Internet DRAFT - draft-heitz-idr-diagnostic-attr
draft-heitz-idr-diagnostic-attr
IDR J. Heitz
Internet-Draft P. Narasimha
Intended status: Standards Track S. Gulrajani
Expires: September 26, 2019 Cisco
March 25, 2019
BGP Diagnostic Path Attribute
draft-heitz-idr-diagnostic-attr-01
Abstract
A BGP path attribute for the purpose of network diagnostics is
described. It is non-transitive, such that BGP speakers will not
forward it by default. It is structured as a list of elements. An
element begins with the BGP identifier and AS number of the speaker
that appends the element and includes a list of TLVs. Any speaker
can add or remove an element to/from the list. TLVs for a timestamp
and for a checksum are described.
Requirements Language
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].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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This Internet-Draft will expire on September 26, 2019.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Data Formats . . . . . . . . . . . . . . . . . . . . . . . . 2
2.1. Checksum TLV . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Timestamp TLV . . . . . . . . . . . . . . . . . . . . . . 4
3. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Operational Considerations . . . . . . . . . . . . . . . . . 5
5. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
9. Normative References . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
A BGP path attribute for the purpose of network diagnostics is
described. It is non-transitive, such that BGP speakers that do not
recognize the attribute will not propagate it by default. Even
speakers that do recognize the attribute MUST NOT propagate it by
default. A speaker MAY propagate the attribute if it is configured
to do so and MAY add it's own information as it does so. The
attribute is structured as a list of elements. An element begins
with the BGP identifier and AS number of the speaker that appends the
element and includes a list of TLVs. Any speaker can append or
remove an element to/from the list. TLVs for a timestamp and for a
checksum are described. The diagnostic attribute may be sent in a
withdraw message.
2. Data Formats
The BGP diagnostic consists of a series of elements, each of which is
formatted as follows.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ASN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BGP Identfifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
+ TLVs +
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields are as follows:
ASN - 4 octet Autonomous System Number of the speaker
that appended this element.
BGP Identfifier - BGP Identifier of the speaker that appended this
element.
Length - The number of octets comprising the TLVs of this
element. If there were no TLVs included, this
length would be 0.
TLVs - Any number of TLVs as further described. Each
TLV is optional. Each TLV comprises 2 octets of
Type, then 2 octets specifying the number of
octets in the value, then the octets of the
value.
2.1. Checksum TLV
A checksum of the BGP message, including the marker field. The
checksum is only valid between the sending and receiving speaker.
Since a receiving speaker may propagate an update, it will likely
change the set of attributes or their order in its own update
message, thus making the checksum useless in the propagated update.
A BGP speaker MAY remove the checksum TLV from a propagated
Diagnostic Path Attribute.
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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 = 1 | Length = 6 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Magic = 0xABCD | Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields are as follows:
Type - 1.
Length - 6.
Magic - The value 0xABCD. This helps to diagnose corruption
when looking at a hexdump.
Offset - The number of octets from the start of the UPDATE
message (start of the marker) to the start of this
TLV. This can help to identify corruption due to
misaligned segment reassembly.
Checksum - The 16 bit checksum computed according to [RFC1071].
2.2. Timestamp TLV
The time at which the indicated speaker processed the indicated set
of NLRI in the UPDATE message. There are several stages of
processing for each NLRI, each of which may be timestamped. These
stages vary widely between implementations. Therefore, the type code
used for each stage is implementation dependent. One stage is
universal. That is the stage when BGP hands the UPDATE message to
TCP for transmission. The Type code for the timestamp for that stage
is 256. The accuracy of the timestamp depends upon the diagnostic
application that requires it and is out of scope of this document.
The timestamp has enough bits to describe a time point within a
period of 136 years. As time passes, the timestamp will simply wrap
from one period to the next. For example, there exist some time
points in the year 1900 and the year 2036 with identical timestamps.
The determination of the period in which a timestamp occurs is out of
scope of this document.
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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 = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Seconds |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Fraction |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields are as follows:
Type - 256: The time when BGP hands the UPDATE message off
to TCP.
- 257 - 511: Timestamps for any other stages of
processing within BGP. The actual values and stages
are implementation dependent.
Length - 8.
Seconds - The number of Seconds since 0 h 1 January 1900 UTC as
further described in Section 6 of [RFC5905].
Fraction - A fraction of the above seconds also described in
Section 6 of [RFC5905].
3. Usage
The Checksum TLV is useful to narrow down a source of corruption of
UPDATE messages in each of the software and hardware layers between
the actual BGP processes.
Because the Diagnostic Attribute contains a list of speakers that
propagated an UPDATE and the attribute can be attached to a withdraw
message, it can assist in the diagnosis of route oscillations.
The timestamp TLV is used to narrow down delays in UPDATE processing
between BGP speakers and between the various stages of processing
within a BGP speaker.
4. Operational Considerations
As with any new BGP attribute, if it is propagated, NLRI packing into
BGP UPDATE messages may be affected. This needs to be taken into
consideration when using the Timestamp TLV to measure bulk update
message timing.
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The Diagnostic Path Attribute MAY be sent in an UPDATE message that
does not contain an NLRI field [RFC4271] or an MP_REACH_NLRI Path
Attribute [RFC4760]. When carried in such a message, it is unlikely
to be propagated, although it is possible.
If the addition or extension of the Diagnostic Path Attribute would
cause the UPDATE message length to be exceeded, then the attribute
SHOULD NOT be added or extended.
If the timestamps among participating speakers are not well
synchronized, then the timestamps added by each speaker may appear
out of order. In any case, the order in which elements are added to
the Diagnostic Attribute can always be determined, because each
speaker appends its element to the attribute.
The experimental TLV types may clash. That means that multiple
vendors may use the same expreimental TLV type code for different
purposes unbeknown to each other. To reduce the chance of TLV type
code clashes, the type code for an experimental TLV SHOULD be
configurable on the speaker. Because the propagation of the
Diagnostic Attribute must be configured on each speaker, it is
unlikely that two uncoordinated experiments will interfere with each
other.
5. Error Handling
A checksum error SHALL NOT be treated as a protocol error. The
response is implementation dependent.
A TLV length error SHALL be treated as attribute-discard according to
[RFC7606].
An unrecognized TLV MUST not be treated as a protocol error.
6. Security Considerations
This attribute is not forwarded by default. Therefore, it should
cause no unexpected ill effects.
7. IANA Considerations
IANA is requested to assign a BGP path attribute value for the BGP
Diagnostic Path Attribute.
IANA is requested to create and maintain a registry for the TLV
types. The allocation policies as per [RFC8126] are stated for the
range of values.
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Range Allocation Policy
----------- ------------------------------
0-32767 First Come First Served
32768-65535 Experimental
Value Description Reference
--------- ------------------------------ ---------
0 Reserved This RFC
1 Checksum This RFC
256 - 511 Timestamp This RFC
8. Acknowledgements
The authors would like to thank Shyam Sethuram and Bruno Decraene for
suggestions that have been added to the document.
9. Normative References
[RFC1071] Braden, R., Borman, D., and C. Partridge, "Computing the
Internet checksum", RFC 1071, DOI 10.17487/RFC1071,
September 1988, <https://www.rfc-editor.org/info/rfc1071>.
[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>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<https://www.rfc-editor.org/info/rfc4760>.
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<https://www.rfc-editor.org/info/rfc5905>.
[RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
Patel, "Revised Error Handling for BGP UPDATE Messages",
RFC 7606, DOI 10.17487/RFC7606, August 2015,
<https://www.rfc-editor.org/info/rfc7606>.
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[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
Authors' Addresses
Jakob Heitz
Cisco
170 West Tasman Drive
San Jose, CA, CA 95134
USA
Email: jheitz@cisco.com
Prasad S. Narasimha
Cisco
170 West Tasman Drive
San Jose, CA, CA 95134
USA
Email: snprasad@cisco.com
Sameer Gulrajani
Cisco
170 West Tasman Drive
San Jose, CA, CA 95134
USA
Email: sameerg@cisco.com
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