Network Working Group H. Song, Ed.
Internet-Draft M. McBride
Intended status: Informational Futurewei Technologies
Expires: January 2, 2020 July 1, 2019
Requirement and Solution for Multicast Traffic Telemetry
draft-song-multicast-telemetry-00
Abstract
This document discusses the requirement of on-path telemetry for
multicast traffic. The existing solutions are examined and their
issues are addressed with new modifications that adapt to the
multicast scenario.
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 [RFC2119][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."
This Internet-Draft will expire on January 2, 2020.
Copyright Notice
Copyright (c) 2019 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements for Multicast Traffic Telemetry . . . . . . . . 3
3. Issues of Existing Techniques . . . . . . . . . . . . . . . . 3
4. Proposed Modifications to Existing Techniques . . . . . . . . 4
4.1. Per-hop postcard . . . . . . . . . . . . . . . . . . . . 4
4.2. Per-section postcard . . . . . . . . . . . . . . . . . . 5
5. Considerations for Different Multicast Protocols . . . . . . 6
5.1. Application in PIM . . . . . . . . . . . . . . . . . . . 6
5.2. Application in P2MP . . . . . . . . . . . . . . . . . . . 7
5.3. Application in BIER . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 8
10.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
Multicast traffic is an important traffic type in today's Internet.
Multicast provides services that are often real time (e.g., online
meeting) or have strict QoS requirements (e.g., IPTV, Market Data).
Multicast packet drop and delay can severely affect the application
performance and user experience.
It is important to monitor the performance of the multicast traffic.
Existing OAM techniques cannot gain direct and accurate information
about the multicast traffic. New on-path telemetry techniques such
as In-situ OAM [I-D.brockners-inband-oam-data] and Postcard-based
Telemetry [I-D.song-ippm-postcard-based-telemetry] provide promising
means to directly monitor the network experience of multicast
traffic. However, multicast traffic has some unique characteristics
which pose some challenges on efficiently applying such techniques.
This document describes the requirement for multicast traffic
telemetry and shows the issues of the existing on-path telemetry
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techniques. We then propose modifications to make these techniques
adapt to the multicast application.
2. Requirements for Multicast Traffic Telemetry
Multicast traffic is forwarded through a multicast tree. With PIM
and P2MP (MLDP, RSVP-TE) the forwarding tree is established and
maintained by the multicast routing protocol. With BIER, no state is
created in the network to establish a forwarding tree, instead, a
bier header provides the necessary information for each packet to
know the egress points. Multicast packets are only replicated at
each tree branch node for efficiency.
There are several requirements for multicast traffic telemetry:
o Reconstruct and visualize the multicast tree through data plane
monitoring.
o Gather the multicast packet delay and jitter performance.
o Find the multicast packet drop location and reason.
o Gather the VPN state and tunnel information in case of P2MP
multicast.
All of these requirements need to directly monitor the multicast
traffic and derive data from the multicast packets. The conventional
OAM mechanisms such as multicast ping and trace are insufficient to
meet these requirements.
3. Issues of Existing Techniques
On-path Telemetry techniques that directly retrieve data from
multicast traffic's live network experience are ideal to address the
above mentioned requirements. The representative techniques include
In-situ OAM (IOAM) [I-D.brockners-inband-oam-data] and Postcard-based
Telemetry (PBT) [I-D.song-ippm-postcard-based-telemetry]. However,
unlike unicast, multicast poses some unique challenges to applying
these techniques.
Multicast packets are replicated at each branch node in the
corresponding multicast tree. Therefore, there are multiple copies
of a packets in the network.
If IOAM is used for on-path data collection, the partial trace data
will also be replicated into multiple copies. The end result is that
each copy of the multicast packet has a complete trace. Most of the
data is redundant. Data redundancy introduces unnecessary header
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overhead, wastes network bandwidth, and complicates the data
processing. In case the multicast tree is large and the path is
long, the redundancy problem becomes severe.
PBT can be used to eliminate such data redundancy, because each node
on the tree only sends a postcard covering local data. However, PBT
cannot track the tree branches properly so it can bring confusion
about the multicast tree topology. For example, Node A has two
branches, one to Node B and one to node D, and Node B leads to Node C
and Node D leads to Node E. From the received postcard, one cannot
tell whether or not Node C(E) is the next hop of Node B(D).
The fundamental reason for this problem is that there is not an
identifier (either implicit or explicit) to correlate the data on
each branch.
4. Proposed Modifications to Existing Techniques
We propose two solutions to address the above issues. One is built
on PBT and requires augmentation to the instruction header of PBT-I;
the other combines the IOAM trace mode and PBT for an optimized
solution.
4.1. Per-hop postcard
The straightforward way to mitigate the PBT's drawback is to augment
it with a branch identifier field. Note that this only works for the
PBT-I variation where an instruction header is present. To make the
branch identifier globally unique, the branch node ID plus an index
is used. For example, if Node A has two branches, to Nodes B and C,
Node A will use [A, 0] as the branch identifier for the branch to B,
and [A, 1] for the branch to C. The identifier is unchanged and
carried with the multicast packet until the next branch node. Each
postcard needs to include the branch identifier in the export data.
The branch identifier and the other fields such as flow ID and
sequence number are sufficient for the data analyzer to reconstruct
the topology of the multicast tree.
Figure 1 shows an example of this solution. "P" stands for the
postcard packet. The square brackets contains the branch identifier.
The curly brace contains the telemetry data about a specific node.
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P:[A,0]{A} P:[A,0]{B} P:[B,1]{D} P:[B,0]{C}
^ ^ ^ ^
: : : :
: : : :
: : : +-:-+
: : : | |
: : +---:----->| C |--...
+-:-+ +-:-+ | : | |
| | | |----+ : +---+
| A |------->| B | :
| | | |--+ +-:-+
+---+ +---+ | | |
+-->| D |--....
| |
+---+
Figure 1: Per-hop Postcard
4.2. Per-section postcard
The second solution is a combination of the IOAM trace mode and PBT.
To avoid the data redundancy, at each branch node, the trace data
accumulated so far is exported by a postcard before the packet is
replicated. In this case, each branch still needs to keep some
identifier to help correlate the postcards for each tree section.
The natural way is to simply carry the branch node's data (including
its ID) in the trace of each branch. This is also necessary because
each replicated multicast packet can have different telemetry data
pertaining to this particular copy (e.g., node delay, egress
timestamp, and egress interface). As a consequence of, the local
data exported by each branch node can only contain partial data
(e.g., ingress interface and ingress timestamp).
Figure 2 shows an example in a part of a multicast tree. Node B and
D are two branch nodes so they will export a postcard covering the
trace data for the previous section. The end node of each path need
to export the data of the last section as a postcard as well.
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P:{A,B'} P:{B,C,D}
^ ^
: :
: :
: : {D}
: : +--...
: +---+ +---+ |
: {B} | |{B,C}| |--+
: +-->| C |---->| D |
+---+ +---+ | | | | |--+
| | {A} | |--+ +---+ +---+ |
| A |---->| B | +--...
| | | |--+ +---+ {D}
+---+ +---+ | | |{B,E}
+-->| E |--...
{B} | |
+---+
Figure 2: Per-section Postcard
There is no need to modify the IOAM trace mode header format. We
just need to configure the branch node to export the postcard and
refresh the IOAM header and data.
5. Considerations for Different Multicast Protocols
MTRACEv2 [RFC8487] provides an active probing approach for the
tracing of an IP multicast routing path. Mtrace can also provide
information such as the packet rates and losses, as well as other
diagnostic information. New on-path telemetry techniques will
enhance Mtrace, and other existing OAM solutions, with more granular
and realtime network status data through direct measurements. There
are various multicast protocols that are used to forward the
multicast data. Each will require their own unique on-path telemetry
solution.
5.1. Application in PIM
PIM-SM [RFC7761] is the most widely used multicast routing protocol
deployed today. Of the various PIM modes (PIM-SM, PIM-DM, BIDIR-PIM,
PIM-SSM), PIM-SSM is the preferred method due to its simplicity and
removal of network source discovery complexity. With all PIM modes,
control plane state is established in the network in order to forward
multicast UDP data packets. But with PIM-SSM, the discovery of
multicast sources is performed outside of the network via HTTP, SDN,
etc. IP Multicast packets fall within the range of 224.0.0.0 through
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239.255.255.255. The telemetry solution will need to work within
this address range and provide telemetry data for this UDP traffic.
The proposed solutions for encapsulating the telemetry instruction
header and metadata in IPv4/IPv6 UDP packets are described in
[I-D.herbert-ipv4-udpencap-eh] and
[I-D.ioametal-ippm-6man-ioam-ipv6-deployment].
5.2. Application in P2MP
Multicast Label Distribution Protocol (MLDP) and P2MP RSVP-TE are
commonly used within a Multicast VPN (MVPN) environment. MLDP
provides extensions to LDP to establish point-to-multipoint (P2MP)
and multipoint-to-multipoint (MP2MP) label switched paths (LSPs) in
MPLS networks. P2MP RSVP-TE provides extensions to RSVP-TE for
establish traffic-engineered P2MP LSPs in MPLS networks. The
telemetry solution will need to be able to follow theses P2MP paths.
The telemetry instruction header and data should be encapsulated into
MPLS packets on P2MP paths. A corresponding proposal is described in
[I-D.song-mpls-extension-header].
5.3. Application in BIER
BIER [RFC8279] adds a new header to multicast packets and allows the
multicast packets to be forwarded according to the header only. By
eliminating the requirement of maintaining per multicast group state,
BIER is more scalable than the traditional multicast solutions.
OAM Requirements for BIER [I-D.ietf-bier-oam-requirements] lists many
of the requirements for OAM at the BIER layer which will help in the
forming of on-path telemetry requirements as well.
There is also current work to provide solutions for BIER forwarding
in ipv6 networks. For instance, a solution, BIER in Non-MPLS IPv6
Networks [I-D.xie-bier-ipv6-encapsulation], proposes a new bier
Option Type codepoint from the "Destination Options and Hop-by-Hop
Options" IPv6 sub-registry. This is similar to what IOAM proposes
for IPv6 transport.
Depending on how the BIER header is encapsulated into packets with
different transport protocols, the method to encapsulate the
telemetry instruction header and metadata also varies. It is also
possible to make the instruction header and metadata a part of the
BIER header itself, such as in a TLV.
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6. Security Considerations
No new secuirty issues are identified other than those discovered by
the IOAM and PBT drafts.
7. IANA Considerations
The document makes no request of IANA.
8. Contributors
TBD
9. Acknowledgments
TBD
10. References
10.1. Normative References
[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>.
[RFC4687] Yasukawa, S., Farrel, A., King, D., and T. Nadeau,
"Operations and Management (OAM) Requirements for Point-
to-Multipoint MPLS Networks", RFC 4687,
DOI 10.17487/RFC4687, September 2006,
<https://www.rfc-editor.org/info/rfc4687>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
[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>.
[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC8279, November 2017,
<https://www.rfc-editor.org/info/rfc8279>.
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[RFC8487] Asaeda, H., Meyer, K., and W. Lee. Ed., "Mtrace Version 2:
Traceroute Facility for IP Multicast", RFC 8487,
DOI 10.17487/RFC8487, October 2018,
<https://www.rfc-editor.org/info/rfc8487>.
10.2. Informative References
[I-D.brockners-inband-oam-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-brockners-inband-oam-data-07 (work
in progress), July 2017.
[I-D.herbert-ipv4-udpencap-eh]
Herbert, T., "IPv4 Extension Headers and UDP Encapsulated
Extension Headers", draft-herbert-ipv4-udpencap-eh-01
(work in progress), March 2019.
[I-D.ietf-bier-oam-requirements]
Mirsky, G., Nordmark, E., Pignataro, C., Kumar, N.,
Aldrin, S., Zheng, L., Chen, M., Akiya, N., and S.
Pallagatti, "Operations, Administration and Maintenance
(OAM) Requirements for Bit Index Explicit Replication
(BIER) Layer", draft-ietf-bier-oam-requirements-07 (work
in progress), February 2019.
[I-D.ioametal-ippm-6man-ioam-ipv6-deployment]
Bhandari, S., Brockners, F., Mizrahi, T., Kfir, A., Gafni,
B., Spiegel, M., Krishnan, S., and M. Smith, "Deployment
Considerations for In-situ OAM with IPv6 Options", draft-
ioametal-ippm-6man-ioam-ipv6-deployment-01 (work in
progress), March 2019.
[I-D.song-ippm-postcard-based-telemetry]
Song, H., Zhou, T., Li, Z., Shin, J., and K. Lee,
"Postcard-based On-Path Flow Data Telemetry", draft-song-
ippm-postcard-based-telemetry-04 (work in progress), June
2019.
[]
Song, H., Li, Z., Zhou, T., and L. Andersson, "MPLS
Extension Header", draft-song-mpls-extension-header-02
(work in progress), February 2019.
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[I-D.xie-bier-ipv6-encapsulation]
Xie, J., Geng, L., McBride, M., Dhanaraj, S., Yan, G., and
Y. Xia, "Encapsulation for BIER in Non-MPLS IPv6
Networks", draft-xie-bier-ipv6-encapsulation-01 (work in
progress), June 2019.
Authors' Addresses
Haoyu Song (editor)
Futurewei Technologies
2330 Central Expressway
Santa Clara
USA
Email: hsong@futurewei.com
Mike McBride
Futurewei Technologies
2330 Central Expressway
Santa Clara
USA
Email: mmcbride@futurewei.com
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