July 2, 2011, 7:22 p.m.
posted by whitehat
Determine the Tunnel Status
[[email protected] tmp]# ipsec auto --status ... ... 000 algorithm ESP encrypt: id=2, name=ESP_DES, ivlen=8, key- sizemin=64, keysizemax=64 000 algorithm ESP encrypt: id=3, name=ESP_3DES, ivlen=8, key- sizemin=192, keysizemax=192 000 algorithm ESP encrypt: id=7, name=ESP_BLOWFISH, ivlen=8, key- sizemin=40, keysizemax=448 ... ... 000 algorithm IKE encrypt: id=7, name=OAKLEY_AES_CBC, block- size=16, keydeflen=128 000 algorithm IKE encrypt: id=5, name=OAKLEY_3DES_CBC, block- size=8, keydeflen=192 000 algorithm IKE hash: id=2, name=OAKLEY_SHA, hashsize=20 ... ... 000 "net-to-net": IKE algorithms wanted: 5_000-1-5, 5_000- 1-2, 5_000-2-5, 5_000-2-2, flags=-strict 000 "net-to-net": IKE algorithms found: 5_192-1_128-5, 5_192-1_128-2, 5_192-2_160-5, 5_192-2_160-2, 000 "net-to-net": IKE algorithm newest: 3DES_CBC_192-MD5- MODP1536 000 "net-to-net": ESP algorithms wanted: 3_000-1, 3_000-2, flags=-strict 000 "net-to-net": ESP algorithms loaded: 3_000-1, 3_000-2, flags=-strict 000 "net-to-net": ESP algorithm newest: 3DES_0-HMAC_MD5; pfsgroup=<Phase1> ... ... 000 #4: "net-to-net" STATE_QUICK_R2 (IPsec SA established); EVENT_SA_REPLACE in 3635s; newest IPSEC; eroute owner 000 #4: "net-to-net" [email protected] [email protected] [email protected] [email protected] 000 #12: "net-to-net" STATE_MAIN_R3 (sent MR3, ISAKMP SA established); EVENT_SA_REPLACE in 1153s; newest ISAKMP [[email protected] tmp]#
It is important to know the status of your VPN as it can provide valuable troubleshooting clues when there are problems. This can be especially important when establishing a VPN between your Linux firewall and a non-Linux device. The IKE and ESP timers and encryption, hash, and key exchange algorithms must match at both ends to have success. This command allows you to see the value combinations Openswan is using and helps you configure the VPN device on the other end to have compatible settings.
Testing VPN Connectivity
You can test the VPN connectivity by sending a simple ping from one private network to the other. In this case, the ping goes to the Windows server 10.0.0.105, which is protected by vpn2, from server 172.16.1.1, which is protected by vpn1.
If the tunnel is up but ICMP pings don't work, then you need to check that the servers at both ends of the tunnel have routes pointing to the VPN firewalls. Also, check for additional network access controls between the servers and the VPN firewall. There may be additional firewalls in the way or the servers themselves may be running firewall software.
C:\>ping 10.0.0.105 Pinging 10.0.0.105 with 32 bytes of data: Reply from 10.0.0.105: bytes=32 time=20ms TTL=253 Reply from 10.0.0.105: bytes=32 time<10ms TTL=253 Reply from 10.0.0.105: bytes=32 time=10ms TTL=253 Reply from 10.0.0.105: bytes=32 time<10ms TTL=253 Ping statistics for 10.0.0.105: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 0ms, Maximum = 20ms, Average = 7ms C:\>
Check the Routes
You'll need to check the routes after the VPN tunnel is up as well. As you can see, there is an additional route to the 172.16.1.0 network on firewall vpn2. Incorrect routing on the firewalls can cause problems, check your leftnexthop and rightnexthop values in your /etc/ipsec.conf file:
[[email protected] tmp]# netstat -nr Kernel IP routing table Destination Gateway Genmask Flags MSS Window irtt Iface 10.0.0.0 0.0.0.0 255.255.255.0 U 40 0 0 eth1 188.8.131.52 0.0.0.0 255.255.255.248 U 40 0 0 eth0 172.16.1.0 184.108.40.206 255.255.255.0 UG 40 0 0 eth0 127.0.0.0 0.0.0.0 255.0.0.0 U 40 0 0 lo 0.0.0.0 220.127.116.11 0.0.0.0 UG 40 0 0 wlan0 [[email protected] tmp]#
If the tunnel doesn't appear to become established, use the tcpdump command as explained in Chapter 4, "Simple Network Troubleshooting," to determine whether the traffic is being seen at both ends of the tunnel. You need to know whether the IPSec packets are even reaching your VPN firewall. Check routing and your Openswan configuration if not.
Protected Interface TCPDump Output from vpn2
Here the TCPdump is done on server2 where you see unencrypted ICMP ping traffic successfully passing back and forth between the two servers:
[[email protected] tmp]# tcpdump -n -i eth1 icmp 03:05:53.971308 IP 172.16.1.1 > 10.0.0.105: icmp 64: echo request seq 89 03:05:53.995297 IP 10.0.0.105 > 172.16.1.1: icmp 64: echo reply seq 89 03:05:54.972759 IP 172.16.1.1 > 10.0.0.105: icmp 64: echo request seq 90 03:05:54.972789 IP 10.0.0.105 > 172.16.1.1: icmp 64: echo reply seq 90 03:05:55.972985 IP 172.16.1.1 > 10.0.0.105: icmp 64: echo request seq 91 03:05:55.972999 IP 10.0.0.105 > 172.16.1.1: icmp 64: echo reply seq 91 ^C [[email protected] tmp]#
Unprotected Interface TCPDump Output from vpn2
Here the encrypted ESP traffic is encapsulating the pings passing back and forth between the two VPN boxes. The true source and destination IP addresses (10.0.0.105 and 172.16.1.1) are hidden.
[[email protected] tmp]# tcpdump -n -i eth1 host 18.104.22.168 02:08:23.637149 IP 22.214.171.124 > 126.96.36.199: ESP(spi=0xf4909a7e,seq=0x73) 02:08:24.635302 IP 188.8.131.52 > 184.108.40.206: ESP(spi=0x808e9a87,seq=0x74) 02:08:24.637988 IP 220.127.116.11 > 18.104.22.168: ESP(spi=0xf4909a7e,seq=0x74) 02:08:25.638015 IP 22.214.171.124 > 126.96.36.199: ESP(spi=0x808e9a87,seq=0x75) ^C [[email protected] tmp]#
Check syslog Error Messages
As always, check your /var/log/messages file for any messages that may provide clues as to the source of your problems.
Invalid Key Messages
If your left and right public keys were incorrectly applied to your /etc/ipsec.conf file or your regenerated keys were not updated in your /etc/ipsec.secrets file, then you will get messages stating that the keys are invalid and that information is being ignored:
003 "net-to-net" #1: ignoring informational payload, type INVALID_KEY_INFORMATION 003 "net-to-net" #1: received and ignored informational message 003 "net-to-net" #1: discarding duplicate packet; already STATE_MAIN_I3 031 "net-to-net" #1: max number of retransmissions (2) reached STATE_MAIN_I3. Possible authentication failure: no acceptable response to our first encrypted message