Add VLAN-aware MLD Snooping support

doc/SAI-Proposal-MLD-Snooping.md

@@ -0,0 +1,197 @@
+ VLAN MLD Snooping Support
+-------------------------------------------------------------------------------
+ Title       | VLAN MLD Snooping Support
+:-------------|:-----------------------------------------------------------------
+ Authors     | Anandhi Dhanabalan, Marvell Technology Inc 
+ Status      | In review
+ Type        | Standards track
+ Created     | 08/04/2026: Initial Draft
+ -------------------------------------------------------------------------------
+
+
+## 1. Overview
+
+This enhancement adds support for MLD (Multicast Listener Discovery)
+snooping control at the VLAN level. MLD is the IPv6 equivalent of IGMP,
+used for managing IPv6 multicast group memberships. As networks transition
+to IPv6 and dual-stack deployments, the ability to control MLD snooping
+independently is essential for efficient multicast traffic management.
+
+
+
+## 2. Motivation
+
+### Problem
+
+- No independent IPv6 multicast snooping control.
+
+### Current SAI State
+
+- Existing SAI VLAN attribute provides per-VLAN IGMP snooping control.
+- No corresponding per-VLAN MLD snooping control exists.
+- IPv4 and IPv6 multicast snooping cannot be configured independently.
+
+This proposal addresses these limitations by introducing independent MLD
+snooping control.
+
+
+
+# 3. Proposed SAI Attribute Changes
+
+## 3.1 New VLAN Attribute
+
+```c
+    /**
+     * @brief MLD Snooping enable or disable control for VLAN
+     *
+     * @type bool
+     * @flags CREATE_AND_SET
+     * @default false
+     */
+    SAI_VLAN_ATTR_MLD_SNOOPING_ENABLE,
+```
+
+## 3.2 Canonical IGMP Snooping Attribute Name
+
+The canonical attribute name SAI_VLAN_ATTR_IGMP_SNOOPING_ENABLE is introduced to establish a consistent naming convention between IPv4 and IPv6 snooping controls. The existing SAI_VLAN_ATTR_CUSTOM_IGMP_SNOOPING_ENABLE is retained as a backward-compatible alias.
+
+```c
+    /* New canonical name */
+    SAI_VLAN_ATTR_IGMP_SNOOPING_ENABLE
+
+    /* Backward compatibility alias */
+    SAI_VLAN_ATTR_CUSTOM_IGMP_SNOOPING_ENABLE =
+        SAI_VLAN_ATTR_IGMP_SNOOPING_ENABLE
+```
+
+# 4. Behavioral Model
+
+## 4.1 MLD Snooping Operation
+
+When VLAN MLD snooping is enabled, MLD protocol messages are delivered to the CPU according to
+the configured MLD traps (see Section 4.1.1). The control plane learns multicast
+listener membership and programs multicast forwarding entries in hardware.
+The interaction between VLAN MLD snooping and global MLD HOSTIF traps is
+described in Section 4.2.
+
+### 4.1.1 MLD Traps
+
+In this document, "MLD traps" refers to the following HOSTIF trap types:
+
+- `SAI_HOSTIF_TRAP_TYPE_IPV6_MLD_V1_V2`
+- `SAI_HOSTIF_TRAP_TYPE_IPV6_MLD_V1_REPORT`
+- `SAI_HOSTIF_TRAP_TYPE_IPV6_MLD_V1_DONE`
+- `SAI_HOSTIF_TRAP_TYPE_MLD_V2_REPORT`
+
+### **When MLD Snooping is ENABLED (per VLAN):**
+```
+Control Traffic:
+  MLD Protocol Messages (ICMPv6 Types 130, 131, 132, 143)
+    └─ Delivered to the CPU via configured MLD traps
+          → Control plane learns multicast listener membership
+
+Data Traffic:
+  IPv6 Multicast Data (FF00::/8)
+    └─ Forwarding behavior is determined by multicast forwarding entries
+       programmed by the control plane and the configured unknown multicast
+       handling policy (see Section 4.4).
+```
+
+> **Note on Unregistered Group Handling:**
+> The behavior for unregistered IPv6 multicast groups is not defined by `SAI_VLAN_ATTR_MLD_SNOOPING_ENABLE`. It follows the platform's existing unregistered multicast handling policy, which may vary across implementations. Refer to Section 4.4
+
+### **When MLD Snooping is DISABLED (per VLAN):**
+```
+Control Traffic:
+  MLD Protocol Messages (ICMPv6 Types 130, 131, 132, 143)
+    └─ Not delivered to the CPU via configured MLD traps
+         → No multicast listener membership learning
+
+Data Traffic:
+  IPv6 Multicast Data (FF00::/8)
+    └─ Existing multicast forwarding entries, if any, continue to apply.
+       No multicast forwarding entries are learned through MLD snooping.
+       Unknown multicast traffic follows the configured unknown multicast
+       handling policy (see Section 4.4).
+```
+
+
+
+## 4.2 Interaction with Global MLD HOSTIF Traps
+
+The VLAN-level MLD snooping attribute only controls whether MLD protocol
+messages on the VLAN participate in multicast listener learning. It does
+not create MLD HOSTIF traps by itself.
+
+Both of the following conditions must be satisfied:
+
+- At least one global MLD HOSTIF trap is configured.
+- VLAN MLD snooping is enabled.
+
+| Global MLD HOSTIF Traps | VLAN MLD Snooping | Listener Learning |
+|-------------------------|-------------------|-------------------|
+| Yes | Enabled | Enabled |
+| Yes | Disabled | Disabled |
+| No | Enabled | Unavailable |
+| No | Disabled | Unavailable |
+
+> **Note on HOSTIF trap packet action:**
+>
+> The configured HOSTIF trap packet action is applied only when an MLD packet
+> matches a configured MLD HOSTIF trap and VLAN MLD snooping is enabled for
+> that VLAN. This proposal does not modify the behavior of other HOSTIF traps
+> or packet classification mechanisms.
+---
+
+## 4.3 Interaction with IGMP Snooping
+These attributes should be independent.
+
+Valid configurations:
+```
+IGMP=true,  MLD=true   // Both IPv4 & IPv6
+IGMP=true,  MLD=false  // IPv4 only
+IGMP=false, MLD=true   // IPv6 only
+IGMP=false, MLD=false  // No IGMP/MLD snooping
+```
+
+
+## 4.4 Interaction with Unknown Multicast Flood Attributes
+The protocol-specific unknown multicast output group attributes
+- `SAI_VLAN_ATTR_UNKNOWN_IPV4_MCAST_OUTPUT_GROUP_ID` and
+- `SAI_VLAN_ATTR_UNKNOWN_IPV6_MCAST_OUTPUT_GROUP_ID`
+
+take precedence over
+
+- `SAI_VLAN_ATTR_UNKNOWN_MULTICAST_FLOOD_GROUP`.
+
+```
+                Unknown Multicast
+                       │
+            Is a protocol-specific
+           OUTPUT_GROUP_ID configured?
+                       │
+          ┌────────────┴─────────────────┐
+          │                              │
+         Yes                             No
+          │                              │
+Use protocol-specific          Is UNKNOWN_MULTICAST_
+ OUTPUT_GROUP_ID               FLOOD_GROUP configured?
+          │                              │
+          │                   ┌──────────┴──────────┐
+          │                  Yes                    No
+          │                   │                     │
+          ▼                   ▼                     ▼
+   Forward using        Use UNKNOWN_        Platform default
+ protocol-specific       MULTICAST_         behavior
+   output group          FLOOD_GROUP
+
+```
+> **Platforms without protocol-specific unknown multicast output group attributes**
+>
+> Platforms that support only
+> `SAI_VLAN_ATTR_UNKNOWN_MULTICAST_FLOOD_GROUP`
+> support independent IGMP and MLD snooping. Registered multicast traffic
+> continues to be forwarded based on multicast listener learning.
+> The only limitation is that unknown IPv4 and unknown IPv6 multicast
+> traffic share the same fallback forwarding policy because separate
+> protocol-specific output groups are unavailable.

inc/saivlan.h

@@ -388,7 +388,10 @@ typedef enum _sai_vlan_attr_t
      * @flags CREATE_AND_SET
      * @default false
      */
-    SAI_VLAN_ATTR_CUSTOM_IGMP_SNOOPING_ENABLE,
+    SAI_VLAN_ATTR_IGMP_SNOOPING_ENABLE,
+
+    /** @ignore - for backward compatibility */
+    SAI_VLAN_ATTR_CUSTOM_IGMP_SNOOPING_ENABLE = SAI_VLAN_ATTR_IGMP_SNOOPING_ENABLE,
 
     /**
      * @brief Vlan bind point for TAM object
@@ -422,6 +425,15 @@ typedef enum _sai_vlan_attr_t
      */
     SAI_VLAN_ATTR_SELECTIVE_COUNTER_LIST,
 
+    /**
+     * @brief MLD Snooping enable or disable control for VLAN
+     *
+     * @type bool
+     * @flags CREATE_AND_SET
+     * @default false
+     */
+    SAI_VLAN_ATTR_MLD_SNOOPING_ENABLE,
+
     /**
      * @brief End of attributes
      */

meta/acronyms.txt

@@ -106,6 +106,7 @@ MAC - Medium Access Control
 MDIO - Management Data Input/Output
 MDIX - Medium Dependent Interface Crossover
 MILLI - milli (1/1000)
+MLD - Multicast Listener Discovery
 MMU - Memory Management Unit
 MPLS - Multi Protocol Label Switching
 MTU - Maximum Transmission Unit