Internet DRAFT - draft-chen-mpls-source-label
draft-chen-mpls-source-label
Network Working Group M. Chen
Internet-Draft X. Xu
Intended status: Standards Track Z. Li
Expires: April 16, 2015 Huawei
L. Fang
Microsoft
G. Mirsky
Ericsson
October 13, 2014
MultiProtocol Label Switching (MPLS) Source Label
draft-chen-mpls-source-label-06
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, and optionally Class of Service. 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 Identifier (SI) that
identifies the ingress Label Switching Router (LSR) of a Label
Switched Path (LSP). A SI is unique within a domain that is referred
to as Source Identifier Administrative Domain (SIAD).
This document also introduces the concept of Source Label (SL) that
is carried in the label stack and carries the SI of the ingress LSR
of an LSP. Source Label is preceded by a Source Label Indicator
(SLI) when included the label stack and is not used for forwarding.
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
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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
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 April 16, 2015.
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. Performance Measurement Use Case . . . . . . . . . . . . . . 5
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 Capability Signaling . . . . . . . . . . . . . . 6
6.1. LDP Extensions . . . . . . . . . . . . . . . . . . . . . 6
6.2. BGP Extensions . . . . . . . . . . . . . . . . . . . . . 7
6.2.1. Sending/Receiving Restriction . . . . . . . . . . . . 8
6.3. IGP Extensions . . . . . . . . . . . . . . . . . . . . . 9
7. Source Identifier Distribution . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8.1. Source Label Indication . . . . . . . . . . . . . . . . . 9
8.2. LDP Source Label Capability TLV . . . . . . . . . . . . . 10
8.3. BGP Source Label Capability Attribute . . . . . . . . . . 10
9. Security Considerations . . . . . . . . . . . . . . . . . . . 10
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
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11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
11.1. Normative References . . . . . . . . . . . . . . . . . . 10
11.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
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, in many cases 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:
o Point-to-Point (P2P)
o Point-to-Multipoint (P2MP)
o Multipoint-to-Point (MP2P)
o 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 signaled through the control plane. Such LSP may be
characterized as MPLS-TP LSP [RFC5960].
However, for MP2P and MP2MP LSPs (e.g., the Label 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.
This document introduces the concept of Source Label (SL). An SL is
carried in the label stack and carries the identifier of the ingress
LSR that originated the MPLS frame.
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2. Terminology
SI - Source Identifier
SIAD - Source Identifier Administrative Domain
SL - Source Label
SLC - Source Label Capability
SLI - Source Label Indicator
3. Source Label
A Source Label is defined to carry an identifier (Source Identifier)
of a node that is (one of) the ingress LSR(s) to specific LSP.
Source Label SHOULD NOT be used for forwarding and is not signaled.
A Source Identifier (SI) is a number in the range of [16, 65535].
Each node in a domain MUST be allocated one or more unique SIs, the
domain is referred as a "Source Identifier Administrative Domain"
(SIAD). For most of the use cases, one SI per LSR would be
sufficient. But for some cases, there may be need for more than one
SIs. For example, in the L3VPN scenario, it may be necessary to
allocate a dedicated SI to identify each VPN instance.
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 [RFC7274] 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. The value of SLI is TBD1. The SL
is an example of context label [RFC5331], the SLI is the context.
To prevent the Source Label from leaking to unintended domains, two
aspects need to be considered:
o In the control plane, the Source Label MUST NOT be distributed
outside the SIAD where it is used. Since the ingress LSR is based
on the Source Label Capability signaled by the egress LSR to
determine whether to insert the Source Label, the SLC signaling
MUST make sure that the SLC will not be signaled to the LSRs that
reside in other SIADs.
o In the data plane, the domain boundary nodes (e.g., the ASBR)
SHOULD have the capability to filter out the packets that carry
the SL/SLI and are received from other SIADs. For example, some
policies (e.g., using ACL) could be deployed at the ASBR to filter
out the packets that carry SL/SLI and are from other SIADs.
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4. Performance Measurement Use Case
There are two general types of performance measurement: one is active
performance measurement, and the other is passive performance
measurement.
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 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 currently it can only be measured for
MPLS-TE LSPs. For a specific receiver, in order to count the
received packets of a flow, the system doing the measurement (e.g.,
egress router) needs to know which target flow a received packet
belongs to. Source identification is therefore necessary. Source
identification may be achieved by including appropriate MEP-ID
[RFC6428].
As discussed in the previous section, the existing MPLS label or
label stack does not carry the source information. So, for an LSP,
the ingress LSR can put its SI in the Source Label, and then the
egress LSR can use the SI to identify the packet's source, in order
to facilitate 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) 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;
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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 combinations of SLI and SL inserted into the label stack,
each combination is related to an LSP. For the given LSP, only one
combination 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 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 SLI and SL.
Therefore, an egress LSR SHOULD signal to the ingress LSRs its
ability to process the SLI and SL. This is called Source Label
Capability (SLC), it is very similar to the "Entropy Label Capability
(ELC)"[RFC6790].
6.1. 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.
LDP is normally running within an AS, technically, it can be deployed
across ASes. An implementation supports the SLC MUST support a per-
session/per-interface configuration item to enable/disable the SLC.
For the session/interface that connects to other SLADs, the SLC MUST
be disabled.
6.2. 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
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SLC attribute as part of the Path Attributes. This is an optional,
non-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.
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.
6.2.1. Sending/Receiving Restriction
An implementation that supports the SLC MUST support per-session
configuration item, SL_SESSION, that indicates whether the SLC is
enabled or disabled for use on that session.
- The default value of SL_SESSION, for EBGP sessions, MUST be
"disabled".
- The default value of SL_SESSION, for IBGP and confederation-EBGP
[RFC5065]sessions, SHOULD be "enabled."
The SLC attribute MUST NOT be sent on any BGP session for which
SL_SESSION is disabled.
If an SLC attribute is received on a BGP session for which SL_SESSION
is disabled, the attribute MUST be treated exactly as if it were an
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unrecognized non-transitive attribute. That is, "it MUST be quietly
ignored and not passed along to other BGP peers" (see [RFC4271],
section 5).
6.3. IGP Extensions
IGP based SLC applies to the scenarios where IGP is used for label
mapping (e.g., Segment Routing). IGP SLC signaling is defined in
[I-D.chen-isis-source-identifier-distribution] and
[I-D.chen-ospf-source-identifier-distribution], the presence of a
Source Identifier TLV/sub-TLV MUST be interpreted as support of SLC
by the LSR. That means the SLC is implicitly indicated by receiving
a SI distribution from an LSR.
7. Source Identifier Distribution
Based on the Source Identifier, 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 Identifier before using the Source Identifier
to derive the source information. Therefore, there needs to be a
mechanism to distribute the mapping information between an ingress
LSR and its SI(s).
IGP based SI distribution documents,
[I-D.chen-isis-source-identifier-distribution],
[I-D.chen-ospf-source-identifier-distribution], define extensions to
corresponding IGP protocols necessary for intra-AS scenario.
For inter-AS scenario, BGP extension is a naturally choice and can be
used to convey SI mapping information from one AS to other ASes. The
BGP extension draft is work in progress. For BGP based SI
distribution, it requires that SIs MUST not be sent out of a SIAD.
The similar sending and receiving restriction as defined in
Section 6.2.1 is also needed.
8. IANA Considerations
8.1. 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.
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8.2. 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".
8.3. 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".
9. Security Considerations
This document introduces the SIAD that is the scope of a SL. The SLC
and SI MUST NOT be signaled and distributed outside one SIAD. BGP
based SLC and SI distribution is controlled by SL_SESSION
configuration. Improper configuration on both ends of an EBGP
connection could result in the SLC and SI being passed from one SIAD
to another. This would likely result in potential SI conflicts.
To prevent packets carrying SL/SLI from leaking from one SIAD to
another, the SIAD boundary nodes SHOULD deploy some policies (e.g.,
ACL) to filter out the packets. Specifically, in the sending end,
the SIAD boundary node SHOULD filter out the packets that carry the
SLI and are sent to other SIADs; in the receiving end, the SIAD
boundary node SHOULD drop the packets that carry the SLI and are from
other SIADs.
10. 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 ,
Curtis Villamizar, Eric Osborne, Eric Rosen, Yimin Shen, Lizhong Jin,
Ross Callon and Yakov Rekhter for their review, suggestion and
comments to this document.
11. References
11.1. Normative References
[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.
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[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.
[RFC7274] Kompella, K., Andersson, L., and A. Farrel, "Allocating
and Retiring Special-Purpose MPLS Labels", RFC 7274, June
2014.
11.2. Informative References
[I-D.chen-isis-source-identifier-distribution]
Chen, M. and G. Mirsky, "Extensions to ISIS for Source
Identifier Distribution", draft-chen-isis-source-
identifier-distribution-00 (work in progress), October
2014.
[I-D.chen-ospf-source-identifier-distribution]
Chen, M. and G. Mirsky, "Extensions to OSPF for Source
Identifier Distribution", draft-chen-ospf-source-
identifier-distribution-00 (work in progress), October
2014.
[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.
[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.
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[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.
[RFC5065] Traina, P., McPherson, D., and J. Scudder, "Autonomous
System Confederations for BGP", RFC 5065, August 2007.
[RFC5331] Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream
Label Assignment and Context-Specific Label Space", RFC
5331, August 2008.
[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.
[RFC6428] Allan, D., Swallow Ed. , G., and J. Drake Ed. , "Proactive
Connectivity Verification, Continuity Check, and Remote
Defect Indication for the MPLS Transport Profile", RFC
6428, 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
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Zhenbin Li
Huawei
Email: lizhenbin@huawei.com
Luyuan Fang
Microsoft
Email: lufang@microsoft.com
Greg Mirsky
Ericsson
Email: Gregory.mirsky@ericsson.com
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