ippm H. Song, Ed.
Internet-Draft T. Zhou
Intended status: Standards Track Huawei
Expires: October 18, 2018 April 16, 2018
In-situ OAM Data Type Extension
draft-song-ippm-ioam-data-extension-01
Abstract
This document describes a proposal which extends in-situ OAM to
support potential future standard tracing data in addition to those
currently defined. We provide use cases to motivate our proposal and
base the modifications on the latest in-situ OAM header format
specification.
Status of This Memo
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Table of Contents
1. Motivation for Data Type Extension . . . . . . . . . . . . . 2
2. Scalable Data Type Extension . . . . . . . . . . . . . . . . 3
2.1. Data Type Bitmap . . . . . . . . . . . . . . . . . . . . 3
2.2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Consideration for Efficient Data Packing . . . . . . . . 5
2.4. Alternative Data Extension Possibilities . . . . . . . . 5
3. Security Considerations . . . . . . . . . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6
7. Informative References . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Motivation for Data Type Extension
In-situ OAM (iOAM) [I-D.brockners-inband-oam-requirements] records
OAM information within user packets while the packets traverse a
network. The data types and data formats for in-situ OAM data
records have been defined in [I-D.ietf-ippm-ioam-data].
Currently 12 data types and associated formats (including wide format
and short format of the same data) are defined in
[I-D.ietf-ippm-ioam-data] . The presence of data is indicated by a
16-bit bitmap in the "OAM-Trace-Type" field.
In the current specification only four bits are left to identify new
standard data types. Moreover, some data is forced to be bundled
together as a single unit to save bitmap space and pack data to the
ideal size (e.g., the hop limit and the node id are bundled, and the
ingress interface id and the egress interface id are bundled),
regardless of the fact that an application may only ask for a part of
the data. Last but not the least, each data is forced to be 4-byte
aligned for easier access, resulting in waste of header space in many
cases.
Since the data plane bandwidth, the data plane packet processing, and
the management plane data handling are all precious yet scarce
resource, the scheme should strive to be simple and precise. The
application should be able to control the exact type and format of
data it needs to collect and analyze. It is conceivable that more
types of data may be introduced in the future. However, the current
scheme cannot support it after all the bits in the bitmap are used
up.
For example, when a flow traverses a series of middleboxes (e.g.,
Firewall, NAT, and load balancer), its identity (e.g., the 5-tuple)
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is often altered, which makes the OAM system lose track of the flow
trace. In this case, we may want to copy some of the original packet
header fields into the iOAM header so the original flow can be
identified at any point of the network.
For another example, in wireless, mobile, and optical network
environments, some physical data associated with a flow (e.g., power,
temperature, signal strength, GPS location) need to be collected to
monitor the service performance.
For another example, some data may have different semantics and
formats in different networks and application scenarios. An example
is the timestamp data type in which NTP, PTP, or any other local
defined approaches can be used.
All the above cases require new iOAM data types. More examples are
listed in Section 2.2.
There are some other issues about the current specification. For
example, bit 7 is used to indicate the presence of variable length
opaque state snapshot data; Bit 5 and bit 10 are used to indicate the
presence of the application specific data. While these data fields
can be used to store arbitrary data, the data is difficult to be
standardized and another schema is needed to decode the data, which
may lead to low data plane performance as well as interoperability
issues. More important, the existence of the variable length data
complicates the data processing such as data packing and
encapsulation. It is preferred to know the data type and size in
advance for efficient hardware implementation.
2. Scalable Data Type Extension
Based on the observation in Section 1, we propose a method for data
type encoding which can solve the current limitation and address
future data requirements.
2.1. Data Type Bitmap
Bitmap is simple and efficient data structure for high performance
data plane implementation. The base bitmap size is kept to be 16
bits. We use one bit to indicate a single type of data in a single
format. The last bit in the bitmap (i.e., bit 15), if set, is used
to indicate the presence of the next data type bitmap, which is 32
bits long. In the second bitmap, bit 31 is again reserved to
indicate a third bitmap, and so on. With each extra bitmap, 31 more
data types can be defined.
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Figure 1 shows an example of the in-situ OAM header format with two
extended OAM trace type fields. Except the OAM Trace Type fields,
all other fields remain the same as defined in
[I-D.ietf-ippm-ioam-data].
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Base OAM Trace Type |1|NodeLen| Flags | Octets-left |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended OAM Trace Type 1 |1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended OAM Trace Type 2 |0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Node Data List [] |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Extended OAM Trace Type Header Format
The specification of the Base OAM Trace Type is the same as the OAM
Trace Type in [I-D.ietf-ippm-ioam-data] except the last bit, which is
defined as follows:
o Bit 15: When set indicates presence of next bit map.
The OAM trace type fields are labeled as Base OAM Trace Type,
Extended OAM Trace Type 1, Extended OAM Trace Type 2, and so on. The
Base OAM Trace Type is always present. If no data type is asked by
the application in Extended OAM Trace Type n and beyond, then the
last bit in the previous bitmap is set to 1 and these extended fields
are not included in the header. On the other hand, to eliminate
ambiguity, if any data is asked for by the application in Extended
OAM Trace Type n, then Extended OAM Trace Type 1 to (n-1) must be
included in the header, even though no data type in these bitmaps are
needed (i.e., all zero bitmap except the last bit).
The actual data in a node is packed together in the same order as
listed in the OAM Trace Type bitmap. Each node is padded to be the
multiple of 4 bytes.
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2.2. Use Cases
New types of data can be potentially added and standardized, which
demand new bits allocated in the OAM Trace Type bitmaps. Some
examples are listed here.
o Metered flow bandwidth.
o Time gap between two consecutive flow packets.
o Remaining time budget to the packet delivery deadline.
o Buffer occupancy on the Node.
o Queue depth on each level of hierarchical QoS queues.
o Packet jitter at the Node.
o Current packet IP addresses.
o Current packet port numbers.
o Time using different network timing protocol.
o Other node statistics.
2.3. Consideration for Efficient Data Packing
The length of each data must be the multiple of 2 bytes. However,
allowing different data type to have different length, while
efficient in storage, makes data alignment and packing difficult.
If we can define the maximum number of data types that can be carried
per packet, the offset of each data in the node can be pre-calculated
and carried in the iOAM header. The overhead can be justified by the
overall space saving of the node data list. Otherwise, each data's
offset in the node must be calculated in each device, with the help
of a table which stores the size of each data type. We can also
arrange the bitmap to reflect the data availability order in the
system (e.g., the bit for egress_if_id must be after the bit for
ingress_if_id), so in a pipeline-based system, the required data can
be packed one after one.
2.4. Alternative Data Extension Possibilities
Bitmap is simple and support parallel processing in hardware.
However, it is not the only option to support data type extension.
For example, cascaded TLV can be used to support arbitrary number of
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new data types. This can be implemented by using a flag bit to
indicate the presence of extra data types and packing the number of
types and the list of the type IDs after the trace option header.
The corresponding data is therefore added in each node data list in
the order as its type ID is listed in the extended trace option
header.
3. Security Considerations
There is no extra security considerations beyond those have been
identified by the original in-situ OAM proposals.
4. IANA Considerations
This memo includes no request to IANA.
5. Acknowledgments
We would like to thank Frank Brockners, Carlos Pignataro, and Shwetha
Bhandari for helpful comments and suggestions.
6. Contributors
The document is inspired by numerous discussions with James N.
Guichard. He also provided significant comments and suggestions to
help improve this document.
7. Informative References
[I-D.brockners-inband-oam-requirements]
Brockners, F., Bhandari, S., Dara, S., Pignataro, C.,
Gredler, H., Leddy, J., Youell, S., Mozes, D., Mizrahi,
T., <>, P., and r. remy@barefootnetworks.com,
"Requirements for In-situ OAM", draft-brockners-inband-
oam-requirements-03 (work in progress), March 2017.
[I-D.ietf-ippm-ioam-data]
Brockners, F., Bhandari, S., Pignataro, C., Gredler, H.,
Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov,
P., Chang, R., and d. daniel.bernier@bell.ca, "Data Fields
for In-situ OAM", draft-ietf-ippm-ioam-data-00 (work in
progress), September 2017.
Authors' Addresses
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Haoyu Song (editor)
Huawei
2330 Central Expressway
Santa Clara, 95050
USA
Email: haoyu.song@huawei.com
Tianran Zhou
Huawei
156 Beiqing Road
Beijing, 100095
P.R. China
Email: zhoutianran@huawei.com
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