draft-ietf-mpls-ldp-restart-applic-00.txt   draft-ietf-mpls-ldp-restart-applic-01.txt 
Network Working Group Adrian Farrel A new Request for Comments is now available in online RFC libraries.
Internet Draft Movaz Networks
Category: Informational
Expiration Date: August 2003 February 2003
Applicability Statement for Restart Mechanisms for the
Label Distribution Protocol
draft-ietf-mpls-ldp-restart-applic-00.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [RFC2026].
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Abstract
Multiprotocol Label Switching (MPLS) systems will be used in core
networks where system downtime must be kept to a minimum. Similarly,
where MPLS is at the network edges (for example, in Provider Edge
routers) system downtime must also be kept as small as possible.
Many MPLS Label Switching Routers (LSRs) may, therefore, exploit
Fault Tolerant (FT) hardware or software to provide high availability
of the core networks.
The details of how FT is achieved for the various components of an
FT LSR, including the switching hardware and the TCP stack are
implementation specific. How the software module itself chooses to
implement FT for the state created by the Label Distribution Protocol
(LDP) is also implementation specific but there are several issues in
the LDP specification in RFC 3036 "LDP Specification" that make it
difficult to implement an FT LSR using the LDP protocols without some
extensions to those protocols.
Proposals have been made in "Fault Tolerance for the Label
Distribution Protocol (LDP)" [LDP-FT] and "Graceful Restart Mechanism
for LDP" [LDP-RESTART] to address these issues.
This document gives guidance on when it is advisable to implement
some form of LDP restart mechanism and which approach might be more
suitable. The issues and extensions described here are equally
applicable to RFC 3212, "Constraint-Based LSP Setup Using LDP"
(CR-LDP).
1. Requirements of an LDP FT System
MPLS is a technology that will be used in core networks where system
downtime must be kept to an absolute minimum. Similarly, where MPLS
is at the network edges (for example, in PE routers in RFC2547)
system downtime must also be kept as small as possible.
Many MPLS LSRs may, therefore, exploit FT hardware or software to
provide high availability (HA) of core networks.
In order to provide HA, an MPLS system needs to be able to survive a
variety of faults with minimal disruption to the Data Plane,
including the following fault types:
- failure/hot-swap of the switching fabric in an LSR
- failure/hot-swap of a physical connection between LSRs
- failure of the TCP or LDP stack in an LSR
- software upgrade to the TCP or LDP stacks in an LSR.
The first two examples of faults listed above may be confined to the
Data Plane in which case such faults can be handled by providing
redundancy in the Data Plane which is transparent to LDP operating in
the Control Plane. However, the failure of the switching fabric or a
physical link may have repercussions in the Control Plane since
signaling may be disrupted.
The third example may be caused by a variety of events including
processor or other hardware failure, and software failure.
Any of the last three examples may impact the Control Plane and will
require action in the Control Plane to recover. Such action should
be designed to avoid disrupting traffic in the Data Plane. This is
possible because many recent router architectures separate the
Control and Data Planes such that forwarding can continue unaffected
by recovery action in the Control Plane.
In other scenarios, the Data and Control Planes may be impacted by a
fault but the needs of HA require the coordinated recovery of the
Data and Control Planes to state that existed before the fault.
The provision of protection paths for MPLS LSP and the protection of
links, IP routes or tunnels through the use of protection LSPs is
outside the scope of this document. See [MPLS-RECOV] for further
information on this subject.
2. General Considerations
In order that the Data and Control Plane states may be successfully
recovered after a fault, procedures are required to ensure that the
state held on a pair of LDP peers (at least one of which was affected
directly by the fault) are synchronized. Such procedures must be
implemented in the Control Plane software modules on the peers using
Control Plane protocols.
The required actions may be operate fully after the failure
(reactive recovery) or may contain elements that operate before the
fault in order to minimize the actions taken after the fault
(proactive recovery). It is rarely feasible to implement actions that
operate solely in advance of the failure and do not require any
further processing after the failure (preventive recovery) - this is
because of the dynamic nature of signaling protocols and the
unpredictability of fault timing.
Reactive recovery actions may include full re-signaling of state,
re-synchronization of state between peers and synchronization based on
checkpointing.
Proactive recovery actions may include hand-shaking state transitions
and checkpointing.
3. Specific Issues with the LDP Protocol
LDP uses TCP to provide reliable connections between LSRs over which
to exchange protocol messages to distribute labels and to set up
LSPs. A pair of LSRs that have such a connection are referred to as
LDP peers.
TCP enables LDP to assume reliable transfer of protocol messages.
This means that some of the messages do not need to be acknowledged
(for example, Label Release).
LDP is defined such that if the TCP connection fails, the LSR should
immediately tear down the LSPs associated with the session between
the LDP peers, and release any labels and resources assigned to those
LSPs.
It is notoriously hard to provide a Fault Tolerant implementation of
TCP. To do so might involve making copies of all data sent and
received. This is an issue familiar to implementers of other TCP
applications such as BGP.
During failover affecting the TCP or LDP stacks, therefore, the TCP
connection may be lost. Recovery from this position is made worse by
the fact that LDP control messages may have been lost during the
connection failure. Since these messages are unconfirmed, it is
possible that LSP or label state information will be lost.
The solution to this problem must at the very least include a change
to the basic requirements of LDP so that the failure of an LDP
session does not require that associated LDP or forwarding state be
torn down.
Any changes made to LDP in support of recovery processing must meet
the following requirements:
- offer backward-compatibility with LSRs that do not implement the
extensions to LDP
- preserve existing protocol rules described in [RFC3036] for
handling unexpected duplicate messages and for processing
unexpected messages referring to unknown LSPs/labels.
Ideally, any solution applicable to LDP should be equally applicable
to CR-LDP.
4. Summary of the Features of LDP FT
LDP Fault Tolerance extensions are described in [LDP-FT]. This
approach involves:
- negotiation between LDP peers of the intent to support extensions
to LDP that facilitate recovery from failover without loss of LSPs
- selection of FT survival on a per LSP/label basis or for all labels
on a session
- sequence numbering of LDP messages to facilitate acknowledgement
and checkpointing
- acknowledgement of LDP messages to ensure that a full handshake is
performed on those messages either frequently (such as per message)
or less frequently as in checkpointing
- solicitation of up-to-date acknowledgement (checkpointing) of
previous LDP messages to ensure the current state is secured, with
an additional option that allows an LDP partner to request that
state is flushed in both directions if graceful shutdown is
required
- a timer to control for how long LDP and forwarding state should
be retained after LDP session failure before being discarded if
LDP communications are not re-established
- exchange of checkpointing information on LDP session recovery to
establish what state has been retained by recovering LDP peers
- re-issuing lost messages after failover to ensure that LSP/label
state is correctly recovered after reconnection of the LDP session.
The FT procedures in [LDP-FT] concentrate on the preservation of
label state for labels exchanged between a pair of adjacent LSRs when
the TCP connection between those LSRs is lost. There is no intention
within these procedures to support end-to-end protection for LSPs.
5. Summary of the Features of LDP Graceful Restart
LDP graceful restart extensions are defined in [LDP-RESTART]. This
approach involves:
- negotiation between LDP peers of the intent to support extensions
to LDP that facilitate recovery from failover without loss of LSPs
- a mechanism whereby an LSR that restarts can relearn LDP state
by resynchronization with its peers
- use of the same mechanism to allow LSRs recovering from an LDP
session failure to resynchronize LDP state with their peers
provided that at least one of the LSRs has retained state across
the failure or has itself resynchronized state with its peers
- a timer to control for how long LDP and forwarding state should
be retained after LDP session failure before being discarded if
LDP communications are not re-established
- a timer to control the length of the period during which
resynchronization of state between adjacent peers should be
completed
The procedures in [LDP-RESTART] are applicable to all LSRs, both
those with the ability to preserve forwarding state during LDP
restart and those without. An LSRs that can not preserve its MPLS
forwarding state across the LDP restart would impact MPLS traffic
during restart, but by implementing a subset of the mechanisms in
[LDP-RESTART] it can minimize the impact if their neighbor(s) are
capable of preserving their forwarding state across the restart of
their LDP sessions or control planes by implementing the mechanism
in [LDP-RESTART].
6. Applicability Considerations
This section considers the applicability of fault tolerance schemes
within LDP networks and considers issues that might lead to the
choice of one method or another. Many of the points raised below
should be viewed as implementation issues rather than specific
drawbacks of either solution.
6.1 General Applicability
The procedures described in [LDP-FT] and [LDP-RESTART] are intended
to cover two distinct scenarios. In Session Failure the LDP peers at
the ends of a session remain active, but the session fails and is
restarted. Note that session failure does not imply failure of the
data channel even when using an in-band control channel. In Node
Failure the session fails because one of the peers has been restarted
(or at least, the LDP component of the node has been restarted).
These two scenarios have different implications for the ease of
retention of LDP state within an individual LSR, and are described in
sections below.
These techniques are only applicable in LDP networks where at least
one LSR has the capability to retain LDP signaling state and the
associated forwarding state across LDP session failure and recovery.
In [LDP-RESTART] the LSRs retaining state do not need to be adjacent
to the failed LSR or session.
If traffic is not to be impacted, both LSRs at the ends of an LDP
session must at least preserve forwarding state. Preserving LDP state
is not a requirement to preserve traffic.
[LDP-FT] requires that the LSRs at both ends of the session implement
the procedures that is describes. Thus, either traffic is preserved
and recovery resynchronizes state, or no traffic is preserved and the
LSP fails.
Further, to use the procedures of [LDP-FT] to recover state on a
session both LSRs must have a mechanism for maintaining some
session state and a way of auditing the forwarding state and the
resynhcronized control state.
[LDP-RESTART] is scoped to support preservation of traffic if both
LSRs implement the procedures that it describes. Additionally, it
functions if only one LSR on the failed session supports retention of
forwarding state, and implements the mechanisms in the document - in
this case traffic will be impacted by the session failure, but the
forwarding state will be recovered on session recovery. Further, in
the event of simultaneous failures, [LDP-RESTART] is capable of
relearning and redistributing state across multiple LSRs by combining
its mechanisms with the usual LDP message exchanges of [RFC 3036].
6.2 Session Failure
In Session Failure an LDP session between two peers fails and is
restarted. There is no restart of the LSRs at either end of the
session and LDP continues to function on those nodes.
In these cases, it is simple for LDP implementations to retain LDP
state associated with the failed session and to associate the state
with the new session when it is established. Housekeeping may be
applied to determine that the failed session is not returning and to
release the old LDP state. Both [LDP-FT] and [LDP-RESTART] handle
this case.
Applicability of [LDP-FT] and [LDP-RESTART] to the Session Failure
scenario should be considered with respect to the availability of the
data plane.
In some cases the failure of the LDP session may be independent of
any failure of the physical (or virtual) link(s) between adjacent
peers; for example, it might represent a failure of the TCP/IP stack.
In these cases the data plane is not impacted and both [LDP-FT] and
[LDP-RESTART] are applicable to preserve or restore LDP state.
LDP signaling may also operate out of band; that is, it may use
different links from the data plane. In this case, a failure of the
LDP session may be a result of a failure of the control channel, but
there is no implied failure of the data plane. For this scenario
[LDP-FT] and [LDP-RESTART] are both applicable to preserve or restore
LDP state.
In the case where the failure of the LDP session also implies the
failure of the data plane it may be an implementation decision
whether LDP peers retain forwarding state, and for how long. In such
situations, if forwarding state is retained, and if the LDP session
is re-established, both [LDP-FT] and [LDP-RESTART] are applicable to
preserve or restore LDP state.
When the data plane has been disrupted an objective of a recovery
implementation might be to restore data traffic as quickly as
possible.
6.3 Controlled Session Failure
In some circumstances the LSRs may know in advance that an LDP
session is going fail - perhaps a link is going to be taken out of
service.
[RFC 3036] includes provision for controlled shutdown of a session.
[LDP-FT] and [LDP-RESTART] allow resynchronization of LDP state upon
re-establishment of the session.
[LDP-FT] offers the facility to both checkpoint all state before the
shut-down, and to quiesce the session so that no new state changes
are attempted between the checkpoint and the shut-down. This means
that on recovery, resynchronization is simple and fast.
[LDP-RESTART] resynchronizes all state on recovery regardless of the
nature of the shut-down.
6.4 Node Failure
Node Failure describes events where a whole node is restarted or
where the component responsible for LDP signaling is restarted. Such
an event will be perceived by the LSR's peers as session failure, but
the restarting node sees the restart as full re-initialization.
The basic requirement is that forwarding state is retained otherwise
the data plane will necessarily be interrupted. If forwarding state
is not retained, it may be relearned from saved control state in
[LDP-FT]. [LDP-RESTART] does not utilize or expect saved control
state, and if a node restarts without preserved forwarding state it
informs its neighbors which immediately delete all label-FEC bindings
previously received from the restarted node.
The ways to retain forwarding and control state are numerous and
implementation specific, and it is not the purpose of this document
to espouse one mechanism or another nor even to suggest how this
might be done. If state has been preserved across the restart,
synchronization with peers can be carried out as though recovering
from Session Failure as in the previous section. Both [LDP-FT] and
[LDP-RESTART] support this case.
How much control state is retained is largely an implementation
choice, but [LDP-FT] requires that at least small amount of per-
session control state be retained. [LDP-RESTART] does not require
or expect control state to be retained.
It is also possible that the restarting LSR has not preserved any
state. In this case [LDP-FT] is of no help. [LDP-RESTART] however
allows the restarting LSR to relearn state from each adjacent peer
through the processes for resynchronizing after Session Failure.
Further, in the event of simultaneous failure of multiple adjacent
nodes, the nodes at the edge of the failure zone can recover state
from their active neighbors and distribute it to the other recovering
LSRs without any failed LSR having to have saved state.
6.5 Controlled Node Failure
In some cases (hardware repair, software upgrade, etc.) node failure
may be predictable. In these cases all sessions with peers may be
shutdown and existing state retention may be enhanced by special
actions.
[LDP-FT] checkpointing and quiesce may be applied to all sessions
so that state is up-to-date.
As above, [LDP-RESTART] does not require that state is retained by
the restarting node, but can utilize it if it is.
6.6 Speed of Recovery
Speed of recovery is impacted by the amount of signaling required.
If forwarding state is preserved on both LSRs on the failed session
then the recovery time is constrained by the time to resynchronize
the state between the two LSRs.
[LDP-FT] may resynchronize very quickly. In a stable network this
resolves to a handshake of a checkpoint. At the most,
resynchronization involves this handshake plus an exchange of
messages to handle state changes since the checkpoint was taken.
Implementations that support only the periodic checkpointing subset
of [LDP-FT] are more likely to have additional state to
resynchronize.
[LDP-RESTART] must resynchronize state for all label mappings that
have been retained. At the same time, resources that have be retained
by a restarting upstream LSR but are not actually required because
they have been released by the downstream LSR (perhaps because it was
in the process of releasing the state) must be held for the full
resynchronization time to ensure that they are not needed.
The impact of recovery time will vary according to the use of the
network. Both [LDP-FT] and [LDP-RESTART] allow advertisement of new
labels while resynchronization is in progress. Issues to consider are
re-availability of falsely retained resources and conflict between
retained label mappings and newly advertised ones since this may
cause incorrect forwarding of data - since labels are advertised
from downstream, an LSR upstream of a failure may continue to
forward data for one FEC on an old label while the recovering
downstream LSR might re-assign that label to another FEC and
advertise it. For this reason, restarting LSRs may choose to not
advertise new labels until resynchronization with their peers has
completed, or may decide to use special techniques to cover the short
period of overlap between resynchronization and new LSP setup.
6.7 Scalability
Scalability is largely the same issue as speed of recovery and is
governed by the number of LSPs managed through the failed session(s).
Note that there are limits to how small the resynchronization time in
[LDP-RESTART] may be made given the capabilities of the LSRs, the
throughput on the link between them, and the number of labels that
must be resynchronized.
Impact on normal operation should also be considered.
[LDP-FT] requires acknowledgement of all messages. These
acknowledgements may be deferred as for checkpointing described in
section 6.4, or may be frequent. Although acknowledgements can be
piggy-backed on other state messages, an option for frequent
acknowledgement is to send a message solely for the purpose of
acknowledging a state change message. Such an implementation would
clearly be unwise in a busy network.
[LDP-RESTART] has no impact on normal operations.
6.8 Rate of Change of LDP State
Some networks do not show a high degree of change over time, such as
those using targeted LDP sessions; others change the LDP forwarding
state frequently, perhaps reacting to changes in routing information
on LDP discovery sessions.
Rate of change of LDP state exchanged over an LDP session depends
on the application for which the LDP session is being used. LDP
sessions used for exchanging <FEC, label> bindings for establishing
hop by hop LSPs will typically exchange state reacting to IGP
changes. Such exchanges could be frequent. On the other hand
LDP sessions established for exchanging MPLS Layer 2 VPN FECs
will typically exhibit a smaller rate of state exchange.
In [LDP-FT] two options exist. The first uses a frequent (up to per-
message) acknowledgement system which is most likely to be applicable
in a more dynamic system where it is desirable to preserve the
maximum amount of state over a failure to reduce the level of
resynchronization required and to speed the recovery time.
The second option in [LDP-FT] uses a less-frequent acknowledgement
scheme known as checkpointing. This is particularly suitable to
networks where changes are infrequent or bursty.
[LDP-RESTART] resynchronizes all state on recovery regardless of the
rate of change of the network before the failure. This consideration
is thus not relevant to the choice of [LDP-RESTART].
6.9 Label Distribution Modes
Both [LDP-FT] and [LDP-RESTART] are suitable for use with Downstream
Unsolicited label distribution.
[LDP-RESTART] describes Downstream-On-Demand as an area for future
study and is therefore not applicable for a network in which this
label distribution mode is used. It is possible that future
examination of this issue will reveal that once a label has been
distributed in either distribution mode, it can be redistributed
by [LDP-RESTART] upon session recovery.
[LDP-FT] is suitable for use in a network that uses Downstream-On-
Demand label distribution.
In theory, and according to [RFC3036], even in networks configured to
utilize Downstream Unsolicited label distribution, there may be
occasions when the use of Downstream-On-Deman distribution is
desirable. The use of the Label Request message is not prohibited in
a Downstream Unsolicited label distribution LDP network.
Opinion varies as to whether there is a practical requirement for the
use of the Label Request message in a Downstream Unsolicited label
distribution LDP netowrk. Current deployment experience suggests that
there is no requirement.
6.10 Implementation Complexity
Implementation complexity has consequences for the implementer and
also for the deployer since complex software is more error prone and
harder to manage.
[LDP-FT] is a more complex solution than [LDP-RESTART]. In
particular, [LDP-RESTART] does not require any modification to the
normal signaling and processing of LDP state changing messages.
[LDP-FT] implementations may be simplified by implementing only
the checkpointing subest of the functionality.
6.11 Implementation Robustness
In addition to the implication for robustness associated with
complexity of the solutions, consideration should be given to the
effects of state preservation on robustness.
If state has become incorrect for whatever reason then state
preservation may retain incorrect state. In extreme cases it may be
that the incorrect state is the cause of the failure in which case
preserving that state would be bad.
When state is preserved, the precise amount that is retained is an
implementation issue. The basic requirement is that forwarding state
is retained (to preserve the data path) and that that state can be
accessed by the LDP software component.
In both solutions, if the forwarding state is incorrect and is
retained, it will continue to be incorrect. Both solutions have a
mechanism to housekeep and free unwanted state after
resynchronization is complete. [LDP-RESTART] may be better at
eradicating incorrect forwarding state because it replays all
messages exchanges that caused the state to be populated.
In [LDP-RESTART] no more data than the forwarding state needs to have
been saved by the recovering node. All LDP state may be relearned by
message exchanges with peers. Whether those exchanges may cause the
same incorrect state to arise on the recovering node is an obvious
concern.
In [LDP-FT] the forwarding state must be supplemented by a small
amount of state specific to the protocol extensions. LDP state may
be retained directly or reconstructed from the forwarding state. The
same issues apply when reconstructing state but are mitigated by the
fact that this is likely a different code path. Errors in the
retained state specific to the protocol extensions will persist.
6.12 Interoperability and Backward Compatibility
It is important that new additions to LDP interoperate with existing
implementations at least in provision of the existing levels of
function.
Both [LDP-FT] and [LDP-RESTART] do this through rules for handling
the absence of the FT optional negotiation object during session
initialization.
Additionally, [LDP-RESTART] is able to perform limited recovery (that
is, redistribution of state) even when only one of the participating
LSRs supports the procedures. This may offer considerable advantages
in interoperation with legacy implementations.
6.13 Interaction With Other Label Distribution Mechanisms
Many LDP LSRs also run other label distribution mechanisms. These
include management interfaces for configuration of static label
mappings, other distinct instances of LDP, and other label
distribution protocols. The last example includes traffic engineering
label distribution protocol that are used to construct tunnels
through which LDP LSPs are established.
As with re-use of individual labels by LDP within a restarting LDP
system, care must be taken to prevent labels that need to be retained
by a restarting LDP session or protocol component from being used by
another label distribution mechanism since that might compromise
data security amongst other things.
It is a matter for implementations to avoid this issue through the
use of techniques such as a common label management component or
segmented label spaces.
6.14 Applicability to CR-LDP
CR-LDP [RFC 3212] utilizes Downstream-On-Demand label distribution.
[LDP-RESTART] describes Downstream-On-Demand as an area for future
study and is therefore not applicable for CR-LDP. [LDP-FT] is
suitable for use in a network entirely based on CR-LDP or in one
that is mixed between LDP and CR-LDP.
7. Security Considerations
This document is informational and introduces no new security
concerns.
The security considerations pertaining to the original LDP protocol
[RFC3036] remain relevant.
[LDP-RESTART] introduces the possibility of additional denial-of-
service attacks. All of these attacks may be countered by use of an
authentication scheme between LDP peers, such as the MD5-based scheme
outlined in [LDP].
In MPLS, a data mis-delivery security issue can arise if an LSR
continues to use labels after expiration of the session that first
caused them to be used. Both [LDP-FT] and [LDP-RESTART] are open to
this issue.
8. Intellectual Property Considerations
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
Parts of [LDP-FT] are the subject of a patent application by
Data Connection Ltd.
Parts of [LDP-RESTART] are the subject of patent applications by
Juniper Networks and Redback Networks.
In all cases, the parties have indicated that if technology is
adopted as a standard they agree to license, on reasonable and non-
discriminatory terms, any patent rights they obtain covering such
technology to the extent necessary to comply with the standard.
9. References
9.1 Normative References
[RFC2026] Bradner, S., "The Internet Standards Process --
Revision 3", BCP 9, RFC 2026, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3036] Andersson, L., et. al., LDP Specification, RFC 3036,
January 2001.
[LDP-FT] Farrel, A., et al., Fault Tolerance for the Label
Distribution Protocol (LDP), draft-ietf-mpls-ldp-
ft-06.txt, September 2002, work in progress.
[LDP-RESTART] Leelanivas, M., et al., Graceful Restart Mechanism for
LDP, draft-ietf-ldp-restart-05.txt, September 2002,
work in progress.
9.2 Informational References RFC 3612
[MPLS-RECOV] Sharma, Hellstrand, et al., Framework for MPLS-based Title: Applicability Statement for Restart Mechanisms
Recovery, draft-ietf-mpls-recovery-frmwrk-07.txt, for the Label Distribution Protocol (LDP)
September 2002, work in progress. Author(s): A. Farrel
Status: Informational
Date: September 2003
Mailbox: adrian@olddog.co.uk
Pages: 16
Characters: 35677
Updates/Obsoletes/SeeAlso: None
[RFC3212] Jamoussi, B., et. al., Constraint-Based LSP Setup I-D Tag: draft-ietf-mpls-ldp-restart-applic-01.txt
using LDP, RFC 3212, January 2002.
10. Acknowledgements URL: ftp://ftp.rfc-editor.org/in-notes/rfc3612.txt
The author would like to thank the authors of [LDP-FT] and This document provides guidance on when it is advisable to implement
[LDP-RESTART] for their work on fault tolerance of LDP. some form of Label Distribution Protocol (LDP) restart mechanism and
Many thanks to Yakov Rekhter, Rahul Aggarwal, Manoj Leelanivas which approach might be more suitable. The issues and extensions
and Andrew Malis for their considered input to this applicability described in this document are equally applicable to RFC 3212,
statement. "Constraint-Based LSP Setup Using LDP".
11. Author Information This document is a product of the Multiprotocol Label Switching
Working Group of the IETF.
Adrian Farrel This memo provides information for the Internet community. It does
Movaz Networks, Inc. not specify an Internet standard of any kind. Distribution of this
7926 Jones Branch Drive, Suite 615 memo is unlimited.
McLean, VA 22102
Phone: +1 703-847-1867
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