Internet Engineering Task Force (IETF) S. Hegde
Request for Comments: 9703 M. Srivastava
Category: Standards Track Juniper Networks Inc.
ISSN: 2070-1721 K. Arora
Individual Contributor
S. Ninan
Ciena
X. Xu
China Mobile
December 2024
Label Switched Path (LSP) Ping/Traceroute for Segment Routing (SR)
Egress Peer Engineering (EPE) Segment Identifiers (SIDs) with MPLS Data
Plane
Abstract
Egress Peer Engineering (EPE) is an application of Segment Routing
(SR) that solves the problem of egress peer selection. The SR-based
BGP-EPE solution allows a centralized controller, e.g., a Software-
Defined Network (SDN) controller, to program any egress peer. The
EPE solution requires the node or the SDN controller to program 1)
the PeerNode Segment Identifier (SID) describing a session between
two nodes, 2) the PeerAdj SID sub-TLV describing the link or links
that are used by the sessions between peer nodes, and 3) the PeerSet
SID describing any connected interface to any peer in the related
group. This document provides new sub-TLVs for EPE-SIDs that are
used in the Target FEC Stack TLV (Type 1) in MPLS Ping and Traceroute
procedures.
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/rfc9703.
Copyright Notice
Copyright (c) 2024 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
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include Revised BSD License text as described in Section 4.e of the
Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.
Table of Contents
1. Introduction
2. Theory of Operation
3. Requirements Language
4. FEC Definitions
4.1. PeerNode SID Sub-TLV
4.2. PeerAdj SID Sub-TLV
4.3. PeerSet SID Sub-TLV
5. EPE-SID FEC Validation
5.1. EPE-SID FEC Validation Rules
6. IANA Considerations
7. Security Considerations
8. References
8.1. Normative References
8.2. Informative References
Appendix A. Examples of Programmed States
Acknowledgments
Authors' Addresses
1. Introduction
Egress Peer Engineering (EPE), as defined in [RFC9087], is an
effective mechanism that is used to select the egress peer link based
on different criteria. In this scenario, egress peers may belong to
a completely different ownership. The EPE-SIDs provide the means to
represent egress peer nodes, links, sets of links, and sets of nodes.
Many network deployments have built their networks consisting of
multiple Autonomous Systems (ASes) either for the ease of operations
or as a result of network mergers and acquisitions. The inter-AS
links connecting any two ASes could be traffic-engineered using EPE-
SIDs in this case, where there is single ownership but different AS
numbers. It is important to validate the control plane to forwarding
plane synchronization for these SIDs so that any anomaly can be
easily detected by the network operator. EPE-SIDs may also be used
in an ingress Segment Routing (SR) policy [RFC9256] to choose exit
points where the remote AS has a completely different ownership.
This scenario is out of scope for this document.
+---------+ +------+
| | | |
| H B------D G
| | +---/| AS2 |\ +------+
| |/ +------+ \ | |---L/8
A AS1 C---+ \| |
| |\\ \ +------+ /| AS4 |---M/8
| | \\ +-E |/ +------+
| X | \\ | K
| | +===F AS3 |
+---------+ +------+
Figure 1: Reference Diagram
In Figure 1, EPE-SIDs are configured on AS1 towards AS2 and AS3 and
advertised in the Border Gateway Protocol - Link State (BGP-LS)
[RFC9086]. In certain cases, the EPE-SIDs advertised by the control
plane may not be in synchronization with the label programmed in the
data plane. For example, on C, a PeerAdj SID sub-TLV could be advertised to
indicate it is for the link C->D. Due to some software anomaly, the
actual data forwarding on this PeerAdj SID sub-TLV could be happening over
the C->E link. If E had relevant data paths for further forwarding
the packet, this kind of anomaly would go unnoticed by the network
operator. A detailed example of a correctly programmed state and an
incorrectly programmed state along with a description of how the
incorrect state can be detected is described in Appendix A. A
Forwarding Equivalence Class (FEC) definition for the EPE-SIDs will
detail the control plane association of the SID. The data plane
validation of the SID will be done during the MPLS Traceroute
procedure. When there is a multi-hop External BGP (EBGP) session
between the ASBRs, a PeerNode SID is advertised, and the traffic MAY
be load-balanced between the interfaces connecting the two nodes. In
Figure 1, C and F could have a PeerNode SID advertised. When the
Operations, Administration, and Maintenance (OAM) packet is received
on F, it needs to be validated that the packet came from one of the
two interfaces connected to C.
This document provides Target Forwarding Equivalence Class (FEC)
Stack TLV definitions for EPE-SIDs. This solution requires the node
constructing the Target FEC Stack TLV to determine the types of SIDs
along the path of the LSP. Other procedures for MPLS Ping and
Traceroute, as defined in Section 7 of [RFC8287] and clarified in
[RFC8690], are applicable for EPE-SIDs as well.
2. Theory of Operation
[RFC9086] provides mechanisms to advertise the EPE-SIDs in BGP-LS.
These EPE-SIDs may be used to build SR paths and may be communicated
using extensions described in [BGP-SR-SEGTYPES-EXT] and
[SR-BGP-POLICY] or Path Computation Element Protocol (PCEP)
extensions as defined in [RFC8664]. Data plane monitoring for such
paths that consist of EPE-SIDs will use extensions defined in this
document to build the Target FEC Stack TLV. The MPLS Ping and
Traceroute procedures MAY be initiated by the head-end of the SR path
or a centralized topology-aware data plane monitoring system, as
described in [RFC8403]. The extensions in [BGP-SR-SEGTYPES-EXT],
[SR-BGP-POLICY], and [RFC8664] do not define how to acquire and carry
the details of the SID that can be used to construct the FEC. Such
extensions are out of scope for this document. The node initiating
the data plane monitoring may acquire the details of EPE-SIDs through
BGP-LS advertisements, as described in [RFC9086]. There may be other
possible mechanisms that can be used to learn the definition of the
SID from the controller. Details of such mechanisms are out of scope
for this document.
The EPE-SIDs are advertised for inter-AS links that run EBGP
sessions. [RFC9086] does not define the detailed procedures of how
to operate EBGP sessions in a scenario with unnumbered interfaces.
Therefore, these scenarios are out of scope for this document.
Anycast and multicast addresses are not in the scope of this
document. During the AS migration scenario, procedures described in
[RFC7705] may be in force. In these scenarios, if the local and
remote AS fields in the FEC (as described in Section 4) carry the
globally configured AS Number and not the "local AS" (as defined in
[RFC7705]), then the FEC validation procedures may fail.
As described in Section 1, this document defines Target FEC Stack
TLVs for EPE-SIDs that can be used in detecting MPLS data plane
failures [RFC8029]. This mechanism applies to paths created across
ASes of cooperating administrations. If the ping or traceroute
packet enters a non-cooperating AS domain, it might be dropped by the
routers in the non-cooperating domain. Although a complete path
validation cannot be done across non-cooperating domains, it still
provides useful information that the ping or traceroute packet
entered a non-cooperating domain.
3. 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.
4. FEC Definitions
In this document, three new sub-TLVs are defined for the Target FEC
Stack TLV (Type 1), the Reverse-Path Target FEC Stack TLV (Type 16),
and the Reply Path TLV (Type 21); see Table 1.
4.1. PeerNode SID Sub-TLV
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Type = 39 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local AS Number (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote AS Number (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local BGP Router ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote BGP Router ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: PeerNode SID Sub-TLV
Type: 2 octets
Value: 39
Length: 2 octets
Value: 16
Local AS Number: 4 octets. The unsigned integer representing the AS
number [RFC6793] of the AS to which the PeerNode SID advertising
node belongs. If Confederations [RFC5065] are in use, and if the
remote node is a member of a different Member-AS within the local
Confederation, this is the Member-AS Number inside the
Confederation and not the Confederation Identifier.
Remote AS Number: 4 octets. The unsigned integer representing the
AS number [RFC6793] of the AS of the remote node for which the
PeerNode SID is advertised. If Confederations [RFC5065] are in
use, and if the remote node is a member of a different Member-AS
within the local Confederation, this is the Member-AS Number
inside the Confederation and not the Confederation Identifier.
Local BGP Router ID: 4 octets. The unsigned integer representing
the BGP Identifier of the PeerNode SID advertising node as defined
in [RFC4271] and [RFC6286].
Remote BGP Router ID: 4 octets. The unsigned integer representing
the BGP Identifier of the remote node as defined in [RFC4271] and
[RFC6286].
When there is a multi-hop EBGP session between two ASBRs, a PeerNode
SID is advertised for this session, and traffic can be load-balanced
across these interfaces. An EPE controller that performs bandwidth
management for these links should be aware of the links on which the
traffic will be load-balanced. As per [RFC8029], the node
advertising the EPE-SIDs will send a Downstream Detailed Mapping
(DDMAP) TLV specifying the details of the next-hop interfaces. Based
on this information, the controller MAY choose to verify the actual
forwarding state with the topology information that the controller
has. On the router, the validation procedures will include the
received DDMAP validation, as specified in [RFC8029], to verify the
control state and the forwarding state synchronization on the two
routers. Any discrepancies between the controller's state and the
forwarding state will not be detected by the procedures described in
this document.
4.2. PeerAdj SID Sub-TLV
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Type = 38 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Adj type | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local AS Number (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote AS Number (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local BGP Router ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote BGP Router ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface Address (4/16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Interface Address (4/16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: PeerAdj SID Sub-TLV
Type: 2 octets
Value: 38
Length: 2 octets
Value: Variable based on the IPv4/IPv6 interface address. Length
excludes the length of the Type and Length fields. For IPv4
interface addresses, the length will be 28 octets. In the case of
an IPv6 address, the length will be 52 octets.
Adj type: 1 octet
Value: Set to 1 when the Adjacency Segment is IPv4. Set to 2 when
the Adjacency Segment is IPv6.
RESERVED: 3 octets. MUST be zero when sending and ignored on
receiving.
Local AS Number: 4 octets. The unsigned integer representing the AS
number [RFC6793] of the AS to which the PeerAdj SID sub-TLV advertising
node belongs. If Confederations [RFC5065] are in use, and if the
remote node is a member of a different Member-AS within the local
Confederation, this is the Member-AS Number inside the
Confederation and not the Confederation Identifier.
Remote AS Number: 4 octets. The unsigned integer representing the
AS number [RFC6793] of the remote node's AS for which the PeerAdj
SID sub-TLV is advertised. If Confederations [RFC5065] are in use, and if
the remote node is a member of a different Member-AS within the
local Confederation, this is the Member-AS Number inside the
Confederation and not the Confederation Identifier.
Local BGP Router ID: 4 octets. The unsigned integer representing
the BGP Identifier of the PeerAdj SID sub-TLV advertising node as defined
in [RFC4271] and [RFC6286].
Remote BGP Router ID: 4 octets. The unsigned integer representing
the BGP Identifier of the remote node as defined in [RFC4271] and
[RFC6286].
Local Interface Address: 4 octets or 16 octets. In the case of
PeerAdj SID sub-TLV, SID, the local interface address corresponding to the
PeerAdj SID sub-TLV should be specified in this field. For IPv4, this
field is 4 octets; for IPv6, this field is 16 octets. Link-local
IPv6 addresses are not in the scope of this document.
Remote Interface Address: 4 octets or 16 octets. In the case of
PeerAdj SID sub-TLV, SID, the remote interface address corresponding to the
PeerAdj SID sub-TLV should be specified in this field. For IPv4, this
field is 4 octets; for IPv6, this field is 16 octets. Link-local
IPv6 addresses are not in the scope of this document.
[RFC9086] mandates sending a local interface ID and remote interface
ID in the link descriptors and allows a value of 0 in the remote
descriptors. It is useful to validate the incoming interface for an
OAM packet, but if the remote descriptor is 0, this validation is not
possible. Optional link descriptors of local and remote interface
addresses are allowed as described in Section 4.2 of [RFC9086]. In
this document, it is RECOMMENDED to send these optional descriptors
and use them to validate incoming interfaces. When these local and
remote interface addresses are not available, an ingress node can
send 0 in the local and/or remote interface address field. The
receiver SHOULD skip the validation for the incoming interface if the
address field contains 0.
4.3. PeerSet SID Sub-TLV
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Type = 40 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local AS Number (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local BGP Router ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| No. of elements in set | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote AS Number (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote BGP Router ID (4 octets) |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++
One element in set consists of the details below
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote AS Number (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote BGP Router ID (4 octets) |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++
Figure 4: PeerSet SID Sub-TLV
Type: 2 octets
Value: 40
Length: 2 octets
Value: Expressed in octets and is a variable based on the number of
elements in the set. The length field does not include the length
of Type and Length fields.
Local AS Number: 4 octets. The unsigned integer representing the AS
number [RFC6793] of the AS to which the PeerSet SID advertising
node belongs. If Confederations [RFC5065] are in use, and if the
remote node is a member of a different Member-AS within the local
Confederation, this is the Member-AS Number inside the
Confederation and not the Confederation Identifier.
Local BGP Router ID: 4 octets. The unsigned integer representing
the BGP Identifier of the PeerSet SID advertising node, as defined
in [RFC4271] and [RFC6286].
No. of elements in set: 2 octets. The number of remote ASes over
which the set SID performs load-balancing.
Reserved: 2 octets. MUST be zero when sent and ignored when
received.
Remote AS Number: 4 octets. The unsigned integer representing the
AS number [RFC6793] of the remote node's AS for which the PeerSet
SID is advertised. If Confederations [RFC5065] are in use, and if
the remote node is a member of a different Member-AS within the
local Confederation, this is the Member-AS Number inside the
Confederation and not the Confederation Identifier.
Remote BGP Router ID: 4 octets. The unsigned integer representing
the BGP Identifier of the remote node as defined in [RFC4271] and
[RFC6286].
PeerSet SID may be associated with a number of PeerNode SIDs and
PeerAdj SID sub-TLVs. SIDs. The remote AS number and the Router ID of each of
these PeerNode SIDs and PeerAdj SID sub-TLVs SIDs MUST be included in the FEC.
5. EPE-SID FEC Validation
When a remote ASBR of the EPE-SID advertisement receives the MPLS OAM
packet with the top FEC being the EPE-SID, it MUST perform validity
checks on the content of the EPE-SID FEC sub-TLV. The basic length
check should be performed on the received FEC.
PeerAdj SID sub-TLV
-----------
If Adj type = 1, Length should be 28 octets
If Adj type = 2, Length should be 52 octets
PeerNode SID sub-TLV
-------------
Length = (20 + No. of IPv4 interface pairs * 8 +
No. of IPv6 interface pairs * 32) octets
PeerSet SID sub-TLV
-----------
Length = (9 + No. of elements in the set *
(8 + No. of IPv4 interface pairs * 8 +
No. of IPv6 interface pairs * 32) octets
Figure 5: Length Validation
If a malformed FEC sub-TLV is received, then a return code of 1,
"Malformed echo request received", as defined in [RFC8029] MUST be
sent. The section below is appended to the procedure given in step
4a of Section 7.4 of [RFC8287].
5.1. EPE-SID FEC Validation Rules
This is an example of Segment Routing IGP-Prefix, IGP-Adjacency SID,
and EPE-SID validations. Note that the term "receiving node" in this
section corresponds to the node that receives the OAM message with
the Target FEC Stack TLV.
Else, if the Label-stack-depth is 0 and the Target FEC Stack sub-TLV
at FEC stack-depth is 38 (PeerAdj SID sub-TLV), {
Set the Best-return-code to 10, "Mapping for this FEC is not
the given label at stack-depth <RSC>" [RFC8029]. Check if
any below conditions fail:
- Validate that the receiving node's BGP Local AS matches
with the remote AS field in the received PeerAdj SID
sub-TLV.
- Validate that the receiving node's BGP Router-ID
matches with the Remote Router ID field in the
received PeerAdj SID sub-TLV.
- Validate that there is an EBGP session with a peer
having a local AS number and BGP Router-ID as
specified in the local AS number and Local Router-ID
field in the received PeerAdj SID sub-TLV.
If the remote interface address is not zero, validate the
incoming interface. Set the Best-return-code to 35,
"Mapping for this FEC is not associated with the incoming
interface" [RFC8287]. Check if any below conditions fail:
- Validate that the incoming interface on which the
OAM packet was received matches with the remote
interface specified in the PeerAdj SID sub-TLV.
If all above validations have passed, set the return code to 3,
"Replying router is an egress for the FEC at stack-depth <RSC>"
[RFC8029].
}
Else, if the Target FEC Stack sub-TLV at FEC stack-depth is 39
(PeerNode SID sub-TLV), {
Set the Best-return-code to 10, "Mapping for this FEC is not
the given label at stack-depth <RSC>" [RFC8029]. Check if any
below conditions fail:
- Validate that the receiving node's BGP Local AS matches
with the remote AS field in the received PeerNode SID
FEC sub-TLV.
- Validate that the receiving node's BGP Router-ID matches
with the Remote Router ID field in the received
PeerNode SID FEC.
- Validate that there is an EBGP session with a peer
having a local AS number and BGP Router-ID as
specified in the local AS number and Local Router-ID
field in the received PeerNode SID FEC sub-TLV.
If all above validations have passed, set the return code to 3,
"Replying router is an egress for the FEC at stack-depth <RSC>"
[RFC8029].
}
Else, if the Target FEC Stack sub-TLV at FEC stack-depth is 40
(PeerSet SID sub-TLV), {
Set the Best-return-code to 10, "Mapping for this FEC is not
the given label at stack-depth <RSC>" [RFC8029]. Check if any
below conditions fail:
- Validate that the receiving node's BGP Local AS matches
with one of the remote AS fields in the received
PeerSet SID FEC sub-TLV.
- Validate that the receiving node's BGP Router-ID matches
with one of the Remote Router ID fields in the
received PeerSet SID FEC sub-TLV.
- Validate that there is an EBGP session with a peer having
a local AS number and BGP Router-ID as specified in the
local AS number and Local Router-ID fields in the received
PeerSet SID FEC sub-TLV.
If all above validations have passed, set the return code to 3,
"Replying router is an egress for the FEC at stack-depth <RSC>"
[RFC8029].
}
6. IANA Considerations
IANA has allocated three new Target FEC Stack sub-TLVs in the "Sub-
TLVs for TLV Types 1, 16, and 21" registry
[IANA-MPLS-LSP-PING-Parameters] within the "TLVs" registry of the
"Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs)
Ping Parameters" registry group.
+==========+==============+
| Sub-Type | Sub-TLV Name |
+==========+==============+
| 38 | PeerAdj SID |
+----------+--------------+
| 39 | PeerNode SID |
+----------+--------------+
| 40 | PeerSet SID |
+----------+--------------+
Table 1: Sub-TLVs for
TLV Types 1, 16, and 21
Registry
7. Security Considerations
The EPE-SIDs are advertised for egress links for EPE purposes or for
inter-AS links between cooperating ASes. When cooperating domains
are involved, they can allow the packets arriving on trusted
interfaces to reach the control plane and be processed.
When EPE-SIDs are created for egress TE links where the neighbor AS
is an independent entity, it may not allow the packets arriving from
the external world to reach the control plane. In such deployments,
the MPLS OAM packets will be dropped by the neighboring AS that
receives the MPLS OAM packet.
In MPLS Traceroute applications, when the AS boundary is crossed with
the EPE-SIDs, the Target FEC Stack TLV is changed. [RFC8287] does
not mandate that the initiator, upon receiving an MPLS Echo Reply
message that includes the Target FEC Stack Change TLV with one or
more of the original segments being popped, remove the corresponding
FEC(s) from the Target FEC Stack TLV in the next (TTL+1) traceroute
request.
If an initiator does not remove the FECs belonging to the previous AS
that has traversed, it may expose the internal AS information to the
following AS being traversed in the traceroute.
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>.
[RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet
Autonomous System (AS) Number Space", RFC 6793,
DOI 10.17487/RFC6793, December 2012,
<https://www.rfc-editor.org/info/rfc6793>.
[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>.
[RFC8287] Kumar, N., Ed., Pignataro, C., Ed., Swallow, G., Akiya,
N., Kini, S., and M. Chen, "Label Switched Path (LSP)
Ping/Traceroute for Segment Routing (SR) IGP-Prefix and
IGP-Adjacency Segment Identifiers (SIDs) with MPLS Data
Planes", RFC 8287, DOI 10.17487/RFC8287, December 2017,
<https://www.rfc-editor.org/info/rfc8287>.
[RFC8690] Nainar, N., Pignataro, C., Iqbal, F., and A. Vainshtein,
"Clarification of Segment ID Sub-TLV Length for RFC 8287",
RFC 8690, DOI 10.17487/RFC8690, December 2019,
<https://www.rfc-editor.org/info/rfc8690>.
[RFC9086] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Patel, K.,
Ray, S., and J. Dong, "Border Gateway Protocol - Link
State (BGP-LS) Extensions for Segment Routing BGP Egress
Peer Engineering", RFC 9086, DOI 10.17487/RFC9086, August
2021, <https://www.rfc-editor.org/info/rfc9086>.
8.2. Informative References
[BGP-SR-SEGTYPES-EXT]
Talaulikar, K., Filsfils, C., Previdi, S., Mattes, P., and
D. Jain, "Segment Routing Segment Types Extensions for BGP
SR Policy", Work in Progress, Internet-Draft, draft-ietf-
idr-bgp-sr-segtypes-ext-06, 7 November 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
sr-segtypes-ext-06>.
[IANA-MPLS-LSP-PING-Parameters]
IANA, "Sub-TLVs for TLV Types 1, 16, and 21",
<https://www.iana.org/assignments/mpls-lsp-ping-
parameters>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC5065] Traina, P., McPherson, D., and J. Scudder, "Autonomous
System Confederations for BGP", RFC 5065,
DOI 10.17487/RFC5065, August 2007,
<https://www.rfc-editor.org/info/rfc5065>.
[RFC6286] Chen, E. and J. Yuan, "Autonomous-System-Wide Unique BGP
Identifier for BGP-4", RFC 6286, DOI 10.17487/RFC6286,
June 2011, <https://www.rfc-editor.org/info/rfc6286>.
[RFC7705] George, W. and S. Amante, "Autonomous System Migration
Mechanisms and Their Effects on the BGP AS_PATH
Attribute", RFC 7705, DOI 10.17487/RFC7705, November 2015,
<https://www.rfc-editor.org/info/rfc7705>.
[RFC8403] Geib, R., Ed., Filsfils, C., Pignataro, C., Ed., and N.
Kumar, "A Scalable and Topology-Aware MPLS Data-Plane
Monitoring System", RFC 8403, DOI 10.17487/RFC8403, July
2018, <https://www.rfc-editor.org/info/rfc8403>.
[RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "Path Computation Element Communication
Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
DOI 10.17487/RFC8664, December 2019,
<https://www.rfc-editor.org/info/rfc8664>.
[RFC9087] Filsfils, C., Ed., Previdi, S., Dawra, G., Ed., Aries, E.,
and D. Afanasiev, "Segment Routing Centralized BGP Egress
Peer Engineering", RFC 9087, DOI 10.17487/RFC9087, August
2021, <https://www.rfc-editor.org/info/rfc9087>.
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/info/rfc9256>.
[SR-BGP-POLICY]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., and
D. Jain, "Advertising Segment Routing Policies in BGP",
Work in Progress, Internet-Draft, draft-ietf-idr-sr-
policy-safi-10, 7 November 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-sr-
policy-safi-10>.
Appendix A. Examples of Programmed States
This section describes examples of both a correctly and an
incorrectly programmed state and provides details on how the new sub-
TLVs described in this document can be used to validate the
correctness. Consider the diagram from Figure 1.
Correctly programmed state:
* C assigns label 16001 and binds it to adjacency C->E
* C signals that label 16001 is bound to adjacency C->E (e.g., via
BGP-LS)
* The controller/ingress programs an SR path that has SID/label
16001 to steer the packet on the exit point from C onto adjacency
C->E
* Using MPLS Traceroute procedures defined in this document, the
PeerAdj SID sub-TLV is populated with entities to be validated by
C when the OAM packet reaches it
* C receives the OAM packet and validates that the top label (16001)
is indeed corresponding to the entities populated in the PeerAdj
SID sub-TLV
Incorrectly programmed state:
* C assigns label 16001 and binds it to adjacency C->D
* The controller learns that PeerAdj SID sub-TLV label 16001 is bound to
adjacency C->E (e.g., via BGP-LS) -- this could be a software bug
on C or on the controller
* The controller/ingress programs an SR path that has SID/label
16001 to steer the packet on the exit point from C onto adjacency
C->E
* Using MPLS Traceroute procedures defined in this document, the
PeerAdj SID sub-TLV is populated with entities to be validated by
C (including a local/remote interface address of C->E) when the
OAM packet reaches it
* C receives the OAM packet and validates that the top label (16001)
is NOT bound to C->E as populated in the PeerAdj SID sub-TLV and
then responds with the respective error code
Acknowledgments
Thanks to Loa Andersson, Dhruv Dhody, Ketan Talaulikar, Italo Busi,
Alexander Vainshtein, and Deepti Rathi for careful reviews and
comments. Thanks to Tarek Saad for providing the example described
in Appendix A.
Authors' Addresses
Shraddha Hegde
Juniper Networks Inc.
Exora Business Park
Bangalore 560103
Karnataka
India
Email: shraddha@juniper.net
Mukul Srivastava
Juniper Networks Inc.
Email: msri@juniper.net
Kapil Arora
Individual Contributor
Email: kapil.it@gmail.com
Samson Ninan
Ciena
Email: samson.cse@gmail.com
Xiaohu Xu
China Mobile
Beijing
China
Email: xuxiaohu_ietf@hotmail.com