Internet DRAFT - draft-ninan-spring-mpls-inter-as-oam
draft-ninan-spring-mpls-inter-as-oam
Routing area S. Hegde
Internet-Draft K. Arora
Intended status: Standards Track S. Ninan
Expires: May 6, 2020 M. Srivastava
Juniper Networks Inc.
N. Kumar
Cisco Systems, Inc.
November 3, 2019
PMS/Head-end based MPLS Ping and Traceroute in Inter-AS SR Networks
draft-ninan-spring-mpls-inter-as-oam-02
Abstract
Segment Routing (SR) architecture leverages source routing and
tunneling paradigms and can be directly applied to the use of a
Multiprotocol Label Switching (MPLS) data plane. Segment Routing
also provides an easy and efficient way to provide inter connectivity
in a large scale network as described in [RFC8604]. [RFC8287]
illustrates the problem and defines extensions to perform LSP Ping
and Traceroute for Segment Routing IGP-Prefix and IGP-Adjacency
Segment Identifiers (SIDs) with an MPLS data plane. It is useful to
have the LSP Ping and traceroute procedures when an SR end-to-end
path spans across multiple ASes. This document describes mechanisms
to facilitae LSP ping and traceroute in inter-AS SR networks in an
efficient manner with simple OAM protocol extension which uses
dataplane forwarding alone for sending Echo-Reply.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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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 May 6, 2020.
Copyright Notice
Copyright (c) 2019 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
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Reverse Path Segment List TLV . . . . . . . . . . . . . . . . 4
2.1. Reverse Path Segment List TLV definition . . . . . . . . 5
2.1.1. Segment sub-TLV . . . . . . . . . . . . . . . . . . . 5
2.2. SRv6 Dataplane . . . . . . . . . . . . . . . . . . . . . 9
3. Detailed Procedures . . . . . . . . . . . . . . . . . . . . . 10
3.1. Sending an Echo-Request . . . . . . . . . . . . . . . . . 10
3.2. Receiving an Echo-Request . . . . . . . . . . . . . . . . 10
3.3. Sending an Echo-Reply . . . . . . . . . . . . . . . . . . 10
4. Detailed Example . . . . . . . . . . . . . . . . . . . . . . 10
4.1. Procedures for Segment Routing LSP ping . . . . . . . . . 11
4.2. Procedures for Segment Routing LSP Traceroute . . . . . . 12
5. Building Reverse Path Segment List TLV dynamically . . . . . 12
5.1. The procedures to build the reverse path . . . . . . . . 12
5.2. Details with example . . . . . . . . . . . . . . . . . . 13
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 13
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.1. Normative References . . . . . . . . . . . . . . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
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1. Introduction
+----------------+
| Controller/PMS |
+----------------+
|---------AS1----------| |--------AS2----------|
ASBR2-------ASBR3
/ \
/ \
PE1------P1------P2 P3------P4------PE4
\ /
\ /
ASBR1-------ASBR4
Figure 1: Inter-AS Segment Routing topology
Many network deployments have built their networks consisting of
multiple Autonomous Systems either for ease of operations or as a
result of network mergers and acquisitions. Segment Routing can be
deployed in such scenarios to provide end to end paths, traversing
multiple Autonomous systems(AS). These paths consist of Segment
Identifiers(SID) of different type as per [RFC8402].
[I-D.ietf-spring-segment-routing-mpls] specifies the forwarding plane
behaviour to allow Segment Routing to operate on top of MPLS data
plane. [I-D.ietf-spring-segment-routing-central-epe] describes BGP
peering SIDs, which will help in steering packet from one Autonomous
system to another. Using above SR capabilities, paths which span
across multiple Autonomous systems can be created.
For example Figure 1 describes an inter-AS network scenario
consisting of ASes AS1 and AS2. Both AS1 and AS2 are Segment Routing
enabled and the EPE links have EPE labels configured and advertised
via [I-D.ietf-idr-bgpls-segment-routing-epe]. Controller or head-end
can build end-to-end Traffic-Engineered path Node-SIDs, Adjacency-
SIDs and EPE-SIDs. It is advantageous for operations to be able to
perform LSP ping and traceroute procedures on these inter-AS SR
paths. LSP ping/traceroute procedures use ip connectivity for Echo-
reply to reach the head-end. In inter-AS networks, ip connectivity
may not be there from each router in the path.For example in Figure 1
P3 and P4 may not have ip connectivity for PE1.
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[RFC8403] describes mechanisms to carry out the MPLS ping/traceroute
from a PMS. It is possible to build GRE tunnels or static routes to
each router in the network to get IP connectivity for the reverse
path. This mechanism is operationally very heavy and requires PMS to
be capable of building huge number of GRE tunnels, which may not be
feasible.
It is not possible to carry out LSP ping and Traceroute functionality
on these paths to verify basic connectivity and fault isolation using
existing LSP ping and Traceroute mechanism([RFC8287] and [RFC8029]).
This is because, there exists no IP connectivity to source address of
ping packet, which is in a different AS, from the destination of
Ping/Traceroute.
[RFC7743] describes a Echo-relay based solution based on advertising
a new Relay Node Address Stack TLV containing stack of Echo-relay ip
addresses. This mechanism requires the return ping packet to reach
the control plane on every relay node.
This document describes a mechanism which is efficient and simple and
can be easily deployed in SR networks. This mechanism uses a new
Reverse Path Segment List TLV to convey the reverse path. The TLV
can either be derived by a smart application/controller which has a
full topology view or by the help of intermediate nodes.
2. Reverse Path Segment List TLV
Segment Routing networks statically assign the labels to nodes and
PMS/Head-end may know the entire database. The reverse path can be
built from PMS/Head-end by stacking segments for the reverse path. A
new TLV "Reverse Path Segment List TLV" is defined. Each TLV
contains a list of segment sub-TLVs which may be a prefix/adjacency/
binding SID/EPE SID. MPLS Echo -request should contain this TLV,
which defines reverse path to reach source from the destination.
The new Reverse Path Segment List TLV is an optional TLV. This TLV
is carried in the Echo-Request message. This optional TLV MAY appear
in the Echo-request message in any order before or after Target FEC
Stack TLV. The Reverse Path Segment List TLV is defined as below.
Each MPLS Echo-request SHOULD contain this TLV in inter-AS cases,
which will enable remote end(egress/transit routers) to send the
reply to source.
In some cases, the head-end may not have complete visibility. In
such cases, it can rely on downstream routers to build the reverse
path. For this purpose, the TLV is carried in the Echo-Reply
message. Section 5 describes one basic idea in this direction.
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2.1. Reverse Path Segment List TLV definition
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 = TBD | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Segment sub TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Reverse Path Segment List TLV
Type: TBD
Length: Length of TLV including TLV header and length of sub TLV.
There can be one or more segment sub-TLVs in a Reverse Path Segment
List TLV. The applicable segment types are described in
Section 2.1.1. The Segment type in a Reverse Path Segment List TLV
MAY be same or different.
2.1.1. Segment sub-TLV
[I-D.ietf-spring-segment-routing-policy] defines various types of
segments. These segment types are applicable here. One or more
segment sub-TLV can be included. The segment sub-TLVs included MAY
be of different types.
Below types of segment sub-TLVs are applicable for the Reverse Path
Segment List Tlv.
Type 1: SID only, in the form of MPLS Label
Type 3: IPv4 Node Address with optional SID
Type 4: IPv6 Node Address with optional SID for SR MPLS
2.1.1.1. Type 1: SID only, in the form of MPLS Label
The Type-1 Segment Sub-TLV encodes a single SID in the form of an
MPLS label. The format is as follows:
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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 | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Type 1 Segment sub-TLV
where:
Type: 1 (to be assigned by IANA from the registry "SR Policy List
Sub-TLVs" defined in [I-D.ietf-idr-segment-routing-te-policy]).
Length is 6.
Flags: 1 octet of flags as defined in Section Section 2.1.1.4.
RESERVED: 1 octet of reserved bits. SHOULD be unset on transmission
and MUST be ignored on receipt.
Label: 20 bits of label value.
TC: 3 bits of traffic class
S: 1 bit of bottom-of-stack.
TTL: 1 octet of TTL.
The following applies to the Type-1 Segment sub-TLV:
The S bit SHOULD be zero upon transmission, and MUST be ignored upon
reception.
If the originator wants the receiver to choose the TC value, it sets
the TC field to zero.
If the originator wants the receiver to choose the TTL value, it sets
the TTL field to 255.
If the originator wants to recommend a value for these fields, it
puts those values in the TC and/or TTL fields.
The receiver MAY override the originator's values for these fields.
This would be determined by local policy at the receiver. One
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possible policy would be to override the fields only if the fields
have the default values specified above.
2.1.1.2. Type 3: IPv4 Node Address with optional SID for SR-MPLS
The Type-3 Segment Sub-TLV encodes an IPv4 node address, SR Algorithm
and an optional SID in the form of an MPLS label. The format is as
follows:
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 | Length | Flags | SR Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Node Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID (optional, 4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Type 3 Segment sub-TLV
where:
Type: 3 (to be assigned by IANA from the registry "SR Policy List
Sub-TLVs" defined in [I-D.ietf-idr-segment-routing-te-policy]).
Length is 6 or 10.
Flags: 1 octet of flags as defined in Section Section 2.1.1.4.
SR Algorithm: 1 octet specifying SR Algorithm as described in section
3.1.1 in [RFC8402], when A-Flag as defined in
Section Section 2.1.1.4is present. SR Algorithm is used by SRPM as
described in section 4 in [I-D.ietf-spring-segment-routing-policy].
When A-Flag is not encoded, this field SHOULD be unset on
transmission and MUST be ignored on receipt.
IPv4 Node Address: a 4 octet IPv4 address representing a node.
SID: 4 octet MPLS label.
The following applies to the Type-3 Segment sub-TLV:
The IPv4 Node Address MUST be present.
The SID is optional and specifies a 4 octet MPLS SID containing
label, TC, S and TTL as defined in Section Section 2.1.1.1.
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If length is 6, then only the IPv4 Node Address is present.
If length is 10, then the IPv4 Node Address and the MPLS SID are
present.
2.1.1.3. Type 4: IPv6 Node Address with optional SID for SR MPLS
The Type-4 Segment Sub-TLV encodes an IPv6 node address, SR Algorithm
and an optional SID in the form of an MPLS label. The format is as
follows:
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 | Length | Flags | SR Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IPv6 Node Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID (optional, 4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Type 4 Segment sub-TLV
where:
Type: 4 (to be assigned by IANA from the registry "SR Policy List
Sub-TLVs" defined in [I-D.ietf-idr-segment-routing-te-policy]).
Length is 18 or 22.
Flags: 1 octet of flags as defined in Section Section 2.1.1.4.
SR Algorithm: 1 octet specifying SR Algorithm as described in section
3.1.1 in [RFC8402], when A-Flag as defined in Section Section 2.1.1.4
is present. SR Algorithm is used by SRPM as described in section 4
in [I-D.ietf-spring-segment-routing-policy]. When A-Flag is not
encoded, this field SHOULD be unset on transmission and MUST be
ignored on receipt.
IPv6 Node Address: a 16 octet IPv6 address representing a node.
SID: 4 octet MPLS label.
The following applies to the Type-4 Segment sub-TLV:
The IPv6 Node Address MUST be present.
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The SID is optional and specifies a 4 octet MPLS SID containing
label, TC, S and TTL as defined in Section Section 2.1.1.1 .
If length is 18, then only the IPv6 Node Address is present.
If length is 22, then the IPv6 Node Address and the MPLS SID are
present.
2.1.1.4. Segment Flags
The Segment Types described above MAY contain following flags in the
"Flags" field (codes to be assigned by IANA from the registry "SR
Policy Segment Flags" defined
in[I-D.ietf-idr-segment-routing-te-policy])
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|V|A| |
+-+-+-+-+-+-+-+-+
Figure 6: Flags
where:
V-Flag: This flag is used by SRPM for the purpose of "SID
verification" as described in Section 5.1 in
[I-D.ietf-spring-segment-routing-policy].
A-Flag: This flag indicates the presence of SR Algorithm id in the
"SR Algorithm" field applicable to various Segment Types. SR
Algorithm is used by SRPM as described in section 4 in
[I-D.ietf-spring-segment-routing-policy].
Unused bits in the Flag octet SHOULD be set to zero upon transmission
and MUST be ignored upon receipt.
The following applies to the Segment Flags:
V-Flag is applicable to all Segment Types.
A-Flag is applicable to Segment Types 3, 4 and 9. If A-Flag appears
with any other Segment Type, it MUST be ignored.
2.2. SRv6 Dataplane
SRv6 dataplane is not in the scope of this document and will be
addressed in a separate document.
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3. Detailed Procedures
3.1. Sending an Echo-Request
In the inter-AS scenario when there is no reverse path connectivity,
LSP ping initiator MUST add a Reverse Path Segment List TLV in the
Echo-request message. The reverse Segment List MUST correspond to
the return path from the egress. The Reverse Path Segment List TLV
is an ordered list of Segments. The first Segment corresponds to the
top Segment in MPLS header that the responder MUST use while sending
the Echo-reply.
3.2. Receiving an Echo-Request
When a receiver does not understand the Reverse Path Segment List
TLV, it SHOULD silently ignore the TLV and proceed with normal
processing as described in [RFC8029].When a Reverse Path Segment List
TLV is received, and the responder supports processing it, it MUST
use the Segments in Reverse Path Segment List TLV to build the echo-
reply. The responder MUST follow the normal FEC validation
procedures as described in [RFC8029] and [RFC8287] and this document
does not suggest any change to those procedures. When the Echo-reply
has to be sent out the Reverse Path Segment List TLV is used to
construct the MPLS packet to send out.
3.3. Sending an Echo-Reply
The Echo-Reply message is sent as MPLS packet with a MPLS label
stack. The Echo-Reply message MUST be constructed as described in
the [RFC8029]. An MPLS packet is constructed with Echo-reply in the
payload. The top label MUST be constructed from the first Segment
from the Reverse Path Segment List TLV. The remaining labels MUST
follow the order from the Reverse Path Segment List TLV. The
responder MAY check the reachability of the top label in its own LFIB
before sending the Echo-Reply.
4. Detailed Example
An example topology is given in Figure 1 . This will be used in below
sections to explain LSP Ping and Traceroute procedures. The PMS/
Head-end has complete view of topology. PE1, P1, P2, ASBR1 and ASBR2
are in AS1. Similarly ASBR3, ASBR4, P3, P4 and PE4 are in AS2.
AS1 and AS2 have Segment Routing enabled. IGPs like OSPF/ISIS are
used to flood SIDs in each Autonomous System. The ASBR1, ASBR2,
ASBR3, ASBR4 advertise BGP EPE SIDs for the inter-AS links. Topology
of AS1 and AS2 are advertised via BGP-LS to the controller/PMS or
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Head-end node. The EPE-SIDs are also advertised via BGP-LS as
described in [I-D.ietf-idr-bgpls-segment-routing-epe]
The description in the document uses below notations for Segment
Identifiers(SIDs).
Node SIDs : N-PE1, N-P1, N-ASBR1 etc.
Adjacency SIDs : Adj-PE1-P1, Adj-P1-P2 etc.
EPE SIDS : EPE-ASBR2-ASBR3, EPE-ASBR1-ASBR4, EPE-ASBR3-ASBR2 etc.
Let us consider a traffic engineered path built from PE1 to PE4 with
Segment List stack as below. N-P1, N-ASBR1, EPE-ASBR1-ASBR4, N-PE4
for following procedures. This stack may be programmed by
controller/PMS or Head-end router PE1 may have imported the whole
topology information from BGP-LS and computed the inter-AS path.
4.1. Procedures for Segment Routing LSP ping
To perform LSP ping procedure on an SR-Path from PE1 to PE4
consisting of label stacks [N-P1,N-ASBR1,EPE-ASBR1-ASBR4, N-PE4], The
remote end(PE4) needs IP connectivity to head end(PE1) for the
Segment Routing ping to succeed, because Echo-reply needs to travel
back to PE1 from PE4. But in typical deployment scenario there will
be no ip route from PE4 to PE1 as they belong to different ASes.
PE1 adds Reverse Path from PE4 to PE1 in the MPLS Echo-request using
multiple Segments in "Reverse Path Segment List TLV" as defined
above. An example reverse path Segment List for PE1 to PE4 for LSP
ping is [N-ASBR4, EPE-ASBR4-ASBR1, N-PE1]. An implementation may
also build a Reverse Path Segment List consisting of labels to reach
its own AS. Once the label stack is popped-off the Echo-reply
message will be exposed.The further packet forwarding will be based
on ip lookup. An example Reverse Path Segment List for this case
could be [N-ASBR4, EPE-ASBR4-ASBR1].
On receiving MPLS Echo-request PE4 first validates FEC in the Echo-
request. PE4 then builds label stack to send the response from PE4
to PE1 by copying the labels from "Reverse Path Segment List TLV".
PE4 builds the Echo-reply packet with the MPLS label stack
constructed and imposes MPLS headers on top of Echo-reply packet and
sends out the packet towards PE1. This Segment List stack can
successfully steer reply back to Head-end node(PE1).
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4.2. Procedures for Segment Routing LSP Traceroute
As described in the procedures for LSP ping, the reverse Segment List
may be sent from head-end in which case the LSP Traceroute procedures
are similar to LSP ping. The head-end constructs the Reverse Path
Segment List TLV and the egress node uses the Reverse Path Segment
List to construct the Echo-reply packet header. Head-end/PMS is
aware of the reverse path from every node visited in the network and
builds the Reverse Path Segment List for every visited node
accordingly.
For Example:
For the same traffic engineered path PE1 to PE4 mentioned in above
sections, let us assume there is no reverse path available from the
nodes ASBR4 to PE1. During the Traceroute procedure, when PE1 has to
visit ASBR4, it builds reverse Path Label Stack TLV and includes
label to the border-node which has the route to, PE1. In this
example the Reverse Path Segment List TLV will contain [EPE-
ASBR4-ASBR1]. Further down the traceroute procedure when P3 or P4
node is being visited, PE1 build the Reverse Path Segment List TLV
containing [N-ASBR4, EPE-ASBR4-ASBR1]. The Echo-reply will be an
MPLS packet with this label stack and will be forwarded to PE1.
5. Building Reverse Path Segment List TLV dynamically
In some cases, the head-end may not have complete visibility of
Inter-AS topology. In such cases, it can rely on downstream routers
to build the reverse path for mpls traceroute procedures. For this
purpose, the Reverse Path Segment List TLV is carried in the Echo-
Reply.
5.1. The procedures to build the reverse path
When an ASBR receives an echo-request from another AS, and ASBR is
configured to build the Reverse Path dynamically, ASBR MUST build a
Reverse Path Segmnet List TLV and add it in echo-reply. ASBR MUST
locally decide the outgoing interface for the echo-reply packet.
Generally, remote ASBR will choose interface on which the incoming
OAM packet was receieved to send the echo-reply out. Reverse Path
Segment List TLV is built by adding two segment sub TLVs. The top
segment sub TLV consists of the ASBR's Node SID and second segment
consists of the EPE SID in the reverse direction to reach the AS from
which the OAM packet was received.The type of segment chosen to build
Reverse Path Segment List TLV is implementation dependent. In cases
where the AS is configured with different SRGBs, the Node SID of the
ASBR should be represented using type 3 segment so that all the nodes
inside the AS can correctly translate the Node-SID to a label.
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Irrespective of which type of segment is included in the Reverse Path
Segment List TLV, the responder of echo-request always translates the
Reverse Path Segment List TLV to a label stack and builds MPLS header
for the the echo-reply packet.
5.2. Details with example
Let us consider a traffic engineered path built from PE1 to PE4 with
a label stack as below. N-P1, N-ASBR1, EPE-ASBR1-ASBR4, N-PE4 for
the following procedures. This traceroute doesn't need any Reverse
Path Segment List TLV till it leaves AS1, because IP connectivity
will be there to send echo-reply. But this traceroute requires
Reverse Path Segment List TLV once it starts probing AS2 routers.
According to this procedure, ASBR4 should add Reverse Path Segment
List TLV in its echo-reply. ASBR4 should form this Reverse Path
Segment List TLV using its own Node SID(N-ASBR4) and EPE SID (EPE-
ASRB4-ASBR1) labels. Then PE1 should use this Reverse Path Segment
List TLV in subsequent echo-requests. In this example, when the
subsequent echo-request reaches P3, it should use this Reverse Path
Segment List TLV for sending the echo-reply. The same Reverse Path
Segment List TLV is enough for any router in AS2 to send the reply.
Because the first label(N-ASBR4) can direct echo-reply to ASBR4 and
second one (EPE-ASBR4-ASBR1) to direct echo-reply to AS1. Once echo
reply reaches AS1, normal IP forwarding helps it to reach PE1 or the
head-end.
6. Security Considerations
TBD
7. IANA Considerations
Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping
Parameters TLVs Registry
Reverse Path Segment List TLV : TBD
8. Contributors
1.Carlos Pignataro
Cisco Systems, Inc.
cpignata@cisco.com
2. Zafar Ali
Cisco Systems, Inc.
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zali@cisco.com
9. Acknowledgments
Thanks to Bruno Decreane for suggesting use of generic Segment sub-
TLV.
10. References
10.1. Normative References
[I-D.ietf-idr-segment-routing-te-policy]
Previdi, S., Filsfils, C., Mattes, P., Rosen, E., Jain,
D., and S. Lin, "Advertising Segment Routing Policies in
BGP", draft-ietf-idr-segment-routing-te-policy-07 (work in
progress), July 2019.
[I-D.ietf-spring-segment-routing-central-epe]
Filsfils, C., Previdi, S., Dawra, G., Aries, E., and D.
Afanasiev, "Segment Routing Centralized BGP Egress Peer
Engineering", draft-ietf-spring-segment-routing-central-
epe-10 (work in progress), December 2017.
[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>.
10.2. Informative References
[I-D.ietf-idr-bgpls-segment-routing-epe]
Previdi, S., Talaulikar, K., Filsfils, C., Patel, K., Ray,
S., and J. Dong, "BGP-LS extensions for Segment Routing
BGP Egress Peer Engineering", draft-ietf-idr-bgpls-
segment-routing-epe-19 (work in progress), May 2019.
[I-D.ietf-mpls-interas-lspping]
Nadeau, T. and G. Swallow, "Detecting MPLS Data Plane
Failures in Inter-AS and inter-provider Scenarios", draft-
ietf-mpls-interas-lspping-00 (work in progress), March
2007.
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Internet-Draft Inter-as-OAM November 2019
[I-D.ietf-spring-segment-routing-mpls]
Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing with MPLS
data plane", draft-ietf-spring-segment-routing-mpls-22
(work in progress), May 2019.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Sivabalan, S., daniel.voyer@bell.ca, d.,
bogdanov@google.com, b., and P. Mattes, "Segment Routing
Policy Architecture", draft-ietf-spring-segment-routing-
policy-03 (work in progress), May 2019.
[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>.
[RFC7743] Luo, J., Ed., Jin, L., Ed., Nadeau, T., Ed., and G.
Swallow, Ed., "Relayed Echo Reply Mechanism for Label
Switched Path (LSP) Ping", RFC 7743, DOI 10.17487/RFC7743,
January 2016, <https://www.rfc-editor.org/info/rfc7743>.
[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>.
[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>.
[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>.
[RFC8604] Filsfils, C., Ed., Previdi, S., Dawra, G., Ed.,
Henderickx, W., and D. Cooper, "Interconnecting Millions
of Endpoints with Segment Routing", RFC 8604,
DOI 10.17487/RFC8604, June 2019,
<https://www.rfc-editor.org/info/rfc8604>.
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Authors' Addresses
Shraddha Hegde
Juniper Networks Inc.
Exora Business Park
Bangalore, KA 560103
India
Email: shraddha@juniper.net
Kapil Arora
Juniper Networks Inc.
Email: kapilaro@juniper.net
Samson Ninan
Juniper Networks Inc.
Email: samsonn@juniper.net
Mukul Srivastava
Juniper Networks Inc.
Email: msri@juniper.net
Nagendra Kumar
Cisco Systems, Inc.
Email: naikumar@cisco.com
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