MPLS Working Group N. Kumar
Internet-Draft G. Swallow
Intended status: Standards Track C. Pignataro
Expires: April 24, 2014 N. Akiya
Cisco Systems, Inc.
M. Chen
Huawei
October 21, 2013
Label Switched Path (LSP) Ping/Trace for Segment Routing Networks Using
MPLS Dataplane
draft-kumar-mpls-spring-lsp-ping-00
Abstract
Segment Routing architecture leverages the source routing and
tunneling paradigm and can be directly applied to MPLS dataplane. A
node steers a packet through a controlled set of instructions called
segments, by prepending the packet with Segment Routing header.
The segment assignment and forwarding semantic nature of Segment
Routing raises additional consideration for connectivity verification
and fault isolation in LSP with SPRING architecture. This document
illustrates the problem and describe a mechanism to perform LSP Ping
and Traceroute on Segment Routing network over MPLS dataplane.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
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This Internet-Draft will expire on April 24, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements notation . . . . . . . . . . . . . . . . . . . . 3
3. Path validation in Segment Routing networks . . . . . . . . . 3
4. Segment Routing Sub-TLV Format . . . . . . . . . . . . . . . 4
4.1. IPv4 Prefix Node Segment ID . . . . . . . . . . . . . . . 4
4.2. IPv6 Prefix Node Segment ID . . . . . . . . . . . . . . . 6
4.3. IGP Adjacency Segment ID . . . . . . . . . . . . . . . . 7
5. Extension to Downstream Mapping TLV . . . . . . . . . . . . . 8
6. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. FECs in Target FEC Stack TLV . . . . . . . . . . . . . . 8
6.2. FEC Stack Change TLV . . . . . . . . . . . . . . . . . . 9
6.3. PHP, Adjacency SID Pop, Implicit NULL . . . . . . . . . . 9
6.4. Segment Protocol Check . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 11
9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 11
10. Contributing Authors . . . . . . . . . . . . . . . . . . . . 11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
11.1. Normative References . . . . . . . . . . . . . . . . . . 11
11.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
[I-D.filsfils-rtgwg-segment-routing] introduces and explains Segment
Routing architecture that leverages the source routing and tunneling
paradigm. A node steers a packet through a controlled set of
instructions called segments, by prepending the packet with SR
header. A detailed definition about Segment Routing architecture is
available in draft-filsfils-rtgwg-segment-routing and different use-
cases are discussed in draft-filsfils-rtgwg-segment-routing-use-
cases.
The Segment Routing architecture can be directly applied to MPLS
dataplane in a way that, the segment will be of 20-bits size and SR
header is the label stack.
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[RFC4379] describes the mechanism to perform connectivity
verification and fault isolation in Label Switched Path (LSP).
Unlike LDP or RSVP which are the other well-known MPLS control plane
protocols, segment assignment in Segment Routing architecture is not
hop-by-hop basis.
This nature of Segment Routing raises additional consideration for
connectivity verification and fault isolation in Segment Routing
network. This document illustrates the problem and describe a
mechanism to perform LSP Ping and Traceroute on Segment Routing
network over MPLS dataplane.
2. Requirements notation
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 [RFC2119].
3. Path validation in Segment Routing networks
[RFC4379] defines the OAM machinery that helps with connectivity
check and fault isolation in MPLS dataplane path with the use of
various Target FEC Stack Sub-TLV that are carried in MPLS Ping
packets and used by the responder for FEC validation. While it is
obvious that new Sub-TLVs need to be assigned, the unique nature of
SPRING architecture raises a need for additional machinery for path
validation. This section discuss the challenges as below:
L1
+--------+
| L2 |
R3-------R6
/ \
/ \
R1----R2 R7----R8
\ / L3
\ /
R4-------R5
Figure 1: SPRING network
500x --> Node Segment ID for Router X
(Ex: 5006 is node segment ID for R6)
9axy --> Adj Segment ID from Router X to Y over link a
(Ex: 9136 is Adj segment ID from R3 to R6 via link 1)
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The forwarding semantic of Adjacency segment is to pop the segment
and send the packet to a specific neighbor over a specific link. A
malfunctioning node may forward packets using Adjacency segment to
incorrect neighbor or over incorrect link. Exposed segment (after
incorrectly forwarded Adjacency segment) might still allow such
packet to traverse to intended destination, yet intended strict
traversal has been broken.
Assume in above topology, R1 sends traffic with segment stack as
{9124, 5007, 9378} so that the path taken will be R1-R2-R4-R5-R7-R8.
If the adjacency segment 9124 is misprogrammed in R2 to send the
packet to R1 or R3, it will still be delivered to R8 but is not via
the expected path.
MPLS traceroute may help with detecting such deviation in above
mentioned scenario. However, it may not be helpful if R3, due to
misprogramming, forwards packet with adjacency segment 9236 via link
L1 while it is expected to be forwarded over Link L2.
This document defines Target FEC Stack sub-TLVs and explains how they
can be used to tackle above challenges.
4. Segment Routing Sub-TLV Format
The format of the following FEC Sub-TLVs follows the philosophy of
Target FEC Stack TLV carrying FECs corresponding to each label in the
label stack. When operated with the procedures defined in [RFC4379],
this allows LSP ping/traceroute operations to function when Target
FEC Stack TLV contains more FECs than received label stack at
responder nodes.
Type Sub-Type Value Field
---- -------- ---------------
1 TBD1 IPv4 Prefix Node Segment ID
TBD2 IPv6 Prefix Node Segment ID
TBD3 Adjacency Segment ID
Service Segments and FRR will be considered in future version.
4.1. IPv4 Prefix Node Segment ID
The format is as below:
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
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Prefix Length | Resv | Protocol | SID Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Node Segment ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Advertising Node Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IPv4 Prefix
This field carries the IPv4 prefix to which the Node Segment ID is
assigned.
Prefix Length
One octet of prefix length in bits.
Protocol
Set to 1 if the IGP protocol is OSPF and 2 if IGP protocol is
ISIS.
SID Length
Set to 3 or 4 depending on the Segment ID.
Node Segment ID
This field carries the Node segment ID. If the SID Length is 3,
then the 20 rightmost bits represent the segment. If length is 4,
then the value represent a 32 bits Segment ID.
Advertising Node Identifier
Specifies the advertising node identifier.When Protocol is set to
1, then the 32 rightmost bits represent OSPF Router ID and if
protocol is set to 2, this field carries 48 bit ISIS System ID.
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4.2. IPv6 Prefix Node Segment ID
The format is as below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 Prefix |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Prefix Length | Resv | Protocol | SID Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Node Segment ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Advertising Node Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IPv6 Prefix
This field carries the IPv6 prefix to which the Node Segment ID is
assigned.
Prefix Length
One octet of prefix length in bits.
Protocol
Set to 1 if the IGP protocol is OSPF and 2 if IGP protocol is
ISIS.
SID Length
Set to 3 or 4 depending on the Segment ID.
Node Segment ID
This field carries the Node segment ID. If the SID Length is 3,
then the 20 rightmost bits represent the segment. If length is 4,
then the value represent a 32 bits Segment ID.
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Advertising Node Identifier
Specifies the advertising node identifier.When Protocol is set to
1, then the 32 rightmost bits represent OSPF Router ID and if
protocol is set to 2, this field carries 48 bit ISIS System ID.
4.3. IGP Adjacency Segment ID
The format is as below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol | SID Length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Advertising Node Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IGP Adjacency Segment ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Local Interface ID
An identifier that is assigned by local LSR for a link on which
Adjacency SID is binded. If the Adj-SID represents parallel
adjacencies (Section 3.3.2.1 of
[I-D.filsfils-rtgwg-segment-routing]) this field MUST be set to
zero.
Remote Interface ID
An identifier that is assigned by remote LSR for a link on which
Adjacency SID is binded. If the Adj-SID represents parallel
adjacencies (Section 3.3.2.1 of
[I-D.filsfils-rtgwg-segment-routing]) this field MUST be set to
zero.
Protocol
Set to 1 if the IGP protocol is OSPF and 2 if IGP protocol is ISIS
SID Length
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Set to 3 or 4 depending on the Segment ID.
Advertising Node Identifier
Specifies the advertising node identifier.When Protocol is set to
1, then the 32 rightmost bits represent OSPF Router ID and if
protocol is set to 2, this field carries 48 bit ISIS System ID.
IGP Adjacency Segment ID
This field carries the adjacency segment ID.
5. Extension to Downstream Mapping TLV
In an echo reply, the Downstream Mapping TLV [RFC4379] is used to
report for each interface over which a FEC could be forwarded. For
an FEC, there are multiple protocols that may be used to distribute
label mapping. The "Protocol" field of the Downstream Mapping TLV is
used to return the protocol that is used to distribute a specific a
label. The following protocols are defined in section 3.2 of
[RFC4379]:
Protocol # Signaling Protocol
---------- ------------------
0 Unknown
1 Static
2 BGP
3 LDP
4 RSVP-TE
With segment routing, OSPF or ISIS can be used for label
distribution, this document adds two new protocols as follows:
Protocol # Signaling Protocol
---------- ------------------
5 OSPF
6 ISIS
6. Procedures
This section describes aspects of LSP ping/traceroute operations that
require further considerations beyond [RFC4379].
6.1. FECs in Target FEC Stack TLV
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When LSP echo request packets are generated by an initiator, FECs
carried in Target FEC Stack TLV may need to or desire to have
deviating contents. This document outlines expected Target FEC Stack
TLV construction mechanics by initiator for known scenarios.
Ping
Initiator MUST include FEC(s) corresponding to the destination
segment.
Initiator MAY include FECs corresponding to some or all of
segments imposed in the label stack by the initiator to
communicate the segments traversed.
Traceroute
Initiator MUST initially include FECs corresponding to all of
segments imposed in the label stack.
When a received echo reply contains FEC Stack Change TLV with
one or more of original segment(s) being popped, initiator MAY
remove corresponding FEC(s) from Target FEC Stack TLV in the
next (TTL+1) traceroute request.
When a received echo reply does not contain FEC Stack Change
TLV, initiator MUST NOT attempt to remove FEC(s) from Target
FEC Stack TLV in the next (TTL+1) traceroute request. Note
that Downstream Label field of DSMAP/DDMAP contains hints on
how initiator may be able to update the contents of next Target
FEC Stack TLV. However, such hints are ambiguous without full
understanding of PHP capabilities.
6.2. FEC Stack Change TLV
The network node which advertised the node segment ID is responsible
for generating FEC Stack Change TLV of &pop& operation for node
segment ID, regardless of if PHP is enabled or not.
The network node that is immediate downstream of the node which
advertised the adjacency segment ID is responsible for generating FEC
Stack Change TLV of &pop& operation for adjacency segment ID.
6.3. PHP, Adjacency SID Pop, Implicit NULL
Forwarding behavior of node segment ID PHP is equivalent to usage of
implicit Null in MPLS protocols that embraces downstream label
allocation scheme. Adjacency segment ID is also similar in a sense
that it can be thought as nexthop destined locally allocated segment
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that has PHP enabled. Procedures described in Section 4.4 of
[RFC4379] relies on Stack-D and Stack-R explicitly having Implicit
Null value. It may simplify implementations to reuse Implicit Null
for node segment ID PHP and adjacency segment ID cases. However, it
is technically incorrect for Implicit Null value to externally
appear. Therefore, implicit Null MUST NOT be placed in Stack-D and
Interface and Label Stack TLV for node segment ID PHP and adjacency
segment ID cases.
6.4. Segment Protocol Check
If the Target FEC Sub-TLV at FEC-stack-depth is TBD1 (IPv4 Prefix
Node Segment ID), set Best return code to (error code TBD) if any
below conditions fail:
* Validate that Advertising Node Identifier of Protocol is a
local node.
* Validate that Node Segment ID is avertised for IPv4 Prefix by
the Protocol with Advertising Node Identifier.
* Validate that Node Segment ID is advertisement of PHP bit.
If the Target FEC Sub-TLV at FEC-stack-depth is TBD2 (IPv6 Prefix
Node Segment ID), set Best return code to (error code TBD) if any
below conditions fail:
* Validate that Advertising Node Identifier of Protocol is a
local node.
* Validate that Node Segment ID is advertised for IPv6 Prefix by
the Protocol with Advertising Node Identifier.
* Validate that Node Segment ID is advertised of PHP bit.
If the Target FEC sub-TLV at FEC-stack-depth is TBD3 (Adjacency
Segment ID), set Best return code to (error code TBD) if any below
conditions fail:
* Validate that Remote Interface ID matches the local identifier
of the interface on which the packet was received.
* Validate that IGP Adjacency SID is advertised by Advertising
Node Identifier of Protocol in local IGP database.
7. IANA Considerations
To be Updated.
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8. Security Considerations
To be Updated.
9. Acknowledgement
The authors would like to thank Stefano Previdi for his review and
comments.
10. Contributing Authors
Tarek Saad
Cisco Systems
Email: tsaad@cisco.com
Siva Sivabalan
Cisco Systems
Email: msiva@cisco.com
11. References
11.1. Normative References
[I-D.filsfils-rtgwg-segment-routing]
Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe,
"Segment Routing Architecture", draft-filsfils-rtgwg-
segment-routing-01 (work in progress), October 2013.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC 4379,
February 2006.
[RFC6424] Bahadur, N., Kompella, K., and G. Swallow, "Mechanism for
Performing Label Switched Path Ping (LSP Ping) over MPLS
Tunnels", RFC 6424, November 2011.
11.2. Informative References
[RFC6291] Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
D., and S. Mansfield, "Guidelines for the Use of the "OAM"
Acronym in the IETF", BCP 161, RFC 6291, June 2011.
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[RFC6425] Saxena, S., Swallow, G., Ali, Z., Farrel, A., Yasukawa,
S., and T. Nadeau, "Detecting Data-Plane Failures in
Point-to-Multipoint MPLS - Extensions to LSP Ping", RFC
6425, November 2011.
Authors' Addresses
Nagendra Kumar
Cisco Systems, Inc.
7200 Kit Creek Road
Research Triangle Park, NC 27709
US
Email: naikumar@cisco.com
George Swallow
Cisco Systems, Inc.
1414 Massachusetts Ave
Boxborough, MA 01719
US
Email: swallow@cisco.com
Carlos Pignataro
Cisco Systems, Inc.
7200 Kit Creek Road
Research Triangle Park, NC 27709-4987
US
Email: cpignata@cisco.com
Nobo Akiya
Cisco Systems, Inc.
2000 Innovation Drive
Kanata, ON K2K 3E8
Canada
Email: nobo@cisco.com
Mach(Guoyi) Chen
Huawei
Email: mach.chen@huawei.com
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