Internet DRAFT - draft-ietf-bess-mvpn-evpn-aggregation-label
draft-ietf-bess-mvpn-evpn-aggregation-label
BESS Z. Zhang
Internet-Draft Juniper Networks
Updates: 7432, 6514, 7582 (if approved) E. Rosen
Intended status: Standards Track Individual
Expires: 6 April 2024 W. Lin
Juniper Networks
Z. Li
Huawei Technologies
I. Wijnands
Individual
4 October 2023
MVPN/EVPN Tunnel Aggregation with Common Labels
draft-ietf-bess-mvpn-evpn-aggregation-label-14
Abstract
The MVPN specifications allow a single Point-to-Multipoint (P2MP)
tunnel to carry traffic of multiple IP VPNs (abbreviated as VPNs).
The EVPN specifications allow a single P2MP tunnel to carry traffic
of multiple Broadcast Domains (BDs). These features require the
ingress router of the P2MP tunnel to allocate an upstream-assigned
MPLS label for each VPN or for each BD. A packet sent on a P2MP
tunnel then carries the label that is mapped to its VPN or BD (in
some cases, a distinct upstream-assigned label is needed for each
flow.) Since each ingress router allocates labels independently,
with no coordination among the ingress routers, the egress routers
may need to keep track of a large number of labels. The number of
labels may need to be as large (or larger) than the product of the
number of ingress routers times the number of VPNs or BDs. However,
the number of labels can be greatly reduced if the association
between a label and a VPN or BD is made by provisioning, so that all
ingress routers assign the same label to a particular VPN or BD. New
procedures are needed in order to take advantage of such provisioned
labels. These new procedures also apply to Multipoint-to-Multipoint
(MP2MP) tunnels. This document updates RFCs 6514, 7432 and 7582 by
specifying the necessary procedures.
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.
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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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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 6 April 2024.
Copyright Notice
Copyright (c) 2023 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 (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Problem Description . . . . . . . . . . . . . . . . . . . 5
2.2. Proposed Solution . . . . . . . . . . . . . . . . . . . . 6
2.2.1. MP2MP Tunnels . . . . . . . . . . . . . . . . . . . . 8
2.2.2. Segmented Tunnels . . . . . . . . . . . . . . . . . . 8
2.2.3. Summary of Label Allocation Methods . . . . . . . . . 10
3. Specification . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1. Context-Specific Label Space ID Extended Community . . . 11
3.2. Procedures . . . . . . . . . . . . . . . . . . . . . . . 12
4. Security Considerations . . . . . . . . . . . . . . . . . . . 13
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 14
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
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8.1. Normative References . . . . . . . . . . . . . . . . . . 14
8.2. Informative References . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Terminology
Familiarity with MVPN/EVPN protocols and procedures is assumed. Some
terminologies are listed below for convenience.
* VPN: Virtual Private Network. In this document, it is
specifically IP VPN [RFC4364].
* BUM [RFC7432]: Broadcast, Unknown unicast, or Multicast (traffic).
* BD [RFC7432]: Broadcast Domain.
* EC [RFC4360]: Extended Community.
* PMSI [RFC6513]: Provider Multicast Service Interface - a pseudo
overlay interface for PEs to send certain overlay/customer
multicast traffic via underlay/provider tunnels. It includes
I/S-PMSI (often referred to as x-PMSI) for Inclusive/Selective
PMSI. A PMSI is instantiated by the underlay/provider tunnel.
* Inclusive PMSI: A PMSI that enables traffic to be sent to all PEs
of a VPN/BD. The underlay/provider tunnel that instantiates the
Inclusive PMSI is referred to as an inclusive tunnel.
* Selective PMSI: A PMSI that enables traffic to be sent to a subset
of PEs of a VPN/BD. The underlay/provider tunnel that
instantiates the Selective PMSI is referred to as a selective
tunnel.
* Aggregate Tunnel: a tunnel that instantiates x-PMSIs of multiple
MVPNs or EVPN BDs.
* IMET [RFC7432]: Inclusive Multicast Ethernet Tag route. An EVPN
specific name for I-PMSI A-D route.
* PTA [RFC6514]: PMSI Tunnel Attribute. A BGP attribute that may be
attached to an BGP-MVPN/EVPN x-PMXI A-D routes.
* RBR: Regional Border Routers. Border routers between segmentation
regions that participate in segmentation procedures.
* (C-S,C-G): A Customer/overlay <S,G> multicast flow.
* (C-*,C-G): Customer/overlay <*,G> multicast flows.
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* (C-*,C-*): All Customer/overlay multicast flows.
* ESI [RFC7432]: Ethernet Segment Identifier.
* ESI Label[RFC7432]: A label that identifies an Ethernet Segment
* SRGB [RFC8402]: Segment Routing (SR) Global Block, the set of
global segments in the SR domain. In SR-MPLS [RFC8660], SRGB is a
local property of a node and identifies the set of local labels
reserved for global segments.
* DCB: Domain-wide Common Block, a common block of labels reserved
on all nodes in a domain.
* Context-specific Label Space [RFC5331]: A router may maintain
additional label spaces besides its default label space. When the
label at the top of the stack is not from the default label space,
there must be some context in the packet that identifies which one
of those additional label spaces is to be used to look up the
label, hence those label spaces are referred to as context-
specific label spaces.
* Upstream-assigned [RFC5331]: When the label at the top of the
label stack is not assigned by the router receiving the traffic
from its default label space, the label is referred to as
upstream-assigned. Otherwise, it is downstream-assigned. An
upstream-assigned label must be looked up in a context-specific
label space specific for the assigner.
2. Introduction
MVPN can use P2MP tunnels (set up by RSVP-TE, mLDP, or PIM) to
transport customer multicast traffic across a service provider's
backbone network. Often, a given P2MP tunnel carries the traffic of
only a single VPN. There are however procedures defined that allow a
single P2MP tunnel to carry traffic of multiple VPNs. In this case,
the P2MP tunnel is called an "aggregate tunnel". The PE router that
is the ingress node of an aggregate P2MP tunnel allocates an
"upstream-assigned MPLS label" [RFC5331] for each VPN, and each
packet sent on the P2MP tunnel carries the upstream-assigned MPLS
label that the ingress PE has bound to the packet's VPN.
Similarly, EVPN can use P2MP tunnels (set up by RSVP-TE, mLDP, or
PIM) to transport BUM traffic (Broadcast traffic, Unicast traffic
with an Unknown address, or Multicast traffic), across the provider
network. Often a P2MP tunnel carries the traffic of only a single
BD. However, there are procedures defined that allow a single P2MP
tunnel to be an "aggregate tunnel" that carries traffic of multiple
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BDs. The procedures are analogous to the MVPN procedures -- the PE
router that is the ingress node of an aggregate P2MP tunnel allocates
an upstream-assigned MPLS label for each BD, and each packet sent on
the P2MP tunnel carries the upstream-assigned MPLS label that the
ingress PE has bound to the packet's BD.
MVPN and EVPN can also use BIER [RFC8279] to transmit VPN multicast
traffic or EVPN BUM traffic [RFC8556] [I-D.ietf-bier-evpn]. Although
BIER does not explicitly set up P2MP tunnels, from the perspective of
MVPN/EVPN, the use of BIER transport is very similar to the use of
aggregate P2MP tunnels. When BIER is used, the PE transmitting a
packet (the "BFIR" [RFC8279]) must allocate an upstream-assigned MPLS
label for each VPN or BD, and the packets transmitted using BIER
transport always carry the label that identifies their VPN or BD.
(See [RFC8556] and [I-D.ietf-bier-evpn] for the details.) In the
remainder of this document, we will use the term "aggregate tunnels"
to include both P2MP tunnels and BIER transport.
When an egress PE receives a packet from an aggregate tunnel, it must
look at the upstream-assigned label carried by the packet, and must
interpret that label in the context of the ingress PE. Essentially,
for each ingress PE, the egress PE has a context-specific label space
[RFC5331] that matches the default label space from which the ingress
PE assigns the upstream-assigned labels. When an egress PE looks up
the upstream-assigned label carried by a given packet, it looks it up
in the context-specific label space for the ingress PE of the packet.
How an egress PE identifies the ingress PE of a given packet depends
on the tunnel type.
2.1. Problem Description
Note that the upstream-assigned label procedures may require a very
large number of labels. Suppose an MVPN or EVPN deployment has 1001
PEs, each hosting 1000 VPN/BDs. Each ingress PE has to assign 1000
labels, and each egress PE has to be prepared to interpret 1000
labels from each of the ingress PEs. Since each ingress PE allocates
labels from its own label space and does not coordinate label
assignments with others, each egress PE must be prepared to interpret
1,000,000 upstream-assigned labels (across 1000 context-specific
label spaces - one for each ingress PE). This is an evident scaling
problem.
So far, few if any MVPN/EVPN deployments use aggregate tunnels, so
this problem has not surfaced. However, the use of aggregate tunnels
is likely to increase due to the following two factors:
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* In EVPN, a single customer ("tenant") may have a large number of
BDs, and the use of aggregate RSVP-TE or mLDP P2MP tunnels may
become important, since each tunnel creates state at the
intermediate nodes.
* The use of BIER as transport for MVPN/EVPN is becoming more and
more attractive and feasible.
A similar problem also exists with EVPN ESI labels used for multi-
homing. A PE attached to a multi-homed Ethernet Segment (ES)
advertises an ESI label in its Ethernet A-D per Ethernet Segment
Route. The PE imposes the label when it sends frames received from
the ES to other PEs via a P2MP/BIER tunnel. A receiving PE that is
attached to the source ES will know from the ESI label that the
packet originated on the source ES, and thus will not transmit the
packet on its local attachment circuit to that ES. From the
receiving PE's point of view, the ESI label is (upstream-)assigned
from the source PE's label space, so the receiving PE needs to
maintain context-specific label tables, one for each source PE, just
like the VRF/BD label case above. If there are 1,001 PEs, each
attached to 1,000 ESes, this can require each PE to understand
1,000,000 ESI labels. Notice that the issue exists even when no P2MP
tunnel aggregation (i.e. one tunnel used for multiple BDs) is used.
2.2. Proposed Solution
The number of labels could be greatly reduced if a central entity in
the provider network assigned a label to each VPN, BD, or ES, and if
all PEs used that same label to represent a given VPN , BD, or ES.
Then the number of labels needed would just be the sum of the number
of VPNs, BD, and/or ESes.
One method of achieving this is to reserve a portion of the default
label space for assignment by a central entity. We refer to this
reserved portion as the "Domain-wide Common Block" (DCB) of labels.
This is analogous to the identical "Segment Routing Global Block"
(SRGB) on all nodes that is described in [RFC8402]. A PE that is
attached (via L3VPN VRF interfaces or EVPN Access Circuits) would
know by provisioning which label from the DCB corresponds to which of
its locally attached VPNs, BDs, or ESes.
For example, all PEs could reserve a DCB [1000, 2000] and they are
all provisioned that label 1000 maps to VPN 0, 1001 to VPN 1, and so
forth. Now only 1000 labels instead of 1,000,000 labels are needed
for 1000 VPNs.
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The definition of "domain" is loose - it simply includes all the
routers that share the same DCB. In this document, it only needs to
include all PEs of an MVPN/EVPN network.
The "domain" could also include all routers in the provider network,
making it not much different from a common SRGB across all the
routers. However, that is not necessary as the labels used by PEs
for the purposes defined in this document will only rise to the top
of the label stack when traffic arrives at the PEs. Therefore, it is
better to not include internal P routers in the "domain". That way
they do not have to set aside the same DCB used for the purposes in
this document.
In some deployments, it may be impractical to allocate a DCB that is
large enough to contain labels for all the VPNs/BDs/ESes. In this
case, it may be necessary to allocate those labels from one or a few
separate context-specific label spaces independent of each PE. For
example, if it is too difficult to have a DCB of 10,000 labels across
all PEs for all the VPNs/BDs/ESes that need to be supported, a
separate context-specific label space can be dedicated to those
10,000 labels. Each separate context-specific label space is
identified in the forwarding plane by a label from the DCB (which
does not need to be large). Each PE is provisioned with the label-
space-identifying DCB label and the common VPN/BD/ES labels allocated
from that context-specific label space. When sending traffic, an
ingress PE imposes all necessary service labels (for the VPN/BD/ES)
first, then imposes the label-space-identifying DCB label. From the
label-space-identifying DCB label an egress PE can determine the
label space where the inner VPN/BD/ES label is looked up.
The MVPN/EVPN signaling defined in [RFC6514] and [RFC7432] assumes
that certain MPLS labels are allocated from a context-specific label
space for a particular ingress PE. In this document, we augment the
signaling procedures so that it is possible to signal that a
particular label is from the DCB, rather than from a context-specific
label space for an ingress PE. We also augment the signaling so that
it is possible to indicate that a particular label is from an
identified context-specific label space that is not for an ingress
PE.
Notice that, the VPN/BD/ES-identifying labels from the DCB or from
those few context-specific label spaces are very similar to VNIs in
VXLAN. Allocating a label from the DCB or from a context-specific
label spaces and communicating them to all PEs is not different from
allocating VNIs, and is feasible especially with controllers.
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2.2.1. MP2MP Tunnels
MP2MP tunnels present the same problem (Section 2.1) that can be
solved the same way (Section 2.2), with the following additional
requirement.
Per RFC 7582 ("MVPN: Using Bidirectional P-tunnels"), when MP2MP
tunnels are used for MVPN, the root of the MP2MP tunnel may need to
allocate and advertise "PE Distinguisher Labels" (section 4 of
[RFC6513]. These labels are assigned from the label space used by
the root node for its upstream-assigned labels.
It is REQUIRED by this document that the PE Distinguisher labels
allocated by a particular node come from the same label space that
the node uses to allocate its VPN-identifying labels.
2.2.2. Segmented Tunnels
There are some additional issues to be considered when MVPN or EVPN
is using "tunnel segmentation" (see [RFC6514], [RFC7524], and
[I-D.ietf-bess-evpn-bum-procedure-updates] Sections 5 and 6).
2.2.2.1. Selective Tunnels
For "selective tunnels" that instantiate S-PMSIs (see [RFC6513]
Sections 2.1.1 and 3.2.1, and
[I-D.ietf-bess-evpn-bum-procedure-updates] Section 4), the procedures
outlined above work only if tunnel segmentation is not used.
A selective tunnel carries one or more particular sets of flows to a
particular subset of the PEs that attach to a given VPN or BD. Each
set of flows is identified by a Selective PMSI A-D route [RFC6514].
The PTA of the S-PMSI route identifies the tunnel used to carry the
corresponding set of flows. Multiple S-PMSI routes can identify the
same tunnel.
When tunnel segmentation is applied to an S-PMSI, certain nodes are
"segmentation points". A segmentation point is a node at the
boundary between two "segmentation regions". Let's call these
"region A" and "region B". A segmentation point is an egress node
for one or more selective tunnels in region A, and an ingress node
for one or more selective tunnels in region B. A given segmentation
point must be able to receive traffic on a selective tunnel from
region A, and label switch the traffic to the proper selective tunnel
in region B.
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Suppose one selective tunnel (call it T1) in region A is carrying two
flows, Flow-1 and Flow-2, identified by S-PMSI route Route-1 and
Route-2, respectively. However, it is possible that, in region B,
Flow-1 is not carried by the same selective tunnel that carries Flow-
2. Let's suppose that in region B, Flow-1 is carried by tunnel T2
and Flow-2 by tunnel T3. Then, when the segmentation point receives
traffic from T1, it must be able to label switch Flow-1 from T1 to
T2, while also label switching Flow-2 from T1 to T3. This implies
that Route-1 and Route-2 must signal different labels in the PTA.
For comparison, when segmentation is not used, they can all use the
common per-VPN/BD DCB label.
In this case, it is not practical to have a central entity assign
domain-wide unique labels to individual S-PMSI routes. To address
this problem, all PEs can be assigned disjoint label blocks in those
few context-specific label spaces, and each will independently
allocate labels for segmented S-PMSI from its assigned label block
that is different from any other PE's. For example, PE1 allocates
from label block [101~200], PE2 allocates from label block [201~300],
and so on.
Allocating from disjoint label blocks can be used for VPN/BD/ES
labels as well, though it does not address the original scaling
issue, because there would be one million labels allocated from those
few context label spaces in the original example, instead of just one
thousand common labels.
2.2.2.2. Per-PE/Region Tunnels
Similarly, for segmented per-PE (MVPN (C-*,C-*) S-PMSI or EVPN IMET)
or per-AS/region (MVPN Inter-AS I-PMSI or EVPN per-Region I-PMSI)
tunnels ([RFC6514] [RFC7432]
[I-D.ietf-bess-evpn-bum-procedure-updates]), labels need to be
allocated per PMSI route. In case of per-PE PMSI route, the labels
should be allocated from the label block allocated to the advertising
PE. In case of per-AS/region PMSI route, different ASBR/RBRs
(Regional Border Routers) attached to the same source AS/region will
advertise the same PMSI route. The same label could be used when the
same route is advertised by different ASBRs/RBRs, though that
requires coordination and a simpler way is for each ASBR/RBR to
allocate a label from the label block allocated to itself (see
Section 2.2.2.1).
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In the rest of the document, we call the label allocated for a
particular PMSI a (per-)PMSI label, just like we have (per-)VPN/BD/ES
labels. Notice that using per-PMSI label in case of per-PE PMSI
still has the original scaling issue associated with the upstream-
assigned label, so per-region PMSIs is preferred. Within each AS/
region, per-PE PMSIs are still used though they do not go across
border and per-VPN/BD labels can still be used.
Note that, when a segmentation point re-advertises a PMSI route to
the next segment, it does not need to re-advertise a new label unless
the upstream or downstream segment uses Ingress Replication.
2.2.2.3. Alternative to the per-PMSI Label Allocation
The per-PMSI label allocation in case of segmentation, whether for
S-PMSI or for per-PE/Region I-PMSI, is for the segmentation points to
be able to label switch traffic without having to do IP or MAC lookup
in VRFs (the segmentation points typically do not have those VRFs at
all). If the label scaling becomes a concern, alternatively the
segmentation points could use (C-S,C-G) lookup in VRFs for flows
identified by the S-PMSIs. This allows the S-PMSIs for the same VPN/
BD to share a VPN/BD-identifying label that leads to look up in the
VRFs. That label needs to be different from the label used in the
per-PE/region I-PMSIs though, so that the segmentation points can
label switch other traffic (not identified by those S-PMSIs).
However, this moves the scaling problem from the number of labels to
the number of (C-S/*,C-G) routes in VRFs on the segmentation points.
2.2.3. Summary of Label Allocation Methods
In summary, labels can be allocated and advertised in the following
ways:
1. A central entity allocates per-VPN/BD/ES labels from the DCB.
PEs advertise the labels with an indication that they are from
the DCB.
2. A central entity allocates per-VPN/BD/ES labels from a few common
context-specific label spaces, and allocate labels from the DCB
to identify those context-specific label spaces. PEs advertise
the VPN/BD labels along with the context-identifying labels.
3. A central entity assigns disjoint label blocks from a few
context-specific label spaces to each PE, and allocates labels
from the DCB to identify those context-specific label spaces. A
PE independently allocates a label for a segmented S-PMSI from
its assigned label block, and advertises the label along with the
context-identifying label.
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Option 1 is simplest, but it requires that all the PEs set aside a
common label block for the DCB that is large enough for all the
VPNs/BDs/ESes combined. Option 3 is needed only for segmented
selective tunnels that are set up dynamically. Multiple options
could be used in any combination depending on the deployment
situation.
3. Specification
3.1. Context-Specific Label Space ID Extended Community
Context-Specific Label Space ID Extended Community (EC) is a new
Transitive Opaque EC with the following structure:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x03 or 0x43 | 8 | ID-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID-Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* ID-Type: A 2-octet field that specifies the type of Label Space
ID. In this document, the ID-Type is 0, indicating that the ID-
Value field is a label.
* ID-Value: A 4-octet field that specifies the value of Label Space
ID. When it is a label (with ID-Type 0), the most significant
20-bit is set to the label value.
This document introduces a DCB flag (Bit 47 as assigned by IANA) in
the "Additional PMSI Tunnel Attribute Flags" BGP Extended Community
[RFC7902].
In the remainder of the document, when we say a BGP-MVPN/EVPN A-D
route "carries DCB-flag" or "has DCB-flag attached" we mean the
following:
* The route carries a PMSI Tunnel Attribute (PTA) and its Flags
field has the Extension bit set, AND,
* The route carries an "Additional PMSI Tunnel Attribute Flags" EC
and its DCB flag is set
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3.2. Procedures
The protocol and procedures specified in this section MAY be used
when BIER, or P2MP/MP2MP tunnel aggregation is used for MVPN/EVPN, or
BIER/P2MP/MP2MP tunnels are used with EVPN multi-homing. When these
procedures are used, all PE routers and segmentation points MUST
support the procedures. It is outside the scope of this document how
that is ensured.
By means outside the scope of this document, each VPN/BD/ES is
assigned a label from the DCB or one of those few context-specific
label spaces, and every PE that is part of the VPN/BD/ES is aware of
the assignment. The ES label and the BD label MUST be assigned from
the same label space. If PE Distinguisher labels are used [RFC7582],
they MUST be allocated from the same label space as well.
In case of tunnel segmentation, each PE is also assigned a disjoint
label block from one of those few context-specific label spaces and
it allocates labels for its segmented PMSI routes from its assigned
label block.
When a PE originates/re-advertises an x-PMSI/IMET route, the route
MUST carry a DCB-flag if and only if the label in its PTA is assigned
from the DCB.
If the VPN/BD/ES/PMSI label is assigned from one of those few
context-specific label spaces, a Context-Specific Label Space ID
Extended Community MUST be attached to the route. The ID-Type in the
EC is set to 0 and the ID-Value is set to a label allocated from the
DCB and identifies the context-specific label space. When an ingress
PE sends traffic, it imposes the DCB label that identifies the
context-specific label space after it imposes the label (that is
advertised in the Label field of the PTA in the x-PMSI/IMET route)
for the VPN/BD and/or the label (that is advertised in the ESI Label
EC) for the ESI, and then imposes the encapsulation for the transport
tunnel.
When a PE receives an x-PMSI/IMET route with the Context-Specific
Label Space ID EC, it MUST place an entry in its default MPLS
forwarding table to map the label in the EC to a corresponding
context-specific label table. That table is used for the next label
lookup for incoming data traffic with the label signaled in the EC.
Then, the receiving PE MUST place an entry for the label in the PTA
or ESI Label EC into either the default MPLS forwarding table (if the
route carries the DCB-flag) or the context-specific label table (if
the Context-Specific Label Space ID EC is present) according to the
x-PMSI/IMET route.
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An x-PMSI/IMET route MUST NOT both carry the DCB-flag and the
Context-Specific Label Space ID EC. A received route with both the
DCB-flag set and the Context Label Space ID EC attached MUST be
treated as withdrawn. If neither the DCB-flag nor the Context-
Specific Label Space ID EC is attached, the label in the PTA or ESI
Label EC MUST be treated as the upstream-assigned from the label
space of the source PE, and procedures in [RFC6514][RFC7432] MUST be
followed.
If a PE originates two x-PMSI/IMET routes with the same tunnel, it
MUST ensure one of the following so that the PE receiving the routes
can correctly interpret the label that follows the tunnel
encapsulation of data packets arriving via the tunnel.
* They MUST all have the DCB-flag, or,
* They MUST all carry the Context-Specific Label Space ID EC, or,
* None of them has the DCB-flag, or,
* None of them carry the Context-Specific Label Space ID EC.
Otherwise, a receiving PE MUST treat the routes as if they were
withdrawn.
4. Security Considerations
This document allows three methods (Section 2.2.3) of label
allocation for MVPN [RFC6514] or EVPN [RFC7432] PEs and specifies
corresponding signaling and procedures. The first method is the
equivalent of using common SRGBs [RFC8402] from the regular per
platform label space. The second one is the equivalent of using
common SRGBs from a third party label space [RFC5331]. The third
method is a variation of the second, in that the third party label
space is divided into disjoint blocks for use by different PEs, who
will use labels from their respective block to send traffic. In all
cases, a receiving PE is able to identify one of a few label
forwarding tables to forward incoming labeled traffic.
None of the [RFC6514], [RFC7432], [RFC8402] and [RFC5331]
specifications lists any security concerns related to label
allocation methods, and this document does not introduce new security
concerns either.
5. IANA Considerations
IANA has made the following assignments:
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* Bit 47 (DCB) from the "Additional PMSI Tunnel Attribute Flags"
registry
Bit Flag Name Reference
-------- ---------------------- -------------
47 DCB (temporary) This document
* Sub-type 0x08 for "Context-Specific Label Space ID Extended
Community" from the "Transitive Opaque Extended Community Sub-
Types" registry
Sub-Type Value Name Reference
-------------- ---------------------- -------------
0x08 Context-Specific Label Space ID This document
Extended Community
IANA is requested to create a "Context-Specific Label Space ID Type"
registry in the "Border Gateway Protocol (BGP) Extended Communities"
group. The registration procedure is First Come First Served. The
initial assignment is as follows:
ID Type Name Reference
------- ---------------------- -------------
0 MPLS Label This document
1-254 unassigned
255 reserved
6. Acknowledgements
The authors thank Stephane Litkowski, Ali Sajassi and Jingrong Xie
for their review of, comments on and suggestions for this document.
7. Contributors
The following also contributed to this document.
Selvakumar Sivaraj
Juniper Networks
Email: ssivaraj@juniper.net
8. References
8.1. Normative References
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[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>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <https://www.rfc-editor.org/info/rfc4360>.
[RFC6513] Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
2012, <https://www.rfc-editor.org/info/rfc6513>.
[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,
<https://www.rfc-editor.org/info/rfc6514>.
[RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
2015, <https://www.rfc-editor.org/info/rfc7432>.
[RFC7524] Rekhter, Y., Rosen, E., Aggarwal, R., Morin, T.,
Grosclaude, I., Leymann, N., and S. Saad, "Inter-Area
Point-to-Multipoint (P2MP) Segmented Label Switched Paths
(LSPs)", RFC 7524, DOI 10.17487/RFC7524, May 2015,
<https://www.rfc-editor.org/info/rfc7524>.
[RFC7582] Rosen, E., Wijnands, IJ., Cai, Y., and A. Boers,
"Multicast Virtual Private Network (MVPN): Using
Bidirectional P-Tunnels", RFC 7582, DOI 10.17487/RFC7582,
July 2015, <https://www.rfc-editor.org/info/rfc7582>.
[RFC7902] Rosen, E. and T. Morin, "Registry and Extensions for
P-Multicast Service Interface Tunnel Attribute Flags",
RFC 7902, DOI 10.17487/RFC7902, June 2016,
<https://www.rfc-editor.org/info/rfc7902>.
[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>.
8.2. Informative References
[I-D.ietf-bess-evpn-bum-procedure-updates]
Zhang, Z. J., Lin, W., Rabadan, J., Patel, K., and A.
Sajassi, "Updates on EVPN BUM Procedures", Work in
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Progress, Internet-Draft, draft-ietf-bess-evpn-bum-
procedure-updates-14, 18 November 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
evpn-bum-procedure-updates-14>.
[I-D.ietf-bier-evpn]
Zhang, Z., Przygienda, A., Sajassi, A., and J. Rabadan,
"EVPN BUM Using BIER", Work in Progress, Internet-Draft,
draft-ietf-bier-evpn-10, 4 October 2023,
<https://datatracker.ietf.org/api/v1/doc/document/draft-
ietf-bier-evpn/>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
[RFC5331] Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream
Label Assignment and Context-Specific Label Space",
RFC 5331, DOI 10.17487/RFC5331, August 2008,
<https://www.rfc-editor.org/info/rfc5331>.
[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC8279, November 2017,
<https://www.rfc-editor.org/info/rfc8279>.
[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>.
[RFC8556] Rosen, E., Ed., Sivakumar, M., Przygienda, T., Aldrin, S.,
and A. Dolganow, "Multicast VPN Using Bit Index Explicit
Replication (BIER)", RFC 8556, DOI 10.17487/RFC8556, April
2019, <https://www.rfc-editor.org/info/rfc8556>.
[RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing with the MPLS Data Plane", RFC 8660,
DOI 10.17487/RFC8660, December 2019,
<https://www.rfc-editor.org/info/rfc8660>.
Authors' Addresses
Zhaohui Zhang
Juniper Networks
Email: zzhang@juniper.net
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Eric Rosen
Individual
Email: erosen52@gmail.com
Wen Lin
Juniper Networks
Email: wlin@juniper.net
Zhenbin Li
Huawei Technologies
Email: lizhenbin@huawei.com
IJsbrand Wijnands
Individual
Email: ice@braindump.be
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