6man WG X. Li
Internet-Draft C. Bao
Intended status: Standards Track CERNET Center/Tsinghua University
Expires: May 3, 2020 E. Ruan
Fungible Inc.
R. Bonica
Juniper Networks
October 31, 2019
Compressed Routing Header (CRH) Helper Option
draft-bonica-6man-crh-helper-opt-00
Abstract
This document defines the IPv6 CRH Helper option. When an SRm6
ingress node originates a packet, it can use the IPv6 CRH Helper
option to provide SID Forwarding Information Base (SFIB) information
to downstream nodes that do not maintain a complete SFIB.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Option Format . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Option Processing . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
SRm6 [I-D.bonica-spring-srv6-plus] leverages two new IPv6 [RFC8200]
Routing types. Generically, they are called the Compressed Routing
Header (CRH) [I-D.bonica-6man-comp-rtg-hdr]. More specifically, the
16-bit version of the CRH is called the CRH-16, while the 32-bit
version of the CRH is called the CRH-32.
Both CRH versions contain the following fields:
o Next Header - Identifies the header immediately following the CRH.
o Hdr Ext Len - Length of the CRH.
o Routing Type - Identifies the Routing header variant (i.e., CRH-16
or CRH-32).
o Segments Left - The number of segments still to be traversed
before reaching the SRm6 path egress node.
o Segment Identifier (SID) List - Represents the SRm6 path as an
ordered list of Segment Identifiers (SID). SIDs are listed in
reverse order, with SID[0] representing the final segment, SID[1]
representing the penultimate segment, and so forth. SIDs are
listed in reverse order so that Segments Left can be used as an
index to the SID List. The SID indexed by Segments Left is called
the current SID.
As per [RFC8200], when an IPv6 node receives a packet, it examines
the packet's destination address. If the destination address
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represents an interface belonging to the node, the node processes the
next header. If the node encounters and recognizes the CRH, it
processes the CRH as follows:
o If Segments Left equal 0, skip over the CRH and process the next
header in the packet.
o Decrement Segments Left.
o Query a local data structure, called the SID Forwarding
Information Base (SFIB), searching for an entry that is indexed by
the current SID.
o If the above-mentioned query returns an SFIB entry, update the
packet's IPv6 Destination Address and forward the packet.
In a typical SRm6 deployment, every segment ingress node maintains a
complete SFIB and the above-mentioned query returns an SFIB entry.
However, in some SRm6 deployments, some segment ingress nodes
maintain a complete SFIB while others do not. The following are
reasons why a segment ingress node might not maintain a complete
SFIB:
o the node is a Network Interface Card (NIC) in a data center.
Although it originates many segments, it does not participate in
the SRm6 control plane [I-D.bonica-lsr-crh-isis-extensions].
o the node resides in another autonomous system and does not
participate in the SRm6 control plane.
This document defines the IPv6 CRH Helper option. When an SRm6 path
ingress node originates a packet, it can use the IPv6 CRH Helper
option to provide SFIB information to downstream nodes that do not
maintain a complete SFIB.
If a segment ingress node queries its SFIB, searching for an entry
that is indexed by the current SID, and that query returns nothing,
the segment ingress node can obtain the required SFIB information
from the IPv6 CRH Helper option. If the segment ingress node cannot
obtain the required SFIB information from either source, it discards
the packet sends an ICMPv6 [I-D.bonica-lsr-crh-isis-extensions]
Parameter Problem message to the source node.
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
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14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Option Format
The CRH Helper option contains the following fields:
o Option Type - (8-bits) CRH Helper option. Value TBD by IANA.
(Suggested value: 0x11). See Note below.
o Opt Data Len - (8-bits) Length of the option, in octets, excluding
the Option Type and Option Length fields.
o SFIB Helper (SFIBH) List - (Variable length) A list of SFIBHs.
Each SFIBH contains the following fields:
o SFIBH Length - (8-bits) Length of the SFIBH, in octets, excluding
SFIBH Length. Value MUST be greater than 2 and less than 19.
o Low SID - (8-bits) Index to the CRH SID List. References the
first member of the SID List to which this SFIBH applies.
o High SID - (8-bits) Index to the CRH SID List. References the
last member of the SID List to which this SFIBH applies.
o Prefix field (variable length): An IPv6 Prefix.
NOTE : The highest-order two bits of the Option Type (i.e., the "act"
bits) are 00. These bits specify the action taken by a destination
node that does not recognize the option. The required action is to
skip over this option and continue processing the header.
The third highest-order bit of the Option Type (i.e., the "chg" bit)
is 0. This indicates that Option Data cannot be modified along the
path between the packet's source and its destination.
4. Option Processing
When a segment endpoint node processes a CRH, it attempts to resolve
the SID using information contained by its SFIB. If it cannot
resolve the SID using SFIB, it attempts to resolve the SID using
information received in an applicable SFIBH. If no SFIBH applies to
the current SID, the processing node discards the packet and sends an
ICMPv6 Parameter Problem message to the source node.
When the processing node uses an SFIBH to resolve a SID, it executes
the following procedure:
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o Set the IPv6 Destination Address to 0::
o Overwrite the low order bits of the IPv6 Destination Address with
the current SID found in the CRH
o Overwrite the high order bits of the IPv6 Destination Address with
the prefix found in the applicable SFIBH
If the prefix found in the applicable SFIBH is 16 bytes long, it
overwrites the entire IPv6 Destination Address.
The CRH Helper option MAY occur in a Destination Options header that
precedes a CRH. It SHOULD NOT occur in a Hop-by-hop options header
or in a Destination Options header that precedes an upper-layer
header.
When a segment ingress node resolves a SID using information obtained
from the CRH helper option, the SID is understood to be a prefix SID.
Therefore, the packet is forwarded to its destination via the least
cost path.
Information obtained from the CRH Helper option is transient. It is
discarded as soon as the packet that carried it has been processed.
5. Security Considerations
When a segment endpoint node processes a CRH, it attempts to resolve
the SID using information contained by its SFIB. If it can resolve
the SID using SFIB, it MUST ignore the CRH Helper option, even if it
contains an applicable SFIBH.
6. IANA Considerations
IANA is requested to allocate a code point from the Destination
Options and Hop-by-hop Options registry
(https://www.iana.org/assignments/ipv6-parameters/
ipv6-parameters.xhtml#ipv6-parameters-2). This option is called "CRH
Helper Option". The "act" bits are 00 and the "chg" bit is 0.
(Suggested value: 0x11).
7. Acknowledgements
Thanks to TBD for their careful review of this document.
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8. References
8.1. Normative References
[I-D.bonica-6man-comp-rtg-hdr]
Bonica, R., Kamite, Y., Niwa, T., Alston, A., Henriques,
D., Jalil, L., So, N., Xu, F., Chen, G., Zhu, Y., Yang,
G., and Y. Zhou, "The IPv6 Compressed Routing Header
(CRH)", draft-bonica-6man-comp-rtg-hdr-08 (work in
progress), October 2019.
[I-D.bonica-spring-srv6-plus]
Bonica, R., Hegde, S., Kamite, Y., Alston, A., Henriques,
D., Jalil, L., Halpern, J., Linkova, J., and G. Chen,
"Segment Routing Mapped To IPv6 (SRm6)", draft-bonica-
spring-srv6-plus-06 (work in progress), October 2019.
[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>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
[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>.
[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>.
8.2. Informative References
[I-D.bonica-lsr-crh-isis-extensions]
Kaneriya, P., Shetty, R., Hegde, S., and R. Bonica, "IS-IS
Extensions To Support The IPv6 Compressed Routing Header
(CRH)", draft-bonica-lsr-crh-isis-extensions-00 (work in
progress), May 2019.
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Authors' Addresses
Xing Li
CERNET Center/Tsinghua University
Room 225, Main Building, Tsinghua University
Beijing 100084
People's Republic of China
Email: xing@cernet.edu.cn
Congxiao Bao
CERNET Center/Tsinghua University
Room 225, Main Building, Tsinghua University
Beijing 100084
People's Republic of China
Email: congxiao@cernet.edu
Eddie Ruan
Fungible Inc.
3201 Scott Blvd
Santa Clara, California 95054
USA
Email: eddie.ruan@fungible.com
Ron Bonica
Juniper Networks
2251 Corporate Park Drive
Herndon, Virginia 20171
USA
Email: rbonica@juniper.net
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