ZyXEL Communications NXC5200 User Manual page 548

Chapter 39 Troubleshooting
The NXC's performance seems slower after configuring IDP.
Depending on your network topology and traffic load, binding every packet
direction to an IDP profile may affect the NXC's performance. You may want to
focus IDP scanning on certain traffic directions such as incoming traffic.
IDP is dropping traffic that matches a rule that says no action should be taken.
The NXC checks all signatures and continues searching even after a match is
found. If two or more rules have conflicting actions for the same packet, then the
NXC applies the more restrictive action (reject-both, reject-receiver or reject-
sender, drop, none in this order). If a packet matches a rule for reject-receiver
and it also matches a rule for reject-sender, then the NXC will reject-both.
I uploaded a custom signature file and now all of my earlier custom signatures are
gone.
The name of the complete custom signature file on the NXC is 'custom.rules'. If
you import a file named 'custom.rules', then all custom signatures on the NXC are
overwritten with the new file. If this is not your intention, make sure that the files
you import are not named 'custom.rules'.
I cannot configure some items in IDP that I can configure in Snort.
Not all Snort functionality is supported in the NXC.
The NXC's performance seems slower after configuring ADP.
Depending on your network topology and traffic load, applying an anomaly profile to
each and every packet direction may affect the NXC's performance.
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NXC5200 User's Guide