When connecting two geographically separated networks over the Internet, we need to achieve three fundamental objectives:

• Secure encrypted communication
• Transparent network resource access
• Minimal endpoint configuration

The most efficient approach is implementing VPN at the router level. Modern routers support various VPN protocols:

# Sample OpenVPN server configuration (Router A)
dev tun
proto udp
port 1194
topology subnet
server 10.8.0.0 255.255.255.0
push "route 192.168.1.0 255.255.255.0"
keepalive 10 120
cipher AES-256-CBC

# Corresponding client configuration (Router B)
client
dev tun
proto udp
remote vpn.example.com 1194
resolv-retry infinite
nobind
persist-key
persist-tun
remote-cert-tls server
cipher AES-256-CBC

For Windows environments, a domain controller provides several advantages:

• Centralized authentication
• Simplified resource sharing
• Group policy management

However, workgroups can be used with proper DNS configuration:

# Example DNS configuration for cross-site resolution
zone "corp.internal" {
    type forward;
    forwarders { 192.168.1.10; 192.168.2.10; };
};

For a Cisco router setup, here's a basic IPsec configuration:

! Site A Configuration
crypto ikev2 proposal IKE-PROPOSAL
 encryption aes-cbc-256
 integrity sha512
 group 19
!
crypto ipsec profile IPSEC-PROFILE
 set ikev2-profile IKE-PROFILE
!
interface Tunnel0
 tunnel protection ipsec profile IPSEC-PROFILE

To achieve true configuration-free endpoints:

1. Configure route propagation via DHCP
2. Implement split tunneling properly
3. Set up cross-site DNS resolution

# DHCP option for route propagation (Linux dhcpd.conf)
option rfc3442-classless-static-routes code 121 = array of unsigned integer 8;
option rfc3442-classless-static-routes 24, 192, 168, 2, 10, 8, 0, 1;

When connecting two geographically separated networks with independent internet connections, we need to achieve:

• Secure encrypted tunnel for all inter-site traffic
• Transparent network visibility (all nodes should appear as local)
• Minimal endpoint configuration (ideally zero-touch on workstations)
• Proper IP addressing scheme to prevent conflicts

Here are the most common approaches with their trade-offs:

This is the most efficient solution for our requirements. Here's a sample configuration for pfSense routers:

# Site A configuration (192.168.1.0/24 network)
phase1 {
    ikeid = 1;
    remoteid = "site-b.example.com";
    mode = main;
    protocol = esp;
    encryption = aes-256-gcm;
    hash = sha256;
    dhgroup = 14;
    lifetime = 28800;
    nat_traversal = on;
    remote_gateway = 203.0.113.2;
}

phase2 {
    ikeid = 1;
    mode = tunnel;
    protocol = esp;
    encryption = aes-256-gcm;
    hash = sha256;
    pfsgroup = 14;
    lifetime = 3600;
    localid {
        type = lan;
        network = 192.168.1.0/24;
    }
    remoteid {
        type = lan;
        network = 192.168.2.0/24;
    }
}

For optimal performance:

1. Use non-overlapping private IP ranges (e.g., 192.168.1.0/24 and 192.168.2.0/24)
2. Configure proper static routes on both routers
3. Enable MSS clamping for TCP optimization
4. Disable NAT for VPN traffic between sites

While workgroups can function, a domain controller provides better management:

# Sample Windows Server DNS conditional forwarder
Add-DnsServerConditionalForwarderZone 
    -Name "corp.site-b.com" 
    -MasterServers 192.168.2.10 
    -PassThru

Essential monitoring commands for Linux-based routers:

# Check IPsec tunnel status
ipsec statusall

# Monitor VPN throughput
iftop -i eth0 -f "port 500 or port 4500"

# View connection statistics
conntrack -L -j