth (DHLD) to 2 in the Path
message. The DHLD is computed as the maximum number of labels that
the node can push after reserving space for the NNHOP bypass tunnel
label that should be pushed for backup forwarding action. The ETLD
procedures dictate that each LSR add its own ETLD value before
sending the Path message downstream. LSRs C, E and I are
automatically selected as delegation hops by the time the Path
message reaches the egress LER L. LSR C uses the DHLD signaled by
the upstream LSR B as input when calculating the outgoing ETLD in the
Path message.
ETLD:2 ETLD:1 ETLD:2 ETLD:1 ETLD:4
DHLD:2 DHLD:2 DHLD:4 DHLD:4 DHLD:4
-----> -----> -----> -----> ----->
1300d 1500d
+---+ +---+ +---+ +---+ +---+ +---+
| A |-----| B |-----| C |-----| D |-----| E |-----| F | ETLD:3
+---+ +---+ +---+ +---+ +---+ +---+ DHLD:4
| | | |
| | | |
| | 1900d | |
+---+ +---+ +---+ +---+ +---+ +---+ v
| L |-----| K |-----| J |-----| I |-----| H |-----+ G +
+---+ +---+ +---+ +---+ +---+ +---+
DHLD:4 DHLD:4 DHLD:4 DHLD:4 DHLD:4
ETLD:2 ETLD:3 ETLD:4 ETLD:1 ETLD:2
<----- <----- <----- <----- <-----
Notation : <Label>d - delegation label
Figure 2: ETLD and DHLD signaling for node protection
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As shown in Figure 2, delegation hop LSR C does not set outgoing ETLD
to 4 that it would have normally set given that LSR C can push a
maximum of 5 labels on an outgoing packet. Instead, LSR C sets the
outgoing ETLD to the minimum of the ETLD that it computes and the
DHLD value of its previous hop i.e. minimum(computed ETLD = 4,
previous hop DHLD = 2).
The extension for signaling the DHLD in the Path message is defined
in Section 4.1.
3.3.1. Label Allocation and Stacking
An LSR that decides to become a delegation hop for one or more LSPs
requesting node protection MUST allocate a delegation label separate
from delegation label assigned for LSPs that are offered no
protection or link protection - even though the delegation segments
share the same hops. In the example shown in Figure 2, the
delegation hops LSRs C, E and I will set the Delegation Label flag in
the Label sub-object that they add to the Resv message.
A PLR node that offers node protection to a delegation hop SHOULD be
capable of helping the downstream delegation when the primary TE link
to the delegation hop goes down. In the example shown in Figure 1,
the LSRs B, D and H act as helpers for their respective downstream
delegation hops. The PLR nodes that are delegation helpers along the
path of LSPs requesting node protection SHOULD allocate a unique
label for every delegation label signaled by the protected delegation
node.
Before primary TE link failure, the PLR playing the role of a
delegation helper pops the incoming label and forwards the packet on
the primary TE link. During local repair, the delegation helper PLR
pops the incoming label and also the label beneath it and pushes the
label stack on behalf of the next hop delegation LSR and forwards the
packet over the bypass tunnel.
Any LSR that creates label stack upstream of the delegation helper
MUST include the label signaled by the delegation helper onto the
outgoing label stack just as it uses the TE link label to construct
outgoing label stack.
3.4. Backwards Compatibility
3.4.1. LSR does not Support Node Protection for Shared Labels
As defined in Section 3.1, any LSR along the path of an LSP
requesting node protection may choose to instead offer no protection
or link protection. Hence, it must be possible to build an LSP where
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some LSRs along the path support the node protection extensions
defined in this document whereas the rest of the LSRs support only
[RFC8577]. Any PLR along the LSP path that does not support the
procedures defined in this document MUST provide either no protection
or link protection for the LSPs requesting node protection.
ETLD:2 ETLD:1 ETLD:4 ETLD:3 ETLD:2
DHLD:2 DHLD:2 - DHLD:4 DHLD:4
-----> -----> -----> -----> ----->
1300d
+---+ +---+ +---+ +---+ +---+ +---+
| A |-----| B |-----| C |-----| D |-----| E |-----| F | ETLD:1
+---+ +---+ +---+ +---+ +---+ +---+ DHLD:4
| | | |
| | | |
| | 1500d | |
+---+ +---+ +---+ +---+ +---+ +---+ v
| L |-----| K |-----| J |-----| I |-----| H |-----+ G +
+---+ +---+ +---+ +---+ +---+ +---+
1700d
DHLD:4 DHLD:4 DHLD:4 DHLD:4 DHLD:4
ETLD:4 ETLD:1 ETLD:2 ETLD:3 ETLD:4
<----- <----- <----- <----- <-----
Notation : <Label>d - delegation label
Figure 3: Delegation node does not support signaling DHLD
In Figure 3, assume LER A and LSR B can push a maximum of 3 labels to
the MPLS packet while the remaining nodes can push a maximum of 5
labels. Also assume that LSR C supports the extensions defined in
[RFC8577] but does not support the extensions defined in this
document. Based on ETLD signaling procedure, LSR C will become a
delegation hop. However, as LSR C cannot understand the DHLD
signaled by the previous hop LSR B, LSR C will set outgoing ETLD to
4. If LSR C had supported the DHLD signaling, it would have set
outgoing ETLD to 2 (see Section 3.3). When PLR B receives shared
label from the protected next-hop LSR C in the Resv message, it must
determine the number of labels it has to push in order to offer node
protection from the RRO sub-object carried in Resv. As the label
stack depth of the delegation hop C is greater than the number of
labels LSR C can push, it must either not provide local protection or
provide only link protection for the LSP.
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3.4.2. Protected Hop does not Support Shared Labels
If the ingress LER has requested label stacking to reach delegation
hop for the LSP requesting node protection, and if the next-hop LSR
allocates a regular label for the LSP, then the LSR MUST also
allocate a regular label for the LSP.
If the ingress LER has requested label stacking to reach the egress
LER for the LSP requesting node protection, and if the next-hop LSR
has allocated a regular label for the LSP, then the PLR MUST become a
delegation hop and set the RRO Label Subobject delegation label flag
in the RRO carried in Resv message. The PLR MUST set ETLD to 1 in
its outgoing Path message.
3.4.3. PLR does not Support Shared Labels
If an LSR determines that its immediate upstream LSR (PLR) has not
included an ETLD in the incoming Path message, then the LSR MUST
become a delegation hop and set the ETLD to 1 in the outgoing Path
message. The outgoing ETLD is set to 1 because the upstream LSR does
not support shared labels and cannot push the label stack on behalf
of this LSR.
4. Protocol Extensions
This section discusses the protocol extension required to support the
procedures in Section 3.3
4.1. DHLD Encoding in ETLD Attributes TLV
Delegation Helper Label Depth (DHLD) is defined as the number of
labels that an LSR has the capability to push while performing local
repair protecting the next-hop delegation LSR. This document updates
the ETLD Attributes TLV defined in [RFC8577]. The encoding of DHLD
in the ETLD Attributes TLV is shown in Figure 4
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | DHLD | ETLD |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: The ETLD Attributes TLV
The presence of ETLD Attributes TLV in the HOP_ATTRIBUTES sub-object
[RFC7570] of the RRO object carried in Path message indicates that
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the hop identified by the preceding IPv4 or IPv6 or Unnumbered
Interface ID sub-object supports automatic delegation [RFC8577].
An implementation that supports this document MUST set the 8 bits
from bit number 16 to bit number 23 with its DHLD value as indicated
in Figure 4 when signaling Path message for an LSP for which node
protection has been requested.
When processing the ETLD Attributes TLV of the previous hop LSR in
the received Path message, the LSR checks whether it has to be the
delegation hop based on the ETLD algorithm defined in [RFC8577].
If the LSR does not become a delegation hop along the LSP path, then
no further action is required based on the DHLD value set by the
previous hop.
If the LSR does become a delegation hop along the LSP path, then it
MUST decode the 8 bit unsigned value from bit number 16 to bit number
23 as indicated in Figure 4. If the 8 bit value is zero, then the
LSR MUST infer that the previous hop has not included DHLD in the
ETLD Attributes TLV. If the 8 bit value is non-zero, then the LSR
MUST consider that value as the DHLD value signaled by the previous
hop LSR and use that DHLD value for computing its own outgoing ETLD.
5. Acknowledgements
The authors would like to thank Raveendra Torvi for his input from
discussions.
6. IANA Considerations
This document includes no requests to IANA.
7. Security Considerations
This document does not introduce new security issues. The security
considerations pertaining to the original RSVP protocol [RFC2205] and
RSVP-TE [RFC3209] and those that are described in [RFC5920] remain
relevant.
8. References
8.1. 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,
<https://www.rfc-editor.org/info/rfc2119>.
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[RFC2205] Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, DOI 10.17487/RFC2205,
September 1997, <https://www.rfc-editor.org/info/rfc2205>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.
[RFC4090] Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
DOI 10.17487/RFC4090, May 2005,
<https://www.rfc-editor.org/info/rfc4090>.
[RFC7570] Margaria, C., Ed., Martinelli, G., Balls, S., and B.
Wright, "Label Switched Path (LSP) Attribute in the
Explicit Route Object (ERO)", RFC 7570,
DOI 10.17487/RFC7570, July 2015,
<https://www.rfc-editor.org/info/rfc7570>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8577] Sitaraman, H., Beeram, V., Parikh, T., and T. Saad,
"Signaling RSVP-TE Tunnels on a Shared MPLS Forwarding
Plane", RFC 8577, DOI 10.17487/RFC8577, April 2019,
<https://www.rfc-editor.org/info/rfc8577>.
8.2. Informative References
[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
<https://www.rfc-editor.org/info/rfc5920>.
Authors' Addresses
Chandra Ramachandran
Juniper Networks
Email: csekar@juniper.net
Vishnu Pavan Beeram
Juniper Networks
Email: vbeeram@juniper.net
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Harish Sitaraman
Individual
Email: harish.ietf@gmail.com
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