< draft-petrescu-6man-ll-prefix-len-16.txt   draft-petrescu-6man-ll-prefix-len-17.txt >
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Updates: RFC4291, RFC4007 (if approved) L. Velvindron Updates: RFC4291, RFC4007 (if approved) L. Velvindron
Intended status: Standards Track Cyberstorm.mu Intended status: Standards Track Cyberstorm.mu
Expires: November 7, 2019 N. Kottapalli Expires: November 7, 2019 N. Kottapalli
Benu Networks Benu Networks
G. Mishra G. Mishra
Verizon Communications Verizon Communications
May 6, 2019 May 6, 2019
The length of the prefix of an IPv6 link-local address ranges from 10 to The length of the prefix of an IPv6 link-local address ranges from 10 to
127 127
draft-petrescu-6man-ll-prefix-len-16 draft-petrescu-6man-ll-prefix-len-17
Abstract Abstract
A rejected Erratum to RFC4291 "IPv6 Addr Archi" on the topic of link- A rejected Erratum to RFC4291 "IPv6 Addr Archi" on the topic of link-
local addresses 'would need' a draft. This draft is an answer to local addresses 'would need' a draft. This draft is an answer to
that need. that need.
The length of the prefix of an IPv6 link-local address is variable. The length of the prefix of an IPv6 link-local address is variable.
The minimal value is 10 decimal. The maximum value is 127 decimal. The minimal value is 10 decimal. The maximum value is 127 decimal.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Definitions and Statements . . . . . . . . . . . . . . . . . 2 1. Definitions and Statements . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3 3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3
4. Kinds of Solutions . . . . . . . . . . . . . . . . . . . . . 4 4. Kinds of Solutions . . . . . . . . . . . . . . . . . . . . . 4
5. Context . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5. Context . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. Example of use of LL Prefix Length 32 . . . . . . . . . . . . 8 6. Example of use of LL Prefix Length 32 . . . . . . . . . . . . 8
7. Use-Case . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7. Use-Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Use-Case Convoy . . . . . . . . . . . . . . . . . . . . . 9
7.2. Intuitive Next-Hop . . . . . . . . . . . . . . . . . . . 11
8. Security Considerations . . . . . . . . . . . . . . . . . . . 11 8. Security Considerations . . . . . . . . . . . . . . . . . . . 11
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 11 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 12
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
12. Normative References . . . . . . . . . . . . . . . . . . . . 12 12. Normative References . . . . . . . . . . . . . . . . . . . . 12
Appendix A. ChangeLog . . . . . . . . . . . . . . . . . . . . . 12 Appendix A. ChangeLog . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Definitions and Statements 1. Definitions and Statements
The prefix of an IP address is formed by the n leftmost bits of the The prefix of an IP address is formed by the n leftmost bits of the
address. (in a left-to-right writing system). address. (in a left-to-right writing system).
The prefix of an IP address is used for goals such as: identify the The prefix of an IP address is used for goals such as: identify the
type of an IPv6 address (link-local, global, others), identify the type of an IPv6 address (link-local, global, others), identify the
belonging of an IP address to a particular subnetwork, assist the belonging of an IP address to a particular subnetwork, assist the
forwarding (or not forwarding) decisions, and others. forwarding (or not forwarding) decisions, and others.
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i2 address is fe80:12::1:1/32 ('12' means subnet between R1 and R2, i2 address is fe80:12::1:1/32 ('12' means subnet between R1 and R2,
'1' is R1, 2nd '1' is 'front' interface) '1' is R1, 2nd '1' is 'front' interface)
i3 address is fe80:12::2:2/32 i3 address is fe80:12::2:2/32
Figure 2: Figure Figure 2: Figure
One router's interface (connected to the other router) uses address One router's interface (connected to the other router) uses address
fe80:12::1:1/32 and the other router's corresponding interface uses fe80:12::1:1/32 and the other router's corresponding interface uses
address fe80:12::2:2/32. address fe80:12::2:2/32.
7. Use-Case 7. Use-Cases
7.1. Use-Case Convoy
The topology in a linear convoy of cars, in V2V manner is like this: The topology in a linear convoy of cars, in V2V manner is like this:
car1 car2 car3 car1 car2 car3
--------- --------- --------- --------- --------- ---------
| IP-OBU1 | ---subnet1 ---- | IP-OBU2 | --- subnet2--- | IP-OBU3 | | IP-OBU1 | ---subnet1 ---- | IP-OBU2 | --- subnet2--- | IP-OBU3 |
--------- --------- --------- --------- --------- ---------
|in-car | | |in-car | |
|subnets: Ethernet, WiFi, CAN, BT, etc |subnets: Ethernet, WiFi, CAN, BT, etc
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fe80:1::1 to fe80:1::2 that does not reply means the channels are fe80:1::1 to fe80:1::2 that does not reply means the channels are
wrong; otherwise (with fe80::IID) it is impossible to say whether the wrong; otherwise (with fe80::IID) it is impossible to say whether the
channels are wrong or that wrong address was used to ping (all channels are wrong or that wrong address was used to ping (all
fe80::IID64bit) look the same to a human - they are 'random'). fe80::IID64bit) look the same to a human - they are 'random').
- BSD allowing manual configuration of LL addresses may have other - BSD allowing manual configuration of LL addresses may have other
benefits outside the OCB context benefits outside the OCB context
Figure 5: Improvements Figure 5: Improvements
7.2. Intuitive Next-Hop
In some IP networks only link-local addresses are used as next hops,
as described in RFC 7404. The next hop is part of an entry in the
routing table. Make the next hop intuitive. The next hop is
routinely used by sysadmin to ping and check whether it is reachable.
Making the next hop intuitive can be achieved by mapping the global
unicast address into both the subnet and interface id fields; in the
past, experience shown that substituting just 'fe80' for the first 16
bytes of a GUA (such that to transform a GUA into an LL, to be used
as next hop) ended up bleeding into the 54 0 bits required by RFC
4291.
8. Security Considerations 8. Security Considerations
The clarification of the definition of the prefix length of the IPv6 The clarification of the definition of the prefix length of the IPv6
link-local prefix at IANA is: call it 'leading bits' and not link-local prefix at IANA is: call it 'leading bits' and not
'prefix', or state that the IPv6 prefix length of link-local 'prefix', or state that the IPv6 prefix length of link-local
addresses is 10 decimal. This clarification has beneficial impact in addresses is 10 decimal. This clarification has beneficial impact in
the algorithm implementation for calculation of the opaque and stable the algorithm implementation for calculation of the opaque and stable
Interface Identifiers for IPv6 link-local addresses. It also Interface Identifiers for IPv6 link-local addresses. It also
positively impacts some implementations of IPv6 forwarding. positively impacts some implementations of IPv6 forwarding.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
Appendix A. ChangeLog Appendix A. ChangeLog
The changes are listed in reverse chronological order, most recent The changes are listed in reverse chronological order, most recent
changes appearing at the top of the list. changes appearing at the top of the list.
-17: added a new use-case for sysadmins in need of an intuitive LL
address (to check with ping) used for next-hop of routing protocols.
-16: added a description of the behaviour of ifconfig fe80:1::1/32 on -16: added a description of the behaviour of ifconfig fe80:1::1/32 on
MAC and Windows 10 Operating Systems; added a suggestion about the MAC and Windows 10 Operating Systems; added a suggestion about the
use of ULA prefixes instead of LL prefixes; added a reference to an use of ULA prefixes instead of LL prefixes; added a reference to an
RFC 7404 about the use of only LL addresses in an IPv6 network; RFC 7404 about the use of only LL addresses in an IPv6 network;
explained the result from practice of the use of 'fe80::1:2/64'; explained the result from practice of the use of 'fe80::1:2/64';
explained why the text says 'hidden' for '%' on some OSs; mentioned explained why the text says 'hidden' for '%' on some OSs; mentioned
the DNS kind of solutions; added explanation of manual configuration the DNS kind of solutions; added explanation of manual configuration
and automation; added exaplanation of an example of complex to and automation; added exaplanation of an example of complex to
remember and type link-local addresses; added explanation of why DNS remember and type link-local addresses; added explanation of why DNS
solution is a problem mouvement, not problem resolution. solution is a problem mouvement, not problem resolution.
 End of changes. 7 change blocks. 
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