Documentation
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Overview ¶
Package mld decodes MLD — Multicast Listener Discovery — the IPv6 multicast-group membership protocol carried in ICMPv6: MLDv1 (RFC 2710) and MLDv2 (RFC 3810). MLD is the IPv6 counterpart of IGMP: a host emits an MLD Report to tell the on-link router which IPv6 multicast groups it wants to receive, and routers emit Queries to refresh that state. It is a network-reconnaissance source — an MLD Report reveals exactly which multicast groups a host has joined (and, via the MLDv2 source-filter records, which senders it includes or excludes), exposing the host's multicast-based services: mDNS / Bonjour (ff02::fb), LLMNR (ff02::1:3), SSDP / UPnP, the all-DHCP-servers group, PTP, and IPTV / streaming groups. An MLD Query reveals the active querier and its robustness / interval parameters. It is the IPv6 companion to the project's internal/igmp (v1/v2) and internal/igmpv3 (IPv4 multicast), and the MLD member of the ICMPv6 family alongside internal/ndp.
Wrap-vs-native judgement ¶
Native. MLD is a small ICMPv6 message: a fixed header + a multicast address, and for MLDv2 either a source list (Query) or a list of group records (each a fixed header + an array of 16-byte source addresses, Report). A byte-field read + two walks; stdlib only (net for the IPv6 formatting), no new go.mod dep.
Verifiable / no confidently-wrong output ¶
The MLDv1 Query / Report / Done layout, the MLDv2 Query (with the S / QRV / QQIC fields and source list) and the MLDv2 Report group-record array were verified field-for-field against scapy's MLD layers (ICMPv6MLQuery / ICMPv6MLReport / ICMPv6MLDone / ICMPv6MLQuery2 / ICMPv6MLReport2 / ICMPv6MLDMultAddrRec) and RFC 2710 / RFC 3810. The MLDv2 Maximum-Response-Code and QQIC floating-point encodings (RFC 3810 §5.1.3 / §5.1.9) are decoded. The ICMPv6 checksum is computed over an IPv6 pseudo-header that is not present in a bare MLD capture, so it is surfaced as raw hex without a validity claim (matching internal/ndp). A type 130 Query is dispatched to MLDv1 vs MLDv2 by length (RFC 3810 §8.1: an MLDv2 Query is ≥ 28 bytes). A non-MLD ICMPv6 type is rejected.
Index ¶
Constants ¶
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Variables ¶
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Functions ¶
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Types ¶
type GroupRecord ¶
type GroupRecord struct {
RecordType int `json:"record_type"`
RecordTypeName string `json:"record_type_name"`
MulticastAddress string `json:"multicast_address"`
Sources []string `json:"sources,omitempty"`
AuxDataHex string `json:"aux_data_hex,omitempty"`
}
GroupRecord is one MLDv2 multicast address record from a Report.
type Result ¶
type Result struct {
Type int `json:"type"`
TypeName string `json:"type_name"`
Code int `json:"code"`
ChecksumHex string `json:"checksum_hex"`
MLDVersion int `json:"mld_version,omitempty"`
// Query / v1 Report / v1 Done
MaxResponseDelayMs int `json:"max_response_delay_ms,omitempty"`
MulticastAddress string `json:"multicast_address,omitempty"`
GeneralQuery bool `json:"general_query,omitempty"`
// MLDv2 Query extras
SuppressRouterProcessing bool `json:"suppress_router_side_processing,omitempty"`
QRV int `json:"qrv,omitempty"`
QQICSeconds int `json:"qqic_seconds,omitempty"`
QuerierSources []string `json:"querier_sources,omitempty"`
// MLDv2 Report
Records []GroupRecord `json:"records,omitempty"`
Notes []string `json:"notes,omitempty"`
}
Result is the decoded view of an MLD (Multicast Listener Discovery) message.
Source Files