BOOTPD(8) BSD System Manager's Manual BOOTPD(8) NAME bootpd -- DHCP/BOOTP/NetBoot server SYNOPSIS bootpd [options] DESCRIPTION bootpd implements a DHCP/BOOTP server as defined in RFC951, RFC1542, RFC2131, and RFC2132. It is also a NetBoot server implementing Apple-proprietary NetBoot 1.0 (BOOTP-based) and NetBoot 2.0 BSDP (Boot Server Discovery Protocol). BSDP works along with regular DHCP, using DHCP-format packets with a special vendor-class identifier and vendor-specific options. bootpd understands and handles requests that arrive via a DHCP/BOOTP relay agent, allowing the server to be centrally located, and serve many remote subnets. The server is normally invoked by xinetd(8) when a request arrives, but can also be invoked manually. If it is invoked by xinetd(8), bootpd continues to service requests until it is idle for a period of 5 minutes, after which it exits to conserve system resources. If invoked manually, bootpd continues to run indefinitely. If bootpd receives a SIGHUP (-1) signal, it will re-read its configuration and client bind- ing files. When a request from a client arrives, the server logs an entry to /var/log/system.log indi- cating which client made the request, and logs another entry once a reply is sent. This feature can be turned off using the -q option described below. bootpd reads its configuration settings from the local NetInfo domain. There are also a number of command-line options to change its behavior on the fly. Note in particular that options BDmN can also be controlled via service-control properties. See /config/dhcp: Global Controls and Filters below. OPTIONS -a Enable NetInfo anonymous binding for BOOTP clients by supplying NetInfo host infor- mation options 112 and 113. -B Disable BOOTP service. By default, BOOTP service is enabled. -b Only respond if the client's bootfile exists: for BOOTP clients only. -c interval How often to check that the NetInfo host cache is still valid. Default interval is 30 seconds. If the NetInfo database has changed since we last checked, the cache for that database is discarded. -D Enable DHCP service. By default, DHCP service is disabled. -d Remain in the foreground and produce extra debugging output to stderr. -I Disable re-initialization on IP address changes. By default, changes to the server's configured IP addresses cause it to re-initialize. -i interface Enable service on the specified interface. This flag may appear multiple times to enable multiple interfaces. For example, bootpd -i en0 -i en1 forces bootpd to respond only to requests received on ethernet ports en0 and en1. By default, all interfaces are enabled. -m Enable NetBoot 1.0 (BOOTP-based) service. -N Enable NetBoot 2.0 (BSDP/DHCP-based) service. -n netinfo_domain Search for host entries in the given NetInfo domain. This flag may appear multiple times, the order of lookups is the order in which the flags appear. The value "..." means search the entire NetInfo hierarchy (the default). The netinfo_domain value can be specified as a domain path or as host/tag. For example, bootpd -n ... is the same as simply invoking bootpd without any options, and bootpd -n .. -n localhost/local forces bootpd to look in the parent domain then in the local domain. -o hop_count For relay agent operation, the maximum hop count, default is 4 hops. -q Be quiet as possible. Only report serious errors to -r server_ip Relay packets to the specified server_ip, not exceeding the hop count. -v Be more verbose in messages logged to /var/log/system.log. CONFIGURING BOOTPD bootpd reads its configuration from NetInfo (see netinfo(5)). The directories that it scans are: /config/dhcp Global controls and filters /config/dhcp/subnets Subnet entries /config/NetBootServer NetBoot server configuration /config/dhcp: Global Controls and Filters The directory /config/dhcp contains properties to control whether bootpd will respond to a particular request. There are MAC address filters (allow/deny) as well as controls to enable services per interface. The MAC address filter properties are: allow Enables the specified list of MAC addresses. deny Disables the specified list of MAC addresses. When a packet arrives, bootpd checks whether the client's MAC address is in the deny list. If it is, the packet is dropped. Otherwise, if the client's MAC address is in the allow list, the packet continues to be processed, otherwise it is dropped. If neither the allow nor the deny property is specified, the packet continues to be processed. The service-control properties are: bootp_enabled Enables BOOTP on the specified list of interfaces. dhcp_enabled Enables DHCP on the specified list of interfaces. netboot_enabled Enables NetBoot 2.0 (BSDP/DHCP-based) NetBoot on the specified list of interfaces. old_netboot_enabled Enables NetBoot 1.0 (BOOTP-based) NetBoot on the specified list of interface. For each of the above properties dhcp_enabled, bootp_enabled, old_netboot_enabled, and net- boot_enabled, the absence of a value implies that the service is enabled on all interfaces. To disable a service, specify a single value of "". For example (using nidump(8) syntax): "dhcp_enabled" = ( "en2", "en5" ); enables DHCP only on interfaces "en2" and "en5", whereas: "dhcp_enabled" = (); enables DHCP on every interface, and: "dhcp_enabled" = ( "" ); disables DHCP on all interfaces. /config/dhcp/subnets: Subnet Entries A subnet entry describes a range of IP addresses, and associated information, such as the subnet mask, router, DNS servers, and other option data. A subnet entry also indicates whether the range is an address pool from which to allocate vs. simply an informational range in order to fulfill requests for option information, i.e. for answering DHCP Inform requests, and BOOTP requests. A subnet entry is required to supply the DHCP service with pool(s) of IP address(es), and to inform the server of subnet-specific options and parameters. A subnet entry can also be used to convey network topology information via the supernet property described below. Subnet entries may not overlap in the IP ranges the describe, nor specify values that are inconsistent. Specifically, applying the net_mask value to each of the values in the net_range must yield the net_address value. Errors in configuration are logged to /var/log/system.log. There may be multiple entries for a given subnet, allowing different configuration values to be specified for a given range of IP addresses within the subnet. For example, part of the range might be used for statically bound clients, and another for a dynamic address pool. Each subnet entry appears as a sub-directory in /config/dhcp/subnets. A subnet entry must contain the following properties: name A descriptive name for the subnet, e.g. "17.202.40/22". net_mask The network mask, e.g. "255.255.252.0". net_address The network address, e.g. "17.202.40.0". net_range The network address range stored as two values: the first IP address and the last IP address. For example, ( "17.202.40.2", "17.202.43.254" ). client_types Indicates whether the range is a DHCP address pool, or just informational. Must contain "dhcp" for a DHCP address pool, and "bootp" for an informational range. The following properties are optional: lease_min The minimum allowable lease time (in seconds). This is only required/used if the client_types property is set to "dhcp". lease_max The maximum allowable lease time (in seconds). This is only required/used if the client_types property is set to "dhcp". supernet This property indicates that the subnet is on the same physical broadcast domain as other subnets with the same supernet value. The server can also supply clients with the following DHCP option information: dhcp_router The IP address of the default router (DHCP option code 3). If this property is not present, the server will attempt to provide its own default route for this option, if it is applicable. dhcp_domain_name_server The IP address(es) of the DNS server(s) (option code 6). If this property is not present, the server will supply its own DNS server configuration (if available). dhcp_domain_name The default DNS domain name (option code 15). if this property is not present, the server will supply its own default domain name (if available). dhcp_ldap_url The default LDAP URL (option code 95). dhcp_netinfo_server_address The NetInfo parent server IP address(es) (option code 112). dhcp_netinfo_server_tag The NetInfo parent domain tag (option code 113). dhcp_url The default URL to present in a web browser (option code 114). dhcp_time_offset The time offset from GMT in seconds (option code 2). dhcp_network_time_protocol_servers The network time protocol (NTP) server IP address(es) (option code 42). dhcp_nb_over_tcpip_name_server The NetBIOS over TCP/IP name server IP address(es) (option code 44). dhcp_nb_over_tcpip_dgram_dist_server The NetBIOS over TCP/IP datagram distribution server IP address(es) (option code 45). dhcp_nb_over_tcpip_node_type The NetBIOS over TCP/IP node type (option code 46). dhcp_nb_over_tcpip_scope The NetBIOS over TCP/IP scope string (option code 47). dhcp_smtp_server The Simple Mail Transport Protocol (SMTP) server IP address(es) (option code 69). dhcp_pop3_server The Post Office Protocol (POP3) server IP address(es) (option code 70). dhcp_nntp_server The Network News Transport Protocol (NNTP) server IP address(es) (option code 71). dhcp_proxy_auto_discovery_url The default Web Proxy Auto Discovery URL (option code 252). /config/NetBootServer: NetBoot server configuration This directory contains a number of properties that alter the NetBoot server's default behavior. The properties are: afp_uid_start The starting uid used when creating AFP machine users. The default is uid 100. afp_users_max The number of AFP machine users to automaticaly create. The default is 50. Note: the server will never remove a user once it is created, so decreasing this value once the server has read it will have no effect. age_time_seconds The number of seconds since the client last netbooted before before the client is considered "aged". A client that has aged becomes available for resource reclamation. The server will only reclaim aged client bindings when it runs out of free resources. machine_name_format This property is used to generate a unique name to each NetBoot client. The default value is "NetBoot%03d" (without the double quotes). The format string must be a printf(3) compatible format string that takes a single integer value as an argument. The server ensures that the string is valid by testing the string before using it. The only con- version specifiers that should be used are diouxX. shadow_size_meg The size (in megabytes) to allocate for the client shadow file. The default is 48 (megabytes). See Diskless Resources below. BOOTP/DHCP STATIC BINDINGS Static IP address to ethernet address bindings are stored in NetInfo. The bindings appear in host entries. Each host entry is a subdirectory of the /machines directory of a NetInfo domain. The server consults the default NetInfo domain hierarchy unless overridden by -n flags (see OPTIONS above). The server recognizes the following properties in the host entry: name The name of the host (required). en_address Ethernet address(es) of the host stored in colon hex ie. "%x:%x:%x:%x:%x:%x" format (required). ip_address The IP address(es) of the host (required). bootfile Executable image file to be downloaded by the client via TFTP (not required). A client is identified by its unique hardware (MAC) address, and is stored in the en_address property. The server searches for a host entry containing both its hardware address and a relevant IP address. A relevant IP address is one which is useful for the subnet on which the client is attempting to boot. If the request is a BOOTP request, and no static binding exists, the server does not respond. If the request is DHCP, and no static binding exists, the server tries to find an approprate address pool. If none exists, it does not respond. The server supports having more than one IP address associated with a single client: a sin- gle BOOTP/DHCP client can connect to multiple subnets at different times (e.g. a laptop that is frequently moved from one location to another). Multiple host entries may include the same hardware address but should have distinct IP addresses to avoid associating the same IP with more than one host. If there is more than one relevant IP address for a client, the server chooses the first one that it finds. The server also supports multi-homed hosts (host with the same name but multiple IP addresses) by treating the en_address and ip_address properties as parallel arrays. For example, consider a host entry with the following values: "name" = ( "orange" ); "en_address" = ( "0:5:2:f:a:b", "0:5:2:1c:9e:d6" ); "ip_address" = ( "17.202.42.110", "17.202.21.221" ); Host "orange" has two IP addresses associated with its name. The interface with ethernet address "0:5:2:f:a:b" has IP address "17.202.42.110", and interface "0:5:2:1c:9e:d6" has IP address "17.202.21.221". BOOTP SERVICE The server supplies a BOOTP client with its statically-assigned IP address, hostname, subnet mask, default router, domain name server(s), and domain name, and if the -a option was spec- ified, the NetInfo server address and NetInfo server tag options. It will not exceed the default BOOTP packet size however, so it's possible that not all of the options will fit. The client must set the magic number field (first 4 bytes of the vendor extensions field) to 99.130.83.99 (dotted decimal) to have the server supply those options. DHCP SERVICE If DHCP service is enabled for a client, the server processes the client's packet. The packet may be a request for an IP address and option information (DHCP Discover, DHCP Request) or for just option information (DHCP Inform). The packet might also tell the server that the address is in use by some other host (DHCP Decline), or that the client is done with the IP address (DHCP Release). The server uses the DHCP client identifier (option 61) if it is present as the unique client identifier, otherwise it uses the htype/hlen/chaddr fields in the DHCP packet. IP Allocation The DHCP server first tries to find a static binding for the client (see section BOOTP/DHCP STATIC BINDINGS above). If one exists, it uses it. If not, it tries to find an existing dynamic binding from its lease database, stored in /var/db/dhcpd_leases. If one exists and it is applicable to the subnet, the server uses it, otherwise, it tries to allocate an address from one of its address pools. If an address is available, the server uses it, oth- erwise the packet is discarded. After a suitable IP address is found for the client, the server attempts to insert as many of the requested DHCP options from the client's request as it can into the reply. When the server allocates an address dynamically, it automatically excludes addresses that appear in static host entries under NetInfo. For example, if the address range goes from 10.0.0.2 through 10.0.0.10, but there is a NetInfo host entry in /machines like this: "name" = ( "test" ); "ip_address" = ( "10.0.0.3" ); the IP address 10.0.0.3 is automatically excluded from the pool. The server tries to give the same address back to a client by remembering the binding even after it has expired. The server removes an expired lease entry only when it runs out of addresses, and needs to reclaim an address in order to fulfill a new request. When the server receives a DHCP Release packet, it sets the expiration for that lease to now, so that it can immediately reclaim the address if needed. When the server receives a DHCP Decline packet, it removes the client binding from the IP address, and sets the expiration on the "unbound" lease to 10 minutes from now. That allows the address to return to the address pool again without manual intervention and avoids hand- ing out the same in-use IP address over and over. NETBOOT SERVICE The NetBoot server enables a client to perform a network boot, that is, access its operating system image over the network instead of from its local drive. The sequence of events that occur when a NetBoot client is powered are: 1. firmware gets IP address and image information (using BOOTP, or BSDP/DHCP) 2. firmware saves relevant packet(s) in memory to be used by client operating system (see step 4 below) 3. firmware TFTP's the bootfile image, and begins executing it 3.1. (Mac OS X only) secondary loader TFTP's kernel and drivers, and begins executing the kernel 4. client operating system initializes its network stack and accesses its "root" disk using information in packets saved at step 2, uses AFP, NFS, or HTTP to access the image Apple NetBoot uses a technique called "shadowing", whereby an otherwise read-only disk image appears to the client as a read/write image by "mapping" writes to the original image file to an auxilliary "shadow" file. Subsequent reads from portions that have been written also come from the "shadow" file. The disk image driver in the client operating system manages the shadow mapping and provides the illusion of a writable disk. The term diskless NetBoot implies that the client receives all of its necessary booting resources from the network, so that a local disk drive is not required, though may still be present. The NetBoot server supplies a NetBoot client with the resources and information it needs to boot. Two versions of NetBoot are supported: NetBoot 1.0 (BOOTP-based) and NetBoot 2.0 (BSDP/DHCP-based). Service for these two types of NetBoot are controlled individually using command-line options m and N, or using the service configuration properties old_net- boot_enabled and netboot_enabled (described above). The NetBoot 1.0 server supplies the client with its IP address in addition to its boot resources. The server must be able to find a static binding for the client (see BOOTP/DHCP STATIC BINDINGS above), or the server must have an applicable dynamic pool of IP addresses, just as with DHCP. If the server does not also have DHCP service enabled, the pools are only used for NetBoot 1.0 clients. In this case, the server also acts as a DHCP server but only services those clients for which it has an existing binding. There can only be one NetBoot 1.0 server per subnet because the protocol uses BOOTP, and BOOTP does not support multiple servers. However, the NetBoot 1.0 server will co-exist with an existing DHCP server, assuming it only serves DHCP. The NetBoot 2.0 server only supplies the client with boot resources. Unlike NetBoot 1.0, there is no limit on the number of NetBoot servers per subnet. The NetBoot server stores a list of NetBoot client records in the file /var/db/bsdpd_clients. Each client record contains the client name and number assigned by the server, the boot image ID selected by the client, and the client's last boot time. NetBoot Image Location When the NetBoot server initializes, it looks for NetBoot images at well-known locations in the file system. A "NetBoot image" is a directory that ends in the .nbi extension, and con- tains a valid set of files (described below). If no images are found, NetBoot is temporar- ily disabled. If it receives a SIGHUP signal, the server again attempts to initialize itself. The NetBoot server looks for a symbolic link named: Library/NetBoot/.sharepoint at the root of each HFS+ volume. If the symlink is valid, and points to a directory, it assumes that the directory contains NetBoot images and that the contents are accessible via TFTP, AFP, NFS, and HTTP. By convention, the directory is named: Library/NetBoot/NetBootSPx where x is a unique number starting at zero (0). NetBoot Image (.nbi) A NetBoot image is stored in a directory whose name ends with .nbi, and contains a set of files. The directory must contain an NBImageInfo.plist file, one or more bootfiles, and may contain one or more image files. The NBImageInfo.plist file is encoded as an XML property list, and contains information about the image. The properties defined in the NBImageInfo.plist file and their meanings are: Name (String) The name of the image that appears in the Startup Disk UI. BootFile (String) The path relative to .nbi directory of the first bootfile. IsEnabled (Boolean) A flag to mark the image as enabled or not. An image that is disabled will not be offered as a selection by the NetBoot server. Optional, default value is true. IsDefault (Boolean) A flag to mark the image as a default image. Setting this key to true for more than one image can be useful if the EnabledSystemIdentifiers property is also defined (see below). Optional, default value is false. IsInstall (Boolean) A flag to indicate that the image describes an installation image. Optional, default value is false. Type (String) The type of the image. The value "Classic" implies that the Kind is Mac OS 9 NetBoot, "NFS" implies the Kind is Mac OS X NetBoot. Kind (Integer) The image kind: 0 = Mac OS 9 1 = Mac OS X 2 = Mac OS X Server Optional, the default value depends on the Type. Index (Integer) The index of the image. This is a 16-bit value used to differ- entiate between multiple NetBoot images supplied by a server. There are two value ranges: 1 .. 4095 Image is local to this server. 4096 .. 65535 Image is global and may appear on multiple servers, used for load-balancing. The Index forms the lower 16-bits of the unique 32-bit Image ID. IsIn- stall and Kind make up the remaining bits (with 8 bits reserved). RootPath (String) If Type is "NFS", this is the path of the "root" disk image rela- tive to the .nbi directory. The NetBoot server assumes that the path up to and including the NetBootSPx directory is exported via NFS. Indirect NFS paths are also supported using the syntax: <path> = <host>:<mount_path>[:<image_path>] <host> = <IP address> | <host_name> For example, in the path: myserver:/NetBoot:Images/Jaguar.dmg the image is on a server named "myserver" with NFS export "/NetBoot" and the image file appears relative to the mount point as "Images/Jaguar.dmg". If Type is "HTTP", this is the path of the "root" disk image relative to the .nbi directory. The NetBoot server assumes that the .nbi directory under NetBootSPx is exported via HTTP using the convention: http://<server_ip>/NetBoot/NetBootSPx/<image_dir>.nbi Indirect HTTP paths are also supported using the HTTP URL syntax: <path> = http://[<user>@]<host>[:<port>]/<image_path> <user> = <user_name>:<password> <host> = <IP address> | <host_name> Examples: http://myserver:8080/Images/Jaguar.dmg http://joe:secret@someserver/Jaguar/Jaguar.dmg SharedImage (String) If Type is "Classic", this is the path of the system, or read/write, disk image used for Mac OS 9. PrivateImage (String) If Type is "Classic", this is the path of the private, or read- only, disk image used for Mac OS 9. Optional. SupportsDiskless (Boolean) A flag that indicates that the image supports diskless clients, and tells the server to allocate resources. If the Type is "Classic", the value of this property is ignored since the server always allocates resources required for diskless clients. See Diskless Resources below. EnabledSystemIdentifiers (Array of String) The list of system identifiers that are enabled for this image. The system identifier for Apple hardware is the model property from the Open Firmware device-tree. Some example model properties are "PowerMac3,3" and "PowerBook3,1". If this property is not specified, or the list is empty, the image is enabled for all clients (the default). If the server has no images that apply to the client, it will not respond. Due to limitations in the NetBoot 1.0 protocol, there is no way for the NetBoot server to differentiate between older clients such as the original bondi-blue iMac or B&W G3 (Yosemite). To enable an image for all NetBoot 1.0 clients, include the pseudo system identifier "/NetBoot1". NBImageInfo.plist: Mac OS 9 Example The path to the image directory in this example is: /Library/NetBoot/NetBootSP0/Mac OS 9.nbi This directory contains the following files: NBImageInfo.plist Mac OS ROM NetBoot HD.img Applications HD.img The NBImageInfo.plist contains: <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE plist SYSTEM "file://localhost/System/Library/DTDs/PropertyList.dtd"> <plist version="0.9"> <dict> <key>BootFile</key> <string>Mac OS ROM</string> <key>IsEnabled</key> <true/> <key>Index</key> <integer>4</integer> <key>IsInstall</key> <false/> <key>Name</key> <string>Mac OS 9.2</string> <key>SharedImage</key> <string>NetBoot HD.img</string> <key>PrivateImage</key> <string>Applications HD.img</string> <key>Type</key> <string>Classic</string> </dict> </plist> The Type is Classic, which means this is a Mac OS 9 NetBoot image, so the implied Kind value is 0 (Mac OS 9). The BootFile property points to "Mac OS ROM". The system image is "Net- Boot HD.img". The read-only applications image is "Applications HD.img". The Name of the image is "Mac OS 9.2". IsEnabled is supplied and set to true, so the image is active. The Index is 4, which means the image is local to this server, and will always appear as a unique choice in the client image selection UI. NBImageInfo.plist Example: Mac OS X The path to this example is: /Library/NetBoot/NetBootSP0/Jaguar.nbi This directory contains: NBImageInfo.plist booter mach.macosx mach.macosx.mkext Jaguar.dmg The NBImageInfo.plist contains: <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE plist SYSTEM "file://localhost/System/Library/DTDs/PropertyList.dtd"> <plist version="0.9"> <dict> <key>BootFile</key> <string>booter</string> <key>IsEnabled</key> <true/> <key>Index</key> <integer>4096</integer> <key>IsInstall</key> <false/> <key>Name</key> <string>Mac OS X (Jaguar)</string> <key>RootPath</key> <string>Jaguar.dmg</string> <key>Type</key> <string>NFS</string> </dict> </plist> The Type is NFS, and no Kind is specified, so the server assumes this is a Mac OS X image with Kind 1. The BootFile property points to "booter". Mac OS X uses three separate boot- files, so the remaining files which must exist, but are not currently verified to exist by the server, are "mach.macosx" and "mach.macosx.mkext". Those names are non-negotiable, since the booter hard-codes those names. The RootPath property indicates that the image file is "Jaguar.dmg". The Index is 4096, so this is a global image, that may appear on mul- tiple NetBoot servers. If another server serves an image of the same Kind, IsInstall, and Index, this image may appear as a single choice in client image selection UI. Diskless Resources The NetBoot server creates and manages per-client AFP user logins as well as per-client directories to give each client its own protected resources. The AFP users are created in the local NetInfo domain, and are marked with the property and value: "_creator" = ( "bsdpd" ); When the server initializes, it ensures there are at least afp_users_max users with this property. If there are not, it allocates new user entries to make up the difference. Along with the per-client AFP login, the server creates per-client directories to store the "shadow" files. The server creates these directories on each HFS+ volume that contains a symbolic link named: Library/NetBoot/.clients at the root of the volume. If the symlink is valid, and points to a directory, it assumes that the directory should be used for client files. It also assumes that the directory is a valid AFP sharepoint of the same name. By convention, the directory is named: Library/NetBoot/NetBootClientsY where Y is a unique number starting at zero (0). The server "round-robins" client images across each such directory to distribute load amongst multiple disk drives to improve overall performance. When the server responds to the client's NetBoot request, it ensures that the "shadow" file is preallocated to shadow_size_meg megabytes. Setting that property high enough avoids hav- ing every client fail if the server runs out of disk space. The only clients that fail if the server runs out of disk space are those that run of of space in their own pre-allocated "shadow" files. SEE ALSO xinetd(8), tftpd(8), netinfo(5), exports(5) Mac OS X April 16, 2003 Mac OS X