Internet DRAFT - draft-liu-lsr-igp-mpd
draft-liu-lsr-igp-mpd
LSR Y. Liu
Internet-Draft Y. Shen
Intended status: Standards Track ZTE
Expires: 12 April 2024 10 October 2023
Signaling Maximum Packet Depth(MPD) using IGP
draft-liu-lsr-igp-mpd-00
Abstract
This document proposes the concept of Maximum Packet Depth(MPD) to
represent the packet size that a node is able process from an
incoming packet, the signaling mechanism for MPD in IGP is also
defined.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Requirements Language . . . . . . . . . . . . . . . . . . 4
3. ISIS extensions for MPD Advertisement . . . . . . . . . . . . 4
3.1. Node MPD Advertisement . . . . . . . . . . . . . . . . . 4
3.2. Link MPD Advertisement . . . . . . . . . . . . . . . . . 5
4. OSPF extensions for MPD Advertisement . . . . . . . . . . . . 6
5. MPD Types . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. IPv6 Readable MPD . . . . . . . . . . . . . . . . . . . . 6
5.2. MPLS Readable MPD . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
In terms of processing packets, a device has various capabilities.
One of the capabilities is the maximum packet depth(MPD) that a node
can read from an incoming packet.
Being aware of the MPD of related nodes benefits the following
scenarios:
* In IPv6/SRv6,
- the headend node can attach data on the packet, e.g, the hop-by-hop
options header or the destination options header with the IOAM data
fields as introduced in [RFC9486]. With the knowledge of the MPDs of
the nodes along the path, the headend can make sure that the depth of
IOAM field (as well as SRH in the case of SRv6) after encapsulating
doesn't exceed the maximum size that these nodes are able to process.
- the intermediate nodes may increase the size of the packet. The
IPv6 extension headers, as well as their TLVs may be attached by the
intermediate destination nodes(e.g SR Segment Endpoint nodes) via
inserting or tunneling. In this case it is very important for
attaching nodes to obtain the packet processing sizes of the
downstream nodes.
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* In MPLS, there're potential usecases that the intermediate nodes
need to process the Post-Stack Network Actions beyond the label
stack, e.g, IOAM in MPLS as in [I-D.gandhi-mpls-ioam]. The
encapsulating node needs to know the maximum packet processing
size of the IOAM transit nodes to make the IOAM function work.
There're already some related works on packet size signaling, but
they are not sufficient.
The concept Maximum SID Depth (MSD) is originally introduced for SR-
MPLS to represent the number of SIDs supported by a node or a link on
a node. In a non-SR MPLS network, MSD defines the maximum label
depth. MSD is further extended for SRv6 as per [RFC9352]. This can
be collected via IS-IS [RFC8491], OSPF [RFC8476], BGP-LS [RFC8814],
or PCEP [RFC8664].
MSD, regardless of its type, can't fully represent the size of the
packet that the device can read. For MPLS, MSD represents the number
of LSEs, while MPD represents the packet size, regardless of whether
the content in the packet is carried in the form of labels or not.
And MSDs for SRv6 are related with the number of SRv6 SIDs, but other
components such as SRH TLV may exist, which are not in the scope of
MSD. Not to speak of other IPv6 extension headers in the usecases
mentioned above.
Besides MSD, another related concept is link mtu [RFC4821], it's the
maximum transmission unit, i.e., maximum IP packet size in bytes,
that can be conveyed in one piece over a link, which can be collected
via BGP-LS [I-D.ietf-idr-bgp-ls-link-mtu].
Link MTU is the maximum packet size that the device/interface is able
to send, while MPD represents the node's ability to read the packet.
Normally, these two values are not the same. For example, the
maximum packet size a node can read is 256 bytes, and the link mtu is
1500 bytes, after receiving a packet which contains a 512-byte
payload encapsulated in a 10-label MPLS stack, the node is able read
and process the label stack, and then using the label stack after
processing and the payload to form the new packet, whose size is less
than the link mtu and then send it out.
Based on the considerations above, this document defines the concept
of Maximum Packet Depth(MPD) to represent the maximum packet
processing size as well as the signaling mechanism in IGP.
2. Conventions used in this document
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2.1. Terminology
MSD: Maximum SID Depth as in [RFC8491].
Link MTU:As per [RFC4821], the Maximum Transmission Unit, i.e,
maximum IP packet size in bytes, that can be conveyed in one piece
over a link.
Path MTU(PMTU): The minimum link MTU of all the links in a path
between a source node and a destination node.[RFC8201]
MPD: Maximum Packet Depth supported by a node or a link on a node.
2.2. 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.
3. ISIS extensions for MPD Advertisement
3.1. Node MPD Advertisement
The Node MPD sub-TLV is defined within the body of the IS-IS Router
CAPABILITY TLV [RFC7981] to carry the provisioned packet depth of the
router originating the IS-IS Router CAPABILITY TLV. Node MPD is the
smallest MPD supported by the node on the set of interfaces
configured for use by the advertising IGP instance. MPD values may
be learned via a hardware API or may be provisioned. The Node MPD
sub-TLV is optional and the format is shown as follows.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPD-Type | MPD-Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ................... //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPD-Type | MPD-Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Node MPD Sub-TLV
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Where:
Type: TBA1
Length: variable; represents the total length of the Value field
Value: field consists of one or more pairs of a 1-octet MPD-Type and
1-octet MPD-Value
MPD-Type: value defined in the "IGP MPD-Types" registry created by
the IANA Considerations section of this document Section 6
MPD-Value: the packet size in bytes. This value MUST represent the
lowest value supported by any link configured for use by the
advertising IS-IS instance.
3.2. Link MPD Advertisement
The Link MSD sub-TLV is defined for TLVs 22, 23, 25, 141, 222, and
223 to carry the MSD of the interface associated with the link. MPD
values may be learned via a hardware API or may be provisioned. The
sub-TLV is optional and the format is shown as follows.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPD-Type | MPD-Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ................... //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPD-Type | MPD-Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Link MPD Sub-TLV
Where:
Type: TBA2
Length: variable; represents the total length of the Value field
Value: field consists of one or more pairs of a 1-octet MPD-Type and
1-octet MPD-Value
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MPD-Type: value defined in the "IGP MPD-Types" registry created by
the IANA Considerations section of this document Section 6
MPD-Value: the packet size in bytes.
4. OSPF extensions for MPD Advertisement
Tbd
5. MPD Types
5.1. IPv6 Readable MPD
IPv6 Readable MPD is defined as the maximum packet size in bytes,
starting from the IPv6 header, that a node can read from an incoming
IPv6 packet without performance impact.
5.2. MPLS Readable MPD
MPLS Readable MPD is the maximum packet size in bytes, starting from
the top of the MPLS label stack, that a node can read from an
incoming MPLS packet without performance impact.
6. IANA Considerations
This document includes a request to IANA to allocate sub-TLV type
codes for the new Node MPD sub-TLV proposed in Section 3.1 of this
document from IS-IS Router Capability TLV Registry as defined by
[RFC4971]. For Link MPD, IANA is requested to allocate new sub-TLV
codes as defined in Section 3.2 from Sub-TLVs for TLVs 22, 23, 141,
222 and 223 registry.
IANA is also requested to create a new Sub-type registry titled "IGP
MPD-Types" under the "Interior Gateway Protocol (IGP) Parameters"
registry to identify MPD-Types as proposed in Sections 3. The
following values are defined by this document:
Value Name Reference
----- --------------------- -------------
0 Reserved This document
1 IPv6 Readable MPD This document
2 MPLS Readable MPD This document
3-250 Unassigned
251-254 Experimental Use This document
255 Reserved This document
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7. Security Considerations
Security considerations as specified by [RFC7981] are applicable to
this document..
8. References
8.1. 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>.
[RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions
for Advertising Router Information", RFC 7981,
DOI 10.17487/RFC7981, October 2016,
<https://www.rfc-editor.org/info/rfc7981>.
[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>.
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/info/rfc9256>.
8.2. Informative References
[I-D.gandhi-mpls-ioam]
Gandhi, R., Brockners, F., Wen, B., Decraene, B., and H.
Song, "MPLS Data Plane Encapsulation for In Situ OAM
Data", Work in Progress, Internet-Draft, draft-gandhi-
mpls-ioam-11, 9 September 2023,
<https://datatracker.ietf.org/doc/html/draft-gandhi-mpls-
ioam-11>.
[I-D.ietf-idr-bgp-ls-link-mtu]
Zhu, Y., Hu, Z., Peng, S., and R. Mwehair, "Signaling
Maximum Transmission Unit (MTU) using BGP-LS", Work in
Progress, Internet-Draft, draft-ietf-idr-bgp-ls-link-mtu-
05, 26 July 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-idr-bgp-ls-link-mtu-05>.
[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007,
<https://www.rfc-editor.org/info/rfc4821>.
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[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8476] Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak,
"Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476,
DOI 10.17487/RFC8476, December 2018,
<https://www.rfc-editor.org/info/rfc8476>.
[RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
"Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
DOI 10.17487/RFC8491, November 2018,
<https://www.rfc-editor.org/info/rfc8491>.
[RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "Path Computation Element Communication
Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
DOI 10.17487/RFC8664, December 2019,
<https://www.rfc-editor.org/info/rfc8664>.
[RFC8814] Tantsura, J., Chunduri, U., Talaulikar, K., Mirsky, G.,
and N. Triantafillis, "Signaling Maximum SID Depth (MSD)
Using the Border Gateway Protocol - Link State", RFC 8814,
DOI 10.17487/RFC8814, August 2020,
<https://www.rfc-editor.org/info/rfc8814>.
[RFC9352] Psenak, P., Ed., Filsfils, C., Bashandy, A., Decraene, B.,
and Z. Hu, "IS-IS Extensions to Support Segment Routing
over the IPv6 Data Plane", RFC 9352, DOI 10.17487/RFC9352,
February 2023, <https://www.rfc-editor.org/info/rfc9352>.
[RFC9486] Bhandari, S., Ed. and F. Brockners, Ed., "IPv6 Options for
In Situ Operations, Administration, and Maintenance
(IOAM)", RFC 9486, DOI 10.17487/RFC9486, September 2023,
<https://www.rfc-editor.org/info/rfc9486>.
Authors' Addresses
Yao Liu
ZTE
China
Email: liu.yao71@zte.com.cn
Yiming Shen
ZTE
China
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Email: shen.yiming@zte.com.cn
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