Netopia 4553 User Manual
Page 157
Security 11-157
Parts of a filter
A filter consists of criteria based on packet attributes. A typical filter can match a packet on any one of the
following attributes:
■
The source IP address (where the packet was sent from)
■
The destination IP address (where the packet is going)
■
The type of higher-layer Internet protocol the packet is carr ying, such as TCP or UDP
Port numbers
A filter can also match a packet’s por t number attributes, but only if the filter’s protocol type is set to TCP or
UDP, since only those protocols use por t numbers. The filter can be configured to match the following:
■
The source por t number (the por t on the sending host that originated the packet)
■
The destination por t number (the por t on the receiving host that the packet is destined for)
By matching on a por t number, a filter can be applied to selected TCP or UDP ser vices, such as Telnet, FTP, and
World Wide Web. The following tables show a few common ser vices and their associated por t numbers:
Internet service
TCP port
Internet service
TCP port
FTP
20/21
Finger
79
Telnet
23
World Wide Web
80
SMTP (mail)
25
News
144
Gopher
70
rlogin
513
Internet service
UDP port
Internet service
UDP port
Who Is
43
AppleTalk Routing
Maintenance (at-r tmp)
202
World Wide Web
80
AppleTalk Name Binding
(at-nbp)
202
SNMP
161
AURP (AppleTalk)
387
TFTP
69
who
513