Internet DRAFT - draft-ietf-grow-bmp-path-marking-tlv
draft-ietf-grow-bmp-path-marking-tlv
Network Working Group C. Cardona
Internet-Draft P. Lucente
Intended status: Standards Track NTT
Expires: 14 March 2024 P. Francois
INSA-Lyon
Y. Gu
Huawei
T. Graf
Swisscom
11 September 2023
BMP Extension for Path Status TLV
draft-ietf-grow-bmp-path-marking-tlv-00
Abstract
The BGP Monitoring Protocol (BMP) provides an interface for obtaining
BGP Path information. BGP Path Information is conveyed within BMP
Route Monitoring (RM) messages. This document proposes an extension
to BMP to convey the status of a path after being processed by the
BGP process. This extension makes use of the TLV mechanims described
in draft-ietf-grow-bmp-tlv [I-D.ietf-grow-bmp-tlv] and
draft-ietf-grow-bmp-tlv-ebit [I-D.ietf-grow-bmp-tlv-ebit].
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 RFC 2119 [RFC2119] RFC 8174 [RFC8174] when, and only when, they
appear in all capitals, as shown here.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on 14 March 2024.
Copyright Notice
Copyright (c) 2023 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 (https://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 Revised BSD License text as
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Path Status TLV . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. IANA-registered Path Status TLV . . . . . . . . . . . . . 3
2.2. Enterprise-specific Path Status TLV . . . . . . . . . . . 5
3. Implementation notes . . . . . . . . . . . . . . . . . . . . 6
3.1. Configuration of BMP path marking . . . . . . . . . . . . 7
3.2. Paths with no markings . . . . . . . . . . . . . . . . . 7
3.3. Significance of status and origin RIBs . . . . . . . . . 7
3.4. Enterprise-specific status and reasons . . . . . . . . . 8
3.5. Multiple TLVs assigned to the same route. . . . . . . . . 8
4. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Normative References . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
For a given prefix, multiple paths with different path status, e.g.,
the "best-path", "back-up path", "invalid", and so on, may co-exist
in the BGP RIBs after being processed by the BGP decision process.
The path status information is currently not carried in the BGP
Update Message RFC4271 [RFC4271] or in the BMP Update Message RFC7854
[RFC7854].
External systems can use the path status for various applications.
The path status is commonly checked by operators when performing
troubleshooting. Having such status stored in a centralized system
can enable the development of tools that facilitate this process.
Optimisation systems can include the path status in their process,
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and also use the status as a validation source (since it can compare
the calculated state to the actual outcome of the network, such as
primary and backup path). As a final example, path status
information can complement other centralized sources of data, for
example, flow collectors.
This document defines a so-called Path Status TLV to convey the BGP
path status to the BMP server. The BMP Path Status TLV is carried in
the BMP Route Monitoring (RM) Message.
2. Path Status TLV
This document defines two types of Path Status TLVs: one is the IANA-
registered Path Status TLV, and the other is the Enterprise-specific
Path Status TLV.
2.1. IANA-registered Path Status TLV
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
+-------------------------------+-------------------------------+
|E| Type (15 bits) | Length (2 octets) |
+---------------------------------------------------------------+
| Index (2 octets) |
+-------------------------------+-------------------------------+
| Path Status (4 octets) |
+---------------------------------------------------------------+
| Reason Code (2 octets, optional) |
+---------------------------------------------------------------+
Figure 2: Encoding of IANA-Registered Path Status TLV
* E bit: For an IANA-registered TLV, the E bit MUST be set to 0
[I-D.ietf-grow-bmp-tlv-ebit].
* Type = TBD2 (15 Bits): indicates that it is the IANA-registered
Path Status TLV.
* Length (2 Octets): indicates the length of the value field of the
Path Status TLV. The value field further consists of the Path-
Status field and Reason Code field.
* Index (2 Octets): indicates the prefix that this TLV is
describing. Please see [I-D.ietf-grow-bmp-tlv] for details of the
use of the index field to associate the path marking content with
one or more NLRIs.
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* Path Status (4 Octets): indicates the path status of the BGP
Update PDU encapsulated in the RM Message. Currently 10 types of
path status are defined, as shown in Table 1. All zeros are
reserved.
* Reason Code (2 Octets, optional): indicates the reason of the path
status indicated in the Path Status field. The reason code field
is optional. If no reason code is carried, this field is empty.
If a reason code is carried, the reason code is indicated by a
2-byte value, which is defined in Table 2.
+------------+-----------------------------+
| Value | Path type |
+------------------------------------------+
| 0x00000001 | Invalid |
| 0x00000002 | Best |
| 0x00000004 | Non-selected |
| 0x00000008 | Primary |
| 0x00000010 | Backup |
| 0x00000020 | Non-installed |
| 0x00000040 | Best-external |
| 0x00000080 | Add-Path |
| 0x00000100 | Filtered in inbound policy |
| 0x00000200 | Filtered in outbound policy |
| 0x00000400 | Invalid ROV |
+------------+-----------------------------+
Table 1: IANA-Registered Path Type
Figure 1
The Path Status field contains a bitmap where each bit encodes a
specific role of the path. Multiple bits may be set when multiple
path status apply to a path.
* The best-path is defined in RFC4271 [RFC4271] and the best-
external path is defined in draft-ietf-idr-best-external
[I-D.ietf-idr-best-external].
* An invalid path is a route that does not enter the BGP decision
process.
* A non-selected path is a route that is not selected in the BGP
decision process. Back-up routes are considered non-selected,
while the best and ECMP routes are not considered as non-selected.
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* A primary path is a recursive or non-recursive path whose nexthop
resolution ends with an adjacency draft-ietf-rtgwg-bgp-pic
[I-D.ietf-rtgwg-bgp-pic]. A prefix can have more than one primary
path if multipath is configured
draft-lapukhov-bgp-ecmp-considerations
[I-D.lapukhov-bgp-ecmp-considerations]. A best-path is also
considered as a primary path.
* A backup path is also installed in the RIB, but it is not used
until some or all primary paths become unreachable. Backup paths
are used for fast convergence in the event of failures.
* A non-installed path refers to the route that is not installed
into the IP routing table.
* For the advertisement of multiple paths for the same address
prefix without the new paths implicitly replacing any previous
ones, the add-path status is applied [RFC7911].
The path status TLV does not force a BMP client to send any of these
paths. It just provides a method to mark the paths that are
available with their status.
+----------+-----------------------------------------------------+
| Value | Reason code |
+----------------------------------------------------------------+
| [0x0007] | invalid for AS loop |
| [0x0007] | invalid for unresolvable nexthop |
| [0x0016] | not preferred for Local preference |
| [0x0014] | not preferred for AS Path Length |
| [0x0013] | not preferred for origin |
| [0x0012] | not preferred for MED |
| [0x0011] | not preferred for peer type |
| [0x0010] | not preferred for IGP cost |
| [0x000E] | not preferred for router ID |
| [0x000D] | not preferred for peer address |
| [0x0020] | not preferred for AIGP |
+----------+-----------------------------------------------------+
Table 2: IANA-Registered Reason Code
Figure 2
2.2. Enterprise-specific Path Status TLV
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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
+-------------------------------+-------------------------------+
|E| Type (15 bits) | Length (2 octets) |
+-------------------------------+-------------------------------+
| PEN number (4 octets) |
+---------------------------------------------------------------+
| Index (2 octets) |
+---------------------------------------------------------------+
| Path Status (4 octets) |
+---------------------------------------------------------------+
| Reason Code (2 octets, optional) |
+---------------------------------------------------------------+
Figure 3: Encoding of Enterprise-specific Path Status TLV
* E bit: For an Enterprise-specific TLV, the E bit MUST be set to 1
[I-D.ietf-grow-bmp-tlv-ebit].
* Type = 1 (15 Bits): indicates that it's the Enterprise-specific
Path Status TLV.
* Length (2 Octets): indicates the length of the value field of the
Path Status TLV. The value field further consists of the Path-
Status field and Reason Code field.
* Index (2 Octets): indicates the prefix that this TLV is
describing. The index is the encapsulation order, starting from
0, of the prefix in the BGP Update PDU.
* PEN Number (4 octets): indicates the IANA enterprise number IANA-
PEN.
* Path Status (4 Octets): indicates the enterprise-specific path
status. The format is to be determined w.r.t. each PEN number.
* Reason Code (2 octets, optional): indicates the reasons/
explanations of the path status indicated in the Path Status
field. The format is to be determined w.r.t. each PEN number.
3. Implementation notes
The BMP path marking TLV remains optional within BMP implementations.
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An implementation of the BMP path marking TLV may not fully support
marking of all status defined in table Figure 1 or any future
extensions. Similarly, an implementation may choose to support the
inclusion of the reason code (for which support is also optional),
without necessarily incorporating any of the reason codes defined in
table Figure 2 or future extensions.
This document refrains from defining mechanisms for signaling the
status or reason codes an implementation supports. This could be
established through external means (e.g. documentation) or
potentially addressed in a subsequent document.
The remainder of this section encompasses additional points related
to the implementation of the BMP Path marking TLV.
3.1. Configuration of BMP path marking
Implementations supporting the BMP path marking TLV SHOULD provide an
option for enabling or disabling the Path Marking TLV over BMP
sessions. Furthermore, the configuration options for this TLV SHOULD
provide the means to enable and disable the transmission of reason
codes, if the reason code are supported by the implementation.
3.2. Paths with no markings
Some BGP routes might not require any type of status or reasons. For
example, an unfiltered path obtained via the Adj-RIB-IN may fall
under this category since there is really nothing to mark for that
path. We suggest a couple of approaches for signaling that a path
has no markings: (1) An implicit form of marking, achieved by
abstaining from appending any BMP marking TLV pointing toward the
route. (2) Alternatively, an explicit marking of the packet through a
TLV containing no marked status and no associated reason code.
3.3. Significance of status and origin RIBs
This document refrains from imposing any implementation to mark
specific status from specific RIBs. We recognize the diversity among
implementations; some might be able to mark some status over one RIB
while other do it on others. For instance, some might be able to
mark Adj-RIB-in filtered routes when obtained from the Adj-RIB-IN
pre, while other could do it only from the Adj-RIB-IN post. To
remove ambiguities in implementations, we recommend the meaning of
status (and reason codes) to not depend on the origin RIB of a route.
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3.4. Enterprise-specific status and reasons
Implementations introducing their own status and reason codes are
advised to adhere to [I-D.ietf-grow-bmp-tlv-ebit] and use ebit and
vendor specific status and reasons. Additionally, we recommend all
implementations to provide comprehensive documentation for these
codes.
For scenarios where a path state combines a standard status with an
enterprise-specific reason code (or vice versa), the following
alternatives are presented:
* Replication of the standard definitions within the enterprise-
specific space, thus permitting direct marking within the same
packet using the ebit.
* Assigning two TLVs to the same path(s): one containing the
standard part and another housing the vendor-specific part.
3.5. Multiple TLVs assigned to the same route.
We advocate for the employment of TLV grouping wherever feasible.
The inclusion of all marking information within a single message is
recommended, except on the case described in section Section 3.4. In
situations where multiple TLVs are associated with a single route,
all markings will be applicable to that route.
4. Acknowledgments
We would like to thank Jeff Haas and Maxence Younsi for their
valuable comments.
5. IANA Considerations
This document requests that IANA assign the following new parameters
to the BMP parameters name space.
Type = TBD1 (15 Bits): indicates that it is the IANA-registered Path
Status TLV.
6. Security Considerations
It is not believed that this document adds any additional security
considerations.
7. Normative References
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[I-D.ietf-grow-bmp-tlv]
Lucente, P. and Y. Gu, "TLV support for BMP Route
Monitoring and Peer Down Messages", Work in Progress,
Internet-Draft, draft-ietf-grow-bmp-tlv-12, 27 March 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-grow-
bmp-tlv-12>.
[I-D.ietf-grow-bmp-tlv-ebit]
Lucente, P. and Y. Gu, "Support for Enterprise-specific
TLVs in the BGP Monitoring Protocol", Work in Progress,
Internet-Draft, draft-ietf-grow-bmp-tlv-ebit-03, 24 July
2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
grow-bmp-tlv-ebit-03>.
[I-D.ietf-idr-best-external]
Marques, P., Fernando, R., Chen, E., Mohapatra, P., and H.
Gredler, "Advertisement of the best external route in
BGP", Work in Progress, Internet-Draft, draft-ietf-idr-
best-external-05, 3 January 2012,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-
best-external-05>.
[I-D.ietf-rtgwg-bgp-pic]
Bashandy, A., Filsfils, C., and P. Mohapatra, "BGP Prefix
Independent Convergence", Work in Progress, Internet-
Draft, draft-ietf-rtgwg-bgp-pic-19, 1 April 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-rtgwg-
bgp-pic-19>.
[I-D.lapukhov-bgp-ecmp-considerations]
Lapukhov, P. and J. Tantsura, "Equal-Cost Multipath
Considerations for BGP", Work in Progress, Internet-Draft,
draft-lapukhov-bgp-ecmp-considerations-11, 26 June 2023,
<https://datatracker.ietf.org/doc/html/draft-lapukhov-bgp-
ecmp-considerations-11>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
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[RFC7854] Scudder, J., Ed., Fernando, R., and S. Stuart, "BGP
Monitoring Protocol (BMP)", RFC 7854,
DOI 10.17487/RFC7854, June 2016,
<https://www.rfc-editor.org/info/rfc7854>.
[RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder,
"Advertisement of Multiple Paths in BGP", RFC 7911,
DOI 10.17487/RFC7911, July 2016,
<https://www.rfc-editor.org/info/rfc7911>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
Authors' Addresses
Camilo Cardona
NTT
164-168, Carrer de Numancia
08029 Barcelona
Spain
Email: camilo@ntt.net
Paolo Lucente
NTT
Siriusdreef 70-72
2132 Hoofddorp
Netherlands
Email: paolo@ntt.net
Pierre Francois
INSA-Lyon
Lyon
France
Email: Pierre.Francois@insa-lyon.fr
Yunan Gu
Huawei
Huawei Bld., No.156 Beiqing Rd.
Beijing
100095
China
Email: guyunan@huawei.com
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Thomas Graf
Swisscom
Binzring 17
CH-8045 Zurich
Switzerland
Email: thomas.graf@swisscom.com
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