Apple 034-2351_Cvr manual Precautions, Creating IP Filter Rules Using ipfw

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If you want to put your own rules in the ipfw.conf file, you can use a template that is installed at /etc/ipfilter/ipfw.conf.default. Duplicate the file, rename it, and edit it as indicated in the template’s comments.

Precautions

By using the Advanced panel or creating your own rules, you can put the server in a state that is completely cut off from network access. This might require a reboot in single-user-mode to restore network access. To avoid this, consider adding a cron job to disable the firewall periodically while you are testing rules. Be sure to disable this cron job when the machine is put into production.

The following command disables the firewall:

sudo sysctl -w net.inet.ip.fw.enable=0

And this enables it:

sudo sysctl -w net.inet.ip.fw.enable=1

Neither of these operations change the rules loaded into the firewall, they just determine whether those rules are applied.

Creating IP Filter Rules Using ipfw

You can use the ipfw command in conjunction with the firewall module of Server Admin when you want to:

•Display rules created by the firewall module. Each filter translates into one or more rules.

•Create filters with characteristics that can’t be defined using the firewall module. For example, you may want to use rules specific to a particular kind of IP protocol. Or you may want to filter or block outgoing packets.

•Count the number of times rules are applied.

If you use ipfw, make sure you don’t modify rules created using the firewall module. Changes you make to firewall module rules are not permanent. Firewall service recreates any rules defined using the firewall module whenever the service is restarted. Here is a summary of how the firewall module assigns rule numbers:

Rule number

Used by firewall module for

10

Loop back.

 

 

20

Discarding any packet from or to 127.0.0.0/8 (broadcast).

 

 

30

Discarding any packet from 224.0.0.0/3 (broadcast).

 

 

40

Discarding TCP packets to 224.0.0.0/3 (broadcast).

 

 

100–64000

User-defined port-specific filters.

 

 

63200

Denying access for icmp echo reply. Created when “Deny ICMP

 

echo reply” is selected in the Advanced pane of the Configure

 

Firewall window.

 

 

Chapter 3 IP Firewall Service

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Contents Mac OS X Server Network Services Administration 034-2351/9-20-03 Contents Glossary Index Using This Guide How to Use This GuideWhat’s Included in This Guide Getting Help for Everyday Management Tasks Setting Up Mac OS X Server for the First TimeGetting Additional Information Before You Set Up Dhcp Service Dhcp ServiceCreating Subnets Using Static IP AddressesAssigning IP Addresses Dynamically Locating the Dhcp ServerUsing Multiple Dhcp Servers on a Network Setting Up Dhcp Service for the First TimeInteracting With Other Dhcp Servers Assigning Reserved IP AddressesStarting and Stopping Dhcp Service Managing Dhcp ServiceCreating Subnets in Dhcp Service Set up logs for Dhcp serviceTo change subnet settings Changing Subnet Settings in Dhcp ServiceSetting the DNS Server for a Dhcp Subnet Deleting Subnets From Dhcp ServiceChanging IP Address Lease Times for a Subnet Setting Wins Options for a Subnet Setting Ldap Options for a SubnetTo set Ldap options for a subnet Disabling Subnets Temporarily Monitoring Dhcp ServiceViewing the Dhcp Status Overview Viewing Dhcp Log Entries Setting the Log Detail Level for Dhcp ServiceViewing the Dhcp Client List Where to Find More Information DNS Service Setting Up DNS Service for the First Time Before You Set Up DNS ServiceSetting Up Multiple Name Servers DNS and BindLearn and plan Set up a mail exchange MX record optional Configure basic DNS settingsConfigure the reverse lookup zone optional Start DNS serviceStarting and Stopping DNS Service Managing DNS ServiceEnabling or Disabling Zone Transfers Enabling or Disabling RecursionAdding a Master Zone Managing ZonesTo add a master zone Adding a Slave ZoneTo add a slave zone Duplicating a Zone Adding a Forward ZoneTo add a forward zone To duplicate a zoneModifying a Zone Managing RecordsDeleting a Zone To modify a zoneTo add a record Adding a Record to a ZoneDeleting a Record From a Zone Modifying a Record in a ZoneTo modify a record To delete a recordViewing DNS Service Activity Viewing DNS Service StatusMonitoring DNS Viewing DNS Log EntriesViewing DNS Usage Statistics Changing DNS Log File LocationTo change the log detail level DNS Spoofing Securing the DNS ServerServer Mining To see DNS usage statisticsDenial-of-Service DoS DNS Service ProfilingTo specify zone transfer IP addresses To alter BIND’s version responseService Piggybacking Setting Up MX Records Common Network Administration Tasks That Use DNS ServiceExample.com To enable MX records Configuring DNS for Mail ServiceEnabling Redundant Mail Servers Edit the MX record of the primary mail serverTo enable backup or redundant mail servers Setting Up Namespace Behind a NAT RouterNetwork Load Distribution aka Round Robin Setting Up a Private TCP/IP NetworkHosting Several Internet Services With a Single IP Address Configuring Bind Using the Command LineWhat Is BIND? Bind on Mac OS X Server Bind Configuration FilePractical Example Zone Data FilesTo set up the sample files Setting Up Sample Configuration FilesConfiguring Clients If you are using Mac OS X Server as your Dhcp Server Using DNS With Dynamically Assigned IP AddressesCheck Your Configuration Request For Comment Documents For more information on DNS and BIND, see the followingPage IP Firewall Service IP Firewall Service Understanding Firewall Filters What is a Filter?IP Address Subnet MaskCidr Rule Mechanism and Precedence Using Address RangesMultiple IP Addresses Start firewall service Setting Up Firewall Service for the First TimeCreate an IP address group that filters will apply to Add filters to the IP filter listStarting and Stopping Firewall Service Managing Firewall ServiceOpening the Firewall for Standard Services Save firewall service changesCreating an Address Group To open the firewall for standard servicesTo create an address group Duplicating an Address Group Editing or Deleting an Address GroupCreating an Advanced IP Filter for TCP ports To edit or delete an address groupTo create an IP filter for TCP ports Creating an Advanced IP Filter for UDP PortsTo create an IP filter for UDP ports NFSTo change the Default setting Changing the Default FilterEditing Advanced IP Filters To edit advanced IP filtersSetting Up Logs for Firewall Service Monitoring Firewall ServiceViewing the Firewall Status Overview Viewing the Firewall LogViewing Packets Logged by Filter Rules Viewing Denied PacketsLog Example To view denied packetsPractical Examples Block Access to Internet UsersBlock Junk Mail To do thisAllow a Customer to Access the Apple File Server To prevent ping denial-of-service attacks Preventing Denial-of-Service DoS AttacksControlling or Enabling Peer-to-Peer Network Usage Controlling or Enabling Network Game Usage Advanced ConfigurationBackground Creating IP Filter Rules Using ipfw PrecautionsCreating IP Filter Rules Reviewing IP Filter RulesDeleting IP Filter Rules Port ReferencePptp VPN UDP port Used for Reference For more information about ipfw Starting and Stopping NAT Service NAT ServiceTo start NAT service Monitoring NAT Service Configuring NAT ServiceTo configure NAT service Viewing the NAT Status OverviewFor more information about natd To view the NAT divert logPage VPN Service VPN and Security Authentication MethodTransport Protocols Point to Point Tunneling Protocol PptpManaging VPN Service Before You Set Up VPN ServiceStarting or Stopping VPN Service Enabling and Configuring L2TP Transport ProtocolTo enable L2TP Enabling and Configuring Pptp Transport ProtocolTo enable Pptp Configuring VPN Network Routing Definitions Configuring Additional Network Settings for VPN ClientsTo configure addition network settings To set routing definitionsSetting the Log Detail Level for VPN Service Monitoring VPN ServiceSetting the VPN Log Archive Interval Viewing a VPN Status OverviewViewing VPN Client Connections Viewing the VPN LogTo view the log To view client connectionsPage How NTP Works NTP ServiceSetting Up NTP Service Using NTP on Your NetworkTo set up NTP service To configure NTP on clients Configuring NTP on ClientsPage IPv6 Support IPv6 Addresses in the Server Admin IPv6 Enabled ServicesIPv6 Addresses NotationIPv6 Addressing Model IPv6 Reserved AddressesIPv6 Address Types Where to Find More Information Glossary GlossaryGlossary Glossary Name server See DNS Domain Name System Search path See search policy UCE unsolicited commercial email See spam Glossary Page Index Dhcp VPN

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