IP xfrm configuration example: Use the built-in IPSec Implementation of Linux kernel to manually configure IPSec

1. Topology

192.168.18.101 <======> 192.168.18.102

2. Configure 192.168.18.101

ip xfrm state add src 192.168.18.101 dst 192.168.18.102 proto esp spi 0x00000301 mode tunnel auth md5 0x96358c90783bbfa3d7b196ceabe0536b enc des3_ede 0xf6ddb555acfd9d77b03ea3843f2653255afe8eb5573965dfip xfrm state add src 192.168.18.102 dst 192.168.18.101 proto esp spi 0x00000302 mode tunnel auth md5 0x99358c90783bbfa3d7b196ceabe0536b enc des3_ede 0xffddb555acfd9d77b03ea3843f2653255afe8eb5573965dfip xfrm state get src 192.168.18.101 dst 192.168.18.102 proto esp spi 0x00000301ip xfrm policy add src 192.168.18.101 dst 192.168.18.102 dir out ptype main tmpl src 192.168.18.101 dst 192.168.18.102 proto esp mode tunnelip xfrm policy add src 192.168.18.102 dst 192.168.18.101 dir in ptype main tmpl src 192.168.18.102 dst 192.168.18.101 proto esp mode tunnelip xfrm policy ls

3. Configure 192.168.18.102

ip xfrm state add src 192.168.18.101 dst 192.168.18.102 proto esp spi 0x00000301 mode tunnel auth md5 0x96358c90783bbfa3d7b196ceabe0536b enc des3_ede 0xf6ddb555acfd9d77b03ea3843f2653255afe8eb5573965dfip xfrm state add src 192.168.18.102 dst 192.168.18.101 proto esp spi 0x00000302 mode tunnel auth md5 0x99358c90783bbfa3d7b196ceabe0536b enc des3_ede 0xffddb555acfd9d77b03ea3843f2653255afe8eb5573965dfip xfrm state get src 192.168.18.101 dst 192.168.18.102 proto esp spi 0x00000301ip xfrm policy add src 192.168.18.101 dst 192.168.18.102 dir in ptype main tmpl src 192.168.18.101 dst 192.168.18.102 proto esp mode tunnelip xfrm policy add src 192.168.18.102 dst 192.168.18.101 dir out ptype main tmpl src 192.168.18.102 dst 192.168.18.101 proto esp mode tunnelip xfrm policy ls

4. Test 4.1 On 192.168.18.101

ping 192.168.18.102

4.2 capture packets on 192.168.18.102

tcpdump -p esptcpdump: verbose output suppressed, use -v or -vv for full protocol decodelistening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes11:12:00.771364 IP 192.168.18.101 > 192.168.18.102: ESP(spi=0x00000301,seq=0x41d), length 11611:12:00.771498 IP 192.168.18.102 > 192.168.18.101: ESP(spi=0x00000302,seq=0x183), length 11611:12:01.773378 IP 192.168.18.101 > 192.168.18.102: ESP(spi=0x00000301,seq=0x41e), length 11611:12:01.773787 IP 192.168.18.102 > 192.168.18.101: ESP(spi=0x00000302,seq=0x184), length 11611:12:02.774682 IP 192.168.18.101 > 192.168.18.102: ESP(spi=0x00000301,seq=0x41f), length 11611:12:02.774793 IP 192.168.18.102 > 192.168.18.101: ESP(spi=0x00000302,seq=0x185), length 116