117 lines
4.3 KiB
Markdown
117 lines
4.3 KiB
Markdown
# Dante Multicast Flow Discovery
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## Solution (2026-01-23)
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**Problem**: Multicast flows showed `?? (dante-av:xxxxx)` instead of the TX device name.
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**Root Cause**: `UpdateDanteTxChannels()` was never being called, so `GetDanteTxDeviceInGroup()` couldn't identify which member of a multicast group was the transmitter.
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**Fix**: Added call to `t.nodes.UpdateDanteTxChannels(info.Name, ip, ...)` when a device with TX channels is discovered via ARC protocol.
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**How it works now**:
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1. TX device discovered via mDNS, probed via ARC (port 4440)
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2. ARC query 0x1000 returns TX channel count > 0
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3. `UpdateDanteTxChannels()` marks the device as a transmitter
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4. IGMP snooping detects TX device joining multicast group
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5. IGMP snooping detects RX device joining same multicast group
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6. `GetDanteTxDeviceInGroup()` finds the TX device (has TxChannels) in the group
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7. Flow displayed as `TX-DEVICE -> RX-DEVICE`
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---
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## Protocol Notes
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### ARC Protocol Packet Formats
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There are two packet formats observed:
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**Format 1 (0x27xx)** - Used by our code for basic queries:
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```
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27 xx LL LL 13 xx CC CC 00 00 [args...]
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^seq ^0x1300|seq
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```
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**Format 2 (0x2809)** - Used by Dante Controller:
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```
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28 09 LL LL SS SS CC CC 00 00 [args...]
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^len ^seq ^cmd
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```
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Basic commands (0x1000, 0x1003, 0x3000) work with Format 1.
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Advanced commands (0x2600, 0x3600) require Format 2 to avoid error status 0x0030.
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### Commands Tested
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| Command | Purpose | Status |
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|---------|---------|--------|
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| 0x1000 | Channel counts | Works |
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| 0x1003 | Device name | Works |
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| 0x2000 | TX channel names | Works |
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| 0x2010 | TX flow slots | Returns zeros (no flow config) |
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| 0x2600 | TX unicast flows | Returns zeros (multicast not included) |
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| 0x3000 | RX subscriptions | Works for unicast; multicast has empty TX device |
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| 0x3600 | RX unicast source | Returns zeros (multicast not included) |
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### 0x2600/0x3600 Unicast Flow Commands
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These commands work for **unicast** flows but return empty data for **multicast** flows.
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**Query format** (34 bytes):
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```
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28 09 00 22 SS SS 26 00 00 00
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00 00 00 00 00 00 00 00
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00 01 00 01 00 01
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00 00 00 00 00 00 00 00 00 00
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```
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**Successful response** (from pcap with active unicast flows):
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- 148 bytes with status 0x0001
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- Contains MAC address pattern `08 02 10 e2 ef fd XX XX`
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- MAC can be correlated between TX (0x2600) and RX (0x3600) devices
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**Empty response** (current network with multicast flows):
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- 50 bytes with status 0x0001
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- Data section shows `10 00` (0 records) instead of `10 01` (1 record)
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- No MAC data available
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### Multicast vs Unicast
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**Unicast flows**: RX device stores TX device name in subscription record (0x3000 response).
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**Multicast flows**: RX subscription has empty TX device name. Routing is handled at network layer via IGMP. The Dante device doesn't store "which device is transmitting to me" because multicast is anonymous.
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---
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## What Works
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1. **IGMP correlation** - When TX devices are marked via `UpdateDanteTxChannels()`, we can identify the transmitter in a multicast group by checking which group member has TX channels.
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2. **Unicast flow discovery** - 0x3000 returns full TX device name and channel for unicast subscriptions.
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3. **Device discovery** - mDNS + ARC protocol reliably discovers all Dante devices.
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## What Doesn't Work
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1. **MAC-based correlation** - 0x2600/0x3600 return empty data for multicast flows. Only works when unicast flows are active (as seen in pcap from Dante Controller).
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2. **Per-channel multicast routing** - We can identify TX device -> RX device at the device level via IGMP, but not individual channel mappings within a multicast flow.
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3. **0x2010 flow slots** - Always returns zeros on tested devices (AJA, Shure, A&H).
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---
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## Pcap Analysis Notes
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Captured Dante Controller polling the network. Key findings:
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- Dante Controller uses 0x2809 packet format
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- Queries many commands we hadn't tried: 0x2320, 0x2400, 0x3300, 0x3400
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- 0x2600/0x3600 responses contained MAC addresses when unicast flows were active
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- MAC pattern: `08 02` followed by Audinate OUI `10 e2 ef`
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- Same MAC in TX's 0x2600 response matches RX's 0x3600 response = flow link
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Commands observed (sorted by frequency):
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- 0x1000, 0x1003, 0x1100, 0x1102 - Device info
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- 0x2000, 0x2010, 0x2032, 0x2204, 0x2320, 0x2400, 0x2600 - TX queries
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- 0x3000, 0x3300, 0x3400, 0x3600 - RX queries
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