SonicWALL TZ 210 Series Getting Started Manual page 68

TZ_210_GSG.book Page 57 Thursday, November 13, 2008 7:41 PM
providing the connection to the ISP (also connected to this hub
or switch) were to fail, the SonicWALL will continue to believe
the WAN link is usable, because the connection to the hub or
switch is good.
Enabling probe monitoring on the Network > WAN Failover &
Load Balancing page instructs the SonicWALL security
appliance to perform logical checks of upstream targets to
ensure that the line is indeed usable.
Under the default probe monitoring configuration, the
SonicWALL performs an ICMP ping probe of both WAN ports'
default gateways. Unfortunately, this is also not an assured
means of link monitoring, because service interruption may be
occurring farther upstream. If your ISP is experiencing problems
in its routing infrastructure, a successful ICMP ping of their
router causes the SonicWALL security appliance to believe the
line is usable, when in fact it may not be able to pass traffic to
and from the public Internet at all.
To perform reliable link monitoring, you can choose ICMP or
TCP as monitoring method, and can specify up to two targets
for each WAN port.
Configuring WAN Probe Monitoring
To configure WAN probe monitoring, follow these steps:
1. On the Network > WAN Failover & Load Balancing page,
under the WAN Interface Monitoring heading, select the
Enable Probe Monitoring checkbox.
2. Select the Respond to Probes checkbox to have the
SonicWALL security appliance respond to SonicwALL TCP
probes received on any of its WAN ports. Do not select this
checkbox if the SonicWALL security appliance should not
respond to TCP probes.
3. Select the Any TCP-SYN to Port checkbox to instruct the
SonicWALL security appliance to respond to TCP probes to
the specified port number without validating them first. The
Any TCP-SYN to Port box should only be selected when
receiving TCP probes from SonicWALL security appliances
running SonicOS Standard or older, legacy SonicWALL
security appliances.
SonicWALL TZ 210 Series Getting Started Guide Page 57