Network Working Group M. Chen
Internet-Draft X. Xu
Intended status: Standards Track Z. Li
Expires: October 17, 2014 Huawei
L. Fang
Microsoft
G. Mirsky
Ericsson
April 15, 2014
MultiProtocol Label Switching (MPLS) Source Label
draft-chen-mpls-source-label-03
Abstract
A MultiProtocol Label Switching (MPLS) label was originally defined
to identify a Forwarding Equivalence Class (FEC), a packet is
assigned to a specific FEC based on its network layer destination
address. It's difficult or even impossible to derive the source
identity information from the label. For some applications, source
identification is a critical requirement. For example, performance
monitoring, where the monitoring node needs to identify where a
packet was sent from.
This document introduces the concept of Source Label (SL) that is
carried in the label stack and used to identify the ingress Label
Switching Router (LSR) of an Label Switched Path (LSP).
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 http://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 October 17, 2014.
Copyright Notice
Copyright (c) 2014 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
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Table of Contents
1. Problem Statement and Introduction . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Source Label . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Performance Measurement . . . . . . . . . . . . . . . . . 4
5. Data Plane Processing . . . . . . . . . . . . . . . . . . . . 5
5.1. Ingress LSR . . . . . . . . . . . . . . . . . . . . . . . 5
5.2. Transit LSR . . . . . . . . . . . . . . . . . . . . . . . 6
5.3. Egress LSR . . . . . . . . . . . . . . . . . . . . . . . 6
5.4. Penultimate Hop LSR . . . . . . . . . . . . . . . . . . . 6
6. Source Label Signaling . . . . . . . . . . . . . . . . . . . 6
6.1. Source Label Capability Signaling . . . . . . . . . . . . 6
6.1.1. LDP Extensions . . . . . . . . . . . . . . . . . . . 6
6.1.2. BGP Extensions . . . . . . . . . . . . . . . . . . . 7
6.1.3. RSVP-TE Extensions . . . . . . . . . . . . . . . . . 8
6.2. Source Label Distribution . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7.1. Source Label Indication . . . . . . . . . . . . . . . . . 9
7.2. LDP Source Label Capability TLV . . . . . . . . . . . . . 9
7.3. BGP Source Label Capability Attribute . . . . . . . . . . 9
7.4. RSVP-TE Source Label Capability Flag . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1. Normative References . . . . . . . . . . . . . . . . . . 10
10.2. Informative References . . . . . . . . . . . . . . . . . 10
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Problem Statement and Introduction
A MultiProtocol Label Switching (MPLS) label [RFC3031] was originally
defined for packet forwarding and assumes the forwarding/destination
address semantics. As no source identity information is carried in
the label stack, there is no way to directly derive the source
identity information from the label or label stack.
MPLS LSPs can be categorized into four different types:
Point-to-Point (P2P)
Point-to-Multipoint (P2MP)
Multipoint-to-Point (MP2P)
Multipoint-to-Multipoint (MP2MP)
For P2P and P2MP LSPs (e.g., the Resource Reservation Protocol
Traffic Engineering (RSVP-TE) [RFC3209] based and statically
configured P2P and P2MP LSPs), the source identity may be implicitly
derived by the egress LSR from the label when Penultimate Hop Popping
(PHP) is disabled and the correlation between ingress LSR and the LSP
is explicitly signalled through the control plane. Such LSP may be
characterized as MPLS-TP LSP [RFC5960].
However, for MP2P and MP2MP LSPs (e.g., the Distribution Protocol
(LDP) based LSPs [RFC5036] [RFC6388], and Layer 3 Private Network
(L3VPN) [RFC4364] LSPs), ingress LSRs of those LSPs cannot be
identified by egress LSRs.
Comparing to the pure IP forwarding where both source and destination
addresses are encoded in the IP packet header, the essential issue of
the MPLS encoding is that the label stack does not explicitly include
any source identity information. For some applications, source
identification is a critical requirement. For example, performance
monitoring, the monitoring nodes need to identify where packets were
sent from and then can count the packets according to some
constraints.
In addition, Segment Routing [I-D.filsfils-rtgwg-segment-routing]
also explicitly points out that there are requirements to preserve
the ingress information to fulfil the accounting and billing
purposes.
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This document introduces the concept of Source Label (SL). An SL
uniquely identifies a node within an administrative domain, it is
carried in the label stack and used to identify the ingress LSR that
originated the MPLS frame.
2. Terminology
SL - Source Label
SLC - Source Label Capability
SLI - Source Label Indicator
3. Source Label
A Source Label is defined to uniquely identify a node that is (one
of) the ingress LSR(s) to a specific LSP. In its function as a
Source Label, it MUST be unique within a domain. In cases where a
Source Label is used across domains it MUST be unique within the
scope it is used.
Source Labels SHOULD NOT be used for forwarding. The Source Labels
are allocated from a dedicated label space that is completely
different from the space of the normal forwarding labels.
Configuration system (e.g., static configuration) is one way to make
sure the uniqueness of each SL assigned to specific LSR. There may
be some other potential dynamic solutions that can be used for SL
allocation and distribution. This is out of the scope of this
document.
In order to indicate whether a label is a Source Label, a Source
Label Indicator (SLI) is introduced. The SLI is a special purpose
label [I-D.ietf-mpls-special-purpose-labels] that is placed
immediately before the source label in the label stack, which is used
to indicate that the next label in the label stack is the Source
Label. Throughout the document mention to a Source Label refers to
the combination of SLI and SL. The value of SLI is TBD1.
4. Use Cases
This section outlines the use cases which benefit from application of
Source Label.
4.1. Performance Measurement
There are two general types of performance measurement: one is active
performance measurement, and the other is passive performance
measurement.
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In active performance measurement the receiver measures the injected
packets to evaluate the performance of a path. The active
measurement measures the performance of the extra injected packets.
The IP Performance Metrics (IPPM) working group has defined
specifications [RFC4656][RFC5357] for the active performance
measurement.
In passive performance measurement, no additional traffic is injected
into the flow and measurements are taken to record the performance
metrics of the data traffic. The MPLS performance measurement
protocol [RFC6374] for packet loss is an example of passive
performance measurement, but it can only apply to MPLS-TE LSPs. For
a specific receiver, in order to count the received packets of a
flow, it has to know whether a received packet belongs to which
target flow under test and the source identification is a critical
condition.
As discussed in the previous section, the existing MPLS label or
label stack do not carry the source information. So, for an LSP, the
ingress LSR can put its Source Label in the label stack, and then the
egress LSR can use the Source Label for packets identification of
frame's source and accounting.
5. Data Plane Processing
5.1. Ingress LSR
For an LSP, the ingress LSR MUST make sure that the egress LSR is
able to process the Source Label before inserting the SLI/SL
combination into the label stack. Therefore, an egress LSR SHOULD
signal (see Section 6.1) to the ingress LSR whether it is able to
process the Source Label. Once the ingress LSR knows that the egress
LSR can process Source Label, it can choose whether or not to insert
the SL and SLI into the label stack.
When an SL to be included in a label stack, the steps are as follows:
1. Push the SL, the TTL of the SL MUST be set to 1, the BoS bit for
the SL depends on whether the SL is the bottom label. Setting
and interpretation of TC field of the SL is for further study;
2. Push the SLI, the TTL and TC fields for the SLI MUST be set to
the same values as for the LSP Label (L);
3. Push the LSP Label (L).
Then the label stack looks like: <...L, SLI, SL [,...]>. There MAY
be multiple pairs of SLI and SL inserted into the label stack, each
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pair is related to an LSP. For the given LSP, only one pair of SLI
and SL MUST be inserted.
5.2. Transit LSR
There is no change in forwarding behavior for transit LSRs. If a
transit LSR can recognize the SLI, it can use the SL to collect
traffic throughput and/or measure the performance of the LSP.
5.3. Egress LSR
When an egress LSR receives a packet with a SLI/SL combination, if
the egress LSR is able to process the SL; it pops the LSP label (if
any), SLI and SL; then processes remaining packet header as normal.
If the egress LSR is not able to process the SLI, the packet SHOULD
be dropped as specified for the handling of any unknown label
according to [RFC3031].
5.4. Penultimate Hop LSR
There is no change in forwarding behavior for the penultimate hop
LSR.
6. Source Label Signaling
Source label signaling includes two aspects: one is source label
capability signaling, the other is source label distribution.
6.1. Source Label Capability Signaling
Before inserting a Source Label in the label stack, an ingress LSR
SHOULD know whether the egress LSR is able to process the Source
Label. Therefore, an egress LSR SHOULD signal to the ingress LSRs
its ability to process the Source Label. This is called Source Label
Capability (SLC), it is very similar to the "Entropy Label Capability
(ELC)"[RFC6790].
6.1.1. LDP Extensions
A new LDP TLV [RFC5036], SLC TLV, is defined to signal an egress's
ability to process Source Label. The SLC TLV MAY appear as an
Optional Parameter of the Label Mapping Message. The presence of the
SLC TLV in a Label Mapping Message indicates to ingress LSRs that the
egress LSR can process Source Labels for the associated LSP.
The structure of the SLC TLV is shown below.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Type (TBD2) | Length (0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Source Label Capability TLV
This U bit MUST be set to 1. If the SLC TLV is not understood by the
receiver, then it MUST be ignored.
This F bit MUST be set to 1. Since the SLC TLV is going to be
propagated hop-by-hop, it should be forwarded even by nodes that may
not understand it.
Type: TBD2.
Length field: This field specifies the total length in octets of the
SLC TLV and is defined to be 0.
An LSR that receives a Label Mapping with the SLC TLV but does not
understand it MUST propagate it intact to its neighbors and MUST NOT
send a notification to the sender (following the meaning of the U-
and F-bits). If the LSR has no other neighbors and does not
understand the SLC TLV, means it is the ingress LSR, it could just
ignore it. An LSR X may receive multiple Label Mappings for a given
FEC F from its neighbors. In its turn, X may advertise a Label
Mapping for F to its neighbors. If X understands the SLC TLV, and if
any of the advertisements it received for FEC F does not include the
SLC TLV, X MUST NOT include the SLC TLV in its own advertisements of
F. If all the advertised Mappings for F include the SLC TLV, then X
MUST advertise its Mapping for F with the SLC TLV. If any of X's
neighbors resends its Mapping, sends a new Mapping or sends a Label
Withdraw for a previously advertised Mapping for F, X MUST re-
evaluate the status of SLC for FEC F, and, if there is a change, X
MUST re-advertise its Mapping for F with the updated status of SLC.
6.1.2. BGP Extensions
When Border Gateway Protocol (BGP) [RFC4271] is used for distributing
Network Layer Reachability Information (NLRI) as described in, for
example, [RFC3107], [RFC4364], the BGP UPDATE message may include the
SLC attribute as part of the Path Attributes. This is an optional,
transitive BGP attribute of value TBD3. The inclusion of this
attribute with an NLRI indicates that the advertising BGP router can
process Source Labels as an egress LSR for all routes in that NLRI.
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A BGP speaker S that originates an UPDATE should include the SLC
attribute only if both of the following are true:
A1: S sets the BGP NEXT_HOP attribute to itself AND
A2: S can process source labels.
Suppose a BGP speaker T receives an UPDATE U with the SLC attribute.
T has two choices. T can simply re-advertise U with the SLC
attribute if either of the following is true:
B1: T does not change the NEXT_HOP attribute OR
B2: T simply swaps labels without popping the entire label stack and
processing the payload below.
An example of the use of B1 is Route Reflectors. However, if T
changes the NEXT_HOP attribute for U and in the data plane pops the
entire label stack to process the payload, T MAY include an SLC
attribute for UPDATE U' if both of the following are true:
C1: T sets the NEXT_HOP attribute of U' to itself AND
C2: T can process source labels. Otherwise, T MUST remove the SLC
attribute.
6.1.3. RSVP-TE Extensions
[RFC5420] introduces the LSP_ATTRIBUTES object, it gives a perfect
way to carry LSP attribute through the object. To signal the Source
Label Capability in RSVP-TE [RFC3209], this document defines a flag
in the Attribute Flags TLV of the LSP_ATTRIBUTES object [RFC3209].
The presence of the SLC flag in a Path message indicates that the
ingress can process Source Labels in the upstream direction; this
only makes sense for a bidirectional LSP and MUST be ignored
otherwise. The presence of the SLC flag in a Resv message indicates
that the egress can process source labels in the downstream
direction. The bit number for the SLC flag is TBD4.
6.2. Source Label Distribution
Based on the Source Label, an egress or intermediate LSR can identify
from where an MPLS packet is sent. To achieve this, the egress and/
or intermediate LSRs have to know which ingress LSR is related to
which Source Label before using the Source Label to derive the source
information. Therefore, there needs to be a mechanism to distribute
the mapping information between an ingress LSR and its Source Label.
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This can be done, for example, by defining extensions to LDP, BGP,
RSVP-TE and/or Interior Gateway Protocol (IGP) to distribute to
source label mapping. The source label distribution will be defined
in another document(s).
7. IANA Considerations
7.1. Source Label Indication
IANA is required to allocate a special purpose label (TBD1) for the
Source Label Indicator (SLI) from the "Multiprotocol Label Switching
Architecture (MPLS) Label Values" Registry.
7.2. LDP Source Label Capability TLV
IANA is requested to allocate a value of TBD2 from the IETF Consensus
range (0x0001-0x07FF) in the "TLV Type Name Space" registry as the
"Source Label Capability TLV".
7.3. BGP Source Label Capability Attribute
IANA is requested to allocate a Path Attribute Type Code TBD3 from
the "BGP Path Attributes" registry as the "BGP Source Label
Capability Attribute".
7.4. RSVP-TE Source Label Capability Flag
IANA is requested to allocate a new bit from the "Attribute Flags"
sub-registry of the "Resource Reservation Protocol-Traffic
Engineering (RSVP-TE) Parameters" registry.
Bit | Name | Attribute | Attribute | RRO
No | | Flags Path | Flags Resv |
----+-------------------------+------------+------------+-----
TBD4| Source Label Capability | Yes | Yes | No
8. Security Considerations
This document does not introduce extra security issues.
9. Acknowledgements
The process of "Source Label Capability Signaling" is largely
referred to the process of "ELC signaling"[RFC6790].
The authors would like to thank Carlos Pignataro, Loa Andersson , and
Curtis Villamizar for their review, suggestion and comments to this
document.
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10. References
10.1. Normative References
[I-D.ietf-mpls-special-purpose-labels]
Kompella, K., Andersson, L., and A. Farrel, "Allocating
and Retiring Special Purpose MPLS Labels", draft-ietf-
mpls-special-purpose-labels-06 (work in progress), March
2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
[RFC3107] Rekhter, Y. and E. Rosen, "Carrying Label Information in
BGP-4", RFC 3107, May 2001.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP
Specification", RFC 5036, October 2007.
[RFC5420] Farrel, A., Papadimitriou, D., Vasseur, JP., and A.
Ayyangarps, "Encoding of Attributes for MPLS LSP
Establishment Using Resource Reservation Protocol Traffic
Engineering (RSVP-TE)", RFC 5420, February 2009.
[RFC6374] Frost, D. and S. Bryant, "Packet Loss and Delay
Measurement for MPLS Networks", RFC 6374, September 2011.
10.2. Informative 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.
[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, May 2000.
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[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
[RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
Zekauskas, "A One-way Active Measurement Protocol
(OWAMP)", RFC 4656, September 2006.
[RFC4761] Kompella, K. and Y. Rekhter, "Virtual Private LAN Service
(VPLS) Using BGP for Auto-Discovery and Signaling", RFC
4761, January 2007.
[RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
RFC 5357, October 2008.
[RFC5960] Frost, D., Bryant, S., and M. Bocci, "MPLS Transport
Profile Data Plane Architecture", RFC 5960, August 2010.
[RFC6388] Wijnands, IJ., Minei, I., Kompella, K., and B. Thomas,
"Label Distribution Protocol Extensions for Point-to-
Multipoint and Multipoint-to-Multipoint Label Switched
Paths", RFC 6388, November 2011.
[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, November 2012.
Authors' Addresses
Mach(Guoyi) Chen
Huawei
Email: mach.chen@huawei.com
Xiaohu Xu
Huawei
Email: xuxiaohu@huawei.com
Zhenbin Li
Huawei
Email: lizhenbin@huawei.com
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Luyuan Fang
Microsoft
Email: lufang@microsoft.com
Greg Mirsky
Ericsson
Email: Gregory.mirsky@ericsson.com
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