When it comes to implementing IPsec-based VPN solutions, two major open-source projects dominate the landscape: StrongSwan and OpenSwan. Both have evolved from the original FreeS/WAN project, but have taken significantly different development paths.

StrongSwan has embraced a more modular architecture in recent versions, with these key characteristics:

# StrongSwan 5.x configuration example
connections {
    ikev2 {
        version = 2
        mobike = no
        local_addrs = 192.168.1.1
        remote_addrs = 192.168.2.1
        
        local {
            auth = pubkey
            certs = serverCert.pem
        }
        remote {
            auth = pubkey
        }
    }
}

OpenSwan maintains more traditional configuration approaches:

# OpenSwan 2.6 configuration snippet
conn mytunnel
    left=192.168.1.1
    leftsubnet=10.0.1.0/24
    right=192.168.2.1
    rightsubnet=10.0.2.0/24
    authby=secret
    auto=start

StrongSwan generally supports newer cryptographic standards earlier:

• StrongSwan 5.9+ supports Post-Quantum Crypto experiments
• OpenSwan 2.6 still relies on traditional algorithms

In benchmark tests on AWS c5.large instances:

# Throughput test results (Mbps)
+----------------+-----------+-----------+
| Connection Type | StrongSwan | OpenSwan |
+----------------+-----------+-----------+
| AES-256-GCM    | 940       | 720       |
| 3DES-SHA1      | 210       | 190       |
+----------------+-----------+-----------+

The GitHub commit history shows:

• StrongSwan: 150+ commits/month (active maintenance)
• OpenSwan: 10-15 commits/month (minimal maintenance)

Converting from OpenSwan to StrongSwan configuration:

# Original OpenSwan
conn legacy
    left=1.2.3.4
    right=5.6.7.8
    authby=secret

# Equivalent StrongSwan
connections {
    legacy {
        local_addrs = 1.2.3.4
        remote_addrs = 5.6.7.8
        local {
            auth = psk
        }
        remote {
            auth = psk
        }
    }
}

StrongSwan offers several advantages for large deployments:

# Load balancing configuration example
connections {
    lb-group {
        pools = dhcp,radius
        mode = redundant
        local_addrs = 192.168.1.1-192.168.1.5
    }
}

Both OpenSwan and StrongSwan originated from the FreeS/WAN project. OpenSwan 2.6.x remains widely deployed in enterprise environments, while StrongSwan 5.x has gained momentum with its modern cryptographic implementations. The current development cycle shows StrongSwan releasing updates quarterly, whereas OpenSwan's last stable release was in 2019.

StrongSwan 5.9.1 supports:

# SHA-3 and Post-Quantum Crypto options
conn pqc-vpn
  ike=aes256-sha3_512-prfsha3_512-curve448
  esp=aes256gcm16-sha3_512-curve448

OpenSwan 2.6.51 limited to:

conn legacy-vpn
  ike=aes256-sha1-modp2048
  esp=aes256-sha1

StrongSwan utilizes the native Linux NETKEY stack, while OpenSwan maintains KLIPS kernel patches. Performance tests show NETKEY achieves 15% higher throughput on AES-NI enabled hardware.

StrongSwan roadwarrior setup:

# /etc/ipsec.conf
conn remote-access
  auto=add
  left=%defaultroute
  leftsubnet=0.0.0.0/0
  leftcert=serverCert.pem
  right=%any
  rightsourceip=10.0.1.0/24
  rightcert=clientCert.pem
  ikev2=insist

OpenSwan site-to-site:

conn branch-office
  left=203.0.113.1
  leftsubnet=192.168.1.0/24
  leftnexthop=%defaultroute
  right=198.51.100.2
  rightsubnet=10.0.2.0/24
  pfs=yes
  auto=start

StrongSwan's vici protocol enables dynamic control:

# Python control example
from swanctl import SwanController
sc = SwanController()
sc.initiate(connection="corporate-vpn")

OpenSwan relies on legacy ipsec commands:

ipsec auto --up myconnection

StrongSwan's lightweight design (3MB Alpine image) outperforms OpenSwan in Kubernetes deployments. Sample Dockerfile:

FROM alpine:edge
RUN apk add strongswan
COPY ipsec.conf /etc
COPY ipsec.secrets /etc
CMD ["ipsec", "start", "--nofork"]