MultiProtocol Label Switching (MPLS) Source Label
draft-chen-mpls-source-label-01
The information below is for an old version of the document.
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| Authors | Mach Chen , Xiaohu Xu , Zhenbin Li , Luyuan Fang | ||
| Last updated | 2013-10-21 | ||
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draft-chen-mpls-source-label-01
Network Working Group M. Chen
Internet-Draft X. Xu
Intended status: Standards Track Z. Li
Expires: April 24, 2014 Huawei
L. Fang
Cisco
October 21, 2013
MultiProtocol Label Switching (MPLS) Source Label
draft-chen-mpls-source-label-01
Abstract
An MultiProtocol Label Switching (MPLS) label is 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
information from the label. For some applications, source
identification is a critical requirement. For example, performance
monitoring, traffic matrix measurement and collection, 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
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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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.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Problem Statement and Introduction . . . . . . . . . . . . . 3
2. Source Label . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Performance Measurement . . . . . . . . . . . . . . . . . 5
3.2. Traffic Matrix Measurement and Steering . . . . . . . . . 5
3.3. Source Filtering . . . . . . . . . . . . . . . . . . . . 6
4. Data Plane Processing . . . . . . . . . . . . . . . . . . . . 6
4.1. Ingress LSR . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Transit LSR . . . . . . . . . . . . . . . . . . . . . . . 7
4.3. Egress LSR . . . . . . . . . . . . . . . . . . . . . . . 7
4.4. Penultimate Hop LSR . . . . . . . . . . . . . . . . . . . 7
5. Source Label Signaling . . . . . . . . . . . . . . . . . . . 7
5.1. Source Label Capability Signaling . . . . . . . . . . . . 7
5.1.1. LDP Extensions . . . . . . . . . . . . . . . . . . . 8
5.1.2. BGP Extensions . . . . . . . . . . . . . . . . . . . 8
5.1.3. RSVP-TE Extensions . . . . . . . . . . . . . . . . . 9
5.2. Source Label Distribution . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6.1. Source Label Indication . . . . . . . . . . . . . . . . . 10
6.2. LDP Source Label Capability TLV . . . . . . . . . . . . . 10
6.3. BGP Source Label Capability Attribute . . . . . . . . . . 10
6.4. RSVP-TE Source Label Capability . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Problem Statement and Introduction
An MultiProtocol Label Switching (MPLS) label [RFC3031] is originally
defined for packet forwarding and assumes the forwarding/destination
address semantics. As no source address information is carried in
the label stack, there is no way to directly derive the source
address 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)
LSPs that are established by the Resource Reservation Protocol
Traffic Engineering (RSVP-TE) [RFC3209] and Pseudowires (PWs) belong
to P2P or P2MP types. LSPs that are established by the classic Label
Distribution Protocol (LDP) [RFC5036], Layer 3 Private Network
(L3VPN) and Virtual Local Area Network (VPLS) LSPs belong to MP2P or
MP2MP types.
For those LSPs belong to the MP2P and MP2MP types, it is not possible
to derive the source address information from the label. For the P2P
or P2MP LSPs, the source address information may be implicitly
derived from the label (e.g., P2P or P2MP LSPs established by RSVP-
TE) , but it requires that some further information is used (e.g.,
control plane information). However, this is not always possible for
all P2P LSPs. One example is the Multi-Segment Pseudowire (MS-PW),
it is impossible to derive the source address information from the PW
label. Because an MS-PW label assumes the forwarding and destination
address semantics which is quite different from the source address
semantics that a Single-Segment Pseudowire (SS-PW) label assumes.
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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 address information, i.e., a Source Label (SL). 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, traffic matrix
measurement and collection is the precondition of traffic steering,
and capable of traffic steering is an important requirement of
Software Defined Network (SDN). To measure and collect traffic
matrix information, the source address information is necessary.
In addition, Segment Routing [I-D.filsfils-rtgwg-segment-routing]
also explicitly points out that there are requirements to preserve
the ingress information to fulfill the accounting and billing
purposes.
This document introduces the concept of a Source Label. A SL
uniquely identifies a node within an administrative domain, it is
carried in the label stack and used to identify the ingress LSR(s) of
an LSP.
2. 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 (ingress node identifier), 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 are not used
for forwarding.
There are several solutions that can be used to make sure the
uniqueness of the MPLS Source Label. A direct thought is use the
"Global" label, this is proposed in
[I-D.filsfils-rtgwg-segment-routing]. Since the MPLS does not define
/support "Global" label, this may require architecture modifications
to the MPLS. The second way is to use the Domain Wide Label that is
proposed in [I-D.raszuk-mpls-domain-wide-labels] . The third solution
is to use the Label Block idea that is defined in [RFC4761].
In addition, in order to indicate whether a label is a source label,
a Source Label Indicator (SLI) is introduced. The SLI is a reserved
label 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 a source label. The value of SLI is TBD1.
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3. Use Cases
3.1. Performance Measurement
There are two typical 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 for the active performance measurement.
In passive performance measurement, no artificial traffic is injected
into the flow and measurements are taken to record the performance
metrics of the real traffic. The Multiprotocol Label Switching
(MPLS) PM protocol [RFC6374] for packet loss is an example of passive
performance measurement. 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 a source label in the label stack, and then the
egress LSR can use the source label for packets identifying and
counting.
3.2. Traffic Matrix Measurement and Steering
A Traffic Matrix (TM) provides, for every ingress node (i) into the
network and every egress node (j) out of the network, the volume of
traffic T(i,j) from i to j over a given time interval.
Since the ingress node knows the source and destination of the
traffic, it's normal to measure the traffic matrix at every ingress
node. But in some scenarios, it may need to measure the traffic at
the egress or intermediate nodes. Taking Figure 1 as an example,
from the west to east point of view, there are three ingress nodes
(I1, I2 and I3) and three egress nodes (E1, E2 and E3), A, B and C
are intermediate nodes. It is not necessary to measure the traffic
matrix of the whole network all the time, it sometimes just wants to
know the received traffic matrix of a specific egress node (e.g.,
E2). So, to measure received traffic matrix at node E2 would be then
a better choice.
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In addition, for an intermediate node (e.g., A), it may need to
measure the transmitted traffic hence to steer some traffic from the
congestion path to idle path.
Wherever at egress or intermediate node, source identification is
necessary. The ingress LSR can put the source label into the label
stack to help the egress and intermediate LSR to identify and measure
the traffic.
+--+
|I1|
+--+ +--+ +---+
\ /|B |----|E1 |
\ / +--+ +---+
\ / \
\ / \
\ / \+--+
+--+ \+--+ /|E2 |
|I2|--------/|A | / +--+
+--+ / +--+ /
/ \ /
/ \+--+/ +--+
/ |C |-----|E3|
+--+/ +--+ +--+
|I3|
+--+
Figure 1: Traffic Matrix Measurement and Steering
3.3. Source Filtering
Network Ingress Filtering [RFC2827] is an important tool to defeat
DoS attacks and is widely deployed. In the past, since there is no
source information carried in the stack, it's impossible to perform
source filtering. With the Source Label, it enables to filter the
packets with specific Source Label.
4. Data Plane Processing
4.1. Ingress LSR
For an LSP, the ingress LSR MUST make sure that the egress LSR is
able to process the Source Label before inserting a SL and SLI into
the label stack. Therefore, an egress LSR SHOULD signal (see
Section 5.1) 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.
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When a SL to be included in a label stack, the steps are as follows:
1. Push the SL label, the Bos bit for the SL depends on whether the
SL is the bottom label;
2. Push the SLI, the TTL and TC field for the SLI SHOULD 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 pair
is related to an LSP. For an LSP, only one pair of SLI and SL SHOULD
be inserted.
4.2. Transit LSR
There is no change in forwarding behavior for transit LSRs. But if a
transit LSR can recognize the SLI, it may use the SL to collect
traffic throughput and/or measure the performance of the LSP.
4.3. Egress LSR
When an egress LSR receives a packet with a SLI/SL pair, if the
egress LSR is able to process the SL; it pops the LSP label (if
have), SLI and SL; then processes remaining packet header as normal.
If the egress LSR is not able to process the SL, the packet SHOULD be
dropped.
4.4. Penultimate Hop LSR
There is no change in forwarding behavior for the penultimate hop
LSR.
5. Source Label Signaling
Source label signaling includes two aspects: one is source label
capability signaling, the other is source label distribution.
5.1. Source Label Capability Signaling
Before inserting a source label in the label stack, an ingress LSR
MUST 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].
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5.1.1. 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.
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). 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.
5.1.2. BGP Extensions
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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.
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.
5.1.3. RSVP-TE Extensions
Source label support is signaled in RSVP-TE [RFC3209] using the
Source Label Capability (SLC) flag in the Attribute Flags TLV of the
LSP_ATTRIBUTES object [RFC5420]. The presence of the SLC flag in a
Path message indicates that the ingress can process entropy 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 entropy labels in
the downstream direction. The bit number for the SLC flag is TBD4.
5.2. Source Label Distribution
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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 a mechanism to distribute the
mapping information between an ingress LSR and its Source Label. For
example, defines extensions to LDP, BGP, RSVP-TE and/or Interior
Gateway Protocol (IGP) to distribute to source label. The source
label distribution will be defined in future revision or another
document.
6. IANA Considerations
6.1. Source Label Indication
IANA is required to allocate a reserved label (TBD1) for the Source
Label Indicator (SLI) from the "Multiprotocol Label Switching
Architecture (MPLS) Label Values" Registry.
6.2. LDP Source Label Capability TLV
IANA is required 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".
6.3. BGP Source Label Capability Attribute
IANA is required to allocate a Path Attribute Type Code TBD3 from the
"BGP Path Attributes" registry as the "BGP Source Label Capability
Attribute".
6.4. RSVP-TE Source Label Capability
IANA is required 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
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7. Security Considerations
This document does not introduce extra security issues. On the
contrary, with the Source Label carried in the stack, it may bring
additional security enhancement that enables an LSR to perform source
label based checking and/or filtering.
8. 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 for
their review, suggestion and comments to this document.
9. References
9.1. 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.
[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.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
[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.
9.2. Informative References
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[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-00 (work in progress), June 2013.
[I-D.raszuk-mpls-domain-wide-labels]
Raszuk, R., "MPLS Domain Wide Labels", draft-raszuk-mpls-
domain-wide-labels-00 (work in progress), July 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.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC4761] Kompella, K. and Y. Rekhter, "Virtual Private LAN Service
(VPLS) Using BGP for Auto-Discovery and Signaling", RFC
4761, January 2007.
[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
Cisco
Email: luyuanf@gmail.com
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