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ICMP6 RA: recognise PIO PD Preferred flag#1352

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bonktree wants to merge 2 commits intothe-tcpdump-group:masterfrom
bonktree:pr-pio-pflag
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ICMP6 RA: recognise PIO PD Preferred flag#1352
bonktree wants to merge 2 commits intothe-tcpdump-group:masterfrom
bonktree:pr-pio-pflag

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@bonktree
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@bonktree bonktree commented Aug 9, 2025

This is a 1-bit flag in the Prefix Information RA option defined by RFC9762.
If a compliant RA-accepting node receives a PIO with the P flag set, it is expected to ignore the A flag, if set, and make use of DHCPv6 Prefix Delegation to obtain a prefix and assign addresses from that prefix as described in RFC9663, not individual addresses from the PIO-specified prefix.

This is a 1-bit flag in the Prefix Information RA option defined by
RFC9762. If a compliant RA-accepting node receives a PIO with the P flag
set, it is expected to make use of DHCPv6 Prefix Delegation to obtain a
prefix and assign addresses from that prefix, not individual addresses
from the PIO-specified prefix.

Link: https://tools.ietf.org/html/rfc9762
Link: https://tools.ietf.org/html/rfc9663
Link: https://www.iana.org/assignments/icmpv6-parameters/icmpv6-parameters.xhtml#ipv6-neighbor-discovery-prefix-information-options
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Do you have any packets with this bit set as a material for a new test?

@bonktree
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bonktree commented Jan 19, 2026

Do you have any packets with this bit set as a material for a new test?

To this day I have not had any practice with a working impl to capture real-life packets, unfortunately. I am aware that e. g. odhcpd have added support (openwrt/odhcpd#301) for this RA PIO flag in their RA sender, so that functionality might be available in a recent OpenWRT release.

I'd be happy to add a test if someone else (or me) manages to provide some captured packets.

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