ZyXEL Communications ZyWALL USG 200 Series User Manual page 912

Chapter 56 Troubleshooting
Here are some general suggestions. See also
• The system log can often help to identify a configuration problem.
• If you enable NAT traversal, the remote IPSec device must also have NAT
traversal enabled.
• The ZyWALL and remote IPSec router must use the same authentication method
to establish the IKE SA.
• Both routers must use the same negotiation mode.
• Both routers must use the same encryption algorithm, authentication algorithm,
and DH key group.
• When using manual keys, the ZyWALL and remote IPSec router must use the
same encryption key and authentication key.
• When using pre-shared keys, the ZyWALL and the remote IPSec router must
use the same pre-shared key.
• The ZyWALL's local and peer ID type and content must match the remote IPSec
router's peer and local ID type and content, respectively.
• The ZyWALL and remote IPSec router must use the same active protocol.
• The ZyWALL and remote IPSec router must use the same encapsulation.
• The ZyWALL and remote IPSec router must use the same SPI.
• If the sites are/were previously connected using a leased line or ISDN router,
physically disconnect these devices from the network before testing your new
VPN connection. The old route may have been learnt by RIP and would take
priority over the new VPN connection.
• To test whether or not a tunnel is working, ping from a computer at one site to a
computer at the other.
Before doing so, ensure that both computers have Internet access (via the
IPSec routers).
• It is also helpful to have a way to look at the packets that are being sent and
received by the ZyWALL and remote IPSec router (for example, by using a
packet sniffer).
Check the configuration for the following ZyWALL features.
• The ZyWALL does not put IPSec SAs in the routing table. You must create a
policy route for each VPN tunnel. See
• Make sure the To-ZyWALL firewall rules allow IPSec VPN traffic to the ZyWALL.
IKE uses UDP port 500, AH uses IP protocol 51, and ESP uses IP protocol 50.
• The ZyWALL supports UDP port 500 and UDP port 4500 for NAT traversal. If you
enable this, make sure the To-ZyWALL firewall rules allow UDP port 4500 too.
• Make sure regular firewall rules allow traffic between the VPN tunnel and the
rest of the network. Regular firewall rules check packets the ZyWALL sends
before the ZyWALL encrypts them and check packets the ZyWALL receives after
the ZyWALL decrypts them. This depends on the zone to which you assign the
VPN tunnel and the zone from which and to which traffic may be routed.
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Chapter 25 on page
Chapter 15 on page 377.
ZyWALL USG 100/200 Series User's Guide
471.