Network Working Group Dan Li
Huiying Xu
Huawei
Snigdho Bardalai
Fujitsu
Internet Draft
Category: Standards Track
Expires: August 2007 February, 2007
Data Channel Status Confirmation Extensions
for the Link Management Protocol
draft-li-ccamp-confirm-data-channel-status-01.txt
Status of this Memo
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Abstract
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This document defines simple additions to the Link Management
Protocol (LMP) to provide a control plane tool that can assist in the
location of stranded resources by allowing adjacent LSRs to confirm
data channel statuses, and provides triggers for notifying the
management plane if any discrepancies are found.
Conventions used in this document
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].
Table of Contents
1. Introduction................................................2
2. Problem Explanation.........................................4
2.1. Mismatch Caused by Manual Configuration.................4
2.2. Mismatch Caused by LSP Deletion.........................5
2.3. Manual Change of the Cross-Connection State.............5
3. Extensions to LMP...........................................6
3.1. Confirm Data Channel Status Messages....................6
3.1.1. ConfirmDataChannelStatus Messages..................6
3.1.2. ConfirmDataChannelStatusAck Messages...............7
3.1.3. ConfirmDataChannelStatusNack Messages..............7
3.2. Data Channel Status Subobject...........................8
4. Procedures..................................................9
5. Security Considerations.....................................10
6. IANA Considerations........................................10
6.1. LMP Message Types......................................10
6.2. LMP Data Link Object Subobject.........................10
7. Acknowledgments............................................11
8. References.................................................11
8.1. Normative References...................................11
8.2. Informative References.................................11
9. Author's Addresses.........................................12
10. Full Copyright Statement...................................12
11. Intellectual Property Statement............................13
1. Introduction
A data channel status mismatch exists if the Label Switching Router
(LSR) at one end of a Traffic Engineering (TE) link believes that the
data channel is assigned to carry data, but the LSR at the other end
does not. The term "ready to carry data" means cross-connected or
bound to an end-point for the receipt or delivery of data.
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Data channel mismatches cannot be detected from the TE information
advertised by the routing protocols [RFC4203], [RFC4205]. A data
channel in this context corresponds to a resource label in a non-
packet technology (such as a timeslot or a lambda), and this
information is not part of the TE information advertised by the
routing protocols. The existence of some problem may be detected by a
mismatch in the advertised bandwidths where bidirectional TE links
and bidirectional services are in use, but where unidirectional
services exist, or where multiple data channel mismatches occur, it
is not possible to detect such errors through the routing protocol-
advertised TE information. In any case, there is no mechanism to
isolate the mismatches.
If a data channel mismatch exists, any attempt to use the data
channel for a new LSP will fail. One end of the TE link may attempt
to assign the TE link for use, but the other end will report the data
channel as unavailable when the control plane or management plane
attempts to assign it to an LSP.
Although such a situation can be resolved through the use of the
Acceptable Label Set object in GMPLS signaling [RFC3473], such a
procedure is inefficient since it may require an additional signaling
exchange for each LSP that is set up. When many LSPs are to be set up,
and when there are many data channel mismatches, such inefficiencies
become significant. It is desirable to avoid the additional signaling
overhead, and to report the problems to the management plane so that
they can be resolved to improve the efficiency of LSP setup.
Correspondingly, such a mismatch situation may give rise to
misconnections in the data plane especially when LSPs are set up
using management plane operations.
Resources (data channels) that are in a mismatched state are often
described as "stranded resources". They are not in use for any LSP,
but they cannot be assigned for use by a new LSP because they appear
to be in use. Although it is theoretically possible for management
plane applications to audit all network resources to locate stranded
resources and to release them, this process is rarely performed
because of the difficulty of coordinating different Element
Management Systems (EMSs), and the associated risks of accidentally
releasing in-use resources. It is desirable to have a control plane
mechanism that detects and reports stranded resources.
This document defines simple additions to the Link Management
Protocol (LMP) [RFC4204] to provide a control plane tool that can
assist in the location of stranded resources by allowing adjacent
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LSRs to confirm data channel statuses, and provides triggers for
notifying the management plane if any discrepancies are found.
2. Problem Explanation
Examples of data channel mismatches are described in the following
three scenarios.
In all of the scenarios, the specific channel resource of a data link
will be unavailable because of the data channel status mismatch, and
this channel resource will be wasted. Furthermore, a data channel
status mismatch may reduce the possibility of successful LSP
establishment, because a data channel status mismatch may result in
failure when establishing an LSP.
So it is desirable to confirm the data channel statuses as early as
possible.
2.1. Mismatch Caused by Manual Configuration
The operator may have configured a cross-connection at only one end
of a TE link using an EMS. The resource at one end of the data
channel is allocated, but the corresponding resource is still
available at the other end of the same data channel. In this case,
the data channel may appear to be available for use by the control
plane when viewed from one end of the TE link, but will be considered
to be unavailable by the other end of the TE link. Alternatively, the
available end of the data channel may be cross-connected by the
management plane and a misconnection may result from the fact that
the other end of the data channel is already cross-connected.
Figure 1 shows a data channel between nodes A and B. Only the
resource at A end is allocated by manual configuration, while the
resource at B end is available, so the data channel status is
mismatched.
allocated available
+-+------------+-+
A |x| | | B
+-+------------+-+
data channel
Figure 1. Mismatch caused by manual configuration
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2.2. Mismatch Caused by LSP Deletion
The channel status of a data link may become mismatched during the
LSP deletion process. If the LSP deletion process is aborted in the
middle of the process (perhaps because of a temporary control plane
failure), the cross-connection at the upstream node may be removed
while the downstream node still keeps its cross-connection, if the
LSP deletion was initiated by the source node.
For example, in Figure 2 an LSP traverses nodes A, B, and C. Node B
resets abnormally when the LSP is being deleted, which results in the
cross-connections of node A and C being removed, but the cross-
connection of node B is still in use. So the data channel status
between nodes A and B, and between nodes B and C are both mismatched.
<---------LSP--------->
+-+-------+-+-------+-+
| | |X| | |
+-+-------+-+-------+-+
A B C
Figure 2. Mismatch caused by LSP deletion
RSVP-TE restart processes [RFC3473], [GR-EXT] define mechanisms where
adjacent LSRs may resynchronize their control plane state to
reinstate information about LSPs that have persisted in the data
plane. The mechanisms allow LSRs to detect mismatched data plane
state after the expiry of the Recovery Timer. It is a local policy
decision how this mismatched state should be handled. Some
deployments may decide to automatically clean up the data plane state
so it matches the control plane state, but others may choose to raise
an alert to the management plane and leave the data plane untouched
just in case it is in use.
In such cases, data channel mismatches may arise after restart and
might not be cleared up by the restart procedures.
2.3. Manual Change of the Cross-Connection State
In transport nodes it is possible to perform certain manual
operations on a cross-connection such as forced protection switch,
red-line etc. These operations will make it impossible to release the
cross-connection when an LSP is being deleted.
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3. Extensions to LMP
A control plane tool to detect and isolate data channel mismatches is
provided in this document by simple additions to the Link Management
Protocol (LMP) [RFC4204]. It can assist in the location of stranded
resources by allowing adjacent LSRs to confirm data channel statuses.
Outline procedures are described in this section. More detailed
procedures are found in Section 4.
3.1. Confirm Data Channel Status Messages
Extensions to LMP to confirm a data channel status are described
below. In order to confirm a data channel status, the new LMP
messages are sent between adjacent nodes periodically or driven by
some event (such as an operator command, a configurable timer, or the
rejection of an LSP setup message because of an unavailable resource).
Three new messages are defined to check data channel status. Message
Type numbers are found in Section 7.
3.1.1. ConfirmDataChannelStatus Messages
The ConfirmDataChannelStatus message is used to tell the remote end
of the data channel what the status of the local end of the data
channel is, and to ask the remote end to report its data channel. The
message may report on (and request information about) more than one
data channel.
<ConfirmDataChannelStatus Message> ::= <Common Header>
<LOCAL_LINK_ID>
<MESSAGE_ID>
<DATA_LINK>[<DATA_LINK>...]
When a node receives the ConfirmDataChannelStatus message, and the
data channel status confirmation procedure is supported at the node,
the node compares its own data channel statuses with all of the data
channel statuses sent by the remote end in the
ConfirmDataChannelStatus message. If a data channel status mismatch
is found, this mismatch result SHOULD be reported to the management
plane for further action. Management plane reporting procedures and
actions are outside the scope of this document.
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3.1.2. ConfirmDataChannelStatusAck Messages
The ConfirmDataChannelStatusAck message is sent back to the node
which originated the ConfirmDataChannelStatus message to return the
requested data channel statuses.
When the ConfirmDataChannelStatusAck message is received, the node
compares the received data channel statuses at the remote end with
those at the local end (the same operation as performed by the
receiver of the ConfirmDataChannelStatus message). If a data channel
status mismatch is found, the mismatch result SHOULD be reported to
the management plane for further action.
<ConfirmDataChannelStatusAck Message> ::= <Common Header>
<MESSAGE_ID_ACK>
<DATA_LINK>[<DATA_LINK>...]
The contents of the MESSAGE_ID_ACK objects MUST be obtained from the
ConfirmDataChannelStatus message being acknowledged.
Note that the ConfirmDataChannelStatusAck message is used both when
the data channel statuses match and when they do not match.
3.1.3. ConfirmDataChannelStatusNack Messages
When a node receives the ConfirmDataChannelStatus message, if the
data channel status confirmation procedure is not supported but the
message is recognized, a ConfirmDataChannelStatusNack message
containing an ERROR_CODE indicating "Channel Status Confirmation
Procedure not supported" MUST be sent.
If the data channel status confirmation procedure is supported, but
the node is unable to begin the procedure, a
ConfirmDataChannelStatusNack message containing an ERROR_CODE
indicating "Unwilling to Confirm" MUST be sent. If a
ConfirmDataChannelStatusNack message is received with such an
ERROR_CODE, the node which originated the ConfirmDataChannelStatus
message MAY schedule the ConfirmDataChannelStatus message
retransmission after a configured time. A default value of 10 minutes
is suggested for this timer.
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<ConfirmDataChannelStatusNack Message> ::= <Common Header>
[<LOCAL_LINK_ID>]
<MESSAGE_ID_ACK>
<ERROR_CODE>
The contents of the MESSAGE_ID_ACK objects MUST be obtained from the
ConfirmDataChannelStatus message being rejected.
3.2. Data Channel Status Subobject
A new Data Channel Status subobject type is introduced to the DATA
LINK object to hold the data channel status and Data Channel
Identification.
See Section 7 for the Subobject Type value.
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 | Data Channel Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Data Channel ID //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Data Channel Status:
This is a series of bit flags to indicate the status of the data
channel. The following values are defined.
0x0000 : The channel is available/free.
0x0001 : The channel is cross-connected/allocated.
Data Channel ID
This identifies the data channel. The length of this field can be
deduced from the Length field in the subobject. Note that all
subobjects must be padded to a four byte boundary with trailing zeros.
If such padding is required, the Length field MUST indicate the
length of the subobject up to, but not including, the first byte of
padding. Thus, the amount of padding is deduced and not represented
in the Length field.
Note that the Data Channel ID is given in the context of the sender
of the ConfirmChannelStatus message.
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The data-channel ID must be encoded as a label value. Based on the
type of signal e.g. SONET/SDH, Lambda etc. the encoding methodology
used will be different. For SONET/SDH the label value is encoded as
per RFC4606.
4. Procedures
The data channel status confirmation related LMP messages are sent
between adjacent nodes periodically or driven by some events to
confirm the channel status for the data links. The procedure is
described below:
. The SENDER constructs a ConfirmDataChannelStatus message which
contains one or more DATA_LINK objects. Each DATA_LINK object
contains one or more Data Channel Status subobject. The Data
Channel ID field in the Data Channel Status subobject indicates
which data channel needs to be confirmed, and reports the data
channel status at the SENDER. The ConfirmDataChannelStatus message
is sent to the RECEIVER.
. The RECEIVER extracts the data channel statuses from the
ConfirmDataChannelStatus message, and compares these with its data
channel statuses for the reported data channels. If a data channel
status mismatch is found, the mismatch result SHOULD be reported
to the management plane for further action. The RECEIVER also
sends the ConfirmDataChannelStatusAck message which carries all
the local end statuses of the requested data channels to the
SENDER.
. If the RECEIVER is not able to support or to begin the
confirmation procedure, the ConfirmDataChannelStatusNack message
MUST be responded with the ERROR_CODE which indicates the reason
of rejection.
. The SENDER receives the response ConfirmDataChannelStatusAck
message, and compares the received data channel statuses at the
remote end with the data channel statuses at the local end. If a
data channel status mismatch is found, the mismatch result SHOULD
be reported to the management plane for further action.
. The ConfirmDataChannelStatus message SHOULD be resent, if the
ConfirmDataChannelStatusNack message is received or no response
message is received in the configured time by the SENDER.
The data channel status mismatch results MAY be stored, and this
information MAY be queried in the future.
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The data channel status mismatch issue warned about by LMP may be
automatically resolved by RSVP restart. For example, the restarting
node may also have damaged its data plane. This leaves the data
channels mismatched. But RSVP restart will re-install the data plane
state in the restarting node.
5. Security Considerations
[RFC4204] describes how LMP messages between peers can be secured,
and these measures are equally applicable to the new messages defined
in this document.
The operation of the procedures described in this document does not
of themselves constitute a security risk since they do not cause any
change in network state. It would be possible, if the messages were
intercepted or spoofed to cause bogus alerts in the management plane
and so the use of the LMP security measures are RECOMMENDED.
Note that operating the procedures described in this document may
provide a useful additional security measure to verify that data
channels have not been illicitly modified.
6. IANA Considerations
6.1. LMP Message Types
IANA maintains the "Link Management Protocol (LMP)" registry which
has a subregistry called "LMP Message Type". IANA is requested to
make three new allocations from this registry as follows. The message
type values are suggested and to be confirmed by IANA.
Value Description
------- ---------------------------------
21 ConfirmDataChannelStatus
22 ConfirmDataChannelStatusAck
23 ConfirmDataChannelStatusNack
6.2. LMP Data Link Object Subobject
IANA maintains the "Link Management Protocol (LMP)" registry which
has a subregistry called "LMP Object Class name space and Class type
(C-Type)". This subregistry has an entry for the DATA_LINK object,
and there is a further embedded registry called "DATA_LINK Sub-object
Class name space". IANA is requested to make the following allocation
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from this embedded registry. The value shown is suggested and to be
confirmed by IANA.
Value Description
------- ---------------------
9 Data Channel Status
7. Acknowledgments
We would like to thank Adrian Farrel, Dimitri Papadimitriou and Diego
Caviglia for their useful comments.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4204] J. Lang, Ed., "Link Management Protocol (LMP) ", RFC 4204,
October 2005.
8.2. Informative References
[RFC3473] L. Berger, Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation
Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC
3473, January 2003
[GR-EXT] A. Satyanarayana, R. Rahman, "Extensions to GMPLS RSVP
Graceful Restart", Internet Draft, work in progress,
draft-ietf-ccamp-rsvp-restart-ext-05.txt, October 2005
[RFC4203] K. Kompella, Ed., "OSPF Extensions in Support of
Generalized Multi-Protocol Label Switching (GMPLS)", RFC
4203, October 2005
[RFC4205] K. Kompella, Ed., "Intermediate System to Intermediate
System (IS-IS) Extensions in Support of Generalized
Multi-Protocol Label Switching (GMPLS)", RFC 4205,
October 2005
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9. Author's Addresses
Dan Li
Huawei Technologies Co., Ltd.
F3-5-B R&D Center, Huawei Base,
Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28972910
Email: danli@huawei.com
Huiying Xu
Huawei Technologies Co., Ltd.
F3-5-B R&D Center, Huawei Base,
Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28972909
Email: xuhuiying@huawei.com
Fatai Zhang
Huawei Technologies Co., Ltd.
F3-5-B R&D Center, Huawei Base,
Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28979791
Email: zhangfatai@huawei.com
Snigdho C. Bardalai
Fujitsu Network Communications, Inc.
2801 Telecom Parkway,
Richardson, Texas 75082
United States of America
Phone: +1 972 479 2951
Email: snigdho.bardalai@us.fujitsu.com
10. Full Copyright Statement
Copyright (C) The IETF Trust (2007).
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This document is subject to the rights, licenses and restrictions
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Internet-Drafts are draft documents valid for a maximum of six
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