Network Working Group Luca Martini (Ed.)
Internet Draft Cisco Systems Inc.
Expires: June 2014
Intended status: Standards Track Matthew Bocci (Ed.)
Updates: 6073 Florin Balus (Ed.)
Alcatel-Lucent
December 2, 2013
Dynamic Placement of Multi-Segment Pseudowires
draft-ietf-pwe3-dynamic-ms-pw-20.txt
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Abstract
RFC5254 describes the service provider requirements for extending the
reach of pseudowires (PW) across multiple Packet Switched Network
domains. A Multi-Segment PW is defined as a set of two or more
contiguous PW segments that behave and function as a single point-
to-point PW. This document describes extensions to the PW control
protocol to dynamically place the segments of the multi-segment
pseudowire among a set of Provider Edge (PE) routers. This document
also updates RFC6073 as follows: it updates the
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value of the length field of the PW Switching Point PE Sub-TLV Type
0x06 to 14.
Table of Contents
1 Introduction ......................................... 3
1.1 Scope ................................................ 3
1.2 Specification of Requirements ........................ 3
1.3 Terminology .......................................... 3
1.4 Architecture Overview ................................ 4
2 Applicability ........................................ 5
2.1 Changes to Existing PW Signaling ..................... 5
3 PW Layer 2 Addressing ................................ 5
3.1 Attachment Circuit Addressing ........................ 6
3.2 S-PE Addressing ...................................... 7
4 Dynamic Placement of MS-PWs .......................... 7
4.1 Pseudowire Routing Procedures ........................ 7
4.1.1 AII PW Routing Table Lookup Aggregation Rules ........ 8
4.1.2 PW Static Route ...................................... 8
4.1.3 Dynamic Advertisement with BGP ....................... 9
4.2 LDP Signaling ........................................ 10
4.2.1 Equal Cost Multi Path (ECMP) in PW Routing ........... 12
4.2.2 Active/Passive T-PE Election Procedure ............... 12
4.2.3 Detailed Signaling Procedures ........................ 13
5 Failure Handling Procedures .......................... 14
5.1 PSN Failures ......................................... 14
5.2 S-PE Specific Failures ............................... 15
5.3 PW Reachability Changes .............................. 15
6 Operations and Maintenance (OAM) ..................... 16
7 Security Considerations .............................. 16
8 IANA Considerations .................................. 17
8.1 Corrections .......................................... 17
8.2 LDP TLV TYPE NAME SPACE .............................. 17
8.3 LDP Status Codes ..................................... 17
8.4 BGP SAFI ............................................. 17
9 References ........................................... 18
9.1 Normative References ................................. 18
9.2 Informative References ............................... 18
10 Major Co-authors ..................................... 19
11 Acknowledgements ..................................... 19
12 Author's Addresses ................................... 19
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1. Introduction
1.1. Scope
[RFC5254] describes the service provider requirements for extending
the reach of pseudowires across multiple Packet Switched Network
(PSN) domains. This is achieved using a Multi-Segment Pseudowire
(MS-PW). An MS-PW is defined as a set of two or more contiguous PW
segments that behave and function as a single point-to-point PW. This
architecture is described in [RFC5659].
The procedures for establishing PWs that extend across a single PSN
domain are described in [RFC4447], while procedures for setting up
PWs across multiple PSN domains, or control plane domains are
described in [RFC6073].
The purpose of this document is to specify extensions to the
pseudowire control protocol [RFC4447], and [RFC6073] procedures, to
enable multi-segment PWs to be dynamically placed. The procedures
follow the guidelines defined in [RFC5036] and enable the reuse of
existing TLVs, and procedures defined for SS-PWs in [RFC4447].
Dynamic placement of point-to-multipoint (P2MP) PWs is for further
study and outside the scope of this document.
1.2. Specification of Requirements
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.
1.3. Terminology
[RFC5659] provides terminology for multi-segment pseudowires.
This document defines the following additional terms:
- Source Terminating Provider Edge (ST-PE). A Terminating Provider
Edge (T-PE), which assumes the active signaling role and
initiates the signaling for multi-segment PW.
- Target Terminating Provider Edge (TT-PE). A Terminating Provider
Edge (T-PE) that assumes the passive signaling role. It waits and
responds to the multi-segment PW signaling message in the reverse
direction.
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- Forward Direction: ST-PE to TT-PE.
- Reverse Direction: TT-PE to ST-PE.
- Pseudowire Routing (PW routing): The dynamic placement of the
segments that compose an MS-PW, as well as the automatic
selection of S-PEs.
1.4. Architecture Overview
The following figure shows the reference model, derived from
[RFC5659], to support PW emulated services using multi-segment PWs.
Native |<-------------Pseudowire------------>| Native
Service | | Service
(AC) | |<-PSN1-->| |<-PSN2-->| | (AC)
| V V V V V V |
| +-----+ +-----+ +-----+
+----+ | |T-PE1|=========|S-PE1|=========|T-PE2| | +----+
| |-------|.....PW.Seg't1........PW.Seg't3......|----------| |
| CE1| | | | | | | | | |CE2 |
| |-------|.....PW.Seg't2.......|PW.Seg't4......|----------| |
+----+ | | |=========| |=========| | | +----+
^ +-----+ +-----+ +-----+ ^
| Provider Edge 1 ^ Provider Edge 2 |
| | |
| | |
| PW switching point |
| |
|<---------------- Emulated Service -------------------->|
Figure 1: MS-PW Reference Model
T-PE1 and T-PE2 provide an emulated service to Customer Edge (CE) CE1
and CE2. These Provider Edge (PE) nodes reside in different PSNs. A
PSN tunnel extends from T-PE1 to S-PE1 across PSN1, and a second PSN
tunnel extends from S-PE1 to T-PE2 across PSN2. PWs are used to
connect the attachment circuits (ACs) attached to T-PE1 to the
corresponding AC attached to T-PE2. A PW segment on the tunnel across
PSN1 is connected to a PW segment in the tunnel across PSN2 at S-PE1
to complete the multi-segment PW (MS-PW) between T-PE1 and T-PE2. S-
PE1 is therefore the PW switching point and is referred to as the
switching provider edge (S-PE). PW Segment 1 and PW Segment 3 are
segments of the same MS-PW while PW Segment 2 and PW Segment 4 are
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segments of another MS-PW. PW segments of the same MS-PW (e.g., PW
segment 1 and PW segment 3) MUST be of the same PW type, and PSN
tunnels (e.g., PSN1 and PSN2) can be of the same or a different
technology. An S-PE switches an MS-PW from one segment to another
based on the PW identifiers ( PWid, or Attachment Individual
Identifier (AII)). How the PW protocol data units (PDUs) are switched
at the S-PE depends on the PSN tunnel technology: in case of a
multiprotocol label switching (MPLS) PSN to another MPLS PSN, PW
switching involves a standard MPLS label swap operation.
Note that although Figure 1 only shows a single S-PE, a PW may
transit more than one S-PE along its path. For instance, in the
multi-provider case, there can be an S-PE at the border of one
provider domain and another S-PE at the border of the other provider
domain.
2. Applicability
This document describes the case where the PSNs carrying the MS-PW
are only MPLS PSNs using the Generalized PWID FEC element (also known
as FEC129). Interactions with an IP PSN using L2TPv3 as described in
[RFC6073] section 7.4 are for further study.
2.1. Changes to Existing PW Signaling
The procedures described in this document make use of existing LDP
TLVs and related PW signaling procedures described in [RFC4447] and
[RFC6073]. The following optional TLV is also defined:
- A Bandwidth TLV to address QoS Signaling requirements (see
Section 6.2.1).
This document also updates the value of the length field of the PW
Switching Point PE Sub-TLV Type 0x06 to 14.
3. PW Layer 2 Addressing
Single segment pseudowires on an MPLS PSN can use attachment circuit
identifiers for a PW using FEC 129. In the case of a dynamically
placed MS-PW, there is a requirement for the attachment circuit
identifiers to be globally unique, for the purposes of reachability
and manageability of the PW. Referencing figure 1 above, individual
globally unique addresses MUST be allocated to all the ACs and S-PEs
of an MS-PW.
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3.1. Attachment Circuit Addressing
The attachment circuit addressing is derived from [RFC5003] AII type
2, shown here:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type=02 | Length | Global ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global ID (contd.) | Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix (contd.) | AC ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AC ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: AII Type 2 TLV Structure
The fields are defined in [RFC5003], Section 3.2.
AII type 2 based addressing schemes permit varying levels of AII
summarization, thus reducing the scaling burden on PW routing. AII
Type 2 based PW addressing is suitable for point-to-point
provisioning models where auto-discovery of the address at the Target
T-PE is not required. That is, it is known a-priori by provisioning.
Implementations of the following procedure MUST interpret the AII
type to determine the meaning of the address format of the AII,
irrespective of the number of segments in the MS-PW. All segments of
the PW MUST be signaled with same AII Type.
A unique combination of Global ID, Prefix, and AC ID parts of the AII
type 2 are assigned to each AC. In general, the same global ID and
prefix are be assigned for all ACs belonging to the same T-PE. This
is not a strict requirement, however. A particular T-PE might have
more than one prefix assigned to it, and likewise a fully qualified
AII with the same Global ID/Prefix but different AC IDs might belong
to different T-PEs.
For the purpose of MS-PWs, the AII MUST be globally unique across all
PSNs that are spanned by the MS-PW.
The AII for a local attachement circuit of a given T-PE of an MS-PW
and the AII of the corresponding attachment circuit on a far-end T-PE
(with respect to the LDP signaling) are known as the Source
Attachment Individual Identifier (SAII) and Target Attachment
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Individual Identifier (TAII) as per [RFC6074].
3.2. S-PE Addressing
Each S-PE MUST be assigned an address which uniquely identifies it
from a pseudowire perspective, in order to populate the Switching
Point PE (SP-PE) TLV specified in [RFC6073]. For this purpose, at
least one Attachment Identifier (AI) address of the format similar to
AII type 2 [RFC5003] composed of the Global ID, and Prefix part,
only, MUST be assigned to each S-PE.
If an S-PE is capable of Dynamic MS-PW signaling, but is not assigned
with an S-PE address, then on receiving a Dynamic MS-PW label mapping
message the S-PE MUST return a Label Release with the
"LDP_RESOURCES_UNAVAILABLE" ( 0x38)" status code.
4. Dynamic Placement of MS-PWs
[RFC6073] describes a procedure for concatenating multiple
pseudowires together. This procedure requires each S-PE to be
manually configured with the information required for each segment of
the MS-PW. The procedures in the following sections describe a method
to extend [RFC6073] by allowing the automatic selection of pre-
defined S-PEs, and dynamically establishing a MS-PW between two T-
PEs.
4.1. Pseudowire Routing Procedures
The AII type 2 described above contains a Global ID, Prefix, and AC
ID. The Target Attachment Individual Identifier (TAII) is used by S-
PEs to determine the next SS-PW destination for LDP signaling.
Once an S-PE receives a MS-PW label mapping message containing a TAII
with an AII that is not locally present, the S-PE performs a lookup
in a PW AII routing table. If this lookup results in an IP address
for the next-hop PE with reachability information for the AII in
question, then the S-PE will initiate the necessary LDP messaging
procedure to set-up the next PW segment. If the PW AII routing table
lookup does not result in a IP address for a next-hop PE, the
destination AII has become unreachable, and the PW setup MUST fail.
In this case the next PW segment is considered un-provisioned, and a
label release MUST be returned to the T-PE with a status message of
"AII Unreachable".
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If the TAI of a MS-PW label mapping message received by a PE contains
the prefix matching a locally-provisioned prefix on that PE, but an
AC ID that is not provisioned, then the LDP liberal label retention
procedures apply, and the label mapping message is retained.
To allow for dynamic end-to-end signaling of MS-PWs, information must
be present in S-PEs to support the determination of the next PW
signaling hop. Such information can be provisioned (equivalent to a
static route) on each S-PE, or disseminated via regular routing
protocols (e.g. BGP).
4.1.1. AII PW Routing Table Lookup Aggregation Rules
All PEs capable of dynamic MS-PW path selection MUST build a PW AII
routing table to be used for PW next-hop selection.
The PW addressing scheme (AII type 2 in [RFC5003]) consists of a
Global ID, a 32 bit prefix and a 32 bit Attachment Circuit ID.
An aggregation scheme similar to that used for classless IPv4
addresses can be employed. An (8 bits) length mask is specified as a
number ranging from 0 to 96 that indicates which Most Significant
Bits (MSB) are relevant in the address field when performing the PW
address matching algorithm.
0 31 32 63 64 95 (bits)
+-----------+--------+--------+
| Global ID | Prefix | AC ID |
+-----------+--------+--------+
Figure 3: PW Addressing Scheme
During the signaling phase, the content of the (fully qualified) TAII
type 2 field from the FEC129 TLV is compared against routes from the
PW Routing table. Similar with the IPv4 case, the route with the
longest match is selected, determining the next signaling hop and
implicitly the next PW Segment to be signaled.
4.1.2. PW Static Route
For the purpose of determining the next signaling hop for a segment
of the pseudowire, the PEs MAY be provisioned with fixed route
entries in the PW next hop routing table. The static PW entries will
follow all the addressing rules and aggregation rules described in
the previous sections. The most common use of PW static provisioned
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routes is this example of the "default" route entry as follows:
Global ID = 0 Prefix = 0 AC ID = 0 , Prefix Length = 0 Next Signaling
Hop = {IP Address of next hop S-PE or T-PE}
4.1.3. Dynamic Advertisement with BGP
Any suitable routing protocol capable of carrying external routing
information MAY be used to propagate MS-PW path information among S-
PEs and T-PEs. However, T-PEs and S-PEs MAY choose to use Border
Gateway Protocol (BGP) [RFC4271] with the Multiprotocol Extensions as
defined in [RFC4760] to propagate PW address information throughout
the PSN.
Contrary to layer 2 VPN signaling methods that use BGP [RFC6074] for
auto discovery, in the case of the dynamically placed MS-PW, the
source T-PE knows a-priori (by provisioning) the AC ID on the
terminating T-PE that signaling should use. Hence there is no need to
advertise a "fully qualified" 96 bit address on a per PW Attachment
Circuit basis. Only the T-PE Global ID, Prefix, and prefix length
needs to be advertised as part of well known BGP procedures - see
[RFC4760].
Since PW Endpoints are provisioned in the T-PEs, the ST-PE will use
this information to obtain the first S-PE hop (i.e., first BGP next
hop) to where the first PW segment will be established. Any
subsequent S-PEs will use the same information (i.e. the next BGP
next-hop(s)) to obtain the next-signaling-hop(s) on the path to the
TT-PE.
The PW dynamic path Network Layer Reachability Information (NLRI) is
advertised in BGP UPDATE messages using the MP_REACH_NLRI and
MP_UNREACH_NLRI attributes [RFC4760]. The {AFI, SAFI} value pair used
to identify this NLRI is (AFI=25, SAFI=6 (pending IANA allocation)).
A route target MAY also be advertised along with the NLRI.
The Next Hop field of the MP_REACH_NLRI attribute SHALL be
interpreted as an IPv4 address, whenever the length of the NextHop
address is 4 octets, and as a IPv6 address, whenever the length of
the NextHop address is 16 octets.
The NLRI field in the MP_REACH_NLRI and MP_UNREACH_NLRI is a prefix
comprising an 8-octet Route Distinguisher, the Global ID, the Prefix,
and the AC-ID, and encoded as defined in section 4 of [RFC4760].
This NLRI is structured as follows:
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Bit
0 7 8 71 72 103 104 135 136 167
+------+----------------+-----------+--------+--------+
|Length| Route Dist | Global ID | Prefix | AC ID |
+------+----------------+-----------+--------+--------+
Figure 4: NLRI Field Structure
The Length field is the prefix length of the Route Distinguisher +
Global ID + Prefix + AC-ID in bits.
Except for the default PW route, which is encoded as a 0 length
prefix, the minimum value of the length field is 96 bits. Lengths of
128 bits to 159 bits are invalid as the AC ID field cannot be
aggregated. The maximum value of the Length field is 160 bits. BGP
advertisements received with invalid prefix lengths MUST be rejected
as having a bad packet format.
4.2. LDP Signaling
The LDP signaling procedures are described in [RFC4447] and expanded
in [RFC6073]. No new LDP signaling components are required for
setting up a dynamically placed MS-PW. However, some optional
signaling extensions are described below.
One of the requirements that MUST be met in order to enable the QoS
objectives for a PW to be achieved on a segment is that a PSN tunnel
MUST be selected that can support at least the required class of
service and that has sufficient bandwidth available.
Such PSN tunnel selection can be achieved where the next hop for a PW
segment is explicitly configured at each PE, whether the PE is a T-PE
or an S-PE in the case of a segmented PW, without dynamic path
selection (as per RFC6073). In these cases, it is possible to
explicitly configure the bandwidth required for a PW so that the T-PE
or S-PE can reserve that bandwidth on the PSN tunnel.
Where dynamic path selection is used and therefore the next-hop is
not explicitly configured by the operator at the S-PE, a mechanism is
required to signal the bandwidth for the PW from the T-PE to the S-
PEs. This is accomplished by including an optional PW Bandwidth TLV.
The PW Bandwidth TLV is specified 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0| PW BW TLV (0x096E) | TLV Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Forward SENDER_TSPEC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reverse SENDER_TSPEC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: PW Bandwidth TLV Structure
The PW Bandwidth TLV fields are as follows:
- TLV Length: The length of the value fields in octets. Value = 64
- Forward SENDER_TSPEC = The SENDER_TSPEC for the forward direction
of the PW, as defined in [RFC2210] section 3.1.
- Reverse SENDER_TSPEC = The SENDER_TSPEC for the reverse direction
of the PW, as defined in [RFC2210] section 3.1.
The complete definitions of the content of the SENDER_TSPEC objects
are found in [RFC2210] section 3.1. The forward SENDER_TSPEC refers
to the data path in the direction of ST-PE to TT-PE. The reverse
SENDER_TSPEC refers to the data path in the direction TT-PE to ST-PE.
In the forward direction, after a next hop selection is determined, a
T/S-PE SHOULD reference the forward SENDER_TSPEC object to determine
an appropriate PSN tunnel towards the next signaling hop. If such a
tunnel exists, the MS-PW signaling procedures are invoked with the
inclusion of the PW Bandwidth TLV. When the PE searches for a PSN
tunnel, any tunnel which points to a next hop equivalent to the next
hop selected will be included in the search (the LDP address TLV is
used to determine the next hop equivalence)
When an S/T-PE receives a PW Bandwidth TLV, once the PW next hop is
selected, the S/T-PE MUST request the appropriate resources from the
PSN. The resources described in the reverse SENDER_TSPEC are
allocated from the PSN toward the originator of the message or
previous hop. When resources are allocated from the PSN for a
specific PW, the SHOULD account for the usage of the resources by the
PW.
In the case where PSN resources towards the previous hop are not
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available, the following procedure MUST be followed:
-i. The PSN MAY allocate more QoS resources, e.g. Bandwidth, to
the PSN tunnel.
-ii. The S-PE MAY attempt to setup another PSN tunnel to
accommodate the new PW QoS requirements.
-iii. If the S-PE cannot get enough resources to setup the segment
in the MS-PW a label release MUST be returned to the
previous hop with a status message of "Bandwidth resources
unavailable"
In the latter case, the T-PE receiving the status message MUST also
withdraw the corresponding PW label mapping for the opposite
direction if it has already been successfully setup.
If an ST-PE receives a label mapping message the following procedure
MUST be followed:
If the ST-PE has already sent a label mapping message for this PW
then the ST-PE MUST check that this label mapping message originated
from the same LDP peer to which the corresponding label mapping
message for this particular PW was sent. If it is the same peer, the
PW is established. If it is a different peer, then the ST-PE MUST
send a label release message, with a status code of "Duplicate AII"
to the PE that originate the LDP label mapping message.
If the PE has not yet sent a label mapping message for this
particular PW , then it MUST send the label mapping message to this
LDP peer, regardless of what the PW TAII routing lookup result is.
4.2.1. Equal Cost Multi Path (ECMP) in PW Routing
A next hop selection for a specific PW may find a match with a PW
route that has multiple next hops associated with it. Multiple next
hops may be either configured explicitly as static routes or may be
learned through BGP routing procedures. Implementations at an S-PE or
T-PE MAY use selection algorithms, such as CRC32 on the FEC TLV, or
flow-aware transport PW [RFC6391], for load balancing of PWs across
multiple next-hops. The details of such selection algorithms are
outside the scope of this document.
4.2.2. Active/Passive T-PE Election Procedure
When a MS-PW is signaled, each T-PE might independently initiate
signaling the MS-PW. This could result in a different path being used
be each direction of the PW. To avoid this situation one T-PE MUST
initiate PW signaling (i.e. take an active role), while the other T-
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PE waits to receive the LDP label mapping message before sending the
LDP label mapping message for the reverse direction of the PW (i.e.
take a passive role). The Active T-PE (the ST-PE) and the Passive T-
PE (the TT-PE) MUST be identified before signaling begins for a given
MS-PW.
A T-PE SHOULD determine whether it assumes the active role or the
passive role using procedures similar to those of [RFC5036] Section
2.5.2, Bullet 2. The T-PE compares the Source Attachment Individual
Identifier (SAII) [RFC6074] with the Target Attachment Individual
Identifier (TAII) [RFC6074] as unsigned integers, and if the SAII >
TAII, the T-PE assumes the active role. Otherwise it assumes the
passive role.
The following procedure for comparing the SAII and TAII as unsigned
integers SHOULD be used:
- If the SAII Global ID > TAII Global ID, then the T-PE is active
- else if the SAII Prefix > TAII Prefix, then the T-PE is active
- else if the SAII AC-ID > TAII AC-ID, then the T-PE is active
- else the T-PE is passive.
4.2.3. Detailed Signaling Procedures
On receiving a label mapping message, the S-PE MUST inspect the FEC
TLV. If the receiving node has no local AII matching the TAII for
that label mapping then the label mapping message should be forwarded
on to another S-PE or T-PE. The S-PE will check if the FEC is already
installed for the forward direction:
- If it is already installed, and the received mapping was received
from the same LDP peer to which the forward LDP label mapping was
sent, then this label mapping represents signaling in the reverse
direction for this MS-PW segment.
- If it is already installed, and the received mapping was received
from a different LDP peer to which the forward LDP label mapping
was sent, then the received label mapping MUST be released with
the status code of "PW_LOOP_DETECTED".
- If the FEC is not already installed, then this represents
signaling in the forward direction.
For the forward direction:
-i. Determine the next hop S-PE or T-PE according to the
procedures above. If next-hop reachability is not found in
the PW AII routing table in the S-PE then label release MUST
be sent with status code "AII_UNREACHABLE". If the next-hop
S-PE or T-PE is found and is the same LDP Peer that has sent
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the label mapping message then a label Release MUST be
returned with the status code "PW_LOOP_DETECTED". If the
SAII in the received label mapping is local to the S-PE then
a label released MUST be returned with status code
"PW_LOOP_DETECTED".
-ii. Check that a PSN tunnel exists to the next hop S-PE or T-PE.
If no tunnel exists to the next hop S-PE or T-PE the S-PE
MAY attempt to setup a PSN tunnel.
-iii. Check that a PSN tunnel exists to the previous hop. If no
tunnel exists to the previous hop S-PE or T-PE the S-PE MAY
attempt to setup a PSN tunnel.
-iv. If the S-PE cannot get enough PSN resources to setup the
segment to the next or previous S-PE or T-PE, a label
release MUST be returned to the T-PE with a status message
of "Resources Unavailable".
-v. If the label mapping message contains a Bandwidth TLV,
allocate the required resources on the PSN tunnels in the
forward and reverse directions according to the procedures
above.
-vi. Allocate a new PW label for the forward direction.
-vii. Install the FEC for the forward direction.
-viii. Send the label mapping message with the new forward label
and the FEC to the next hop S-PE/T-PE.
For the reverse direction:
-i. Install the received FEC for the reverse direction.
-ii. Determine the next signaling hop by referencing the LDP
sessions used to setup the PW in the Forward direction.
-iii. Allocate a new PW label for the reverse direction.
-iv. Install the FEC for the reverse direction.
-v. Send the label mapping message with a new label and the FEC
to the next hop S-PE/ST-PE.
5. Failure Handling Procedures
5.1. PSN Failures
Failures of the PSN tunnel MUST be handled by PSN mechanisms. An
example of such a PSN mechanism is MPLS fast reroute [RFC4090]. If
the PSN is unable to re-establish the PSN tunnel, then the S-PE
SHOULD follow the procedures defined in Section 8 of [RFC6073].
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5.2. S-PE Specific Failures
For defects in an S-PE, the procedures defined in [RFC6073] SHOULD be
followed. A T-PE or S-PE may receive an unsolicited label release
message from another S-PE or T-PE with various failure codes such
"LOOP_DETECTED", "PW_LOOP_DETECTED", "RESOURCE_UNAVAILBALE",
"BAD_STRICT_HOP", "AII_UNREACHABLE", etc. All these failure codes
indicate a generic class of PW failures at an S-PE or T-PE.
When an unsolicited label release message with such a failure status
code is received at T-PE then the T-PE MUST re-attempt to establish
the PW immediately. However the T-PE MUST throttle its PW setup
message retry attempts with an exponential backoff in situations
where PW setup messages are being constantly released. It is also
recommended that a T-PE detecting such a situation take action to
notify an operator.
S-PEs that receive an unsolicited label release message with a
failure status code should follow the following procedures:
-i. If the label release is received from an S-PE or T-PE in the
forward signaling direction then the S-PE MUST tear down
both segments of the PW. The status code received in the
label release message SHOULD be propagated when sending the
label release for the next-segment.
-ii. If the label release is received from an S-PE or T-PE in the
reverse signaling direction, then then tear down both
segments of the PW as described in i.
5.3. PW Reachability Changes
In general an established MS-PW will not be affected by next-hop
changes in L2 PW reachability information.
If there is a change in next-hop of the L2 PW reachability
information in the forward direction, the T-PE MAY elect to tear down
the MS-PW by sending a label withdraw message to downstream S-PE or
T-PE. The teardown MUST be also accompanied by a unsolicited label
release message, and will be followed by and attempt to re-establish
of the MS-PW by T-PE.
If there is a change in the L2 PW reachability information in the
forward direction at S-PE, the S-PE MAY elect to tear down the MS-PW
in both directions. A label withdrawal is sent on each direction
followed by a unsolicited label release. The unsolicited label
releases MUST be accompanied by the Status code "AII_UNREACHABLE".
This procedure is OPTIONAL.
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A change in L2 reachability information in the reverse direction has
no effect on an MS-PW.
6. Operations and Maintenance (OAM)
The OAM procedures defined in [RFC6073] may be used also for MS-PWs.
A PW switching point PE TLV is used [RFC6073] to record the switching
points that the PW traverses.
In the case of a MS-PW where the PW Endpoints are identified though
using a globally unique, FEC 129-based AII addresses, there is no
PWID defined on a per segment basis. Each individual PW segment is
identified by the address of adjacent S-PE(s) in conjunction with the
SAI and TAI. In this case, the following TLV type (0x06) MUST be used
in place of type 0x01 in the PW switching point PE TLV:
Type Length Description
0x06 14 L2 PW address of PW Switching Point
The above field MUST be included together with type 0x02 in the TLV
once per individual PW Switching Point following the same rules and
procedures as described in [RFC6073]. A more detailed description of
this field is also in setion 7.4.1 of [RFC6073]. However, the length
value MUST be set to 14.
7. Security Considerations
This document specifies only extensions to the protocols already
defined in [RFC4447], and [RFC6073]. The extensions defined in this
document do not affect the security considerations for those
protocols. Note that the protocols for dynamically distributing PW
Layer 2 reachability information may have their own security issues,
however those protocols specifications are outside the scope of this
document.
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8. IANA Considerations
8.1. Corrections
IANA is requested to correct a minor error in the registry
"Pseudowire Switching Point PE sub-TLV Type". The entry 0x06 "L2 PW
address of the PW Switching Point" should have Length 14.
8.2. LDP TLV TYPE NAME SPACE
This document defines one new LDP TLV types. IANA already maintains a
registry for LDP TLV types called "Type, Length, and Value (TLV)
Type Name Space" within the "Label Distribution Protocol (LDP)
Parameters" as defined by RFC5036. IANA is requested to assign on
permanent basis the value (0x096E) that has been assigned to this
document by early allocation (TEMPORARY - Expires 2008-11-21).:
Value Description Reference Notes/Registration Date
------+----------------+---------------+-----------------------
0x096E Bandwidth TLV This document
8.3. LDP Status Codes
This document defines three new LDP status codes. IANA maintains a
registry of these called the "STATUS CODE NAME SPACE" in the "Label
Distribution Protocol (LDP) Parameters" as defined by RFC5036. The
IANA is requested to assign on permanent basis the values that has
been assigned to this document by early allocation
(TEMPORARY - Expires 2008-11-21):
Range/Value E Description Reference
------------- ----- ---------------------- ---------
0x00000037 0 Bandwidth resources unavailable This document
0x00000038 0 Resources Unavailable This document
0x00000039 0 AII Unreachable This document
8.4. BGP SAFI
IANA needs to allocate a new BGP SAFI for "Network Layer Reachability
Information used for Dynamic Placement of Multi-Segment Pseudowires"
from the IANA "Subsequence Address Family Identifiers (SAFI)"
registry. The IANA is requested to assign on permanent basis the
values that has been assigned to this document by early allocation
(TEMPORARY - Expires 2008-11-21)::
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Value Description Reference
----- ----------- ---------
6 Network Layer Reachability Information used This document
for Dynamic Placement of Multi-Segment
Pseudowires
9. References
9.1. Normative References
[RFC6073] Martini et.al. "Segmented Pseudowire", RFC6073,
January 2011
[RFC2210] Wroclawski, J. "The Use of RSVP with IETF Integrated
Services", RFC 2210, September 1997
[RFC5036] Andersson, Minei, Thomas. "LDP Specification"
RFC5036, October 2007
[RFC4447] "Pseudowire Setup and Maintenance Using the Label
Distribution Protocol (LDP)", Martini L.,et al, RFC 4447,
June 2005.
[RFC5003] "Attachment Individual Identifier (AII) Types for
Aggregation", Metz, et al, RFC5003, September 2007
9.2. Informative References
[RFC5254] Martini et al, "Requirements for Multi-Segment Pseudowire
Emulation Edge-to-Edge (PWE3)",
RFC5254, Bitar, Martini, Bocci, October 2008
[RFC5659] Bocci at al, "An Architecture for Multi-Segment Pseudo Wire
Emulation Edge-to-Edge", RFC5659,October 2009.
[RFC4760] Bates, T., Rekhter, Y., Chandra, R. and D. Katz,
"Multiprotocol Extensions for BGP-4", RFC 4760, January 2007.
[RFC6074] E. Rosen, W. Luo, B. Davie, V. Radoaca,
"Provisioning, Autodiscovery, and Signaling in L2VPNs",
RFC6074, January 2011
[RFC4271] Rekhter, Y., et al, "A Border Gateway Protocol 4 (BGP-4)",
RFC4271, January 2006
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Internet Draft draft-ietf-pwe3-dynamic-ms-pw-20.txt December 2, 2013
[RFC6391] Bryant, S., et al, "Flow-Aware Transport of Pseudowires
over an MPLS Packet Switched Network", RFC6391, November 2011
[RFC4090] Pan, P., et al, "Fast Reroute Extensions to RSVP-TE for LSP
Tunnels", RFC4090, May 2005
10. Major Co-authors
The editors gratefully acknowledge the following additional co-
authors: Mustapha Aissaoui, Nabil Bitar, Mike Loomis, David McDysan,
Chris Metz, Andy Malis, Jason Rusmeisel, Himanshu Shah, Jeff
Sugimoto.
11. Acknowledgements
The editors also gratefully acknowledge the input of the following
people: Mike Duckett, Paul Doolan, Prayson Pate, Ping Pan, Vasile
Radoaca, Yeongil Seo, Yetik Serbest, Yuichiro Wada.
12. Author's Addresses
Luca Martini
Cisco Systems, Inc.
9155 East Nichols Avenue, Suite 400
Englewood, CO, 80112
e-mail: lmartini@cisco.com
Matthew Bocci
Alcatel-Lucent,
Voyager Place
Shoppenhangers Road
Maidenhead
Berks, UK
e-mail: matthew.bocci@alcatel-lucent.com
Florin Balus
Alcatel-Lucent
701 E. Middlefield Rd.
Mountain View, CA 94043
e-mail: florin.balus@alcatel-lucent.com
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Nabil Bitar
Verizon
40 Sylvan Road
Waltham, MA 02145
e-mail: nabil.bitar@verizon.com
Himanshu Shah
Ciena Corp
35 Nagog Park,
Acton, MA 01720
e-mail: hshah@ciena.com
Mustapha Aissaoui
Alcatel-Lucent
600 March Road
Kanata
ON, Canada
e-mail: mustapha.aissaoui@alcatel-lucent.com
Jason Rusmisel
Alcatel-Lucent
600 March Road
Kanata
ON, Canada
e-mail: Jason.rusmisel@alcatel-lucent.com
Yetik Serbest
AT&T Labs
9505 Arboretum Blvd.
Austin, TX 78759
e-mail: yetik.serbest@labs.att.com
Andrew G. Malis
Verizon
117 West St.
Waltham, MA 02451
e-mail: andrew.g.malis@verizon.com
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Internet Draft draft-ietf-pwe3-dynamic-ms-pw-20.txt December 2, 2013
Chris Metz
Cisco Systems, Inc.
3700 Cisco Way
San Jose, Ca. 95134
e-mail: chmetz@cisco.com
David McDysan
Verizon
22001 Loudoun County Pkwy
Ashburn, VA, USA 20147
e-mail: dave.mcdysan@verizon.com
Jeff Sugimoto
Alcatel-Lucent
701 E. Middlefield Rd.
Mountain View, CA 94043
e-mail: jeffery.sugimoto@alcatel-lucent.com
Mike Duckett
ATT
Lindbergh Center D481
575 Morosgo Dr
Atlanta, GA 30324
e-mail: md9308@att.com
Mike Loomis
Alcatel-Lucent
701 E. Middlefield Rd.
Mountain View, CA 94043
e-mail: mike.loomis@alcatel-lucent.com
Paul Doolan
Coriant GmbH & Co. KG
St Martin Str. 76
81541 Munich
e-mail: paul.doolan@coriant.com
Ping Pan
Infinera
e-mail: ppan@infinera.com
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Prayson Pate
Overture Networks, Inc.
507 Airport Blvd, Suite 111
Morrisville, NC, USA 27560
e-mail: prayson.pate@overturenetworks.com
Vasile Radoaca
Alcatel-Lucent
388 NINGQIAO RD
PUDONG JINQIAO
SHANGHAI 201206
CHINA
email: vasile.radoaca@alcatel-lucent.com
Yuichiro Wada
NTT
3-9-11 Midori-cho
Musashino-shi
Tokyo 180-8585
Japan
e-mail: wada.yuichiro@lab.ntt.co.jp
Yeong-il Seo
Korea Telecom Corp.
463-1 Jeonmin-dong, Yusung-gu
Daejeon, Korea
e-mail: yohan.seo@kt.com
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
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
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.
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Internet Draft draft-ietf-pwe3-dynamic-ms-pw-20.txt December 2, 2013
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Expiration Date: June 2014
Martini, et al. [Page 23]