AV-over-IP Network Inspector Prototype

Technical Architecture and Systems Engineering Specification

Building a dependable network diagnostic suite for live production requires reconciling low-level network realities with mission-critical broadcast uptime. A single endpoint laptop cannot assume omniscient visibility across VLANs or unicast switch paths; instead, it must correlate observations across four distinct network planes and enforce strict transactional safety whenever manipulating host network interfaces.

Transactional Secondary IP State Machine and VLAN-Aware BPF Pipeline

To capture both untagged access traffic and 802.1Q trunk frames without dropping packets, and to reach isolated off-subnet hardware without disrupting internet routing, the core executes the following pipeline:

// 1. Npcap / libpcap Kernel BPF Filter (Handles Untagged and 802.1Q VLAN-Tagged Frames)
const BPF_4PLANE_FILTER: &str = "
  (arp or ether proto 0x88cc or ether proto 0x88f7 or (ether[14:2] == 0x2000) or
   igmp or udp portrange 8700-8708 or udp port 4440 or udp port 4455 or
   udp port 9875 or udp port 5353 or udp port 2467 or udp port 6504 or
   udp port 3702 or udp port 319 or udp port 320 or udp port 2202 or
   udp port 5568 or udp port 6454 or udp port 67 or udp port 68)
  or (vlan and (arp or igmp or udp))
";

// 2. Transactional Secondary IP State Machine (Windows iphlpapi.dll / macOS BSD AF_ROUTE)
1. DISCOVERY: Off-subnet endpoint observed (e.g., Shure AD4Q at 169.254.88.12/16).
2. CANDIDATE SELECTION and PRE-FLIGHT CHECK:
   - Compute candidate host IP in target prefix (e.g., 169.254.88.249/16).
   - Transmit 3x raw ARP Request probes across target NIC; ABORT if any MAC responds.
3. ROUTE METRIC SNAPSHOT:
   - Snapshot GetAdaptersAddresses() and GetIpForwardTable2().
   - Record primary 0.0.0.0/0 default gateway and interface metric (e.g., Metric 20).
4. ISOLATED ALIAS BINDING:
   - Invoke AddIPAddress(candidate_ip, subnet_mask, if_index, &nte_context, &nte_instance).
   - Leave Default Gateway NULL (0.0.0.0) so internet and VPN traffic never route to the alias.
5. 1Hz IPC HEARTBEAT and 15-MINUTE LEASE WATCHDOG:
   - Write NTE context to transactional Write-Ahead Log (%APPDATA%/state.wal).
   - Background watchdog daemon monitors 1Hz UI heartbeat and 15-minute extendable lease.
6. ATOMIC ROLLBACK and CRASH RECOVERY:
   - Invoke DeleteIPAddress(nte_context) on user click, lease expiry, or process termination.
   - Verify post-rollback routing table parity against initial snapshot.

4-Plane Broadcast Protocol Discovery and Diagnostic Matrix