For comprehensive LAN encryption, IPSec demonstrates strong cross-platform compatibility:

# Linux (strongSwan example)
conn lan-encryption
    authby=secret
    auto=start
    keyexchange=ikev2
    ike=aes256-sha256-modp2048
    esp=aes256-sha256
    left=%any
    leftsubnet=0.0.0.0/0
    right=%any
    rightsubnet=0.0.0.0/0
    type=transport

Windows clients natively support IPSec through Group Policy:

PowerShell:
New-NetIPsecRule -DisplayName "LAN Encryption" -LocalAddress Any -RemoteAddress Any 
-EncryptionRequired Require -AuthenticationTransformConstants GCMAES256 
-KeyModule IKEv2 -Phase1AuthSet ComputerPSK

Complete traffic isolation requires layered controls:

• Network interface binding (Linux example):

  ip xfrm policy flush
  ip xfrm state flush
  ip xfrm policy add dir out tmpl src 0.0.0.0/0 dst 0.0.0.0/0 proto esp mode transport
  ip xfrm policy add dir in tmpl src 0.0.0.0/0 dst 0.0.0.0/0 proto esp mode transport

• Firewall rules to drop non-IPSec:

  iptables -A INPUT ! -p esp -j DROP
  iptables -A OUTPUT ! -p esp -j DROP

For internal LAN communication:

Parameter	Recommended Value
Mode	Transport (reduced overhead)
Protocol	ESP with GCM authentication
Encryption	AES-256-GCM
IKE Version	IKEv2 with PFS

For internet-bound traffic, consider these architectural approaches:

1. Transport Mode with Proxy:

   # Squid configuration with IPSec verification
   acl lan_network src 192.168.1.0/24
   http_access allow lan_network ipsecpolicy=authenticated

2. Tunnel Mode Gateway:

   # strongSwan gateway config
   conn internet-tunnel
       left=gateway.lan
       leftsubnet=0.0.0.0/0
       right=%any
       rightsubnet=0.0.0.0/0
       auto=route
       type=tunnel
       keyexchange=ikev2

• Deploy certificate-based authentication for better scalability than PSK
• Implement monitoring for ESP packet drops:

  # Linux monitoring
  watch -n 1 "ip -s xfrm state"

• Test compatibility with multicast traffic if needed for protocols like mDNS

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For comprehensive LAN traffic encryption, IPSec support varies across platforms:

# Linux (strongSwan example)
conn lan-encrypt
    authby=secret
    auto=start
    keyexchange=ikev2
    ike=aes256-sha1-modp1024!
    esp=aes256-sha1!
    left=%defaultroute
    right=%any
    type=transport
    leftprotoport=0
    rightprotoport=0

Windows Server 2022 implements similar policies through Group Policy Objects (GPOs) with AES-256 encryption, while macOS uses the native racoon daemon with configuration profiles.

IPSec can be enforced at multiple levels:

• Host-based policies (entire machine encryption)
• Network interface binding
• Firewall integration (Windows Filtering Platform or Linux netfilter)

Example Windows PowerShell command for host-level enforcement:

New-NetIPsecRule -DisplayName "Block Non-IPSec" -InboundSecurity Require -OutboundSecurity Require

To block non-IPSec traffic:

# Linux iptables example
iptables -A INPUT -m policy --dir in --pol ipsec --strict -j ACCEPT
iptables -A INPUT -j DROP

For certificate-based authentication to prevent unauthorized IPSec traffic:

# strongSwan configuration
conn %default
    leftcert=hostCert.pem
    rightcert=clientCert.pem
    leftid=@vpn.example.com
    rightid=%any
    auto=add

For intra-LAN communication, ESP with authentication in transport mode provides optimal performance:

# ESP configuration parameters
esp_proposals=aes256-sha256-modp2048
ike_proposals=aes256-sha256-modp2048

This combines confidentiality (AES-256) with integrity protection (SHA-256) without the overhead of AH.

For internet-bound traffic, consider these approaches:

Tunnel Mode to Gateway

conn internet-tunnel
    left=192.168.1.1
    leftsubnet=0.0.0.0/0
    right=internet-gw
    rightsubnet=0.0.0.0/0
    type=tunnel
    auto=start

Transport Mode with Proxy

Requires explicit proxy configuration on clients:

conn internet-transport
    left=%any
    right=proxy-server
    type=transport
    leftprotoport=tcp/3128
    rightprotoport=tcp/3128

• Performance impact on latency-sensitive applications
• Multicast/broadcast traffic handling limitations
• ICMP message filtering requirements
• DHCP and other bootstrap protocol considerations

# Multicast exception example
conn multicast-exception
    left=%any
    right=%any
    type=passthrough
    auto=route