Here's a **structured summary** of your network requirements and design, incorporating your latest updates and clarifications:

---

### **Network Overview**

#### **1. VLANs and Subnets**
| VLAN | Subnet                         | Gateway IP       | Avahi Server IP | mDNS Proxy IP |
|------|--------------------------------|------------------|------------------|----------------|
| 15   | 172.16.19.0/255.255.252.0     | 172.16.19.254    | 172.16.19.250    | 172.16.19.251  |
| 19   | 192.168.151.0/255.255.252.0  | 192.168.151.254  | 192.168.151.250  | 192.168.151.251 |
| 7    | 172.16.111.0/255.255.248.0   | 172.16.111.254   | 172.16.111.250   | 172.16.111.251 |

**Note:** All VLANs are routed via the **Sophos XGS4300**, which acts as the **DHCP server** for all VLANs.

---

#### **2. Avahi Server Configuration**
- **Local Avahi Servers**:
  - **VLAN 15**: Runs Avahi on `172.16.19.250` for local discovery.
  - **VLAN 19**: Runs Avahi on `192.168.151.250` for local discovery.
  - **VLAN 7**: Runs Avahi on `172.16.111.250` for local discovery.
- **Central Avahi Server** (mDNS Proxy):
  - **IPs**: `172.16.19.251`, `192.168.151.251`, `172.16.111.251` (untagged interfaces for each VLAN).
  - **Configuration**:
    ```ini
    [reflector]
    enable-reflector=yes
    #reflect-ipv=no
    #reflect-filters=_airplay._tcp.local,_raop._tcp.local
    ```
  - **Purpose**: Acts as a **central mDNS reflector** to forward traffic between VLANs, enabling Apple devices in VLANs 15/19 to discover Apple TVs in VLAN 7.

---

#### **3. mDNS Proxy VM (Central Avahi Server)**
- **OS**: Debian.
- **Network Configuration**:
  - Uses **`/etc/network/interfaces`** to assign static IPs for each VLAN (ending in `.251`).
  - Interfaces are **untagged** (virtual) for each VLAN.
- **Function**: 
  - Forwards mDNS traffic between VLANs (e.g., `_airplay._tcp.local`, `_raop._tcp.local`).
  - Ensures Apple devices in VLANs 15/19 can discover Apple TVs in VLAN 7 via Bonjour.

---

#### **4. ESXi and VLAN Management**
- **Hyper-Visor**: ESXi.
- **vSwitch Configuration**:
  - Each VLAN is assigned a **virtual port group** with the corresponding subnet.
  - VMs (Avahi servers, mDNS proxy, etc.) are assigned to the appropriate VLAN port group.
- **IP Assignment**:
  - VMs use **static IPs** (`.250` for local Avahi servers, `.251` for central Avahi server).

---

#### **5. Switch Configuration**
- **Switches**: Managed Level 2 switches.
- **IGMP Snooping**: 
  - **Recommendation**: **Enable IGMP snooping** on all switches.
  - **Rationale**: 
    - While mDNS (Bonjour) uses **UDP** and not IGMP, **other multicast services** (e.g., `546/udp` for DHCPv6, `80/443` for HTTP/HTTPS) may rely on IGMP.
    - IGMP snooping prevents unnecessary multicast traffic flooding, improving network efficiency.
  - **Note**: If only mDNS is used, IGMP snooping is **not strictly required**, but enabling it is **beneficial for future scalability**.

---

### **Key Considerations**
- **Resource Allocation for VMs**:
  - **Avahi Servers (VLANs 15, 19, 7)**: Minimal resources (1 vCPU, 512MB RAM).
  - **Central Avahi Server (mDNS Proxy)**: Slightly higher resources (2 vCPUs, 1GB RAM) due to traffic forwarding.
- **Firewall Rules**:
  - Ensure **UDP ports 80, 443, 546/udp, 546/tcp** are open between VLANs 15/19 and VLAN 7.
  - Allow **mDNS traffic (UDP 5353)** for Bonjour discovery.
- **Testing**:
  - Use `avahi-browse` on Apple devices to verify Apple TV discovery.
  - Test service ports (e.g., `curl http://<AppleTV-IP>:80`) to confirm connectivity.

---

### **Summary of Design**
- **VLAN Isolation**: Each VLAN operates independently with its own subnet and Avahi server.
- **Central mDNS Proxy**: Acts as a bridge for Bonjour discovery between VLANs, enabling cross-VLAN service discovery.
- **Network Efficiency**: IGMP snooping is enabled to optimize multicast traffic handling.
- **Scalability**: The design supports future additions (e.g., more Apple devices, services) without overhauling the architecture.

Let me know if you’d like a **diagram** or **Debian interface configuration examples**! 🚀