3Com 2200 - page 141

12-4 CHAPTER 12: CREATING AND USING PACKET FILTERS

Concepts for Writing

a Filter Before writing a packet ﬁlter, you should understand thsee basic concepts:

■How the packet ﬁlter language works

■The basic elements of a packet ﬁlter

■How to implement sequential tests in a packet ﬁlter

■The pre-processed and run-time storage requirements

How the Packet Filter Language Works

You deﬁne packet ﬁlters using a simple, stack-oriented language. Stack-

oriented means that the language uses a LIFO (last in, ﬁrst out) queue when

the packet ﬁlter is running. The program places values (called operands) on

the stack and tests them with various logical expressions (called operators),

such as and, or, equal, and not equal (see Table 12-3 and Table 12-4). These

expressions typically test the values of various ﬁelds in the received packet,

which include MAC addresses, type ﬁelds, IP addresses, and Service Access

Points (SAPs).

A program in the packet ﬁlter language consists of a series of one or more

instructions that results in the top of the stack containing a byte value after

execution of the last instruction in the program. This byte value determines

whether to forward or discard the packet.

In this stack-oriented language, instructions:

■push operands onto the stack

■pop the operands from the stack for comparison purposes

■push the results back onto the stack

Therefore, with the exception of the push instructions, instructions (such as

logical operators) locate their operands implicitly and do not require

additional operand speciﬁers in the instruction stream.

Opcodes are the variables used to identify the type of operands and

operators you are specifying in the packet ﬁlter instructions.

Contents

Main 3Com Corporation 95052-8145 Santa Clara, California 5400 Bayfront Plaza C ONTENTS II II S -L F III E FDDI P IV B P Page 13 PART APPENDIXES A B I ABOUT THIS GUIDE How to Use This Guide Switch 2200. The parts of the guide are described in Table 1. Conventions this guide. Switch 2200 Documentation Documentation Comments Page S UPER Conguration Tasks VERVIEW O S WITCH TACK II S 2200 A Page Page Page Page Page Page 2 A Initial User Access Levels of User Access Page Using Menus to Perform Tasks Page Page 2-6 CHAPTER 2: HOW TO USE THE ADMINISTRATION CONSOLE Figure 2-4 Bridging Menu Hierarchy for Administer Access Figure 2-5 IP Menu Hierarchy for Administer Access Page Page Page Administration Console Interface Remote Access Parameters Page Running Scripts of Administration Console Tasks Page Page Getting Help in the Administration Exiting the Administration Page Page 3 ACCESS TO THE SYSTEM About Management Access Setting Up the Console Serial Port Setting Up an IP Interface for Management Page Page Page Page Page Page Page Page Page Page Displaying IP Statistics The IP statistics you can view are described in Table 3-3. To display IP statistics, enter the following from the top level of the Administration Console: Statistics are displayed, as shown in this example: Setting Up SNMP on Y our System Page Here is an example display of the SNMP trap reporting information: Page Page Page 4 E Displaying the System Conguration Setting Passwords Setting the System Name Changing the Date and Time Rebooting the System 5 About Setting Baselines Displaying the Current Baseline 5-2 CHAPTER 5: BASELINING STATISTICS Setting Baselines system baseline set A message similar to the following appears: Baseline set at 08/07/96 10:42:52 AM. Baselining is automatically enabled when a baseline is set. 6 R About Working with Nonvolatile Data Saving NV Data Restoring NV Data Page Examining a Saved NV Data File Resetting NV Data to Defaults Page Page 7 P Displaying Ethernet Port 7-2 CHAPTER 7: ADMINISTERING ETHERNET PORTS An example of a summary display for Ethernet ports is shown here: Table 7-1 describes the information provided about an Ethernet port. Page Page Ethernet port. However, frames may be discarded for the following reasons: Figure 7-1 shows the order in which these discard tests are made. = Figure 7-1 How Frame Processing Affects Ethernet Receive Frame Statistics = Labeling a Port Setting the Port Sta te 8 R Administering FDDI Stations Table 8-1 describes these statistics. Page To set the connection policies of an FDDI station: Page Administering FDDI Paths Page Page Administering FDDI MACs Page Administering FDDI MACs 8-11 The following example shows the detail display of FDDI MAC information: Table 8-4 describes the information provided for the FDDI MAC. Page MAC. However, a frame might be discarded for the following reasons: Page Page Page Page Administering FDDI Ports Table 8-5 describes the type of information provided for an FDDI port. Page Page Page 9 R About Roving Analysis Displaying the Roving Analysis Conguration Adding an Analyzer Port Removing an Analyzer Port Starting Port Monitoring Stopping Port Monitoring Page 10 Displaying Bridge 10-2 CHAPTER 10: ADMINISTERING THE BRIDGE The following example shows a display of bridge information. Each item in the bridge parameter list is described in Table 10-1. Page Page Enabling and Disabling IP Fragmentation Enabling and Disabling IPX Snap Translation Setting the Address Threshold Setting the Aging Time Administering STP Bridge Page Page Page 11 Displaying Bridge Port 11-2 CHAPTER 11: ADMINISTERING BRIDGE PORTS The following example shows a bridge port summary display. The following example shows a bridge port detail display. Table 11-1 describes the type of information provided for the bridge port. Page Page Page Setting the Multicast Limit Administering STP Bridge Port Page Page Administering Port Addresses 11-11 Administering Port Addresses bridge port address list Page Page 11-14 CHAPTER 11: ADMINISTERING BRIDGE PORTS To freeze all dynamic addresses: bridge port address freeze 12 P About Packet Filtering Listing Packet Filters The listing of packet lters is displayed. An example of the output follows: Displaying Packet Filters Creating Packet Filters Page Table 12-2 describes the instructions and stacks of a packet lter. 12-6 CHAPTER 12: CREATING AND USING PACKET FILTERS Figure 12-1 Ethernet and FDDI Packet Fields Page Page Page Page Page Page Creating Packet Filters 12-13 The pseudocode translates into the following packet lter: Page Page Page Page Page Page Deleting Packet Filters Editing, Checking and Saving Packet Filters Page Loading Packet Filters Assigning Packet Filters to Ports Page Unassigning Packet Filters from Ports 13 PORT GROUPS TO USE IN P Using Groups in Packet Filters Listing Groups Displaying Groups Creating New Groups Page Deleting Groups Adding Addresses and Ports to Groups Page Removing Addresses or Ports from a Group Page Loading Groups Page Page A EXAMPLES, AND SYNTAX ERRORS Page Page Page Page Page Page Page Packet Filter Examples Page Page A-12 APPENDIX A: PACKET FILTER OPCODES, EXAMPLES, AND SYNTAX ERRORS Address Group Filter This lter accepts only frames whose source and destination address are in the same group. Common Syntax Errors errors. The syntax errors and their causes are listed in Table A-1. Page B Online Technical Services Page Support from Your Network Supplier Support from 3Com Returning Products for Repair I Numerics A B C D E F G H I L M N O P R S T U V W X