RFC 8577
Signaling RSVP-TE Tunnels on a Shared MPLS Forwarding Plane
Internet Engineering Task Force (IETF) H. Sitaraman Request for Comments: 8577 V. Beeram Category: Standards Track Juniper Networks ISSN: 2070-1721 T. Parikh Verizon T. Saad Cisco Systems April 2019 Signaling RSVP-TE Tunnels on a Shared MPLS Forwarding PlaneAbstract
As the scale of MPLS RSVP-TE networks has grown, the number of Label Switched Paths (LSPs) supported by individual network elements has increased. Various implementation recommendations have been proposed to manage the resulting increase in the amount of control-plane state information. However, those changes have had no effect on the number of labels that a transit Label Switching Router (LSR) has to support in the forwarding plane. That number is governed by the number of LSPs transiting or terminated at the LSR and is directly related to the total LSP state in the control plane. This document defines a mechanism to prevent the maximum size of the label space limit on an LSR from being a constraint to control-plane scaling on that node. It introduces the notion of preinstalled 'per-TE link labels' that can be shared by MPLS RSVP-TE LSPs that traverse these TE links. This approach significantly reduces the forwarding-plane state required to support a large number of LSPs. This couples the feature benefits of the RSVP-TE control plane with the simplicity of the Segment Routing (SR) MPLS forwarding plane. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8577.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 6 3. Allocation of TE Link Labels . . . . . . . . . . . . . . . . 6 4. Segment Routed RSVP-TE Tunnel Setup . . . . . . . . . . . . . 6 5. Delegating Label Stack Imposition . . . . . . . . . . . . . . 8 5.1. Stacking at the Ingress . . . . . . . . . . . . . . . . . 8 5.1.1. Stack to Reach Delegation Hop . . . . . . . . . . . . 9 5.1.2. Stack to Reach Egress . . . . . . . . . . . . . . . . 10 5.2. Explicit Delegation . . . . . . . . . . . . . . . . . . . 11 5.3. Automatic Delegation . . . . . . . . . . . . . . . . . . 11 5.3.1. Effective Transport Label-Stack Depth (ETLD) . . . . 11 6. Mixing TE Link Labels and Regular Labels in an RSVP-TE Tunnel 13 7. Construction of Label Stacks . . . . . . . . . . . . . . . . 14 8. Facility Backup Protection . . . . . . . . . . . . . . . . . 14 8.1. Link Protection . . . . . . . . . . . . . . . . . . . . . 14 9. Protocol Extensions . . . . . . . . . . . . . . . . . . . . . 15 9.1. Requirements . . . . . . . . . . . . . . . . . . . . . . 15 9.2. Attribute Flags TLV: TE Link Label . . . . . . . . . . . 16 9.3. RRO Label Sub-object Flag: TE Link Label . . . . . . . . 16 9.4. Attribute Flags TLV: LSI-D . . . . . . . . . . . . . . . 16 9.5. RRO Label Sub-object Flag: Delegation Label . . . . . . . 17 9.6. Attributes Flags TLV: LSI-D-S2E . . . . . . . . . . . . . 17 9.7. Attributes TLV: ETLD . . . . . . . . . . . . . . . . . . 18 10. OAM Considerations . . . . . . . . . . . . . . . . . . . . . 18 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 11.1. Attribute Flags: TE Link Label, LSI-D, LSI-D-S2E . . . . 19 11.2. Attribute TLV: ETLD . . . . . . . . . . . . . . . . . . 19 11.3. Record Route Label Sub-object Flags: TE Link Label, Delegation Label . . . . . . . . . . . . . . . . . . . . 20 11.4. Error Codes and Error Values . . . . . . . . . . . . . . 20 12. Security Considerations . . . . . . . . . . . . . . . . . . . 20 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 13.1. Normative References . . . . . . . . . . . . . . . . . . 21 13.2. Informative References . . . . . . . . . . . . . . . . . 22 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 23 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction
The scaling of RSVP-TE [RFC3209] control-plane implementations can be improved by adopting the guidelines and mechanisms described in [RFC2961] and [RFC8370]. These documents do not affect the forwarding-plane state required to handle the control-plane state. The forwarding-plane state remains unchanged and is directly proportional to the total number of Label Switching Paths (LSPs) supported by the control plane. This document describes a mechanism that prevents the size of the platform-specific label space on a Label Switching Router (LSR) from being a constraint to pushing the limits of control-plane scaling on that node. This work introduces the notion of preinstalled 'per-TE link labels' that are allocated by an LSR. Each such label is installed in the MPLS forwarding plane with a 'pop' operation and instructions to forward the received packet over the TE link. An LSR advertises this label in the Label object of a Resv message as LSPs are set up, and they are recorded hop by hop in the Record Route Object (RRO) of the Resv message as it traverses the network. The ingress Label Edge Router (LER) constructs and pushes a stack of labels [RFC3031] using the labels received in the RRO. These 'TE link labels' can be shared by MPLS RSVP-TE LSPs that traverse the same TE link. This forwarding-plane behavior fits in the MPLS architecture [RFC3031] and is the same as that exhibited by Segment Routing (SR) [RFC8402] when using an MPLS forwarding plane and a series of adjacency segments [SEG-ROUTING]. This work couples the feature benefits of the RSVP-TE control plane with the simplicity of the SR MPLS forwarding plane. RSVP-TE using a shared MPLS forwarding plane offers the following benefits: 1. Shared labels: The transit label on a TE link is shared among RSVP-TE tunnels traversing the link and is used independently of the ingress and egress of the LSPs. 2. Faster LSP setup time: No forwarding-plane state needs to be programmed during LSP setup and teardown, resulting in faster provisioning and deprovisioning of LSPs. 3. Hitless rerouting: New transit labels are not required during make-before-break (MBB) in scenarios where the new LSP instance traverses the exact same path as the old LSP instance. This saves the ingress LER and the services that use the tunnel from
needing to update the forwarding plane with new tunnel labels,
thereby making MBB events faster. Periodic MBB events are
relatively common in networks that deploy the 'auto-bandwidth'
feature on RSVP-TE LSPs to monitor bandwidth utilization and
periodically adjust LSP bandwidth.
4. Mix-and-match labels: Both 'TE link labels' and regular labels
can be used on transit hops for a single RSVP-TE tunnel (see
Section 6). This allows backward compatibility with transit LSRs
that provide regular labels in Resv messages.
No additional extensions to routing protocols are required in order
to support key functionalities such as bandwidth admission control,
LSP priorities, preemption, and auto-bandwidth on this shared MPLS
forwarding plane. This document also discusses how Fast Reroute
[RFC4090] via facility backup link protection using regular bypass
tunnels can be supported on this forwarding plane.
The signaling procedures and extensions discussed in this document do
not apply to Point to Multipoint (P2MP) RSVP-TE tunnels.
2. Terminology
The following terms are used in this document:
TE link label: An incoming label at an LSR that will be popped by
the LSR with the packet being forwarded over a specific outgoing
TE link to a neighbor.
Shared MPLS forwarding plane: An MPLS forwarding plane where every
participating LSR uses TE link labels on every LSP.
Segment Routed RSVP-TE tunnel: An MPLS RSVP-TE tunnel that requests
the use of a shared MPLS forwarding plane at every hop of the LSP.
The corresponding LSPs are referred to as "Segment Routed RSVP-TE
LSPs".
Delegation hop: A transit hop of a Segment Routed RSVP-TE LSP that
is selected to assist in the imposition of the label stack in
scenarios where the ingress LER cannot impose the full label
stack. There can be multiple delegation hops along the path of a
Segment Routed RSVP-TE LSP.
Delegation label: A label assigned at the delegation hop to
represent a set of labels that will be pushed at this hop.
2.1. 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.3. Allocation of TE Link Labels
An LSR that participates in a shared MPLS forwarding plane MUST allocate a unique TE link label for each TE link. When an LSR encounters a TE link label at the top of the label stack, it MUST pop the label and forward the packet over the TE link to the downstream neighbor on the RSVP-TE tunnel. Multiple TE link labels MAY be allocated for the TE link to accommodate tunnels requesting protection. Implementations that maintain per-label bandwidth accounting at each hop must aggregate the reservations made for all the LSPs using the shared TE link label.4. Segment Routed RSVP-TE Tunnel Setup
This section provides an example of how the RSVP-TE signaling procedure works to set up a tunnel utilizing a shared MPLS forwarding plane. The sample topology below is used to explain the example. Labels shown at each node are TE link labels that, when present at the top of the label stack, indicate that they should be popped and that the packet should be forwarded on the TE link to the neighbor. +---+100 +---+150 +---+200 +---+250 +---+ | A |-----| B |-----| C |-----| D |-----| E | +---+ +---+ +---+ +---+ +---+ |110 |450 |550 |650 |850 | | | | | | |400 |500 |600 |800 | +---+ +---+ +---+ +---+ +-------| F |-----|G |-----|H |-----|I | +---+300 +---+350 +---+700 +---+ Figure 1: Sample Topology -- TE Link Labels
Consider two tunnels:
RSVP-TE tunnel T1: From A to E on path A-B-C-D-E
RSVP-TE tunnel T2: From F to E on path F-B-C-D-E
Both tunnels share the TE links B-C, C-D, and D-E.
RSVP-TE is used to signal the setup of tunnel T1 (using the TE link
label attributes flag defined in Section 9.2). When LSR D receives
the Resv message from the egress LER E, it checks the next-hop TE
link (D-E) and provides the TE link label (250) in the Resv message
for the tunnel placing the label value in the Label object. It also
provides the TE link label (250) in the Label sub-object carried in
the RRO and sets the TE link label flag as defined in Section 9.3.
Similarly, LSR C provides the TE link label (200) for the TE link
C-D, and LSR B provides the TE link label (150) for the TE link B-C.
For tunnel T2, the transit LSRs provide the same TE link labels as
described for tunnel T1 as the links B-C, C-D, and D-E are common
between the two LSPs.
The ingress LERs (A and F) will push the same stack of labels (from
top of stack to bottom of stack) {150, 200, 250} for tunnels T1 and
T2, respectively.
It should be noted that a transit LSR does not swap the top TE link
label on an incoming packet (the label that it advertised in the Resv
message it sent); all it has to do is pop the top label and forward
the packet.
The values in the Label sub-objects in the RRO are of interest to the
ingress LERs when constructing the stack of labels to impose on the
packets.
If, in this example, there were another RSVP-TE tunnel T3 from F to I
on path F-B-C-D-E-I, then this tunnel would also share the TE links
B-C, C-D, and D-E and traverse link E-I. The label stack used by F
would be {150, 200, 250, 850}. Hence, regardless of where the LSPs
start and end, they will share LSR labels at shared hops in the
shared MPLS forwarding plane.
There MAY be a local operator policy at the ingress LER that
influences the maximum depth of the label stack that can be pushed
for a Segment Routed RSVP-TE tunnel. Prior to signaling the LSP, the
ingress LER may determine that it is unable to push a label stack
containing one label for each hop along the path. In some scenarios,
the ingress LER may not have sufficient information to make that determination. In these cases, the LER SHOULD adopt the techniques described in Section 5.5. Delegating Label Stack Imposition
One or more transit LSRs can assist the ingress LER by imposing part of the label stack required for the path. Consider the example in Figure 2 with an RSVP-TE tunnel from A to L on path A-B-C-D-E-F-G-H-I-J-K-L. In this case, the LSP is too long for LER A to impose the full label stack, so it uses the assistance of delegation hops LSR D and LSR I to impose parts of the label stack. Each delegation hop allocates a delegation label to represent a set of labels that will be pushed at this hop. When a packet arrives at a delegation hop LSR with a delegation label, the LSR pops the label and pushes a set of labels before forwarding the packet. 1250d +---+100p +---+150p +---+200p +---+250p +---+300p +---+ | A |------| B |------| C |------| D |------| E |------| F | +---+ +---+ +---+ +---+ +---+ +---+ |350p | 1500d | +---+ 600p+---+ 550p+---+ 500p+---+ 450p+---+ 400p+---+ | L |------| K |------| J |------| I |------| H |------+ G + +---+ +---+ +---+ +---+ +---+ +---+ Notation: <Label>p - TE link label <Label>d - Delegation label Figure 2: Delegating Label Stack Imposition5.1. Stacking at the Ingress
When delegation labels come into play, there are two stacking approaches from which the ingress can choose. Section 7 explains how the label stack can be constructed.
5.1.1. Stack to Reach Delegation Hop
In this approach, the stack pushed by the ingress carries a set of labels that will take the packet to the first delegation hop. When this approach is employed, the set of labels represented by a delegation label at a given delegation hop will include the corresponding delegation label from the next delegation hop. As a result, this delegation label can only be shared among LSPs that are destined to the same egress and traverse the same downstream path. This approach is shown in Figure 3. The delegation label 1250 represents the stack {300, 350, 400, 450, 1500}, and the delegation label 1500 represents the label stack {550, 600}. +---+ +---+ +---+ | A |-----.....-----| D |-----.....-----| I |-----..... +---+ +---+ +---+ Pop 1250 & Pop 1500 & Push Push Push ...... ...... ...... : 150: 1250->: 300: 1500->: 550: : 200: : 350: : 600: :1250: : 400: ...... ...... : 450: :1500: ...... Figure 3: Stack to Reach Delegation Hop With this approach, the ingress LER A will push {150, 200, 1250} for the tunnel in Figure 2. At LSR D, the delegation label 1250 will get popped, and {300, 350, 400, 450, 1500} will get pushed. At LSR I, the delegation label 1500 will get popped, and the remaining set of labels {550, 600} will get pushed.
5.1.2. Stack to Reach Egress
In this approach, the stack pushed by the ingress carries a set of labels that will take the packet all the way to the egress so that all the delegation labels are part of the stack. When this approach is employed, the set of labels represented by a delegation label at a given delegation hop will not include the corresponding delegation label from the next delegation hop. As a result, this delegation label can be shared among all LSPs traversing the segment between the two delegation hops. The downside of this approach is that the number of hops that the LSP can traverse is dictated by the label stack push limit of the ingress. This approach is shown in Figure 4. The delegation label 1250 represents the stack {300, 350, 400, 450}, and the delegation label 1500 represents the label stack {550, 600}. +---+ +---+ +---+ | A |-----.....-----| D |-----.....-----| I |-----..... +---+ +---+ +---+ Pop 1250 & Pop 1500 & Push Push Push ...... ...... ...... : 150: 1250->: 300: 1500->: 550: : 200: : 350: : 600: :1250: : 400: ...... :1500: : 450: ...... ...... |1500| ...... Figure 4: Stack to Reach Egress With this approach, the ingress LER A will push {150, 200, 1250, 1500} for the tunnel in Figure 2. At LSR D, the delegation label 1250 will get popped, and {300, 350, 400, 450} will get pushed. At LSR I, the delegation label 1500 will get popped, and the remaining set of labels {550, 600} will get pushed. The signaling extension required for the ingress to indicate the chosen stacking approach is defined in Section 9.6.
5.2. Explicit Delegation
In this delegation option, the ingress LER can explicitly delegate one or more specific transit LSRs to handle pushing labels for a certain number of their downstream hops. In order to accurately pick the delegation hops, the ingress needs to be aware of the label stack depth push limit (total number of MPLS labels that can be imposed, including all service/transport/special labels) of each of the transit LSRs prior to initiating the signaling sequence. The mechanism by which the ingress or controller (hosting the path computation element) learns this information is outside the scope of this document. Base MPLS Imposition MSD (BMI-MSD) advertisement, specified in [RFC8491], is an example of such a mechanism. The signaling extension required for the ingress LER to explicitly delegate one or more specific transit hops is defined in Section 9.4. The extension required for the delegation hop to indicate that the recorded label is a delegation label is defined in Section 9.5.5.3. Automatic Delegation
In this approach, the ingress LER lets the downstream LSRs automatically pick suitable delegation hops during the initial signaling sequence. The ingress does not need to be aware up front of the label stack depth push limit of each of the transit LSRs. This approach SHOULD be used if there are loose hops [RFC3209] in the explicit route. The delegation hops are picked based on a per-hop signaled attribute called the Effective Transport Label-Stack Depth (ETLD), as described in the next section.5.3.1. Effective Transport Label-Stack Depth (ETLD)
The ETLD is signaled as a per-hop recorded attribute in the Path message [RFC7570]. When automatic delegation is requested, the ingress MUST populate the ETLD with the maximum number of transport labels that it can potentially send to its downstream hop. This value is then decremented at each successive hop. If a node is reached and it is determined that this hop cannot support automatic delegation, then it MUST NOT use TE link labels and use regular labels instead. If a node is reached where the ETLD set from the previous hop is 1, then that node MUST select itself as the delegation hop. If a node is reached and it is determined that this hop cannot receive more than one transport label, then that node MUST select itself as the delegation hop. If there is a node or a sequence of nodes along the path of the LSP that do not support ETLD, then the immediate hop that supports ETLD MUST select itself as the delegation hop. The ETLD MUST be decremented at each non-delegation transit hop by either 1 or some appropriate number based on the local
policy. For example, consider a transit node with a local policy that mandates it to take the label stack read limit into account when decrementing the ETLD. With this policy, the ETLD is decremented in such a way that the transit hop does not receive more labels in the stack than it can read. At each delegation hop, the ETLD MUST be reset to the maximum number of transport labels that the hop can send, and the ETLD decrements start again at each successive hop until either a new delegation hop is selected or the egress is reached. As a result, by the time the Path message reaches the egress, all delegation hops are selected. During the Resv processing, at each delegation hop, a suitable delegation label is selected (either an existing label is reused or a new label is allocated) and recorded in the Resv message. Consider the example shown in Figure 5. Let's assume ingress LER A can push up to three transport labels while the remaining nodes can push up to five transport labels. The ingress LER A signals the initial Path message with ETLD set to 3. The ETLD value is adjusted at each successive hop and signaled downstream as shown. By the time the Path message reaches the egress LER L, LSRs D and I are automatically selected as delegation hops. ETLD:3 ETLD:2 ETLD:1 ETLD:5 ETLD:4 -----> -----> -----> -----> -----> 1250d +---+100p +---+150p +---+200p +---+250p +---+300p +---+ | A |-----| B |-----| C |-----| D |-----| E |-----| F | ETLD:3 +---+ +---+ +---+ +---+ +---+ +---+ | |350p | | | 1500d | | +---+ 600p+---+ 550p+---+ 500p+---+ 450p+---+ 400p+---+ v | L |-----| K |-----| J |-----| I |-----| H |-----+ G + +---+ +---+ +---+ +---+ +---+ +---+ ETLD:3 ETLD:4 ETLD:5 ETLD:1 ETLD:2 <----- <----- <----- <----- <----- Figure 5: ETLD When an LSP that requests automatic delegation also requests facility backup protection [RFC4090], the ingress or the delegation hop MUST account for the bypass tunnel's label(s) when populating the ETLD. Hence, when a regular bypass tunnel is used to protect the facility, the ETLD that gets populated on these nodes is one less than what gets populated for a corresponding unprotected LSP.
Signaling extension for the ingress LER to request automatic delegation is defined in Section 9.4. The extension for signaling the ETLD is defined in Section 9.7. The extension required for the delegation hop to indicate that the recorded label is a delegation label is defined in Section 9.5.6. Mixing TE Link Labels and Regular Labels in an RSVP-TE Tunnel
Labels can be mixed across transit hops in a single MPLS RSVP-TE LSP. Certain LSRs can use TE link labels and others can use regular labels. The ingress can construct a label stack appropriately based on what type of label is recorded from every transit LSR. (#) (#) +---+100 +---+150 +---+200 +---+250 +---+ | A |-----| B |-----| C |-----| D |-----| E | +---+ +---+ +---+ +---+ +---+ |110 |450 |550 |650 |850 | | | | | | |400 |500 |600 |800 | +---+ +---+ +---+ +---+ +-------| F |-----|G |-----|H |-----|I | +---+300 +---+350 +---+700 +---+ Notation: (#) denotes regular labels Other labels are TE link labels Figure 6: Sample Topology -- TE Link Labels and Regular Labels If the transit LSR allocates a regular label to be sent upstream in the Resv, then the label operation at the LSR is a swap to the label received from the downstream LSR. If the transit LSR is using a TE link label to be sent upstream in the Resv, then the label operation at the LSR is a pop and forward regardless of any label received from the downstream LSR. There is no change in the behavior of a penultimate hop popping (PHP) LSR [RFC3031]. Section 7 explains how the label stack can be constructed. For example, the LSP from A to I using path A-B-C-D-E-I will use a label stack of {150, 200}.
7. Construction of Label Stacks
The ingress LER or delegation hop MUST check the type of label received from each transit hop as recorded in the RRO in the Resv message and generate the appropriate label stack to reach the next delegation hop or the egress. The following logic is used by the node constructing the label stack: Each RRO label sub-object MUST be processed starting with the label sub-object from the first downstream hop. Any label provided by the first downstream hop MUST always be pushed on the label stack regardless of the label type. If the label type is a TE link label, then any label from the next downstream hop MUST also be pushed on the constructed label stack. If the label type is a regular label, then any label from the next downstream hop MUST NOT be pushed on the constructed label stack. If the label type is a delegation label, then the type of stacking approach chosen by the ingress for this LSP (Section 5.1) MUST be used to determine how the delegation labels are pushed in the label stack.8. Facility Backup Protection
The following section describes how link protection works with facility backup protection [RFC4090] using regular bypass tunnels for the Segment Routed RSVP-TE tunnels. The procedures for supporting node protection are not discussed in this document. The use of Segment Routed bypass tunnels for providing facility protection is left for further study.8.1. Link Protection
To provide link protection at a Point of Local Repair (PLR) with a shared MPLS forwarding plane, the LSR MUST allocate a separate TE link label for the TE link that will be used for RSVP-TE tunnels that request link protection from the ingress. No signaling extensions are required to support link protection for RSVP-TE tunnels over the shared MPLS forwarding plane. At each LSR, link-protected TE link labels can be allocated for each TE link, and a link-protecting facility backup LSP can be created to protect the TE link. The link-protected TE link label can be sent by the LSR for LSPs requesting link protection over the specific TE link. Since the facility backup terminates at the next hop (merge point), the incoming label on the packet will be what the merge point expects.
Consider the network shown in Figure 7. LSR B can install a facility backup LSP for the link-protected TE link label 151. When the TE link B-C is up, LSR B will pop 151 and send the packet to C. If the TE link B-C is down, the LSR can pop 151 and send the packet via the facility backup to C. 101(*) 151(*) 201(*) 251(*) +---+100 +---+150 +---+200 +---+250 +---+ | A |------| B |------| C |------| D |------| E | +---+ +---+ +---+ +---+ +---+ |110 |450 |550 |650 |850 | | | | | | |400 |500 |600 |800 | +---+ +---+ +---+ +---+ +--------| F |------|G |------|H |------|I | +---+300 +---+350 +---+700 +---+ Notation: (*) denotes link-protected TE link labels Figure 7: Link Protection Topology9. Protocol Extensions
9.1. Requirements
The functionality discussed in this document imposes the following requirements on the signaling protocol. o The ingress of the LSP needs to have the ability to mandate/ request the use and recording of TE link labels at all hops along the path of the LSP. o When the use of TE link labels is mandated/requested for the path: * the node recording the TE link label needs to have the ability to indicate whether the recorded label is a TE link label. * the ingress needs to have the ability to delegate label stack imposition by: + explicitly mandating specific hops to be delegation hops, or + requesting automatic delegation.
* When explicit delegation is mandated or automatic delegation is
requested:
+ the ingress needs to have the ability to indicate the chosen
stacking approach, and
+ the delegation hop needs to have the ability to indicate
that the recorded label is a delegation label.
9.2. Attribute Flags TLV: TE Link Label
Bit Number 16: TE Link Label
The presence of this flag in the LSP_ATTRIBUTES/
LSP_REQUIRED_ATTRIBUTES object [RFC5420] of a Path message indicates
that the ingress has requested/mandated the use and recording of TE
link labels at all hops along the path of this LSP. When a node that
recognizes this flag but does not cater to the mandate because of
local policy receives a Path message carrying the
LSP_REQUIRED_ATTRIBUTES object with this flag set, it MUST send a
PathErr message with an error code of 'Routing Problem (24)' and an
error value of 'TE link label usage failure (70)'. A transit hop
that caters to this request/mandate MUST also check for the presence
of other Attribute Flags introduced in this document (Sections 9.4
and 9.6) and process them as specified. An ingress LER that sets
this bit MUST also set the "label recording desired" flag [RFC3209]
in the SESSION_ATTRIBUTE object.
9.3. RRO Label Sub-object Flag: TE Link Label
Flag (0x02): TE Link Label
The presence of this flag indicates that the recorded label is a TE
link label. This flag MUST be used by a node only if the use and
recording of TE link labels are requested/mandated for the LSP.
9.4. Attribute Flags TLV: LSI-D
Bit Number 17: Label Stack Imposition - Delegation (LSI-D)
Automatic Delegation: The presence of this flag in the LSP_ATTRIBUTES
object of a Path message indicates that the ingress has requested
automatic delegation of label stack imposition. This flag MUST be
set in the LSP_ATTRIBUTES object of a Path message only if the use
and recording of TE link labels are requested/mandated for this LSP.
If the transit hop does not support this flag, it MUST NOT use TE
link labels and use regular labels instead. If the use of TE link
labels was mandated in the LSP_REQUIRED_ATTRIBUTES object, it MUST send a PathErr message with an error code of 'Routing Problem (24)' and an error value of 'TE link label usage failure (70)'. Explicit Delegation: The presence of this flag in the HOP_ATTRIBUTES sub-object [RFC7570] of an Explicit Route Object (ERO) in the Path message indicates that the hop identified by the preceding IPv4 or IPv6 or Unnumbered Interface ID sub-object has been picked as an explicit delegation hop. The HOP_ATTRIBUTES sub-object carrying this flag MUST have the R (Required) bit set. This flag MUST be set in the HOP_ATTRIBUTES sub-object of an ERO object in the Path message only if the use and recording of TE link labels are requested/ mandated for this LSP. If the hop recognizes this flag but is not able to comply with this mandate because of local policy, it MUST send a PathErr message with an error code of 'Routing Problem (24)' and an error value of 'Label stack imposition failure (71)'.9.5. RRO Label Sub-object Flag: Delegation Label
Flag (0x04): Delegation Label The presence of this flag indicates that the recorded label is a delegation label. This flag MUST be used by a node only if the use and recording of TE link labels and delegation are requested/mandated for the LSP.9.6. Attributes Flags TLV: LSI-D-S2E
Bit Number 18: Label Stack Imposition - Delegation - Stack to Reach Egress (LSI-D-S2E) The presence of this flag in the LSP_ATTRIBUTES object of a Path message indicates that the ingress has chosen to use the "Stack to reach egress" approach for stacking. The absence of this flag in the LSP_ATTRIBUTES object of a Path message indicates that the ingress has chosen to use the "Stack to reach delegation hop" approach for stacking. This flag MUST be set in the LSP_ATTRIBUTES object of a Path message only if the use and recording of TE link labels and delegation are requested/mandated for this LSP. If the transit hop is not able to support the "Stack to reach egress" approach, it MUST send a PathErr message with an error code of 'Routing Problem (24)' and an error value of 'Label stack imposition failure (71)'.
9.7. Attributes TLV: ETLD
The format of the ETLD Attributes TLV is shown in Figure 8. The Attribute TLV Type is 6. 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 | ETLD | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 8: The ETLD Attributes TLV The presence of this TLV in the HOP_ATTRIBUTES sub-object of an RRO object in the Path message indicates that the hop identified by the preceding IPv4 or IPv6 or Unnumbered Interface ID sub-object supports automatic delegation. This attribute MUST be used only if the use and recording of TE link labels are requested/mandated and automatic delegation is requested for the LSP. The ETLD field specifies the effective number of transport labels that this hop (in relation to its position in the path) can potentially send to its downstream hop. It MUST be set to a non-zero value. The Reserved field is for future specification. It SHOULD be set to zero on transmission and MUST be ignored on receipt to ensure future compatibility.10. OAM Considerations
MPLS LSP ping and traceroute [RFC8029] are applicable for Segment Routed RSVP-TE tunnels. The existing procedures allow for the label stack imposed at a delegation hop to be reported back in the Label Stack Sub-TLV in the MPLS echo reply for traceroute.
11. IANA Considerations
11.1. Attribute Flags: TE Link Label, LSI-D, LSI-D-S2E
IANA manages the 'Attribute Flags' subregistry as part of the 'Resource Reservation Protocol-Traffic Engineering (RSVP-TE) Parameters' registry located at <http://www.iana.org/assignments/ rsvp-te-parameters>. This document introduces three new Attribute Flags: Bit Name Attribute Attribute RRO ERO Reference No Flags Path Flags Resv 16 TE Link Label Yes No No No [RFC8577], Section 9.2 17 LSI-D Yes No No Yes [RFC8577], Section 9.4 18 LSI-D-S2E Yes No No No [RFC8577], Section 9.611.2. Attribute TLV: ETLD
IANA manages the "Attribute TLV Space" registry as part of the 'Resource Reservation Protocol-Traffic Engineering (RSVP-TE) Parameters' registry located at <http://www.iana.org/assignments/ rsvp-te-parameters>. This document introduces a new Attribute TLV. Type Name Allowed on Allowed on Allowed on Reference LSP_ATTRIBUTES LSP_REQUIRED LSP Hop _ATTRIBUTES Attributes 6 ETLD No No Yes [RFC8577], Section 9.7
11.3. Record Route Label Sub-object Flags: TE Link Label, Delegation Label
IANA manages the "Record Route Object Sub-object Flags" registry as part of the "Resource Reservation Protocol-Traffic Engineering (RSVP- TE) Parameters" registry located at <http://www.iana.org/assignments/ rsvp-te-parameters>. Prior to this document, this registry did not include Label Sub-object Flags. This document creates the addition of a new subregistry for Label Sub-object Flags as shown below. Flag Name Reference 0x1 Global Label [RFC3209] 0x02 TE Link Label [RFC8577], Section 9.3 0x04 Delegation Label [RFC8577], Section 9.511.4. Error Codes and Error Values
IANA maintains a registry called "Resource Reservation Protocol (RSVP) Parameters" with a subregistry called "Error Codes and Globally-Defined Error Value Sub-Codes". Within this subregistry is a definition of the "Routing Problem" Error Code (24). The definition lists a number of error values that may be used with this error code. IANA has allocated further error values for use with this Error Code as described in this document. The resulting entry in the registry is as follows. 24 Routing Problem [RFC3209] This Error Code has the following globally defined Error Value sub-codes: 70 = TE link label usage failure [RFC8577] 71 = Label stack imposition failure [RFC8577]12. 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.
13. References
13.1. 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>. [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>. [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, DOI 10.17487/RFC3031, January 2001, <https://www.rfc-editor.org/info/rfc3031>. [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>. [RFC5420] Farrel, A., Ed., Papadimitriou, D., Vasseur, JP., and A. Ayyangarps, "Encoding of Attributes for MPLS LSP Establishment Using Resource Reservation Protocol Traffic Engineering (RSVP-TE)", RFC 5420, DOI 10.17487/RFC5420, February 2009, <https://www.rfc-editor.org/info/rfc5420>. [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>. [RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N., Aldrin, S., and M. Chen, "Detecting Multiprotocol Label Switched (MPLS) Data-Plane Failures", RFC 8029, DOI 10.17487/RFC8029, March 2017, <https://www.rfc-editor.org/info/rfc8029>.
[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>.13.2. Informative References
[RFC2961] Berger, L., Gan, D., Swallow, G., Pan, P., Tommasi, F., and S. Molendini, "RSVP Refresh Overhead Reduction Extensions", RFC 2961, DOI 10.17487/RFC2961, April 2001, <https://www.rfc-editor.org/info/rfc2961>. [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>. [RFC8370] Beeram, V., Ed., Minei, I., Shakir, R., Pacella, D., and T. Saad, "Techniques to Improve the Scalability of RSVP-TE Deployments", RFC 8370, DOI 10.17487/RFC8370, May 2018, <https://www.rfc-editor.org/info/rfc8370>. [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, July 2018, <https://www.rfc-editor.org/info/rfc8402>. [RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491, DOI 10.17487/RFC8491, November 2018, <https://www.rfc-editor.org/info/rfc8491>. [SEG-ROUTING] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing with MPLS data plane", Work in Progress, draft-ietf-spring-segment-routing-mpls-18, December 2018.
Acknowledgements
The authors would like to thank Adrian Farrel, Kireeti Kompella, Markus Jork, and Ross Callon for their input from discussions. Adrian Farrel provided a review and a text suggestion for clarity and readability.Contributors
The following individuals contributed to this document: Raveendra Torvi Juniper Networks Email: rtorvi@juniper.net Chandra Ramachandran Juniper Networks Email: csekar@juniper.net George Swallow Email: swallow.ietf@gmail.com
Authors' Addresses
Harish Sitaraman Juniper Networks 1133 Innovation Way Sunnyvale, CA 94089 United States of America Email: harish.ietf@gmail.com Vishnu Pavan Beeram Juniper Networks 10 Technology Park Drive Westford, MA 01886 United States of America Email: vbeeram@juniper.net Tejal Parikh Verizon 400 International Parkway Richardson, TX 75081 United States of America Email: tejal.parikh@verizon.com Tarek Saad Cisco Systems 2000 Innovation Drive Kanata, Ontario K2K 3E8 Canada Email: tsaad.net@gmail.com