TICTOC Working Group S. Davari
Internet-Draft A. Oren
Intended status: Standards Track Broadcom Corp.
Expires: July 30, 2011 L. Martini
Cisco Systems
M. Bhatia
P. Roberts
Alcatel-Lucent
January 26, 2011
Transporting PTP messages (1588) over MPLS Networks
draft-ietf-tictoc-1588overmpls-00
Abstract
This document defines the method for transporting PTP messages (PDUs)
over an MPLS network to enable a proper handling of these packets
(e.g. implementation of Transparent Clocks (TC)) in LSRs.
The basic idea is to transport PTP messages inside dedicated MPLS
LSPs. These LSPs only carry PTP messages and possibly Control and
Management packets, but they do not carry customer traffic.
Two methods for transporting 1588 over MPLS are defined. The first
method is to transport PTP messages directly over the dedicated MPLS
LSP via UDP/IP encapsulation, which is suitable for IP/MPLS networks.
The second method is to transport PTP messages inside a PW via
Ethernet encapsulation, which is more suitable for MPLS-TP networks.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 30, 2011.
Copyright Notice
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Copyright (c) 2011 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
carefully, as they describe your rights and restrictions with respect
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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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 9
4. Dedicated LSPs for PTP messages . . . . . . . . . . . . . . . 10
5. 1588 over MPLS Encapsulation . . . . . . . . . . . . . . . . . 11
5.1. 1588 over LSP Encapsulation . . . . . . . . . . . . . . . 11
5.2. 1588 over PW Encapsulation . . . . . . . . . . . . . . . . 11
5.3. 1588 over pure MPLS mode . . . . . . . . . . . . . . . . . 13
6. 1588 Message Transport . . . . . . . . . . . . . . . . . . . . 14
7. Protection and Redundancy . . . . . . . . . . . . . . . . . . 16
8. ECMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
9. OAM, Control and Management . . . . . . . . . . . . . . . . . 18
10. QoS Considerations . . . . . . . . . . . . . . . . . . . . . . 19
11. FCS Recalculation . . . . . . . . . . . . . . . . . . . . . . 20
12. UDP Checksum Correction . . . . . . . . . . . . . . . . . . . 21
13. Routing extensions for 1588aware LSRs . . . . . . . . . . . . 22
13.1. 1588aware Node Capability for OSPF . . . . . . . . . . . . 22
13.2. 1588aware Node Capability for IS-IS . . . . . . . . . . . 23
14. RSVP-TE Extensions for support of 1588 . . . . . . . . . . . . 26
15. Distributing PW labels . . . . . . . . . . . . . . . . . . . . 27
15.1. LDP extensions for distributing PW labels . . . . . . . . 27
15.2. BGP extensions for distributing PW labels . . . . . . . . 27
16. Behavior of LER/LSR . . . . . . . . . . . . . . . . . . . . . 28
16.1. Behavior of 1588-aware LER . . . . . . . . . . . . . . . . 28
16.2. Behavior of 1588-aware LSR . . . . . . . . . . . . . . . . 28
16.3. Behavior of non-1588-aware LSR . . . . . . . . . . . . . . 28
17. Other considerations . . . . . . . . . . . . . . . . . . . . . 30
18. Security Considerations . . . . . . . . . . . . . . . . . . . 31
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19. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
19.1. IANA Considerations for OSPF . . . . . . . . . . . . . . . 32
19.2. IANA Considerations for IS-IS . . . . . . . . . . . . . . 32
19.3. IANA Considerations for RSVP . . . . . . . . . . . . . . . 32
20. References . . . . . . . . . . . . . . . . . . . . . . . . . . 33
20.1. Normative References . . . . . . . . . . . . . . . . . . . 33
20.2. Informative References . . . . . . . . . . . . . . . . . . 33
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35
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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 RFC2119 [RFC2119].
When used in lower case, these words convey their typical use in
common language, and are not to be interpreted as described in
RFC2119 [RFC2119].
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1. Introduction
The objective of Precision Time Protocol (PTP) is to synchronize
independent clocks running on separate nodes of a distributed system.
[IEEE] defines PTP messages for clock and time synchronization. The
PTP messages include PTP PDUs over UDP/IP (Annex D & E of [IEEE]) and
PTP PDUs over Ethernet (Annex F of [IEEE]). This document defines
mapping and transport of the PTP messages defined in [IEEE] over MPLS
networks.
PTP defines intermediate clock functions (called transparent clocks)
between the source of time (Master) and the Slave clocks. Boundary
Clocks (BC) form Master-Slave hierarchy with the Master clock as
root. The messages related to synchronization, establishing the
Master-Slave hierarchy, and signaling, terminate in the protocol
engine of a boundary clock and are not forwarded. Management
messages however, are forwarded to other ports on the boundary clock.
Transparent clocks modify a "correction field" (CF) within the
synchronization messages to compensate for residence and propagation
delays. Transparent clocks do not terminate synchronization, Master-
Slave hierarchy control messages or signaling messages.
There is a need to transport PTP messages over MPLS networks. The
MPLS network could be a transit network between 1588 Masters and
Slaves. The accuracy of the recovered clock improves and the Slave
logic simplifies when intermediate nodes (e.g. LSRs) properly handle
PTP messages (e.g. perform TC), otherwise the jitter at the 1588
Slave may be excessive and therefore the Slave may not be able to
properly recover the clock and time of day.
This document defines a "1588-aware LSR" that is able to identify
1588 timing flows carried over MPLS.
Transparent Clock (TC) function requires a 1588-aware LSR in the
middle of an LSP to identify the PTP messages and perform proper
update of the CF, via a 1-step or 2-step process.
More generally this document requires that an LSR should be able to
properly handle the PTP messages. For instance for those cases when
the TC function is not viable (e.g. due to layer violation) as an
alternative it should be possible to instead control the delay for
these messages on both directions across the node.
In the above cases it is beneficial that PTP packets can be easily
identified when carried over MPLS.
This document provides two methods for transporting PTP messages over
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MPLS. The main objectives are for LSRs to be able to
deterministically detect and identify the PTP messages.
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2. Terminology
1588: The timing and synchronization as defined by IEEE 1588
PTP: The timing and synchronization protocol used by 1588
Master: The Source of 1588 Timing and clock
Slave: The Destination of 1588 Timing and clock that tries to follow
the Master clock
OC: Ordinary Clock
TC: Transparent Clock, a time stamping method applied by intermediate
nodes between Master and Slave
BC: Boundary Clock, is a node that recovers the Master clock via a
Slave function and uses that clock as the Master for other Slaves
PTP LSP: An LSP dedicated to carry PTP messages
PTP PW: A PW within a PTP LSP that is dedicated to carry PTP
messages.
CW: Pseudowire Control Word
LAG: Link Aggregation
ECMP: Equal Cost Multipath
CF: Correction Field, a field inside certain PTP messages (message
type 0-3)that holds the accumulative transit time inside intermediate
switches
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3. Problem Statement
When PTP messages are transported over MPLS networks, there is a need
for intermediate LSRs to detect such messages and perform proper
processing (e.g. Transparent Clock (TC)). Note the TC processing
could be in the form of 1-Step or 2-Step time stamping.
PTP messages over Ethernet or IP can always be tunneled over MPLS.
However the 1588 over MPLS mapping defined in this document is
applicable whenever MPLS LSRs are 1588-aware and the intention is for
those LSRs to perform proper processing on these packets.
When 1588-awareness is needed, PTP messages should not be transported
over LSPs or PWs that are carrying customer traffic because LSRs
perform Label switching based on the top label in the stack. To
detect PTP messages inside such LSPs require special Hardware (HW) to
do deep packet inspection at line rate. Even if one assumes a deep
packet inspection HW at line rate exists, the payload can't be
deterministically identified by LSRs because the payload type is a
context of the PW label and the PW label and its context are only
known to the Edge routers (PEs) and LSRs don't know what is a PW's
payload (Ethernet, ATM, FR, CES, etc). Even if one assumes only
Ethernet PWs are permitted in an LSP, the LSRs don't have the
knowledge of whether PW Control Word (CW) is present or not and
therefore can't deterministically identify the payload.
Therefore a generic method is defined in this document that does not
require deep packet inspection at line rate, and can
deterministically identify PTP messages. The defined method is
applicable to both MPLS and MPLS-TP networks.
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4. Dedicated LSPs for PTP messages
Many methods were considered for identifying the 1588 messages when
they are encapsulated in MPLS such as by using GAL/ACH or a new
reserved label. These methods were not attractive since they either
required deep packet inspection and snooping at line rate or they
required use of scarce new reserved label. Also one of the goals was
to reuse existing OAM and protection mechanisms.
The method defined in this document can be used by LSRs to identify
PTP messages in MPLS tunnels by using dedicated LSPs to carry PTP
messages.
Compliant implementations MUST use dedicated LSPs to carry PTP
messages over MPLS. Let's call these LSPs as the "PTP LSPs" and the
labels associated with these LSPs as "PTP labels". These LSPs could
be P2P or P2MP LSPs. The PTP LSP between Master and Slaves MAY be
P2MP or P2P LSP while the PTP LSP between each Slave and Master
SHOULD be P2P LSP. The PTP LSP between a Master and a Slave and the
PTP LSP between the same Slave and Master MUST be co-routed.
Alternatively, a single bidirectional co-routed LSP can be used. The
PTP LSP MAY be MPLS LSP or MPLS-TP LSP.
The PTP LSPs could be configured or signaled via RSVP-TE/GMPLS. New
RSVP-TE/GMPLS TLVs and objects are defined in this document to
indicate that these LSPs are PTP LSPs.
We should be selective about the kind of traffic that flows over PTP
LSPs as these will be handled as a special case by the LSR. The only
LSP user plane traffic MUST be PTP, but the LSP MAY also carry
essential MPLS/MPLS-TP control plane traffic such as BFD and LSP-
Ping.
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5. 1588 over MPLS Encapsulation
This document defines two methods for carrying PTP messages over
MPLS. The first method is carrying IP encapsulated PTP messages over
PTP LSPs and the second method is to carry PTP messages over
dedicated Ethernet PWs (called PTP PWs) inside PTP LSPs.
5.1. 1588 over LSP Encapsulation
The simplest method of transporting PTP messages over MPLS is to
encapsulate PTP PDUs in UDP/IP and then encapsulate them in PTP LSP.
The 1588 over LSP format is shown in Figure 1.
+----------------------+
| PTP Tunnel Label |
+----------------------+
| IPv4/6 |
+----------------------+
| UDP |
+----------------------+
| PTP PDU |
+----------------------+
Figure 1 - 1588 over LSP Encapsulation
This encapsulation is very simple and is useful when the networks
between 1588 Master and Slave are IP/MPLS networks.
In order for an LSR to process PTP messages, the PTP Label must be
the top label of the label stack.
The UDP/IP encapsulation of PTP MUST follow Annex D and E of [IEEE].
5.2. 1588 over PW Encapsulation
Another method of transporting 1588 over MPLS networks is by
encapsulating PTP PDUs in Ethernet and then transporting them over
Ethernet PW (PTP PW) as defined in [RFC4448], which in turn is
transported over PTP LSPs. Alternatively PTP PDUs MAY be
encapsulated in UDP/IP/Ethernet and then transported over Ethernet
PW.
Both Raw and Tagged modes for Ethernet PW are permitted. The 1588
over PW format is shown in Figure 2.
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+----------------+
|PTP Tunnel Label|
+----------------+
| PW Label |
+----------------+
| Entropy Label |
| (optional) |
+----------------+
| Control Word |
+----------------+
| Ethernet |
| Header |
+----------------+
| VLANs |
| (optional) |
+----------------+
| IPV4/V6 |
| (optional) |
+----------------+
| UDP |
| (optional) |
+----------------+
| PTP PDU |
+----------------+
Figure 2 - 1588 over PW Encapsulation
The Control Word (CW) as specified in [RFC4448] SHOULD be used to
ensure a more robust detection of PTP messages inside the MPLS
packet. If CW is used, the use of Sequence number is optional.
The use of VLAN and UDP/IP are optional. Note that 1 or 2 VLANs MAY
exist in the PW payload.
In order for an LSR to process PTP messages, the top label of the
label stack (the Tunnel Label) MUST be from PTP label range. However
in some applications the PW label may be the top label in the stack,
such as cases where there is only one-hop between PEs or in case of
PHP. In such cases, the PW label SHOULD be chosen from the PTP Label
range.
An Entropy label [I-D.ietf-pwe3-fat-pw] MAY be present at the bottom
of stack.
The Ethernet encapsulation of PTP MUST follow Annex F of [IEEE] and
the UDP/IP encapsulation of PTP MUST follow Annex D and E of [IEEE].
For 1588 over MPLS encapsulations that are PW based, there are some
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cases in which the PTP LSP label may not be present:
o When PHP is applied to the PTP LSP, and the packet is received
without PTP LSP label at PW termination point .
o When the PW is established between two routers directly connected
to each other and no PTP LSP is needed.
In such cases it is required for a router to identify these packets
as PTP packets. This would require the PW label to also be a label
that is distributed specifically for carrying PTP traffic (aka PTP PW
label). Therefore there is a need to add extension to LDP/BGP PW
label distribution protocol to indicate that a PW label is a PTP PW
labels.
5.3. 1588 over pure MPLS mode
Editor Note: The encapsulation is general enough and can support
transporting 1588 in a pure MPLS mode (i.e., without any IP/UDP or
Ethernet headers). Should the WG pursue this?
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6. 1588 Message Transport
1588 protocol comprises of the following message types:
o Announce
o SYNC
o FOLLOW UP
o DELAY REQ (Delay Request)
o DELAY RESP (Delay Response)
o PDELAY REQ (Peer Delay Request)
o PDELAY RESP (Peer Delay Response)
o PDELAY RESP FOLLOW UP (Peer Delay Response Follow up)
o Management
o Signaling
A subset of PTP message types that require TC processing are called
Event messages:
o SYNC
o DELAY REQ (Delay Request)
o PDELAY REQ (Peer Delay Request)
o PDELAY RESP (Peer Delay Response)
SYNC and DELAY_REQ are exchanged between Master and Slave and MUST be
transported over PTP LSPs. PDELAY_REQ and PDELAY_RESP are exchanged
between adjacent routers and MAY be transported over single hop PTP
LSPs. If Two Step Transparent clocks are present, then the FOLLOW_UP
and DELAY_RESP messages must also be transported over the PTP LSPs.
For a given instance of 1588 protocol, SYNC and DELAY_REQ MUST be
transported over two PTP LSPs that are in opposite directions. These
PTP LSPs, which are in opposite directions MUST be congruent and co-
routed. Alternatively, a single bidirectional co-routed LSP can be
used.
Except as indicated above for the two-step Transparent clocks, Non-
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Event PTP message types don't need to be processed by intermediate
routers. These message types MAY be carried in PTP Tunnel LSPs.
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7. Protection and Redundancy
In order to ensure continuous uninterrupted operation of 1588 Slaves,
usually as a general practice, Redundant Masters are tracked by each
Slave. It is the responsibility of the network operator to ensure
that physically disjoint PTP tunnels that don't share any link are
used between the redundant Masters and a Slave.
When redundant Masters are tracked by a Slave, any PTP LSP or PTP PW
failure will trigger the slave to switch to the Redundant Master.
However LSP/PW protection such as Linear Protection Switching
(1:1,1+1), Ring protection switching or MPLS Fast Reroute (FRR)
SHOULD still be used to ensure the LSP/PW is ready for a future
failure.
Note that any protection or reroute mechanism that adds additional
label to the label stack, such as Facility Backup Fast Reroute, MUST
ensure that the pushed label is a PTP Label to ensure proper
processing of PTP messages by LSRs in the backup path.
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8. ECMP
To ensure the proper operation of 1588 Slaves, the physical path for
PTP messages from Master to Slave and vice versa must be the same for
all PTP messages listed in section 7 and must not change even in the
presence of ECMP in the MPLS network.
To ensure the forward and reverse paths are the same PTP LSPs and PWs
MUST not be subject to ECMP.
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9. OAM, Control and Management
In order to manage PTP LSPs and PTP PWs, they MAY carry OAM, Control
and Management messages. These control and management messages can
be differentiated from PTP messages via already defined IETF methods.
In particular BFD [RFC5880], [RFC5884] and LSP-Ping [RFC4389]MAY run
over PTP LSPs via UDP/IP encapsulation or via GAL/G-ACH. These
Management protocols are easily identified by the UDP Destination
Port number or by GAL/ACH respectively.
Also BFD, LSP-Ping and other Management messages MAY run over PTP PW
via one of the defined VCCVs (Type 1, 2 or 3) [RFC5085]. In this
case G-ACH, Router Alert Label (RAL), or PW label (TTL=1) are used to
identify such management messages.
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10. QoS Considerations
The PTP messages are time critical and must be treated with the
highest priority. Therefore 1588 over MPLS messages must be treated
with the highest priority in the routers. This can be achieved by
proper setup of PTP tunnels. It is recommended that the PTP LSPs are
setup and marked properly to indicate EF-PHB for the CoS and Green
for drop eligibility.
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11. FCS Recalculation
Ethernet FCS MUST be recalculated at every LSR that performs the TC
processing and FCS retention described in [RFC4720] MUST not be used.
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12. UDP Checksum Correction
For UDP/IP encapsulation mode of 1588 over MPLS, the UDP checksum is
optional when used for IPv4 encapsulation and mandatory in case of
IPv6. When IPv4/v6 UDP checksum is used each 1588-aware LSR must
either incrementally update the UDP checksum after the CF update or
should verify the UDP checksum on reception from upstream and
recalculate the checksum completely on transmission after CF update
to downstream node.
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13. Routing extensions for 1588aware LSRs
MPLS-TE routing relies on extensions to OSPF [RFC2328] [RFC5340] and
IS-IS [ISO] [RFC1195] in order to advertise Traffic Engineering (TE)
link information used for constraint-based routing.
Indeed, it is useful to advertise data plane TE node capabilities,
such as the capability for a router to be 1588-aware. This
capability MUST then be taken into account during path computation to
prefer nodes that advertise themselves as 1588-aware, so that the PTP
LSPs can be properly handled.
For this purpose, the following sections specify extensions to OSPF
and IS-IS in order to advertise 1588 aware capabilities of a node.
Editor Note: There is an open issue on whether we must consider LSRs
that may not want to support PTP on all ports. An example could be
an LSR where a few blades have been upgraded to support PTP
timestamping in silicon. In such cases, routers must explicitly
indicate the ports that are 1588-aware. If the WG agrees about this
then we will need to change the subsequent OSPF and IS-IS sections to
advertise the 1588-aware capability on per port/interface basis,
rather than per node as is current described.
13.1. 1588aware Node Capability for OSPF
This extension makes use of the Router Information (RI) Opaque LSA
defined in [RFC4970]for both OSPFv2 and OSPFv3, by defining a new
OSPF Router Information (RI) TLV - The 1588-aware Capability TLV.
The 1588-aware Capability TLV is OPTIONAL and is defined 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |
+-+-+-+-+-+-+-+-+
Figure 3: 1588-aware Capability TLV
Where:
Type, 16 bits: 1588-aware Capability TLV where the value is TBD
Length, 16 bits: Gives the length of the flags field in octets, and
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is currently set to 1
Flags, 8 bits: The bits are defined least-significant-bit (LSB)
first, so bit 7 is the least significant bit of the flags octet.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Reserved |C|
+-+-+-+-+-+-+-+-+
Figure 4: Flags Format
Correction (C) field Update field, 1 bit: Setting the C bit to 1
indicates that the node is capable of recognizing the PTP event
packets and can compensate for residence time by updating the PTP
packet Correction Field. When this is set to 0, it means that this
node cannot perform the residence time correction but is capable of
performing MPLS frame forwarding of the frames with PTP labels using
a method that support the end to end delivery of accurate timing.
The exact method is not defined herein.
Reserved, 7 bits: Reserved for future use. The reserved bits must be
ignored by the receiver.
The 1588-aware Capability TLV is applicable to both OSPFv2 and
OSPFv3.
The 1588-aware Capability TLV MAY be advertised within an area-local
or autonomous system (AS) scope Router Information (RI) LSA. But the
1588-aware Capability TLV SHOULD NOT be advertised into an area in
more than one RI LSA irrespective of the scope of the LSA.
The flooding scope is controlled by the Opaque LSA type in OSPFv2 and
by the S1 and S2 bits in OSPFv3. For area scope, the 1588-aware
Capability TLV MUST be carried within an OSPFv2 Type 10 RI LSA or an
OSPFv3 RI LSA with the S1 bit set and S2 bit clear. If the flooding
scope is the entire routing domain (AS scope), the 1588-aware
Capability TLV MUST be carried within an OSPFv2 Type 11 RI LSA or
OSPFv3 RI LSA with the S1 bit clear and the S2 bit set.
13.2. 1588aware Node Capability for IS-IS
Generic capability advertisement mechanisms for IS-IS are defined in
[RFC4971]. These allow a router to advertise its capabilities within
an IS-IS area or an entire IS-IS routing domain. This document
defines a new sub-TLV (named the 1588-aware Capability) to be carried
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within the IS-IS Router Capability TLV.
The IS-IS extensions defined in this document allow for discovering
1588-aware nodes within an IS-IS routing domain. Solutions for 1588-
aware nodes discovery across AS boundaries are beyond the scope of
this document, and are for further study.
The format of the IS-IS 1588-aware sub-TLV is identical to the TLV
format used by the Traffic Engineering Extensions to IS-IS [RFC3784].
That is, the TLV is comprised of 1 octet for the type, 1 octet
specifying the TLV length, and a value field. The Length field
defines the length of the value portion in octets.
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: 1588-aware Capability sub-TLV
Where:
Type, 8 bits: 1588-aware Capability sub-TLV where the value is TBD
Length, 8 bits: Gives the length of the flags field in octets, and is
currently set to 1
Flags, 8 bits: The bits are defined least-significant-bit (LSB)
first, so bit 7 is the least significant bit of the flags octet.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Reserved |C|
+-+-+-+-+-+-+-+-+
Figure 6: Flags Format
Correction (C) field Update field, 1 bit: Setting the C bit to 1
indicates that the node is capable of recognizing the PTP event
packets and can compensate for residence time by updating the PTP
packet Correction Field. When this is set to 0, it means that this
node cannot perform the residence time correction but is capable of
performing MPLS frame forwarding of the frames with PTP labels using
a method that support the end to end delivery of accurate timing.
The exact method is not defined herein.
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Reserved, 7 bits: Reserved for future use. The reserved bits must be
ignored by the receiver.
The 1588-aware sub-TLV is optional and is carried within an IS-IS
Capability TLV [RFC4971] to facilitate selection of 1588-aware nodes.
The flooding scope for 1588-aware node information advertised through
IS-IS can be a single L1 area, an L1 area and the L2 sub-domain, or
the entire IS-IS routing domain.
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14. RSVP-TE Extensions for support of 1588
RSVP-TE signaling MAY be used to setup the PTP LSPs. A new RSVP
object is defined to signal that this is a PTP LSP. The OFFSET to
the start of the PTP message header MAY also be signaled.
Implementations can trivially locate the correctionField (CF)
location given this information. The OFFSET points to the start of
the PTP header as a node may want to check the PTP messageType before
it touches the correctionField (CF).
The LSRs that receive and process the RSVP-TE/GMPLS messages MAY use
the OFFSET to locate the start of the PTP message header.
Note that the new object/TLV Must be ignored by LSRs that are not
compliant to this specification.
The new RSVP 1588_PTP_LSP object should be included in signaling PTP
LSPs and is defined as follows:
0 1 2 3
+-------------+-------------+-------------+-------------+
| Length (bytes) | Class-Num | C-Type |
+-------------+-------------+-------------+-------------+
| Offset to locate the start of the PTP message header |
+-------------+-------------+-------------+-------------+
Figure 7: RSVP 1588_PTP_LSP object
The ingress LSR MUST include this object in the RSVP PATH Message.
It is just a normal RSVP path that is exclusively set up for PTP
messages
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15. Distributing PW labels
15.1. LDP extensions for distributing PW labels
TBD
15.2. BGP extensions for distributing PW labels
TBD
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16. Behavior of LER/LSR
16.1. Behavior of 1588-aware LER
A 1588-aware LER advertises it's 1588-awareness via the OSPF
procedure explained in earlier section of this specification. The
1588-aware LER then signals PTP LSPs by including the 1588_PTP_LSP
object in the RSVP-TE signaling.
When a 1588 message is received from a non-MPLS interface, the LER
MUST redirect them to a previously established PTP LSP. When a 1588
over MPLS message is received from an MPLS interface, the processing
is similar to 1588-aware LSR processing.
16.2. Behavior of 1588-aware LSR
1588-aware LSRs are LSRs that understand the 1588_PTP_LSP RSVP object
and can perform 1588 processing (e.g. TC processing).
A 1588-aware LSR advertises it's 1588-awareness via the OSPF
procedure explained in earlier section of this specification.
When a 1588-aware LSR distributes a label for PTP LSP, it maintains
this information. When the 1588-aware LSR receives an MPLS packet,
it performs a label lookup and if the label lookup indicates it is a
PTP label then further parsing must be done to positively identify
that the payload is 1588 and not OAM, BFD or control and management.
Ruling out non-1588 messages can easily be done when parsing
indicates the presence of GAL, ACH or VCCV (Type 1, 2, 3) or when the
UDP port number does not match one of the 1588 UDP port numbers.
After a 1588 message is positively identified in a PTP LSP, the PTP
message type indicates what type of processing (TC) if any is
required. After 1588 processing the packet is forwarded as a normal
MPLS packet to downstream node.
16.3. Behavior of non-1588-aware LSR
It is most beneficial that all LSRs in the path of a PTP LSP be 1588-
aware LSRs. This would ensure the highest quality time and clock
synchronization by 1588 Slaves. However, this specification does not
mandate that all LSRs in path of a PTP LSP be 1588-aware.
Non-1588-aware LSRs are LSRs that either don't have the capability to
process 1588 packets (e.g. TC processing) or don't understand the
1588_PTP_LSP RSVP object.
Non-1588-aware LSRs ignore the RSVP 1588_PTP_LSP object and just
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switch the MPLS packets carrying 1588 messages as data packets and
don't perform any TC processing. However as explained in QoS section
the 1588 over MPLS packets MUST be still be treated with the highest
priority.
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17. Other considerations
The use of Explicit Null (Label= 0 or 2) is acceptable as long as
either the Explicit Null label is the bottom of stack label
(applicable only to UDP/IP encapsulation) or the label below the
Explicit Null label is a PTP label.
The use of Penultimate Hop Pop (PHP) is acceptable as long as either
the PHP label is the bottom of stack label (applicable only to UDP/IP
encapsulation) or the label below the PHP label is a PTP label.
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18. Security Considerations
MPLS PW security considerations in general are discussed in [RFC3985]
and [RFC4447],and those considerations also apply to this document.
An experimental security protocol is defined in [IEEE]. The PTP
security extension and protocol provides group source authentication,
message integrity, and replay attack protection for PTP messages.
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19. IANA Considerations
19.1. IANA Considerations for OSPF
IANA has defined a registry for TLVs carried in the Router
Information LSA defined in [RFC4970]. IANA is requested to assign a
new TLV code-point for the PCED TLV carried within the Router
Information LSA.
Value Sub-TLV References
----- ---------------------- ----------
TBD 1588aware node sub-TLV (this document)
19.2. IANA Considerations for IS-IS
IANA has defined a registry for the sub-TLVs carried in the IS-IS
Router Capability sub-TLVs defined in [RFC4971]. IANA is requested
to assign a new sub-TLV code-point for the 1588aware node sub-TLV
carried within the Router Capability sub-TLV.
Value Sub-TLV References
----- ---------------------- ----------
TBD 1588aware node sub-TLV (this document)
19.3. IANA Considerations for RSVP
IANA is requested to assign a new Class Number for 1588 PTP LSP
object that is used to signal PTP LSPs.
1588 PTP LSP Object
Class-Num of type 11bbbbbb
Suggested value TBD
Defined CType: 1 (1588 PTP LSP)
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20. References
20.1. Normative References
[IEEE] IEEE 1588-2008, "IEEE Standard for a Precision Clock
Synchronization Protocol for Networked Measurement and
Control Systems".
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3985] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-
Edge (PWE3) Architecture", RFC 3985, March 2005.
[RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, April 2006.
[RFC4447] Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G.
Heron, "Pseudowire Setup and Maintenance Using the Label
Distribution Protocol (LDP)", RFC 4447, April 2006.
[RFC4448] Martini, L., Rosen, E., El-Aawar, N., and G. Heron,
"Encapsulation Methods for Transport of Ethernet over MPLS
Networks", RFC 4448, April 2006.
[RFC4720] Malis, A., Allan, D., and N. Del Regno, "Pseudowire
Emulation Edge-to-Edge (PWE3) Frame Check Sequence
Retention", RFC 4720, November 2006.
[RFC5085] Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for
Pseudowires", RFC 5085, December 2007.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, June 2010.
[RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
"Bidirectional Forwarding Detection (BFD) for MPLS Label
Switched Paths (LSPs)", RFC 5884, June 2010.
20.2. Informative References
[I-D.ietf-pwe3-fat-pw]
Bryant, S., Filsfils, C., Drafz, U., Kompella, V., Regan,
J., and S. Amante, "Flow Aware Transport of Pseudowires
over an MPLS PSN", draft-ietf-pwe3-fat-pw-05 (work in
progress), October 2010.
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[ISO] ISO/IEC 10589:1992, "Intermediate system to Intermediate
system routeing information exchange protocol for use in
conjunction with the Protocol for providing the
Connectionless-mode Network Service (ISO 8473)".
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC3784] Smit, H. and T. Li, "Intermediate System to Intermediate
System (IS-IS) Extensions for Traffic Engineering (TE)",
RFC 3784, June 2004.
[RFC4970] Lindem, A., Shen, N., Vasseur, JP., Aggarwal, R., and S.
Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 4970, July 2007.
[RFC4971] Vasseur, JP., Shen, N., and R. Aggarwal, "Intermediate
System to Intermediate System (IS-IS) Extensions for
Advertising Router Information", RFC 4971, July 2007.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008.
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Authors' Addresses
Shahram Davari
Broadcom Corp.
San Jose, CA 95134
USA
Email: davari@broadcom.com
Amit Oren
Broadcom Corp.
San Jose, CA 95134
USA
Email: amito@broadcom.com
Luca Martini
Cisco Systems
San Jose CA
USA
Email: lmartini@cisco.com
Manav Bhatia
Alcatel-Lucent
Bangalore,
India
Email: manav.bhatia@alcatel-lucent.com
Peter Roberts
Alcatel-Lucent
Kanata,
Canada
Email: peter.roberts@alcatel-lucent.com
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