Generic Delivery Functions
draft-zzhang-intarea-generic-delivery-functions-02
intarea Z. Zhang
Internet-Draft R. Bonica
Intended status: Standards Track K. Kompella
Expires: February 26, 2022 Juniper Networks
G. Mirsky
ZTE
August 25, 2021
Generic Delivery Functions
draft-zzhang-intarea-generic-delivery-functions-02
Abstract
Some functionalities (e.g., fragmentation/reassembly and
Encapsulating Security Payload) provided by IPv6 can be viewed as
delivery functions independent of IPv6 or even IP entirely. This
document proposes to provide those functionalities at different
layers (e.g., MPLS, BIER or even Ethernet) independent of IP.
Status of This Memo
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This Internet-Draft will expire on February 10, 2022.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Specifications . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. MPLS layer . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. BIER layer . . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Other layers . . . . . . . . . . . . . . . . . . . . . . 5
2.4. Generic Fragmentation Header (GFH){#gfh} . . . . . . . . 6
3. Security Considerations . . . . . . . . . . . . . . . . . . . 6
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Normative References . . . . . . . . . . . . . . . . . . 7
5.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Consider an operator providing Ethernet services such as EVPN. The
Ethernet frames that a Provider Edge (PE) device receives from a
Customer Edge (CE) device may have a larger size than the PE-PE path
MTU (PMTU) in the provider network. This could be because
1. the provider network is built upon virtual connections (e.g.,
pseudowires) provided by another infrastructure provider, or
2. the customer network uses jumbo frames while the provider network
does not, or
3. the provider-side overhead for transporting customer packets
across the network pushes past the PMTU.
In any case, the provider cannot simply require its customers to
change their MTU.
To get those large frames across the provider network, currently, the
only workaround is to encapsulate the frames in IP (with or without
GRE) and then fragment the IP packets. Even if MPLS is used for
service delimiting, IP is used for transportation (MPLS over IP/GRE).
This may not be desirable in certain deployment scenarios, where MPLS
is the preferred transport or IP encapsulation overhead is deemed
excessive.
IPv6 fragmentation and reassembly are based on the IPv6 Fragmentation
header below [RFC8200]:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Reserved | Fragment Offset |Res|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: IPv6 Fragmentation Header
This document proposes adapting this header for use in non-IP
contexts since the fragmentation/reassembly function is actually
independent of IPv6 except for the following aspects:
o The fragment header is identified as such by the "previous"
header.
o The "Next Header" value is from the "Internet Protocol Numbers"
registry.
o The "Identification" value is unique in the (source, destination)
context provided by the IPv6 header.
The "Identification" field, in conjunction with the IPv6 source and
destination addresses identifies fragments of the original packet for
the purpose of reassembly.
Therefore, the fragmentation/reassembly function can be applied at
other layers as long as a) the fragment header is identified as such;
and b) the context for packet identification is provided. Examples
of such layers include MPLS, BIER, and Ethernet (if IEEE determines
it is so desired).
For the same consideration, the IP Encapsulating Security Payload
(ESP) [RFC4303] could also be applied at other layers if ESP is
desired there. For example, if for whatever reason the Ethernet
service provider wants to provide ESP between its PEs, it could do so
without requiring IP encapsulation if ESP is applied at non-IP
layers.
Similarly, In-Situ OAM (IOAM) functions [I-D.ietf-ippm-ioam-data] can
also be applied to many layers.
We refer to these as Generic Delivery Functions (GDFs), which could
be achieved at a shim layer between a source and destination delivery
points, for example:
o Source and destination IP/Ethernet nodes
o Ingress and egress nodes of MPLS Label Switch Paths (LSPs)
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o BIER Forwarding Ingress Routers (BFIRs) and BIER Forwarding Egress
Routers (BFERs)
2. Specifications
A Generic Delivery Function, being generic, is likely applicable to
IP as well. Therefore, IPv6 Extension Headers (for some GDFs) are
directly used at other layers.
2.1. MPLS layer
[I-D.song-mpls-extension-header] specifies MPLS Extension Headers
encoding. A label entry in the stack indicates the presence of
extension headers after the label stack. It starts with a Header of
Extension Headers, as depicted in the following excerpt from that
specification:
0 31
+--------+--------+--------+--------+ \
| | |
~ MPLS Label Stack ~ |
| | |
+--------+--------+--------+--------+ |
| EH Indicator (TBD) | > MPLS Label Stack
+--------+--------+--------+--------+ | (extended with EHI)
| | |
~ MPLS Label Stack ~ |
| | |
+--------+--------+--------+--------+ <
| Header of Extension Headers (HEH) | |
+--------+--------+--------+--------+ |
| | |
~ Extension Header (EH) 1 ~ |
| | |
+--------+--------+--------+--------+ > MPLS EH Fields
~ ~ | (new)
+--------+--------+--------+--------+ |
| | |
~ Extension Header (EH) N ~ |
| | |
+--------+--------+--------+--------+ <
| | |
~ Upper Layer Headers/Payload ~ > MPLS Payload
| | | (as is)
+--------+--------+--------+--------+ /
One or more of the EHs in the above can be an IPv6 Extension Header
for a GDF.
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2.2. BIER layer
For BIER layer, a TBD value for the "proto" field in the outer BIER
header indicates that some BIER Extension Headers follow the BIER
header, including some IPv6 Extension Headers for GDFs.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BIFT-id | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Nibble | Ver | BSL | Entropy |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|OAM|R|H| DSCP | Proto | BFIR-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Header of Extension Headers (HEH) |
+---------------------------------------------------------------+
~ Extension Header (EH) 1 ~
+---------------------------------------------------------------+
~ ... ~
+---------------------------------------------------------------+
~ Extension Header (EH) N ~
+---------------------------------------------------------------+
~ Upper Layer Headers/Payload ~
+---------------------------------------------------------------+
R: The "R" flag bit is reserved. It MUST be set to 0 on transmit and
ignored on receive.
H: If the "H" flag bit, it indicates the presence of at least one
extension header that needs to be processed hop by hop even before
a BFER is reached. In this case, the Proto field must be set to
the TBD value indicating the presence of extension headers.
2.3. Other layers
Similarly, any layer can have an indication in its packet header that
some GDF extension headers follow, including some IPv6 Extension
Headers for GDF purpose.
For example, if the outer header is Ethernet (if IEEE would decide to
provide the generic delivery functions on top of Ethernet directly),
then a new Ethertype would be assigned by IEEE to indicate the
presence of GDF extension headers.
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2.4. Generic Fragmentation Header (GFH){#gfh}
For generic fragmentation/reassembly functionality, the existing IPv6
Fragment Header needs to be enhanced for MPLS as following:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Fragment Offset |R|S|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Fragment/Source Identification (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Generic Fragmentation Header
R: The "R" flag bit is reserved. It MUST be set to 0 on transmit and
ignored on receive.
S: If the "S" flag bit is clear, the context for the Identification
field is provided by the outer header, and only the source-
identifying information in the outer header is used.
If the "S" flag bit is set, the variable Identification field
encodes both source-identifying information (e.g., the IP address
of the node adding the GFH) and an identification number unique
within that source. The length of the Fragment header is encoded
in the 8-bit "Hdr Ext Len" field (which is a Reserved field in the
original IPv6 Fragment Header).
When a GFH is used together with other GDF Headers (GDFH), the GFH
SHOULD be the first GDFH.
The above enhancement is not necessary but MAY be used for BIER as
well. If the outer header is BIER and the "S" flag bit is clear, the
"BFIR-id" field in the BIER header provides the context for the
"Identification" field. If the bit is set, then the source
information embedded in the source/fragment identification field is
used.
3. Security Considerations
To be provided.
4. Acknowledgements
The authors thank Stewart Bryant and Tony Przygienda for their
valuable comments and suggestions.
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5. References
5.1. Normative References
[I-D.song-mpls-extension-header]
Song, H., Li, Z., Zhou, T., Andersson, L., and Z. Zhang,
"MPLS Extension Header", draft-song-mpls-extension-
header-05 (work in progress), July 2021.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120,
DOI 10.17487/RFC5120, February 2008,
<https://www.rfc-editor.org/info/rfc5120>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
DOI 10.17487/RFC5308, October 2008,
<https://www.rfc-editor.org/info/rfc5308>.
[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
2015, <https://www.rfc-editor.org/info/rfc7684>.
[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>.
[RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
F. Baker, "OSPFv3 Link State Advertisement (LSA)
Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
2018, <https://www.rfc-editor.org/info/rfc8362>.
5.2. Informative References
[I-D.ietf-ippm-ioam-data]
Brockners, F., Bhandari, S., and T. Mizrahi, "Data Fields
for In-situ OAM", draft-ietf-ippm-ioam-data-14 (work in
progress), June 2021.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.
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[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,
<https://www.rfc-editor.org/info/rfc6514>.
Authors' Addresses
Zhaohui Zhang
Juniper Networks
Email: zzhang@juniper.net
Ron Bonica
Juniper Networks
Email: rbonica@juniper.net
Kireeti Kompella
Juniper Networks
Email: kireeti@juniper.net
Gregory Mirsky
ZTE
Email: gregory.mirsky@ztetx.com
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