Apple 034-2351_Cvr Creating Subnets, Assigning IP Addresses Dynamically, Locating the Dhcp Server

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Creating Subnets

Subnets are groupings of computers on the same network that simplify administration. You can organize subnets any way that is useful to you. For example, you can create subnets for different groups within your organization or for different floors of a building. Once you have grouped client computers into subnets, you can configure options for all the computers in a subnet at one time instead of setting options for individual client computers. Each subnet needs a way to connect to the other subnets. A hardware device called a router typically connects subnets.

Assigning IP Addresses Dynamically

With dynamic allocation, an IP address is assigned for a limited period of time (the lease time) or until the client computer doesn’t need the IP address, whichever comes first. By using short leases, DHCP can reassign IP addresses on networks that have more computers than available IP addresses.

Addresses allocated to Virtual Private Network (VPN) clients are distributed much like DHCP addresses, but they don’t come out of the same range of addresses as DHCP. If you plan on using VPN, be sure to leave some addresses unallocated by DHCP for use by VPN. To learn more about VPN, see Chapter 5, “VPN Service,” on page 71.

Using Static IP Addresses

Static IP addresses are assigned to a computer or device once and then don’t change. You may want to assign static IP addresses to computers that must have a continuous Internet presence, such as web servers. Other devices that must be continuously available to network users, such as printers, may also benefit from static IP addresses.

Static IP addresses must be set up manually by entering the IP address on the computer or device that is assigned the address. Manually configured static IP addresses avoid possible issues certain services may have with DHCP-assigned addresses and avoid the delay required for DHCP to assign an address.

Don’t include Static IP address ranges in the range distributed by DHCP.

Locating the DHCP Server

When a client computer looks for a DHCP server, it broadcasts a message. If your DHCP server is on a different subnet from the client computer, you must make sure the routers that connect your subnets can forward the client broadcasts and the DHCP server responses. A relay agent or router on your network that can relay BootP communications will work for DHCP. If you don’t have a means to relay BootP communications, you must place the DHCP server on the same subnet as your client.

Chapter 1 DHCP Service

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Contents Mac OS X Server Network Services Administration 034-2351/9-20-03 Contents Glossary Index What’s Included in This Guide How to Use This GuideUsing This Guide Getting Additional Information Setting Up Mac OS X Server for the First TimeGetting Help for Everyday Management Tasks Dhcp Service Before You Set Up Dhcp ServiceUsing Static IP Addresses Creating SubnetsAssigning IP Addresses Dynamically Locating the Dhcp ServerSetting Up Dhcp Service for the First Time Using Multiple Dhcp Servers on a NetworkInteracting With Other Dhcp Servers Assigning Reserved IP AddressesManaging Dhcp Service Starting and Stopping Dhcp ServiceCreating Subnets in Dhcp Service Set up logs for Dhcp serviceChanging Subnet Settings in Dhcp Service To change subnet settingsChanging IP Address Lease Times for a Subnet Deleting Subnets From Dhcp ServiceSetting the DNS Server for a Dhcp Subnet To set Ldap options for a subnet Setting Ldap Options for a SubnetSetting Wins Options for a Subnet Viewing the Dhcp Status Overview Monitoring Dhcp ServiceDisabling Subnets Temporarily Viewing the Dhcp Client List Setting the Log Detail Level for Dhcp ServiceViewing Dhcp Log Entries Where to Find More Information DNS Service Before You Set Up DNS Service Setting Up DNS Service for the First TimeSetting Up Multiple Name Servers DNS and BindLearn and plan Configure basic DNS settings Set up a mail exchange MX record optionalConfigure the reverse lookup zone optional Start DNS serviceManaging DNS Service Starting and Stopping DNS ServiceEnabling or Disabling Zone Transfers Enabling or Disabling RecursionManaging Zones Adding a Master ZoneTo add a slave zone Adding a Slave ZoneTo add a master zone Adding a Forward Zone Duplicating a ZoneTo add a forward zone To duplicate a zoneManaging Records Modifying a ZoneDeleting a Zone To modify a zoneAdding a Record to a Zone To add a recordModifying a Record in a Zone Deleting a Record From a ZoneTo modify a record To delete a recordViewing DNS Service Status Viewing DNS Service ActivityMonitoring DNS Viewing DNS Log EntriesTo change the log detail level Changing DNS Log File LocationViewing DNS Usage Statistics Securing the DNS Server DNS SpoofingServer Mining To see DNS usage statisticsDNS Service Profiling Denial-of-Service DoSTo specify zone transfer IP addresses To alter BIND’s version responseService Piggybacking Example.com Common Network Administration Tasks That Use DNS ServiceSetting Up MX Records Configuring DNS for Mail Service To enable MX recordsEnabling Redundant Mail Servers Edit the MX record of the primary mail serverSetting Up Namespace Behind a NAT Router To enable backup or redundant mail serversSetting Up a Private TCP/IP Network Network Load Distribution aka Round RobinWhat Is BIND? Configuring Bind Using the Command LineHosting Several Internet Services With a Single IP Address Bind Configuration File Bind on Mac OS X ServerPractical Example Zone Data FilesConfiguring Clients Setting Up Sample Configuration FilesTo set up the sample files Check Your Configuration Using DNS With Dynamically Assigned IP AddressesIf you are using Mac OS X Server as your Dhcp Server For more information on DNS and BIND, see the following Request For Comment DocumentsPage IP Firewall Service IP Firewall Service What is a Filter? Understanding Firewall FiltersIP Address Subnet MaskCidr Multiple IP Addresses Using Address RangesRule Mechanism and Precedence Setting Up Firewall Service for the First Time Start firewall serviceCreate an IP address group that filters will apply to Add filters to the IP filter listManaging Firewall Service Starting and Stopping Firewall ServiceOpening the Firewall for Standard Services Save firewall service changesTo create an address group To open the firewall for standard servicesCreating an Address Group Editing or Deleting an Address Group Duplicating an Address GroupCreating an Advanced IP Filter for TCP ports To edit or delete an address groupCreating an Advanced IP Filter for UDP Ports To create an IP filter for TCP portsNFS To create an IP filter for UDP portsChanging the Default Filter To change the Default settingEditing Advanced IP Filters To edit advanced IP filtersMonitoring Firewall Service Setting Up Logs for Firewall ServiceViewing the Firewall Status Overview Viewing the Firewall LogViewing Denied Packets Viewing Packets Logged by Filter RulesLog Example To view denied packetsBlock Access to Internet Users Practical ExamplesBlock Junk Mail To do thisAllow a Customer to Access the Apple File Server Controlling or Enabling Peer-to-Peer Network Usage Preventing Denial-of-Service DoS AttacksTo prevent ping denial-of-service attacks Background Advanced ConfigurationControlling or Enabling Network Game Usage Precautions Creating IP Filter Rules Using ipfwReviewing IP Filter Rules Creating IP Filter RulesPort Reference Deleting IP Filter RulesPptp VPN UDP port Used for Reference For more information about ipfw To start NAT service NAT ServiceStarting and Stopping NAT Service Configuring NAT Service Monitoring NAT ServiceTo configure NAT service Viewing the NAT Status OverviewTo view the NAT divert log For more information about natdPage VPN Service Authentication Method VPN and SecurityTransport Protocols Point to Point Tunneling Protocol PptpBefore You Set Up VPN Service Managing VPN ServiceStarting or Stopping VPN Service Enabling and Configuring L2TP Transport ProtocolTo enable Pptp Enabling and Configuring Pptp Transport ProtocolTo enable L2TP Configuring Additional Network Settings for VPN Clients Configuring VPN Network Routing DefinitionsTo configure addition network settings To set routing definitionsMonitoring VPN Service Setting the Log Detail Level for VPN ServiceSetting the VPN Log Archive Interval Viewing a VPN Status OverviewViewing the VPN Log Viewing VPN Client ConnectionsTo view the log To view client connectionsPage NTP Service How NTP WorksTo set up NTP service Using NTP on Your NetworkSetting Up NTP Service Configuring NTP on Clients To configure NTP on clientsPage IPv6 Support IPv6 Enabled Services IPv6 Addresses in the Server AdminIPv6 Addresses NotationIPv6 Address Types IPv6 Reserved AddressesIPv6 Addressing Model 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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