.. SPDX-FileCopyrightText: 2021 Open Networking Foundation <info@opennetworking.org>
.. SPDX-License-Identifier: Apache-2.0

.. _int:

In-band Network Telemetry (INT)
===============================

Overview
--------

SD-Fabric supports the Inband Network Telemetry (INT) standard for data plane
telemetry.

When INT is enabled, all switches are instrumented to generate INT reports for
all traffic, reporting per-packet metadata such as the switch ID, ingress/egress
ports, latency, queue congestion status, etc. Report generation is handled
entirely at the data plane, in a way that does not affect the performance
observed by regular traffic.

.. image:: ../images/int-overview.png
    :width: 700px

We aim at achieving visibility end-to-end. For this reason, we provide an
implementation of INT for switches as well hosts. For switches, INT report
generation is integrated as part of the same P4 pipeline responsible for
bridging, routing, UPF, etc. For hosts, we provide *experimental* support for
an eBPF-based application that can monitor packets as they are processed by the
Kernel networking stack and Kubernetes CNI plug-ins. In the following, we use
the term INT nodes to refer to both switches and hosts.

SD-Fabric is responsible for producing and delivering INT report packets to an
external collector. The actual collection and analysis of reports is out of
scope, but we support integration with 3rd party analytics platforms. SD-Fabric
is currently being validated for integration with Intel\ :sup:`TM` DeepInsight, a
commercial analytics platform. However, any collector compatible with the INT
standard can be used instead.

Supported Features
~~~~~~~~~~~~~~~~~~

* **Telemetry Report Format Specification v0.5**: report packets generated by
  nodes adhere to this version of the standard.
* **INT-XD mode (eXport Data)**: all nodes generate "postcards". For a given
  packet, the INT collector might receive up to N reports where N is the number
  of INT nodes in the path.
* **Configurable watchlist**: specify which flows to monitor. It could be all
  traffic, entire subnets, or specific 5-tuples.
* **Flow reports**: for a given flow (5-tuple), each node produces reports
  periodically allowing a collector to monitor the path and end-to-end latency,
  as well as detect anomalies such as path loop/change.
* **Drop reports**: when a node drops a packet, it generates a report carrying
  the switch ID and the drop reason (e.g., routing table miss, TTL zero, queue
  congestion, and more).
* **Queue congestion reports**: when queue utilization goes above a configurable
  threshold, switches produce reports for all packets in the queue,
  making it possible to identify exactly which flow is causing congestion.
* **Smart filters and triggers**: generating INT reports for each packet seen by
  a node can lead to excessive network overhead and overloading at the
  collector. For this reason, nodes implement logic to limit the volume of
  reports generated in a way that doesn't cause anomalies to go undetected. For
  flow reports and drop reports, the pipeline generates 1 report/sec for each
  5-tuple, or more when detecting anomalies (e.g., changes in the ingress/egress
  port, queues, hop latency, etc). For queue congestion reports, the number of
  reports that can be generated for each congestion event is limited to a
  configurable "quota".
* **Integration with P4-UPF**: when processing GTP-U encapsulated packets,
  switches can watch inside GTP-U tunnels, generating reports for the inner
  headers and making it possible to troubleshoot issues at the application
  level. In addition, when generating drop reports, we support UPF-specific drop
  reasons to identify if drops are caused by the UPF tables (because of a
  misconfiguration somewhere in the control stack, or simply because the
  specific user device is not authorized).

INT Report Delivery
~~~~~~~~~~~~~~~~~~~

INT reports generated by nodes are delivered to the INT collector using the same
fabric links. In the example below, user traffic goes through three switches.
Each one is generating an INT report packet (postcard), which is forwarded using
the same flow rules for regular traffic.

.. image:: ../images/int-reports.png
    :width: 700px

This choice has the advantage of simplifying deployment and control plane logic,
as it doesn't require setting up a different network and handling installation
of flow rules specific to INT reports. However, the downside is that delivery of
INT reports can be subject to the same issues that we are trying to detect using
INT. For example, if a user packet is getting dropped because of missing routing
entries, the INT report generated for the drop event might also be dropped for
the same reason.

In future releases, we might add support for using the management network for
report delivery, but for now using the fabric network is the only supported
option.

ONOS Configuration
------------------

To enable INT, modify the ONOS netcfg in the following way:

* in the ``devices`` section, use an INT-enabled pipeconf ID (``fabric-int``
  or ``fabric-spgw-int``);
* in the ``apps`` section, add a config block for app ID
  ``org.stratumproject.fabric.tna.inbandtelemetry``, like in the example below:

.. code-block:: json

    {
        "apps": {
            "org.stratumproject.fabric.tna.inbandtelemetry": {
                "report": {
                    "collectorIp": "10.32.11.2",
                    "collectorPort": 32766,
                    "minFlowHopLatencyChangeNs": 256,
                    "watchSubnets": [
                        "10.32.11.0/24"
                    ],
                    "queueReportLatencyThresholds": {
                        "0": {"triggerNs": 2000, "resetNs": 500},
                        "2": {"triggerNs": 1000, "resetNs": 400}
                    }
                }
            }
        }
    }

Here's a reference of the fields that you can configure for the INT app:

* ``collectorIp``: The IP address of the INT collector. Must be an IP address
  routable by the fabric, either the IP address of a host directly connected to
  the fabric and discovered by ONOS, or reachable via an external router.
  *Required*

* ``collectorPort``: The UDP port used by the INT collector to listen for report
  packets. *Required*

* ``minFlowHopLatencyChangeNs``: Minimum latency difference in nanoseconds to
  trigger flow report generation. *Optional, default is 256.*

  Used by the smart filters to immediately report abnormal latency changes. In
  normal conditions, switches generate 1 report per second for each active
  5-tuple. During congestion, when packets experience higher latency, the
  switch will generate a report immediately if the latency difference between
  this packet and the previous one of the same 5-tuple is greater than
  ``minFlowHopLatencyChangeNs``.

  **Warning:** Setting ``minFlowHopLatencyChangeNs`` to ``0`` or small values
  (lower than the switch normal jitter) will cause the switch to generate a lot
  of reports. The current implementation only supports powers of 2.

* ``watchSubnets``: List of IPv4 prefixes to add to the watchlist.
  *Optional, default is an empty list.*

  All traffic with source or destination IPv4 address included in one of these
  prefixes will be reported (both flow and drop reports). All other packets will
  be ignored. To watch all traffic, use ``0.0.0.0/0``. For GTP-U encapsulated
  traffic, the watchlist is always applied to the inner headers. Hence to
  monitor UE traffic, you should provide the UE subnet.

  INT traffic is always excluded from the watchlist.

  The default value (empty list) implies that flow reports and drop reports
  are disabled.

* ``queueReportLatencyThresholds``: A map specifying latency thresholds to
  trigger queue reports or reset the queue report quota.
  *Optional, default is an empty map.*

  The key of this map is the queue ID. Switches will generate queue congestion
  reports only for queue IDs in this map. Congestion detection for other queues
  is disabled. The same thresholds are used for all devices, i.e., it's not
  possible to configure different thresholds for the same queue on different
  devices.

  The value of this map is a tuple:

  * ``triggerNs``: The latency threshold in nanoseconds to trigger queue
    reports. Once a packet experiences latency **above** this threshold, all
    subsequent packets in the same queue will be reported, independently of the
    watchlist, up to the quota or until latency drops below ``triggerNs``.
    **Required**
  * ``resetNs``: The latency threshold in nanosecond to reset the quota. When
    packet latency goes below this threshold, the quota is reset to its original
    non-zero value. **Optional, default is triggerNs/2**.

  Currently the default quota is 1024 and cannot be configured.


Intel\ :sup:`TM` DeepInsight Integration
----------------------------------------

.. note::
    In this section, we assume that you already know how to deploy DeepInsight
    to your Kubernetes cluster with a valid license. For more information please
    reach out to Intel's support.

To be able to use DeepInsight with SD-Fabric, use the following steps:

* Modify the DeepInsight Helm Chart `values.yml` to include the following setting for `tos_mask`:

  .. code-block:: yaml

    global:
      preprocessor:
        params:
          tos_mask: 0

* Deploy DeepInsight
* Obtain the IPv4 address of the fabric-facing NIC interface of the Kubernetes
  node where the ``preprocessor`` container is deployed. This is the address to
  use as the ``collectorIp`` in the ONOS netcfg. This address must be routable
  by the fabric, i.e., make sure you can ping that from any other host in the
  fabric. Similarly, from within the preprocessor container you should be able
  to ping the loopback IPv4 address of **all** fabric switches (``ipv4Loopback``
  in the ONOS netcfg). If ping doesn't work, check the server's RPF
  configuration, we recommend setting it to ``net.ipv4.conf.all.rp_filter=2``.
* Generate a ``topology.json`` using the
  `SD-Fabric utility scripts
  <https://github.com/opennetworkinglab/sdfabric-utils/tree/main/deep-insight>`_
  (includes instructions) and upload it using the DeepInsight UI. Make sure to
  update and re-upload the ``topology.json`` frequently if you modify the
  network configuration in ONOS (e.g., if you add/remove switches or links,
  static routes, new hosts are discovered, etc.).

Enabling Host-INT
-----------------

Support for INT on hosts is still experimental.

Please check the documentation here to install ``int-host-reporter`` on your
servers:
``https://github.com/opennetworkinglab/int-host-reporter``

Drop Reasons
------------

We use the following reason codes when generating drop reports. Please use this
table as a reference when debugging drop reasons in DeepInsight or other INT
collector.

.. list-table:: SD-Fabric INT Drop Reasons
   :widths: 15 25 60
   :header-rows: 1

   * - Code
     - Name
     - Description
   * - 0
     - UNKNOWN
     - Drop with unknown reason.
   * - 26
     - IP TTL ZERO
     - IPv4 or IPv6 TTL zero. There might be a forwarding loop.
   * - 29
     - IP MISS
     - IPv4 or IPv6 routing table miss. Check for missing routes in ONOS or if
       the host is discovered.
   * - 55
     - INGRESS PORT VLAN MAPPING MISS
     - Ingress port VLAN table miss. Packets are being received with an
       unexpected VLAN. Check the ``interfaces`` section of the netcfg.
   * - 71
     - TRAFFIC MANAGER
     - Packet dropped by traffic manager due to congestion (tail drop) or
       because the port is down.
   * - 80
     - ACL DENY
     - Check the ACL table rules.
   * - 89
     - BRIDGING MISS
     - Missing bridging entry. Check table entry from bridging table.
   * - 128 (WIP)
     - NEXT ID MISS
     - Missing next ID from ECMP (``hashed``) or multicast table.
   * - 129
     - MPLS MISS
     - MPLS table miss. Check the segment routing device config in the netcfg.
   * - 130
     - EGRESS NEXT MISS
     - Egress VLAN table miss. Check the ``interfaces`` section of the netcfg.
   * - 131
     - MPLS TTL ZERO
     - There might be a forwarding loop.
   * - 132
     - UPF DOWNLINK PDR MISS
     - Missing downlink PDR rule for the UE. Check UP4 flows.
   * - 133
     - UPF UPLINK PDR MISS
     - Missing uplink PDR rule. Check UP4 flows.
   * - 134
     - UPF FAR MISS
     - Missing FAR rule. Check UP4 flows.
   * - 150
     - UPF UPLINK RECIRC DENY
     - Missing rules for UE-to-UE communication.