Internet DRAFT - draft-ietf-pwe3-dynamic-ms-pw
draft-ietf-pwe3-dynamic-ms-pw
Network Working Group Luca Martini (Ed.)
Internet Draft Cisco Systems Inc.
Expires: September 2014
Intended status: Standards Track Matthew Bocci (Ed.)
Updates: 6073 Florin Balus (Ed.)
Alcatel-Lucent
March 10, 2014
Dynamic Placement of Multi-Segment Pseudowires
draft-ietf-pwe3-dynamic-ms-pw-22.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 ................................ 6
3.1 Attachment Circuit Addressing ........................ 6
3.2 S-PE Addressing ...................................... 7
4 Dynamic Placement of MS-PWs .......................... 7
4.1 Pseudowire Routing Procedures ........................ 8
4.1.1 AII PW Routing Table Lookup Aggregation Rules ........ 8
4.1.2 PW Static Route ...................................... 9
4.1.3 Dynamic Advertisement with BGP ....................... 9
4.2 LDP Signaling ........................................ 11
4.2.1 Multiple Alternative Paths in PW Routing ............. 13
4.2.2 Active/Passive T-PE Election Procedure ............... 13
4.2.3 Detailed Signaling Procedures ........................ 14
5 Failure Handling Procedures .......................... 15
5.1 PSN Failures ......................................... 15
5.2 S-PE Specific Failures ............................... 16
5.3 PW Reachability Changes .............................. 16
6 Operations and Maintenance (OAM) ..................... 17
7 Security Considerations .............................. 17
8 IANA Considerations .................................. 18
8.1 Corrections .......................................... 18
8.2 LDP TLV TYPE NAME SPACE .............................. 18
8.3 LDP Status Codes ..................................... 19
8.4 BGP SAFI ............................................. 19
9 References ........................................... 19
9.1 Normative References ................................. 19
9.2 Informative References ............................... 20
10 Contributors ......................................... 20
11 Acknowledgements ..................................... 21
12 Author's Addresses ................................... 21
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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
pseudowire (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 Single-Segment Pseudowires
(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 |<------Multi-Segment Pseudowire------>| Native
Service | PSN PSN | Service
(AC) | |<-Tunnel->| |<-Tunnel->| | (AC)
| V V 1 V V 2 V V |
| +----+ +-----+ +----+ |
+----+ | |TPE1|===========|SPE1 |==========|TPE2| | +----+
| |------|..... PW.Seg't1....X....PW.Seg't3.....|-------| |
| CE1| | | | | | | | | |CE2 |
| |------|..... PW.Seg't2....X....PW.Seg't4.....|-------| |
+----+ | | |===========| |==========| | | +----+
^ +----+ +-----+ +----+ ^
| Provider Edge 1 ^ Provider Edge 2 |
| | |
| | |
| PW switching point |
| |
|<------------------ Emulated Service --------------->|
Figure 1: MS-PW Reference Model
The PEs that provide services to CE1 and CE2 are Terminating PE1 (T-
PE1) and Terminating PE2 (T-PE2), respectively. A PSN tunnel extends
from T-PE1 to Switching PE1 (S-PE1), and a second PSN tunnel extends
from S-PE1 to T-PE2 . PWs are used to connect the attachment
circuits (ACs) attached to PE1 to the corresponding ACs attached to
T-PE2.
A PW segment on PSN Tunnel 1 is connected to a PW segment on PSN
Tunnel 2 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
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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 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 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. Although RFC5659 [RFC5659]
describes MS-PWs that span more than one PSN, this document does not
specify how the LDP PW control protocol [RFC4447] is used in an
inter-AS environment.
2. Applicability
This document describes the case where the PSNs carrying the MS-PW
are only MPLS PSNs using the Generalized Pseudowire Identifier (PWID)
Forwarding Equivalence Class (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.
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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.
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
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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
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.
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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".
If the TAII 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.
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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
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. PW address information is only propagated by PEs that are
capable of PW switching. Therefore, the multiprotocol BGP neighbor
topology MUST coincide with the topology of T-PEs and S-PEs.
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].
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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:
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.
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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:
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.
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- 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
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
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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 originated 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. Multiple Alternative Paths 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, so that each PW has a single next hop. 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-
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. Both T-PEs MUST use the same method for identifying which is
Active and which is Passive.
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 Global ID < TAII Global ID then the T-PE is
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passive
- else if the SAII Prefix > TAII Prefix, then the T-PE is
active
- else if the SAII Prefix < TAII Prefix, then the T-PE is
passive
- else if the SAII AC-ID > TAII AC-ID, then the T-PE is
active
- else if the SAII AC-ID < TAII AC-ID, then the T-PE is
passive
- else there is a configuration error
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 the FEC is already installed, and the received Label 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 the FEC is already installed, and the received Label 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.
The following procedures are then executed, depending on whether the
Label Mapping was determined to be for the forward or the reverse
direction of the MS-PW.
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 S-PE's PW AII routing table then a 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 sent 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
Release MUST be returned with status code
"PW_LOOP_DETECTED".
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-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 hop 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 FEC received int he Label Mapping message 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 next hop in the reverse
direction.
-iv. Install the FEC for the next hop in 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 10 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.
If an unsolicited Label Release message with such a failure status
code is received at T-PE, then it is RECOMMENDED that the T-PE
attempt to re-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 or reverse 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.
5.3. PW Reachability Changes
In general an established MS-PW will not be affected by next-hop
changes in AII reachability information.
If there is a change in next-hop of the AII 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 AII 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. Note that this procedure is likely to be
disruptive to the emulated service. PW Redundancy [RFC6718] MAY be
used to maintain the connectivity used by the emulated service in the
case of a failure of the PSN or S-PE.
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A change in AII 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
dynamically placed 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
pseudowire identifier (PWID) defined on a per-segment basis. Each
individual PW segment is identified by the address of the adjacent
S-PE(s) in conjunction with the SAII and TAII.
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 sub-TLV MUST be included in the Switching Point PE TLV once
per individual PW Switching Point following the same rules and
procedures as described in [RFC6073]. A more detailed description of
this sub-TLV is also given in setion 7.4.1 of [RFC6073]. However, the
length value MUST be set to 14 (RFC6073 states that the length value
is 12, but this does not correctly represent the actual length of the
TLV).
7. Security Considerations
This document specifies 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, but
[RFC4447] and [RFC6073] do impose a set of security considerations
that are applicable to the protocol extensions specified in this
document.
It should be noted that the dynamic path selection mechanisms
specified in this document enable the network to automatically select
the S-PEs that are used to forward packets on the MS-PW. Appropriate
tools, such as the VCCV Trace mechanisms specified in [RFC6073], can
be used by an operator of the network to verify the path taken by the
MS-PW and satisfy themselves that it does not represent an additional
security risk.
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Note that the PW control protocol may be used to establish and
maintain an MS-PW across administrative boundaries. Section 13 of
[RFC6073] specifies security considerations applicable to LDP used in
this manner, including considerations on establishing the integrity
of, and authenticating, LDP control messages. This considerations
also apply to the protocol extensions specified in this document.
Note that the protocols for dynamically distributing AII reachability
information may have their own security considerations. However those
protocols specifications are outside the scope of this document.
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 and the
reference changed to [RFC6073] and [RFC-to-be] as follows:
Type Length Description Reference --
-----+---
---+------------------------------------+-------------------------
0x06 14 L2 PW Address of PW Switching Point [RFC6073] and
[RFC-to-be]
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
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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)::
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
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[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
[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
[RFC6718] Muley, P., et al, "Pseudowire Redundancy", RFC6718, August
2012
10. Contributors
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.
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11. Acknowledgements
The editors also gratefully acknowledge the input of the following
people: Mike Duckett, Paul Doolan, Pranjal Dutta, 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
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
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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
Andrew G. Malis
Huawei
2330 Central Expressway
Santa Clara CA 95050
e-mail: agmalis@gmail.com
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
Martini, et al. [Page 22]
Internet Draft draft-ietf-pwe3-dynamic-ms-pw-22.txt March 10, 2014
Mike Loomis
Alcatel-Lucent
701 E. Middlefield Rd.
Mountain View, CA 94043
e-mail: mike.loomis@alcatel-lucent.com
Copyright Notice
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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
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Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
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not be created outside the IETF Standards Process, except to format
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than English.
Expiration Date: September 2014
Martini, et al. [Page 23]
