One document matched: draft-ietf-mpls-lsp-query-08.txt
Differences from draft-ietf-mpls-lsp-query-07.txt
Network Working Group P. Ashwood-Smith
Internet Draft A. Paraschiv
Expiration Date: January 2004 D. Allan
Nortel Networks
June 2003
Multi Protocol Label Switching Label Distribution Protocol
Query Message Description
draft-ietf-mpls-lsp-query-08.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
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http://www.ietf.org/ietf/1id-abstracts.txt
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Abstract
This document describes the encoding and procedures for three new
Label Distribution Protocol (LDP) messages: Query Message, Query-
Reply Message and Partial Query-Reply Message. A Label Edge Router
(LER) sends a Query message when it needs to find out information
about an established Label Switched Path (LSP). The Query message
can be used for LDP LSPs as well as for Constraint-Based Label
Switched Paths (CR-LSPs). The queried data is encoded into the
Query-Reply messages.
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Contents
1. Introduction ........................................3
2. Specification........................................3
3. Overview.............................................3
3.1 LDP Overview .......................................3
3.2 CR-LDP Overview.....................................4
4. LDP Message Structure Overview.......................4
5. LSRs with constraints in handling the query messages.5
5.1 LSR does not support the query messages.............6
5.2 LSR cannot share any information....................6
5.3 LSR cannot share some of the queried information....6
5.4 LSR can share the queried information...............6
6. Query Message........................................7
6.1 Query Message encoding .............................7
6.2 Query Message Procedures............................9
7. Reply Messages.......................................10
7.1 Query-Reply Message encoding .......................10
7.2 Query-Reply Message Procedures......................12
7.3 Partial Query-Reply Message encoding................12
7.4 Partial Query-Reply Message Procedures .............13
8. Query TLVs...........................................13
8.1 Query Label TLV.....................................14
8.2 Query Merge Flags TLV...............................15
8.3 Query Payload TLV ..................................16
8.4 Status code summary.................................16
9. Security Considerations..............................17
10. IANA Considerations..................................17
10.1 Message Type Space Extension......................17
10.2 TLV Type Name Space Extension ....................17
10.3 Status Code Space Extension.......................18
11. Acknowledgments......................................18
12. Normative References.................................18
13. Author's Addresses...................................18
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Changes from previous version:
o Additions to support ECMP
o Editorial changes
o Elaboration on security considerations
o Clarification to message fragmenting issues.
[Editor's note: This section has to be removed prior to publication]
1. Introduction
The original Multiprotocol Label Switching (MPLS) architecture
[MPLS-ARCH] was been defined to support the forwarding of data based
on a label. The MPLS architecture does not assume a single label
distribution protocol. A number of different label distribution
protocols are being standardized. This memo describes the query
mechanism for a Label Switched Path (LSP) or Constraint Based LSP
(CR-LSP). It specifies procedures and encodings for the new messages
added for the query mechanism.
The new LDP messages are: Query Message, Query-Reply Message and
Partial Query-Reply Message. The Partial Query Reply is almost
Identical to the Query Reply message; therefore all references to
the Query Reply message imply the Partial Query Reply Message as
well unless explicitly noted.
The following new TLVs are added to accommodate the encodings for
the new query messages:
- Query TLV
- Query Label TLV
- Query Merge Flags TLV
- Query Payload TLV
LDP uses the TCP transport for session, advertisement and
notification messages; i.e., for everything but the UDP-based
discovery mechanism. The messages which are added to support the
query mechanism are sent over TCP as well.
2. Specification
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].
3. Overview
3.1 LDP Overview
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Label Distribution Protocol (LDP) defined in [4] contains a set of
procedures and messages by which Label Switched Routers (LSR)
establish Label Switch Paths (LSP) through a network by mapping
network layer routing information directly to data-link layer
switched paths. LDP associates a Forwarding Equivalence Class (FEC)
with each LSP it creates. The FEC associated with an LSP specifies
which packets are mapped to that LSP.
3.2 CR-LDP Overview
As described in CR-LDP [1], Constraint Base Routing offers the
opportunity to extend the information used to setup paths beyond
what is available from the routing protocol. For instance, an LSP
can be setup based on explicit route constraints, QoS constraints,
and other constraints.
4. LDP Message Structure Overview
The LDP message format is specified in the LDP Specification [4].
All LDP messages have the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U| Message Type | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| Mandatory Parameters |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| Optional Parameters |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
U bit
Unknown message bit. Upon receipt of an unknown message, if U
is clear (=0), a notification is returned to the message
originator; if U is set (=1), the unknown message is silently
ignored.
Message Type
Identifies the type of message
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Message Length
Specifies the cumulative length in octets of the Message ID,
Mandatory Parameters, and Optional Parameters.
Message ID
32-bit value used to identify this message. It is used by the
sending LSR to facilitate identifying notification messages
that may apply to this message. An LSR sending a notification
message in response to this message should include this
MessageId in the Status TLV carried by the notification
message.
Mandatory Parameters
Variable length set of required message parameters. Some
messages have no required parameters.
For messages that have required parameters, the required parameters
must appear in the order specified by the individual message
specifications in the sections that follow.
Optional Parameters
Variable length set of optional message parameters. Many messages
have no optional parameters.
For messages that have optional parameters, the optional parameters
may appear in any order.
5. LSRs with constraints in handling the query messages
Upon receiving a Query message, an LSR has to behave according to
its configuration constraints in handling the query messages and
returning the queried information. The following cases were
identified:
- The LSR does not support the code to handle the messages
for the query mechanism
- The LSR supports the code to handle the messages for the
query mechanism, but it is configured not to return any
data
- The LSR supports the code to handle the messages for the
query mechanism, but it is configured not to return part of
the queried data
- The LSR supports the code to handle the messages for the
query mechanism, and it is configured to return all the
data which is queried.
This memo provides flexibility to handle each of the above cases.
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5.1 LSR does not support the query messages
In this case, the LSR has to behave as if it received an unknown
message type. It therefore honors the U bit.
5.2 LSR cannot share any information
In this case, the LSR is able to decode and process the query
messages. However, it is configured to hide all the data. It should
propagate the message after it encodes a zero-length TLV for its hop
in the hop list in the Query message. When Query-Reply message is
received from downstream, the LSR is requested to propagate the
reply message upstream after it encodes the zero-length TLVs for the
queried data. When the ingress receives back the reply, it can
identify which TLVs are empty; it can therefore ignore the zero-
length TLVs and process the rest of the data.
Note: zero-length TLV encoding can be used for all types of queried
information except the merge information. The LSR is requested to
signal the fact that the merging information is private by encoding
a special value in the corresponding merge bits (for more
information on the merge flags values please refer to Section 7.2 of
this memo - Query Merge Flags TLV).
5.3 LSR cannot share some of the queried information
In this case, the LSR is able to decode and process the query
messages. It has to propagate the query messages. It has to encode
values for the data types that it is willing to return and zero-
length TLVs for values for the data that is hidden.
Note: zero-length TLV encoding can be used for all types of queried
information except the merge information. The LSR is requested to
signal the fact that the merging information is private by encoding
a special value in the corresponding merge bits (for more
information on the merge flags values please refer to Section 7.2 of
this memo - Query Merge Flags TLV).
5.4 LSR can share the queried information
In this case, the LSR's behavior has to follow the query and replies
procedures described in the following sections of this memo.
In order to have consistency among data encoded in the query and
reply messages, each LSR which can propagate the messages has to
encode its information in the query and in the reply messages.
The decision that an LSR can share the queried information has to be
controlled through configuration flags. This way each node along the
path can protect its data if they consider it private.
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Note: It would be more efficient to control/restrict the private
data per MPLS cloud (inter MPLS domain) and not per LSR node (inter
and intra MPLS domain). When there are different MPLS clouds which
have nodes belonging to different vendors, the control of the
private information could be restricted to the boundary nodes.
Within an MPLS domain, there should be no restrictions on the
queried information. It would be useful to have some knowledge on
which are the nodes on the boundaries and have only those hiding the
queried data. Because there is no mechanism to identify which are
the boundary nodes, this is subject for future study.
6. Query Message
This section describes the Query message and its encodings and
procedures. This message is meant to be used to gather information
about an LSP. It can be sent at any time for an established LSP.
This memo currently describes the procedures for the cases when the
Query Message is initiated by the ingress LER. Additional procedures
may be added in the future for the query message when issued from an
LSR or from egress.
The Query Message can be used to gather information about:
- LSRs which form the LSP
- Labels along the LSP
- Information on what LSRs are merging points along the path
- Unused bandwidth (as described in "Improving Topology Data
Base Accuracy with LSP Feedback" [2])
- What path any specific payload may follow in the presence
of load spreading mechanisms such as ECMP
- Anything that is needed in the future and can be computed
and encoded in a TLV.
It should be noted that useful information can still be extracted
from partial responses due constraints on handling messages placed
on some LSRs along the LSP. In the fault diagnosis scenario
(particularly in the presence of ECMP), those LSRs that at a minimum
return their own LSR ID facilitate diagnosis when combined with data
plane tracing tools as those LSRs can act as segmentation boundaries
for fault isolation.
The queried information is encoded in the Query-Reply message which
is sent back upstream, as a response to the Query message.
6.1 Query Message encoding
The encoding for the Query message is:
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
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Query type TBD IANA | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Query Label TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Query TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hop Count TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message ID
32-bit value used to identify this message.
Query Label TLV
The label associated to the LSP which is queried. This TLV is a
list of Generalized Label TLVs [3]. The Generalized Label TLV
provides a more generic encoding for different types of labels.
Most of the time the list has one element; this is the case when
the LSP is not tunneled. For tunneled LSPs, the Label TLV has
more that one element; it has to behave like a label stack (it
contains the previous label and the tunnel's label). See Section
7.1 of this memo - Query Label TLV - for more information on
Label TLV encoding.
Query TLV
What to query. See Section 7 of this memo - Query TLV - for
encoding.
Hop Count TLV
Specifies the number of LSR hops that can still be traversed
before the message is dropped due to loop detection. It is
initialized to the max default value of 255 (or the configured
value, if any). Every LSR that receives the Query Message has to
subtract 1 from the Hop Count value. The Query message should
be dropped if the hop count value becomes zero; a Notification
signaling Loop Detection should be sent in reply to the sender
of the message. See [4] for Hop Count TLV encoding.
Optional Parameters
This variable length field contains 0 or more parameters, each
encoded as a TLV.
Optional Parameter Length Value
ER TLV var See [1]
LSPID TLV var See [1]
FEC TLV var See [4]
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Query Payload TLV var See below
The ER TLV is a list of hops. It is used when the Query flag Q3 is
set. Every LSR should add its IP address. The address to be added
should be the outgoing interface address. Addresses are organized as
a last-in-first-out stack (the first address in TLV is considered
the top). By carrying this TLV in the Query Message and preserving
this order for the hops, we allow the possibility to interwork the
Query Message with the RSVP Path message.
FEC TLV is used when penultimate hop popping (PHP) is in use, for
LDP.
LSPID TLV is used when PHP is in use, for CR-LDP.
Query Payload TLV is used where ECMP is deployed in order to qualify
the specific LSP hops chosen by intermediate LSRs.
For more details on the FEC, LSPID, or Query Payload TLVs usage,
please refer to the Query Message Procedures below.
6.2 Query Message Procedures
The LER ingress initiates the Query message. It populates the Query
TLV Parameters according to what kind of information it wants to
gather. The query for an LSP is done by its label. The only data
that the Query Message could carry is the list of hops. This way,
each node along the path can have a complete route from source to
destination. This is useful for network management. Please note
that this parameter is optional. If the Query message does not
contain the ER TLV, it should be propagated by LSRs along the path
without the ER TLV.
Upon receiving a Query Message, an LSR decodes the label to identify
which LSP is queried. If it cannot find the LSP which is using the
label, it sends back a Notification message with "No LSP to query"
status. Otherwise, it checks which is the out label which is bound
to the queried in-label and which is the downstream LSR peer. It
replaces the in-label from Query Label TLV with the out-label used
by the LSP. It then passes the Query message to the downstream peer.
Where there is more than one valid downstream peer, AND the Payload
Query TLV is present, the LSR may use the Payload Query TLV to
select the appropriate downstream LSP peer using the same algorithms
that it would use if the payload was carried in the LSP data plane.
If the Payload Query TLV is not present but the ECMP implementation
requires the payload information for downstream path selection, it
sends back a Notification message with "Payload Query TLV Required"
status.
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When the Query message gets to a tunnel, it has to be able to handle
both the previous label and the tunnel's label. The Query Label TLV
behaves like a label stack. The previous label is pushed and the
tunnel label is used. At the end of the tunnel, we need to pop the
stack and start substituting the lower level labels.
Upon receiving the Query message, the egress node has to reply with
a Query Reply Message. The Query-Reply Message contains the Query
TLV which was received in the Query Message. The Query TLV tells the
LSRs along the path which information is being queried and allows
intermediate LSRs to piggy back their own queried information on the
Query reply message.
The initiator of a Query reply might not receive a response back. In
this case, it is the initiator's responsibility to decide if and
when to retry.
If PHP is in use, the Query Message sent from the PHP to the
destination node needs to carry the FEC (for LDP) or LSPID (for CR-
LDP). This information is required because the label between the PHP
and the destination is a special label and the destination cannot
uniquely identify the queried LSP just by using the label value. If
the PHP does not encode the FEC or the LSPID, the destination node
should reply with a notification message with "Ambiguous label
value".
7. Reply Messages
These messages are propagated upstream. There are two types of
reply messages:
- Query-Reply message (final reply)
- Partial Query-Reply message.
The Reply messages carry the queried information upstream. A Query-
Reply message is sent in response to a Query message. The ingress
which initiated the Query message is interested to gather the
information from all the nodes along the queried LSP. However,
there are situations in which the Query message does not reach the
end point of the queried LSP. In these scenarios it would be useful
if the ingress LSR gathered at least some information about the LSRs
which are along the path, up to the one that failed. The Partial
Query-Reply message provides this mechanism. It is recommended to
use the Partial Query-Reply messages when a Query message fails.
Both reply messages are described in the following sections.
7.1 Query-Reply Message encoding
This message is generated by the end point of the LSP. It is
propagated upstream, by each LSR along the path.
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The encoding for the Query-Reply message is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Query-Reply Type TBD IANA | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Query TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MessageId TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message ID
32-bit value used to identify this message.
Query TLV
What is to be queried. See Section 7 of this memo - Query TLV -
for encoding.
MessageId TLV
The value of this parameter is the message id of the
corresponding Query message.
Optional Parameters
This variable length field contains 0 or more parameters, each
encoded as a TLV. The optional parameters are:
Optional Parameter Length Value
------------------ ------ -----
ER TLV var See [1]
Query Label TLV var See Query Label TLV
section
IPV4/6 specified link feedback TLV var See [2]
Query Merge Flags TLV var See Query Merge Flags
TLV section
The TLV types are defined in CR-LDP [1] and LDP [4]. They are:
- IPV4/6 specified link feedback TLV
- ER TLV
- Generalized Label TLV (used in the Query Label TLV
encoding)
- Hop Count TLV.
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The IPV4/6 specified link feedback TLV is used when the Q1 flag from
the Query TLV is set. It is used to encode the bandwidth
information. For more information on query flags, Q1, Q2, Q3 and Q4,
refer to Query TLV section.
The ER TLV is a list of hops. It is used when the Query flag Q3 is
set. Every LSR should add its IP address. The address to be added
should be the outgoing interface address. Addresses are organized as
a last-in-first-out stack (the first address in TLV is considered
the top).
The Query Label TLV is a list of labels. It is used when the Query
flag Q2 is set. It is populated with the labels used for the path
which is queried. For tunneled LSPs, the Query Label TLV represents
a list of labels associated to the lowest level tunnel.
If Q3 and Q2 flags are set, the labels should be encoded in the same
order as the hops.
Query Merge Flags TLV is a list of pairs of bits. It has variable
length and every two bits in the mask will correspond to an LSR
along the path. Its length is rounded up to the next byte. If Q4 is
set, every LSP along the path will have to set its corresponding
bits in the mask. The bits have to be set in the same order as the
labels and hops. Usually, Q4 is set when Q2 set and/or Q3 set.
For more information for the TLV encodings of the TLVs which are
used, please see [1], [4] and [2].
7.2 Query-Reply Message Procedures
A Query-Reply message is initiated by an egress node which receives
a Query message, if the egress is able to identify the queried LSP.
If not, the egress replies with a Notification message with "No LSP
to query" status.
Upon receiving the Query message, the egress node has to reply with
a Query Reply message. The egress node has to encode into the Query-
Reply message a MessageId TLV. The mapping between a Query and a
Query-Reply Message is done based on the message id. Besides the
MessageId TLV, the egress has to encode the information that was
queried (bandwidth, path, etc).
After the encoding is done, the query reply message is sent back, on
the reversed path, towards the ingress. Every LSR across the LSP has
to encode its information according to what query flags are set.
7.3 Partial Query-Reply Message encoding
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The Partial Query-Reply message is initiated by LSRs along the
queried path. The message is generated only if the following rules
apply:
- if the Query message asked for partial
replies (the Query message signals this request
through Q8 bit)
- if the LSR is configured to provide partial replies.
The encoding for the Partial Query-Reply message is identical to the
Query-Reply, except the message type. For more details on the
encoding please refer to the Query-Reply encoding.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|Partial Query-Reply TBD IANA | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Query TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MessageId TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
7.4 Partial Query-Reply Message Procedures
The procedures are similar to the Query-Reply's procedures. Upon
receiving a Query message, an LSR will check the flag from the Query
message (Q8) which signals if the partial replies are requested by
the ingress node. If the flag is set, the LSR has to check next if
it is configured to fulfill this request. If the LSR supports
partial replies, it has to create a Partial Query-Reply and encode
the queried data and send it upstream like any Query-Reply messages.
It has then to process the Query message according to the Query
message procedures. When an LSR receives a Partial Query-Reply from
upstream, it should encode its information according to what is
queried and propagate the message. It is recommended to use the
Partial Query mechanism when the Query message fails (when the
ingress LER does not receive a Query-Reply message in response to a
Query message).
8. Query TLVs
The Query TLV is used to specify the information being queried. The
Query TLV travels in the Query message to the egress node, where it
is copied into a reverse flowing Query-Reply messages and used by
the egress and intermediate LSRs to know what information is being
queried.
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The format for the Query TLV is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Query TLV Type TBD IANA | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Query Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Query Flags can be set according to what the Query is used for.
A query flag is set when it is 1.
+--+--+--+--+--+--+--+--+
|Q8|Reserved|Q4|Q3|Q2|Q1|
+--+--+--+--+--+--+--+--+
They can be:
- Q1 : query the bandwidth; if set, the LSR that
receives the Query message has to encode the bandwidth
that is available on the link (unused bandwidth);
- Q2 : query the labels which are associated to each hop in the
path;
- Q3 : query the LSRs which form the LSP which is queried;
if set, the LSR that received the Query-Reply message
has to encode the current hop in the ER-TLV
- Q4 : query which LSPs along the path are merging points;
if set, the LSR that receives the Query message has
to encode if it is a merging point; the encoding is
done in the Query Merge flags TLV.
- Q8 : if set, the ingress requests partial query-replies;
each LSR along the path is signaled to send a Partial
Query Reply.
The reserved bits need to be set to zero on transmission and must be
ignored on receipt. They might be used in the future to signal other
types of queried information. The Query Flags can only be defined by
updating this memo.
8.1 Query Label TLV
The Query Label TLV is used to encode the labels used along the path
which is queried.
Note: Query Label TLV is used in both Query and Query Reply. It is a
required parameter in the Query message and it is an optional
parameter in Query Reply message. When being used in the Query
message, it carries the label or stack of labels which are being
followed and queried. When being used in the Query Reply message, it
carries the list of labels which make up the queried path.
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The format for the Query Label TLV is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Query Label TLV TBD IANA | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Generalized Label TLV 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Generalized Label TLV n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Generalized Label TLV is used to encode labels along the path.
Please refer to [3] for more information on the Generalized Label
TLV encoding. If the Q2 flag is set, every LSR has to encode the
out-label corresponding to the queried LSP. In the Query Label TLV,
labels are organized as a last-in-first-out stack (the first label
in TLV is considered the top). They should be encoded in the same
order as the hops and the merge flags.
8.2 Query Merge Flags TLV
The Query Merge Flags TLV is used to encode the information about
which LSRs along the path the queried LSP is being merged into.
The format for the Query Merge Flags TLV is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Merge Flags TLV TBD IANA | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of merge flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Merge flags ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Query Merge Flags TLV has 4 bytes field to store the number of
merge flags. This number is equal to the number of LSRs which are
traversed by the Query-Reply Message. The Merge flags field
contains the merge information. It is a variable length field which
is rounded up to the next byte. Each pair of bits in the Merge flags
field carries the merge information for one LSR. The valid values
for the merge bits for an LSR are:
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01 - LSR does not do merge for the queried LSP
10 - LSR does merge for the queried LSP
00 - LSR cannot share the merge information.
Every LSR which is asked to encode the merging info has to update
the number of merge flags and to set its corresponding bits
accordingly.
8.3 Query Payload TLV
The Query Payload TLV is used to encode the payload that LSRs
implementing ECMP or similar load spreading should use when
selecting a downstream peer.
The format for the Query Payload TLV is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Query Payload TLV TBD IANA| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Identifier | Reserved (=0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Example payload ~
~ |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Query Payload TLV carries an example of the payload of the LSP
that is of interest for tracing purposes. The payload example may
be:
- an MPLS label stack,
- an MPLS label stack followed by an IPv4 or IPv6 packet header or
- an IPv4 or IPv6 packet header.
The contents of the Query Payload TLV are identified via use of the
payload identifier (currently used as a bitmap)
0x01 - label stack present
0x02 - IP packet present
When the IP packet present flag is set, the IP version is determined
by examining the version number field of the packet header in the
example payload.
8.4 Status code summary
Status Code E Status Data Section Title
No LSP to query 1 TBD IANA "Query Message Procedures..."
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Ambiguous label value 1 TBD IANA "Query Message Procedures..."
Payload Query TLV 1 TBD IANA "Query Message Procedures..."
Required
Message space 1 TBD IANA "Query Message Procedures..."
exhausted
9. Security Considerations
The Query mechanism inherits the same security mechanism described
in Section 5.0 of [4]. The Query mechanism provides an additional
security measure for cases when a node cannot share the queried
information. Such nodes have the option of hiding their information,
if their configuration requires it. Please refer to Section 4 of
this memo - "Behavior of LSRs with constraints in handling the query
messages" - for more details.
The Query mechanism focuses on the ability to trace the control
plane, the outcome of which may then be compared against the output
of data plane tracing tools to ensure system consistency. If the
control plane maintains a chain of trust from LSP ingress to egress
using mechanisms to secure individual adjacencies against known or
yet to be developed attacks, then LSP Query will produce useful
information. Where the chain of trust is incomplete, the partial-
query reply mechanism may be used to trace the control plane up to
the point of the boundary between trusted and untrusted network
elements on the LSP path.
10. IANA Considerations
RFC 3036 [4] defines several name spaces including the Message Type
Name Space, the TLV Type Name Space, and the Status Code Name Space.
This document makes the following assignments within those spaces.
10.1 Message Type Space Extension
The message types for Query Message, Query-Reply Message and Partial
Query-Reply Message are as follows:
Message Type
-------------------------------------- ----------
Query Message TBD IANA
Query Reply Message TBD IANA
Partial Query Reply Message TBD IANA
10.2 TLV Type Name Space Extension
The TLV types for Query TLV, Query Label TLV and Query Merge Flags
TLV are as follows:
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TLV Type
-------------------------------------- ----------
Query TLV TBD IANA
Query Label TLV TBD IANA
Query Merge Flags TLV TBD IANA
Query Payload TLV TBD IANA
10.3 Status Code Space Extension
The Status codes are as follows:
Status Code Type
-------------------------------------- ----------
No LSP to query TBD IANA
Ambiguous label value TBD IANA
Payload Query TLV Required TBD IANA
Message space exhausted TBD IANA
11. Acknowledgments
The authors would like to acknowledge the careful review and
comments of Jean-Pierre Coupal, Steve Hamilton, Don Fedyk, Gregory
Wright and Adrian Farrel.
12. Normative References
[1] B. Jamoussi et al., "Constraint-Based LSP Setup using LDP", RFC
3212, January 2002
[2] Peter Ashwood-Smith et al., "Improving Topology Data Base
Accuracy with LSP Feedback", Work in Progress, draft-ietf-mpls-te-
feed-03.txt.
[3] Ashwood-Smith P., Berger L., "Generalized MPLS - Signaling
Functional Description", Work in Progress, draft-ietf-mpls-
generalized-signaling-07.txt.
[4] Andersson et al., "LDP Specification", RFC 3036, January 2001.
13. Author's Addresses
Peter Ashwood-Smith Antonela Paraschiv
Nortel Networks Corp. Nortel Networks Corp.
P.O. Box 3511 Station C, 600 Technology Park Drive
Ottawa, ON K1Y 4H7 Billerica, MA 01821
Canada USA
Phone: +1 613-763-4534 phone: +1 978-288-6136
petera@nortelnetworks.com antonela@nortelnetworks.com
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Dave Allan
Nortel Networks Corp.
P.O. Box 3511 Station C,
Ottawa, ON K1Y 4H7
Canada
Phone: +1 613-763-6362
dallan@nortelnetworks.com
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