Справочник Пользователя для Netopia R3100

As described above, a filter applies criteria to an IP packet and then takes one of three actions:

■

Passes the packet to the local or remote network

■

Blocks (discards) the packet

■

Ignores the packet

A filter passes or blocks a packet only if it finds a match after applying its criteria. When no match occurs, the 
filter ignores the packet.

The criteria are based on information contained in the packets. A filter is simply a rule that prescribes cer tain 
actions based on cer tain conditions. For example, the following rule qualifies as a filter:

Block all Telnet attempts that originate from the remote host 199.211.211.17.

This rule applies to Telnet packets that come from a host with the IP address 199.211.211.17. If a match 
occurs, the packet is blocked.

Here is what this rule looks like when implemented as a filter on the Netopia R3100:

To understand this par ticular filter, look at the par ts 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

  +-#--Source IP Addr--Dest IP Addr-----Proto-Src.Port-D.Port--On?-Fwd-+
  +--------------------------------------------------------------------+
  | 1  199.211.211.17  0.0.0.0          TCP   23               Yes No  |
  +--------------------------------------------------------------------+