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Date:      Tue, 21 Oct 2025 19:34:44 +0000
From:      bugzilla-noreply@freebsd.org
To:        bugs@FreeBSD.org
Subject:   [Bug 290407] IPv6 MLD (Multicast Listener Discovery) packets do not contain Router Alert
Message-ID:  <bug-290407-227@https.bugs.freebsd.org/bugzilla/>

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D290407

            Bug ID: 290407
           Summary: IPv6 MLD (Multicast Listener Discovery) packets do not
                    contain Router Alert
           Product: Base System
           Version: 15.0-CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Many People
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: dennypage@me.com

IPv6 Multicast Listener Discovery packets, specifically Multicast Listener
Reports, do not contain a Router Alert option as required by the Multicast
Listener Discovery RFCs. The lack of a Router Alert option causes Listener
Report packets to be discarded by receivers.

Specifics from the RFCs:

* RFC 2710 (MLDv1) Section 3:

All MLD messages described in this document are sent with a link-local IPv6
Source Address, an IPv6 Hop Limit of 1, and an IPv6 Router Alert option
[RTR-ALERT: RFC2711] in a Hop-by-Hop Options header.


* RFC 3810 & RFC 9777 (MLDv2) Section 5:

All MLDv2 messages described in this document MUST be sent with a link-local
IPv6 Source Address, an IPv6 Hop Limit of 1, and an IPv6 Router Alert option
[RFC2711] in a Hop-by-Hop Options header.


* RFC 3810 & RFC 9777 (MLDv2) Section 7.4:

Upon reception of an MLD message that contains a Report, the router checks =
if
the source address of the message is a valid link-local address, if the Hop
Limit is set to 1, and if the Router Alert option is present in the Hop-by-=
Hop
Options header of the IPv6 packet. If any of these checks fail, the packet =
is
dropped.

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