20250907
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Petar Cubela
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### **Comprehensive Project Plan**
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**Objective**: Enable Avahi (mDNS) communication across VLANs using a Sophos XGS firewall and a Linux VM hosted on ESXi with VLAN trunking.
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---
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### **1. Project Overview**
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- **Firewall**: Sophos XGS (enforces VLAN segmentation and allows 5353/UDP traffic).
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- **Avahi Server**: Linux VM on ESXi, receiving VLAN traffic via a physical trunk port.
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- **Goal**: Allow mDNS traffic (5353/UDP) between specified VLANs while maintaining VLAN isolation.
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---
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### **2. Key Requirements**
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1. **Firewall Configuration**:
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- Allow **UDP 5353** traffic between specified VLANs.
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- Enforce VLAN segmentation (no inter-VLAN communication by default).
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2. **Network Infrastructure**:
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- **Physical Trunk Port**: Switch provides tagged VLAN traffic to the ESXi host.
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- **ESXi Host**: Assigns VLAN tagging to the VM’s virtual NIC.
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- **Linux VM**: Single interface receives trunked VLAN traffic.
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3. **Avahi Server**:
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- Installed on Linux VM.
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- Configured to act as an mDNS relay across VLANs.
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---
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### **3. Network Setup**
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#### **A. Physical Layer**
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1. **Switch Configuration**:
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- Configure a **trunk port** on the physical switch to carry all required VLANs (e.g., VLAN 10, VLAN 20).
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- Ensure the trunk port is connected to the ESXi host.
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#### **B. ESXi Host Configuration**
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1. **Port Group Setup**:
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- Create a **port group** on the ESXi host for VLAN trunking.
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- Assign the VLANs (e.g., VLAN 10, VLAN 20) to the port group.
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2. **VM Network Adapter**:
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- Assign the VM a **virtual NIC (vNIC)** connected to the VLAN trunk port group.
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- Ensure the vNIC is configured to **accept VLAN tags** (no need for VLAN sub-interfaces).
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#### **C. Linux VM Configuration**
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1. **Interface Configuration**:
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- Assign **multiple IP addresses** to the VM’s interface (e.g., `eth0` or `vmbr0`) for each VLAN.
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```bash
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auto eth0
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iface eth0 inet static
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address 192.168.20.251
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netmask 255.255.255.0
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address 10.56.1.251
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netmask 255.255.255.0
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gateway 10.56.1.254
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```
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- Ensure IPs are in **different subnets** (e.g., VLAN 10: `10.56.1.0/24`, VLAN 20: `192.168.20.0/26`).
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2. **Routing**:
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- Configure default gateway for the primary VLAN (e.g., `10.56.1.254`).
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- Ensure routing tables allow traffic between VLANs.
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---
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### **4. Sophos XGS Firewall Configuration**
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1. **VLAN Segmentation**:
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- Create VLANs on the Sophos XGS (e.g., VLAN 10, VLAN 20).
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- Assign interfaces to respective VLANs.
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2. **Traffic Rules**:
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- Allow **UDP 5353** traffic between specified VLANs.
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- Example rule:
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```
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Source VLAN: VLAN 10
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Destination VLAN: VLAN 20
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Protocol: UDP
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Destination Port: 5353
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```
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- Ensure **no other traffic** is allowed between VLANs unless explicitly permitted.
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---
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### **5. Avahi Server Setup**
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1. **Install Avahi**:
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- Install Avahi on the Linux VM:
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```bash
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apt update && apt install avahi-daemon libnss-mdns
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```
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2. **Configure Avahi**:
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- Ensure Avahi is set to **broadcast mDNS packets** across VLANs.
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- Adjust `/etc/avahi/avahi-daemon.conf` to allow broadcasting (if needed).
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3. **Firewall Rules (Optional)**:
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- If the VM’s host firewall blocks traffic, add rules to allow **UDP 5353** between VLANs:
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```bash
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iptables -A FORWARD -s 10.56.1.0/24 -d 192.168.20.0/24 -p udp --dport 5353 -m state --state NEW,ESTABLISHED -j ACCEPT
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```
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4. **Verify Operation**:
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- Test mDNS discovery between devices on different VLANs (e.g., ping, `avahi-browse`).
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---
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### **6. Testing & Validation**
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1. **Ping Test**:
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- Confirm connectivity between devices on different VLANs via the Avahi VM.
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2. **Firewall Rule Check**:
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- Ensure Sophos XGS allows **UDP 5353** traffic between VLANs.
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3. **Avahi Discovery**:
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- Use `avahi-browse` to verify mDNS services are visible across VLANs.
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4. **Traffic Monitoring**:
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- Use tools like `tcpdump` or Wireshark to confirm VLAN tagging and traffic flow.
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---
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### **7. Documentation & Maintenance**
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1. **Document VLAN Assignments**:
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- Record VLAN IDs, IP ranges, and firewall rules for reference.
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2. **Backup Configurations**:
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- Save ESXi port group settings, Sophos XGS rules, and Avahi configurations.
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3. **Regular Updates**:
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- Keep the Linux VM and Avahi software updated to avoid vulnerabilities.
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---
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### **8. Known Considerations**
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- **Trunking Limitations**: Ensure the physical switch and ESXi host support VLAN trunking.
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- **Firewall Overlap**: Avoid conflicting rules in Sophos XGS that could block mDNS traffic.
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- **Performance**: Monitor network bandwidth to ensure VLAN traffic does not saturate the link.
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---
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### **9. Success Criteria**
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- **mDNS Communication**: Devices on different VLANs can discover and communicate via Avahi.
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- **Firewall Compliance**: Only allowed traffic (UDP 5353) is permitted between VLANs.
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- **Network Isolation**: VLAN segmentation is enforced, and only required traffic is allowed.
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---
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This plan ensures a secure, scalable, and functional mDNS relay solution across VLANs using Sophos XGS and an ESXi-hosted Avahi VM.
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