Netopia R910 manual Parts of a filter, Port numbers, Port number comparisons, Security

Models: R910

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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 carrying, such as TCP or UDP

Port numbers

A filter can also match a packet’s port number attributes, but only if the filter’s protocol type is set to TCP or UDP, since only those protocols use port numbers. The filter can be configured to match the following:

The source port number (the port on the sending host that originated the packet)

The destination port number (the port on the receiving host that the packet is destined for)

By matching on a port number, a filter can be applied to selected TCP or UDP services, such as Telnet, FTP, and World Wide Web. The tables below show a few common services and their associated port 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

202

 

 

Maintenance (at-rtmp)

 

 

 

 

 

World Wide Web

80

AppleTalk Name Binding

202

 

 

(at-nbp)

 

 

 

 

 

SNMP

161

AURP (AppleTalk)

387

 

 

 

 

TFTP

69

who

513

 

 

 

 

Port number comparisons

A filter can also use a comparison option to evaluate a packet’s source or destination port number. The comparison options are:

No Compare: No comparison of the port number specified in the filter with the packet’s port number.

Not Equal To: For the filter to match, the packet’s port number cannot equal the port number specified in the filter.

Page 129
Image 129
Netopia R910 manual Parts of a filter, Port numbers, Port number comparisons, Security