Least-Common Scope Communications
draft-mudric-6man-lcs-02
6MAN Working Group D. Mudric
Internet-Draft Ciena
Updates: RFC5014, RFC6724 (if approved) A. Petrescu
Intended status: Standards Track CEA, LIST
Expires: May 18, 2021 November 14, 2020
Least-Common Scope Communications
draft-mudric-6man-lcs-02
Abstract
This draft formulates a security problem statement. The problem
arises when a Host uses its Global Unicast Address (GUA) to
communicate with another Host situated on the same link.
To address this problem, we suggest to select and use addresses of a
least scope that are common.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on May 18, 2021.
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Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 2
3. Least Common Scope Communications . . . . . . . . . . . . . . 3
4. LL Address Resolution . . . . . . . . . . . . . . . . . . . . 3
5. Sending algorithm with LL Address . . . . . . . . . . . . . . 7
6. Other Issues with LL Address Resolution . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
11. Normative References . . . . . . . . . . . . . . . . . . . . 9
Appendix A. ChangeLog . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Problem Statement
Sockets listening on a global addresses are exposed to attacks.
RFC6724 Rule 8 selects a candidate address with the smallest scope.
Applications don't always have LL candidate address. They usually
have a GUA address. If GUA is on a local link, an application will
open a socket using GUA. To avoid using GUA on the local link, a
sender needs to find a destination LL address. Currently SASA
algorithm (RFC 6724 "Default Address Selection for Internet Protocol
Version 6 (IPv6)") cannot use the smallest common scope, given
destination GUA.
For security reasons, hosts should use an address with the smallest
scope. To avoid these attacks, the host should use LL or ULA
addresses.
These security reasons, in more detail, are described next. There is
a security problem when a Host uses (one of) its Global Unicast
Address(es) (GUA) to communicate to another Host situated on the same
link. The problem appears even if that second Host uses its link-
local address (LL) for this communication.
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The problem is that the Host that uses the GUA to actively
communicate with another Host situated on the same link opens a
globally reachable entry point in its operating system kernel. This
entry point appears when the GUA is assigned to a socket structure.
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