RFC 7739 on Security Implications of Predictable Fragment Identification Values

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        RFC 7739

        Title:      Security Implications of Predictable Fragment 
                    Identification Values 
        Author:     F. Gont
        Status:     Informational
        Stream:     IETF
        Date:       February 2016
        Mailbox:    fgont@si6networks.com
        Pages:      20
        Characters: 46433
        Updates/Obsoletes/SeeAlso:   None

        I-D Tag:    draft-ietf-6man-predictable-fragment-id-10.txt

        URL:        https://www.rfc-editor.org/info/rfc7739

        DOI:        http://dx.doi.org/10.17487/RFC7739

IPv6 specifies the Fragment Header, which is employed for the
fragmentation and reassembly mechanisms.  The Fragment Header
contains an "Identification" field that, together with the IPv6
Source Address and the IPv6 Destination Address of a packet,
identifies fragments that correspond to the same original datagram,
such that they can be reassembled together by the receiving host.
The only requirement for setting the Identification field is that the
corresponding value must be different than that employed for any
other fragmented datagram sent recently with the same Source Address
and Destination Address.  Some implementations use a simple global
counter for setting the Identification field, thus leading to
predictable Identification values.  This document analyzes the
security implications of predictable Identification values, and
provides implementation guidance for setting the Identification field
of the Fragment Header, such that the aforementioned security
implications are mitigated.

This document is a product of the IPv6 Maintenance Working Group of the IETF.

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