Chapter 30 IDP
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system vulnerabilities with the goal of bringing down the computer/server. Typical “network-based
intrusions” are SQL slammer, Blaster, Nimda MyDoom etc.
Snort Signatures
You may want to refer to open source Snort signatures when creating custom Zyxel Device ones. Most
Snort rules are written in a single line. Snort rules are divided into two logical sections, the rule header
and the rule options as shown in the following example:
alert tcp any any -> 192.168.1.0/24 111 (content:”|00 01 a5|”; msg:”mountd access”;)
The text up to the first parenthesis is the rule header and the section enclosed in parenthesis contains the
rule options. The words before the colons in the rule options section are the option keywords.
The rule header contains the rule's:
• Action
• Protocol
• Source and destination IP addresses and netmasks
• Source and destination ports information.
The rule option section contains alert messages and information on which parts of the packet should be
inspected to determine if the rule action should be taken.
These are some equivalent Snort terms in the Zyxel Device.
Table 222 Zyxel Device - Snort Equivalent Terms
ZYXEL DEVICE TERM
SNORT EQUIVALENT TERM
Type Of Service
tos
Identification
id
Fragmentation
fragbits
Fragmentation Offset
fragoffset
Time to Live
ttl
IP Options
ipopts
Same IP
sameip
Transport Protocol
Transport Protocol: TCP
Port
(In Snort rule header)
Flow
flow
Flags
flags
Sequence Number
seq
Ack Number
ack
Window Size
window
Transport Protocol: UDP
(In Snort rule header)
Port
(In Snort rule header)
Transport Protocol: ICMP
Type
itype
Code
icode
