Enterasys Networks CSX7000 Manuel d'utilisateur télécharger pdf (Page 301)

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Central Site Remote Access Switch 301

ONFIGURING

DVANCED

IP R

OUTING

IP Filters

EQ equal to <port>

NEQ not equal to <port>

LT less than <port>

GT greater than <port>

RANGE inclusive range <port1> <= packet port value> = <port2>

Examples:

EQ 23: TCP port for the Telnet protocol.

RANGE 0 65535:Any TCP port (wild card and default).

TCP C

ONTROL

This element accesses the control bits of the TCP header, which are utilized to initiate and maintain

the state of a TCP connection. “ANY” is the wild card and default value. TCP packets whose ACK

or RST control bits are set will match the ESTABLISHED value, since they belong to an established

connection. Conversely, a TCP packet which is attempting to open a new connection will carry

neither of these bits and will match the NOT-ESTABLISHED value.

ICMP T

YPE AND CODE

These fields allow filtering based on the specific function of an ICMP packet, via the Type and Code

fields. Using an operator of EQUAL or NOT EQUAL, the packet’s Type/Code is compared against

the target values. These values may be a numeric quantity between 0 and 255; or the mnemonic

“ANY” can be used with an EQUAL comparison as the wild card value.

IP FILTERS BACKGROUND INFORMATION

A filter is a list of conditions. It is the logical element which is applied to a point in the routing

process to control packet flow. Each condition within a filter is created from one of the previously-

defined packet types, along with the action to take when a packet matches that type.

IP Filters modify the normal processing flow of an IP packet as it passes through the various stages

of IP Processing. When an IP packet encounters a filter, the filter’s output - DISCARD or

FORWARD - determines if the packet has permission to continue. There are two types of IP Filters.

Forwarding Filters are selectively applied to the key locations in the IP routing process. The

Connection Filter is applied to those datagrams which trigger a WAN connection in order to satisfy

the forwarding process.

The following illustrates a packet that is passing through a filter. The packet is checked against each

of the individual conditions of the filter before an action is performed:

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Enterasys Networks CSX7000 Manuel d'utilisateur Page 301

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