Chapter Packet Filters | USRobotics NETServer/16, NETServer/8

Chapter 8

Packet Filters

This chapter covers setting up packet filters for the NETServer. The following topics are included:

∙Filter overview

∙Creating new packet filters

∙Filter rule format

∙TCP/IP packet filtering

∙IPX packet filtering

∙Editing Packet filters

Packet Filters

Packet filters are primarily used in networks that cross organiza- tional or corporate boundaries. They control inter-network data transmission by permitting or denying the passage of specific packets through network interfaces.

When data packets are received by a network interface such as a modem, the packet filter analyzes their header information. After evaluating the data packet against its set of rules, the filter permits it to pass through or discards it. If an IP packet is discarded, the NETServer sends an ICMP “Host Unreachable” message back to the originator.

Packet Filters 8-1

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USRobotics NETServer/16, NETServer/8 manual Chapter Packet Filters

Contents

NETServer/8 NETServer/16 Page Table of Contents Network Dial-in Access Reference Section Administrative Tools Limited Warranty Warranty and Service Technical Support Service and SupportVii Viii We welcome your suggestions for better documentation Overview Chapter OverviewWhat’s New with Release 3.1? Additional Software Enhancements Accounting Server Support Netmask TableIP Address Spoofing Accounting Servers Icmp Message Logging Multiple Name ServersRandomized Hosts Radius Accounting and ANI/DNIS New Modem Port Features NETServer Overview IP Modem Sharing How do I get there from here? Security Administrative Utilities System Administrator Requirements Chapter Basic InstallationBasic Installation TCP/IP Reference Material Accessing the Command Line Getting Started First step for IPX or IP/IPX networks Getting the LAN port up and running Basic Installation IP Configuration You must also set the Broadcast Address. Type the following Ethernet802.3 ethernet802.2 ethernet802.2II ethernetII IPX Configuration Final Steps Password Recommended Global ConfigurationIP and IPX Default Gateways To set the IP gateway, type the following Save your work Name Service Basic Installation How to Setup Applications Chapter Configuration OverviewConfiguration Overview Application Section Where do I go from here? Separate a parameter and its value by a space Command LineCommands are not case sensitive You can abbreviate commands Save your changes Reset any ports you have changedReboot when necessary How to log out of the command line Quick Command Overview Global Configuration Overview of configurable tablesHosts Table Netmasks Table Initialization Script ConfigurationNet0 LAN Port Configuration Location Table Packet Filter Table Port Type Port Configuration Routes Table Snmp Configuration User Table Configuration Overview Terminal or Workstation Setup Chapter IP Terminal Server SetupIP Terminal Server Setup NETServer Terminal Server Setup Overview Global Default Port DefaultUser Table Set the port’s security Pass-Thru Login Terminal Server Detailed SetupConfiguring a Port Set the port type to User Login Create default user settings for the port Port Default Login Service Optional Friendly Stuff Save sport # Adding a Remote User to the User Table Configure the userAdd the user to the User Table Login Service Configure for dialback use? Example IP Terminal Server Case Studies NETServer will use ports 6, 7, and 8 for this application Save your work and reset all the ports Example IP Terminal Server Setup Dial-in User Setup Chapter Network Dial In AccessNetwork Dial In Access Prework NETServer Setup for Network Dial-In Overview Configuration NETServer Dial-In Detailed Setup Dialback Users on this Port? Save the changes to flash memory Normal or dialback user? Create a new user Add configuration information for the user This is the user’s IP subnet mask. Use the following command Option can be any one of the following Configure the ports IP Remote Access Case Study Create a user table entry for the dialback user Create user table entries for the dial in users Save your work and reset the ports Connecting to the NETServer IPX Remote Access Create User Table entries for the dial in users Chapter LAN-to-LAN Routing Setup for NETServer Routing OverviewLAN-to-LAN Routing IPX routing LAN-to-LAN Routing NETServer Routing An Introduction to NETServer Routing LAN-to-LAN Routing How RIP Dynamically Builds the Routing Table Static vs. Dynamic Routes Establishing Connections to Remote Gateways How Packets are Routed Routing Procedure PAP Password Authentication Protocol PAP/CHAP Authentication Chap Setup for the NETServer Chap Challenge Example Configuring the Port LAN-to-LAN Routing Detailed Setup Creating a Dial-Out Group Create a new location table entry Adding a Remote Device to the Location TableSet Required Location Parameters This is the remote device’s IP address Set location location name netmask netmask Dial Group Number Multiple lines for a single connection Maximum Ports Create a Dial Script Set location Chicago script 1 atds slot#\r Connect Create a User Table Entry Adding the Remote Device to the User TableTell the NETServer about the Remote Device Set user user name protocol ppp slip Set netuser user name compression on off LAN-to-LAN Routing Case Study Add netuser nsb password xyzabc Setting Up NETServer a Setting Up NETServer B Now, save your work and reset the ports Testing the Connection What If I Don’t Want to Use Chap Authentication? Connecting to NETServer a from NETServer B Assign the modem a TCP port number Configure the port as a host deviceChapter Talking to the Modems TCP/IP Modem Sharing Turn modem control carrier detect off Save your work and reset the port Implementing Security with Host Device Dial Out Configuring modems as Unix pseudo TTYs Talking to the Modems Assign Text to an Initialization Script Modem Initialization ScriptsHow To Add a New Initialization Script Delete an Initialization Script Use an Existing Initialization ScriptDisplaying an Initialization Script Initialization Script Example Default initialization string Sending AT commands to the modems Talking to the Modems Packet Filters Chapter Packet FiltersPacket Filters Packet Filters and the NETServer Types of Filters Information Sources Input filters vs. Output filters Adding Packet Filters Input filters vs. Output filters Rule Type Filter Rule FormatName Permit or Deny Rule NumberOptions TCP/IP packet filtering Destination Address TCP and UDP parameters TCP UDP Standard Port Numbers FTP Packet Filtering Filtering RIP messages Client opens a control channel FTP Example Type Description Filtering Icmp packets IPX Rules IPX packet filtering Dsthost SAP Rule Options Delete a Packet Filter Editing Packet FiltersEdit a Packet Filter Delete a Packet Filter Rule View the Packet Filter Table View a Packet Filter Root Access Chapter Administrative ToolsConfiguring the !root account Changing the command prompt Telnet Access Port Dial Command Manually Connecting to a Remote SiteNslogin, Rlogin and Telnet Commands Viewing Debug messages Troubleshooting Commands Turn off the output console by typing the following Ifconfig MTU Ping Ptrace Version Traceroute Show Show command Show flash Show arp Show netconns Show memory Show netstat Show sessions Show sap Administrative Tools Global Configuration Chapter Command ReferenceCommand Reference Get help View the Global Configuration TableSave Changes Connect Message Default HostGlobal user parameters Assigned Address Randomize Hosts Global routing parameters Default Gateways IP Address Spoofing Default Route System Name NetBIOS Packet PropagationPAP Authentication Proxy ARP Service Name ServiceServer name Domain name DNS Cache Reset Time-out Radius Secret Radius securityPrimary Radius Server Alternate Radius Server Syslog Accounting Radius Accounting Icmp Logging View the Hosts Table Hosts TableAdd a Host Delete a Host Change a Location’s Parameters Bring Up the List of CommandsLocation Table Add a Location to the Location Table View the Location Table Save Location Table ChangesView a Particular Location Connection Type Location Table Parameters Netmask IP AddressIPX Network Routing ProtocolCompression Maximum Ports Dial Group High Water Mark Idle Time-out PPP Async Map MTU Input Filter Output FilterDial Script Send Reply Reset the Network Interface Card LAN Port Net0 Configuration LAN Port Parameters View LAN Port ConfigurationEthernet Status Interface Address Configured Ethernet Media Broadcast Address IPX Frame Type Set net0 ifilter filter name View the netmask table Netmask TableAdd a netmask Delete a netmask Change a Port’s Parameters Save Port Configuration View the Ports Table To view all of the S-ports, use the following command Idle Port is idle View an Individual Port Determining a Port’s Type User LoginHost Device Device Service Network Dial In Port Parameters Login MessageLine Hangup Security Pass-Thru Login Login Prompt Dialback Delay User Login Port ParametersAutolog Name Host Login Service Terminal Type IPX Network Number Hardwired Port Parameters Set s0 netmask netmask NETServer sends RIP information across Stopbits Serial Communications ParametersPort Speed Databits Modem Control ParityFlow Control Host Override Add a Route to the Routes Table Routes Table ConfigurationChange a Route’s Information Save Routes Table Changes Delete a Routes Table EntryView the IP Routes Table Flag Parameter Viewing the IPX Routes Table IP Parameters IPX Parameters Enabling/Disabling Snmp Snmp TableDelete Snmp Hosts Save the Snmp Table Changes Write Community Name Snmp Table ParametersView Snmp Table Read Community Name Write Hosts Read Hosts Add a User to the User Table User Table View the User Table Change a User’s ParametersDelete a User Save User Table Changes Access Filter Login User ParametersDialback Number Set user name service rlogin telnet netdata portmux Command Reference Dialback Network User Parameters IPX connections require the PPP protocol NETServer sends RIP information to the dial Set user filter name ofilter filter name Command Reference 16 port NETServer Hardware Appendix a Technical Specifications Typical Input Power Power RequirementsMaximum Output Power Maximum Input Power External Serial Port Console Technical Specifications A-3 10Base-T Ethernet Network Interface Card Isolated GND SignalTechnical Specifications A-5 10Base-2 BNC Technical Specifications Technical Specifications A-7 Token Ring⎯STP ConnectorToken Ring Network Interface Card Token Ring⎯UTP Connector Routing Support NETServer Firmware SpecificationsAdministration Technical Specifications A-9 Industry Standards Support PPP Specific FeaturesClient Dial-up Support Slip and PPP Client Software Support Technical Specifications A-11 Technical Specifications Addressing Schemes B-1 Appendix B Addressing SchemesIPX Addressing Basics IP Addressing Basics Subnetting Address ClassesAddressing Schemes Addressing Schemes B-3 Mask Binary Subnets Hosts Reserved Addresses Addressing Schemes B-5 Supernetting Advanced TCP/IP Cidr Each Supernet is treated as a single entity Addressing Schemes B-7 Step two Select a range of addresses for each supernet Addressing Schemes B-9 Supernetting and the NETServer Software Download C-1 SDL Using a Direct Connection to a PCWhy Perform an SDL Software Download? Appendix C Software Download Starting SDL Make Backup Copies of the NETServer FirmwareSoftware Installation Loading the Software Download SDL Program Software Download C-3 SDL Command Syntax Filename Prefixes Optional -d Parameter Software Download C-5 Entering SDL Mode Upgrading NETServer Firmware From the Windows Management Software Software Download C-7 Upgrading the Modem Firmware For the Isdn NETServer, the file names are Software Download C-9 Error Messages PC SDL program detected unknown command line argu- ments Software Download C-11 Invalid Control Word Software Download C-13 File you are trying to download is not a NETServer file Boot Process D-1 Appendix D Boot Process Boot Process Appendix E Syslog Accounting Using SyslogSyslog Accounting E-1 Syslog Accounting Syslog System MessagesSpotting Unused Ports Syslog System Message Format Syslog Accounting E-3 Syslog System Message Examples Someone has logged in as !root on port S16 Syslog Accounting E-5 Syslog Accounting Obtaining Radius Appendix F Security a Centrally Managed User Table Authentication Items Setting Up Radius User Table Entries Response Items Radius F-5 Framed-Netmask Radius F-7 User Types Radius F-9 Making NETServer talk to a Radius security server Chap authentication using Radius Acct-Status-Type Acct-Delay-TimeRadius Accounting Radius accounting fields Acct-Authentic Accounting ExamplesAcct-Session-Time Radius Index Alphabetical Index Index Icmp MTU NIC PPP SAP Slip Index Index