Lecture notes on System and Networking administration

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1 Chapter 1Introduction to Network Services Administration 1 1 1 An Overview of Network Services Administration 1 NOTE If your system is being run in compliance with the security criteria described in the chapter “Trusted Facility Management” in the System Administration guide, network connections to the system are not allowed; although networking facilities have been enhanced to work with the Enhanced Security Utilities, networking facilities are not part of the Trusted Computing Base. This section provides a brief overview to networking. This section is not intended to be a networking primer. Instead, it places the features of the OS in the context of a general network administration model and presents an overview of the tasks involved in the administration of user-level services. A Model of Network Administration 1 The network facilities are built on the client/server model. A client is a networked machine that uses the resources of another machine on the network. A server is a system that provides resources to other systems on the network. A system can be both a client, utilizing another system's resources, and a server, making local resources available to other systems. Typically, the steps involved in setting up a networked machine are the following: 1. Making the physical connection to the network and installing any software that drives the network hardware. 2. Installing the network software, which packages data according to a set of protocols. The network software includes a transport provider, which manages the transfer of data across the network connection. 3. On the server side, setting up continuous processes, called daemons, that listen for connection requests from other network machines. 4. On the client side, creating an address database that contains the addresses of all machines and services on the network to which the client can connect. The client consults the database before it sends a connection request to another network machine. 1-1Network Administration 5. Setting up security. Typically, each network application has its own mechanism for performing a minimum of authentication. The following section describes the network facilities and explains how they fit into the general model of network administration. Networking Facilities 1 The OS includes a number of network facilities that give the administrator flexibility in building a network. Several facilities relieve the application of the need to know the under- lying characteristics of the network. Thus, the application can run on different networks, and still present a consistent interface to the user. Two distinct styles of network service provision are supported. One is the Berkeley style, implemented as “r-commands” (such as rlogin), which is described in User's Guide. The other style is the new Networking Applications Architecture (NAA), which is depicted in Figure 1-1 and described in the following list. CLIENT CONNECTION SERVER IAF SCHEME Authorize level Identify Select a network Authenticate Map name to address Establish a connection Invoke IAF scheme Establish a connection Identify Invoke IAF scheme Authenticate Set ID Map ID Set level Map level SERVICE SAF PORT MONITOR IAF SCHEME 161050 Figure 1-1. A Diagram of the Networking Applications Architecture • The listen Port Monitor A port monitor is a continuous process, called a daemon, that listens to a given physical port or on a network address for connection requests. listen, also called the listener, is a network port monitor. It listens on addresses associated with a connection-oriented transport network. There may be multiple listen port monitors on the system, each monitoring multiple addresses. The listener listens on the server for incoming connection requests, accepts the requests, and starts services that have been requested. If a service is protected by an authentication scheme, the listener invokes the 1-2Introduction to Network Services Administration authentication scheme. If the authentication protocol completes success- fully, the client user's identity is mapped to an identity on the server; then, the port monitor starts the requested service. All port monitors, including listen, are managed by the Service Access Facility (SAF). The SAF generalizes service access procedures so login access on the local system and network access to local services are managed in similar ways. This means, from the system administrator's perspective, that local and network access are managed similarly, as is access over different networks. (For more information, see the chapter “Managing Ports” in the System Administration guide.) • The Connection Server The Connection Server can be viewed as a counterpart on the client to the server's listener. When a client user attempts to access a service from another machine on the network, the Connection Server verifies the connection is allowable at the client's level. The Connection Server uses Network Selection to determine which network to use, and Name-to- Address Mapping to determine the address of the requested service on the requested host. The Connection Server sends a connection request to the server, manages the client's role in establishing the connection, and invokes the appropriate authentication scheme. If the scheme completes successfully, the Connection Server turns over the connection to the client process. • Identification and Authentication Facility The Identification and Authentication Facility (IAF) authenticates network connections independently of the network application. It consists of three components—an invocation function, the cr1 and login authentication schemes, and the ID Mapping facility. The cr1 schemes (see the chapter entitled “cr1 Bilateral Authentication Scheme), and ID Mapping (see the chapter entitled “Administering ID Mapping), are discussed as separate features. Following the establishment of a connection, the Connection Server and the port monitor each invoke an authentication scheme. Once the client scheme has succeeded, the Connection Server passes the connection to the client application. Once the server scheme has succeeded, it searches the ID Mapping database to determine how the user on the client should be mapped to a user on the server. Minimally, the database consists of a map file that maps user logins on client systems to user logins on the server. Once the scheme maps the client user's identity into a local identity, the port monitor invokes the requested service. Authentication schemes are invoked by the IAF. This release of the OS contains the cr1 authentication scheme. By default, cr1 uses DES encryption, and can also be referenced as cr1.des. Because of export restrictions on DES, cr1 can also use ENIGMA encryption. When using ENIGMA encryption, cr1 is referenced as cr1.enigma. Other than the underlying encryption algorithm used, all cr1 schemes behave identically. The cr1 schemes operate as follows: The client and server schemes exchange a sequence of encrypted messages. Each system uses a secret key, which it retrieves from its local cr1 key database, to encrypt its own messages and decrypt the other's messages. (A secret key is a bit string 1-3Network Administration known only to the client and server.) By successfully decrypting the other's messages, each machine authenticates the other's identity.The client scheme informs the server scheme of its user's security level and identity. • Network Selection Network Selection is a facility that generalizes the way an application chooses a network. It allows an administrator or a user to specify an order of preference among available transport providers. When a user attempts to access a remote service, the system first attempts to make the connection over the primary network; if that attempt fails, it tries each network in order of preference until the connection is made. • Name-to-Address Mapping Name-to-Address Mapping is a feature that allows applications to obtain transport-specific addresses in a transport-independent manner. The administrator maintains a configuration file with records describing each transport provider available to be used by applications. One of the fields in each record is the name of the shared library to use for the transport provider being described in the record. This library contains name-to- address mapping routines specific to the transport protocol. When a new transport protocol is being installed, a new entry in the configuration file is made, allowing network applications to make use of the new protocol with- out being changed. • User-Level Services The facilities that provide services to end-users include the Basic Networking Utilities (BNU) and REXEC. BNU provides basic network communication (such as queued remote execution and file transfer capabilities) and REXEC is an interactive remote execution facility. Whereas many network packages provide remote execution capabilities, BNU and REXEC provide file transfer and remote execution independent of the transport provider. Both BNU and REXEC take advantage of the features of the Network Application Architecture (NAA) described in the previous sections. In addition to BNU and REXEC, the OS includes a distributed file system package, the Network File System (NFS). NFS provides access to files and directories across a network of machines running different operating systems. In addition, TCP/IP includes a number of application level ser- vices in its protocol suite. BNU and REXEC are described in this chapter. Distributed File Systems are described in “Introduction to DFS Administration,” “Setting Up DFS,” “Using DFS Commands and Files,” and “DFS sysadm Interface.” The user services that are provided by TCP/IP are discussed in User's Guide. The following section leads you step-by-step through administration of BNU and REXEC. 1-4Introduction to Network Services Administration Procedural Overview of BNU and REXEC Administration 1 Ultimately, the network administrator's objective is to provide services to users of net- worked machines. This section presents a high-level procedure for setting up REXEC and BNU, as well as all the network services on which they depend. The administration of each component mentioned in the following procedure is described in more detail later in the chapter. This procedure makes the following assumptions: 1. Your network hardware and software have been installed and any administration specific to the network package has been completed. 2. Applications are to be set up to take advantage of the IAF in the OS. For compatibility, BNU can be configured as it was on previous versions of the OS. However, this section assumes BNU connections will be configured using enhanced authentication procedures (primarily cr1). Set Up the Network Administrator's Login 1 If you are running the Least Privilege Module (LPM), which is provided as part of the Enhanced Security Utilities, the concept of the superuser is replaced by administrative roles. Each administrative role is associated with commands and privileges required to administer a certain aspect of the system. To administer network services, you must assume the role of the network administrator, NET. NET is predefined on the system; how- ever, before you can log in as a network administrator, you must create a login and assign it the NET role. This is done using the adminuser command. For information about assigning roles, see the chapter “Securing User Accounts” in the System Administration guide or adminuser(1M). You must complete this task before beginning the following sequence of steps. Step 1: Set Up Network Selection 1 Network Selection consists of the following elements: • netconfig, a network configuration file see netconfig(4) • NETPATH, an environment variable To set up Network Selection, you need to create an entry in the netconfig file for each network available to the local system. Any user, including the administrator, may use the NETPATH variable to modify the default order in which networks are tried by an application seeking a network connection. If a user does not set the NETPATH variable, networks are used in the order specified in netconfig. For more information see Chapter 2, "Administering Network Selection". 1-5Network Administration Step 2: Set Up Name-to-Address Mapping 1 Name-to-Address Mapping consists of routines that application programs can call to determine the addresses of services and machines on the network. These routines are combined into libraries, with one library associated with each available transport provider. For every network available to the local system, the network administrator must create and maintain the following files used by the library routines: • the hosts file, which lists the addresses of machines on the network • the services file, which lists the port numbers of services available across the network The files that support TCP/IP must be located in /etc. The files that support other net- works must be located in /etc/net/transport, where transport is the name of the transport provider. For more information, see Chapter 3, “Administering Name-to-Address Mapping.” Step 3: Set Up the listen Port Monitor 1 The listener is a port monitor under the control of the Service Access Controller (SAC), a daemon process that provides a consistent interface to all services, whether the user's connection to the system is local or across a network. (Because the purpose of the SAC is not limited to managing network access, it is not documented in this chapter. For more information about the SAC and setting up the listener, see the chapter “Managing Ports” in the System Administration guide.) To set up the listener, do the following: 1. Add a listen port monitor to the Service Access Controller's administra- tive file, using sacadm see sacadm(1M). 2. Set up the port monitor's administrative file, using pmadm see pmadm(1M). Setting up the file involves • adding one or more services to the listener's administrative file • enabling the service on a port that the listener is monitoring • associating an authentication scheme with a service Step 4: Set Up the Connection Server 1 The Connection Server is a daemon process running on the client that makes network connections. Applications obtain network connections by calling library routines that access the daemon. An error reporting routine (cs_perror), an associated service (reportscheme), and three optional administrative files are available. To set up the Connection Server, do the following: 1. Optionally, on the client, set up the file /etc/iaf/serve.allow. The /etc/iaf/serve.allow file enforces authentication, in the event the service is not protected by an authentication scheme on the server side. 1-6Introduction to Network Services Administration 2. Optionally, on the client, set up the file /etc/iaf/serve.alias. The /etc/iaf/serve.alias file maps aliases to service names, making it possible to register a service under two names with different authentication schemes associated with each name. 3. Optionally, on the client, set up the authentication file, auth. This file lists network services and their associated authentication schemes. 4. If your system is running Mandatory Access Control (MAC), use attradmin to set up LID authorization. The Connection Server uses attribute mapping to determine if a process at a given security level is authorized to make a connection request to the specified server. (Information on attribute mapping is provided below under Step 6: Setting Up ID Mapping. 5. Add an entry for reportscheme to the port monitor's administrative file on each server to which the Connection Server should be able to connect. For more information about Connection Server administration, see Chapter 4, “Adminis- tering the Connection Server.” Step 5: Set Up the cr1 Authentication Scheme 1 To set up cr1, do the following: 1. Start the keymaster daemon process see keymaster(1M). 2. Administer individual keys using cryptkey see cryptkey(1). If you intend to set up REXEC or BNU, you need to add keys shared by a client machine and the server machines. Each client and server pair must share identical keys. For more information, including detailed procedures, see Chapter 5, “cr1 Bilateral Authentication Scheme.” Step 6: Setting Up ID Mapping 1 cr1 maps remote user identities to the local system using map files that are administered under the ID Mapping facility. On a server, to set up ID Mapping to support cr1, do the following: 1. Use the idadmin command see idadmin(1M) to install cr1 name mapping. 2. If you are running MAC, set up attribute mapping for the RLID attribute, using the attradmin command. cr1 uses the RLID attribute to map level aliases from client systems to level aliases on the server. On the client, to set up attribute mapping, do the following: 1-7Network Administration 1. Set up attribute mapping for the LIDAUTH attribute. The Connection Server uses the LIDAUTH attribute to determine whether or not a process is authorized to make a connection request. Specific instructions for setting up the LIDAUTH attribute appear in Chapter 4, “Adminis- tering the Connection Server.” Instructions for setting up ID mapping and attribute mapping appear in Chapter 6, “Administering ID Mapping.” Instructions for setting up ID mapping appear in Chapter 6, “Administering ID Mapping.” Step 7: Set Up BNU 1 The Basic Networking Utilities package is a collection of programs and support files that provide network communication services such as file transfer capabilities and remote execution. All BNU support files are located in /etc/uucp. To set up BNU, do the following: 1. Create BNU logins. 2. On the server side, for every transport provider on which BNU will be supported, use pmadm to add the uucico service and associate the cr1 authentication scheme with the service. 3. Create or modify the BNU database files as needed. See the Database Sup- port Files section of Chapter 7, “Administering the Basic Networking Util- ities. 4. If your system supports MAC, verify that LIDAUTH attribute mapping has been set up for the Connection Server, and RLID attribute mapping has been set up for cr1. Step 8: Set up REXEC 1 To set up REXEC, do the following: 1. Register REXEC with a network port monitor (the listener) under the Service Access Facility, specifying an associated authentication scheme that uses ID Mapping, that is, cr1. 2. Set up the file /etc/rexec/services on the server. The services file is a database containing all the services on the server system that are available to remote users through REXEC. Typically, the list of available services consists of the pre-defined REXEC services rl, rx, and rquery. For more information, see Chapter 8, "Administering REXEC". 1-8Introduction to Network Services Administration Using the sysadm Menu Interface 1 Any of the functions associated with Network Services may be performed by selecting the appropriate “task” from a series of menus provided for administration. To access the system administration menu for using Network Services, type: sysadm network_services The following menu will appear on your screen: Network Services Management attr_map - Attribute Mapping Administration basic_networking - Basic Networking Utilities Management cr1 - IAF Scheme cr1 Key Management name_map - Name Mapping Administration name_to_address - Machine and Service Address Management remote_files - Distributed File System Management selection - Network Selection Management Screen 1-1. Network Services Management Menu NOTE The Distributed File System Management option is described in the Compilation System Manual. When you have chosen an option, self-explanatory submenus and instructions will be displayed on the screen to lead you through the appropriate procedures. 1-9Network Administration 1-102 Administering Network Selection Introduction to Network Selection Administration . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1 Network Selection Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2 The /etc/netconfig File. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3 The NETPATH Environment Variable. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6Network Administration2 Chapter 2Administering Network Selection 2 2 2 Introduction to Network Selection Administration 2 In order for network applications to be portable to different environments, the application process must have a standard interface into the various transport providers available in any current environment. Network Selection provides a simple and consistent interface that allows user applications to select networks (at the transport level), enabling applications to be protocol- and media-independent. Networking Services applications that allow a user to influence the choice of transports use the standard interface outlined here. Tasks associated with Network Selection administration may be performed either by using the menu system or by entering shell commands on the command line. Screen 2-1 is the top-level menu for Network Selection. It can be brought up on the screen by typing the fol- lowing: sysadm selection Network Selection Management display - Display Network Selection Configuration modify - Modify Network Selection Configuration Screen 2-1. Network Selection Management Menu When you select an option, self-explanatory submenus and instructions lead you through the appropriate procedures. You can also bypass the menu system by issuing commands directly to the shell. Where these commands involve editing sensitive system files, be sure to keep a backup copy of the file you are editing. When you have finished editing the file, use diff see diff(1) on the edited file and the backup copy to verify that only the changes you want have been made. 2-1Network Administration Table 2-1. Command Alternatives to the Network Selection Management Menu Task Description Menu Item Shell Command Display the contents of the netconfig display cat /etc/netconfig file; display the entry for network netid grep netid /etc/netconfig Change a netconfig entry modify vi /etc/netconfig If you want to add networks to the network configuration database, you need to edit /etc/netconfig, and add the appropriate entries. To remove networks from the net- work configuration database, you need to edit /etc/netconfig, and delete the appropriate entries. Network Selection Overview 2 The Network Selection component is built around: • a network configuration database (the /etc/netconfig file) that contains entries for each network available to the system, and • an optional NETPATH environment variable, set by a user or the system administrator and containing an ordered list of network identifiers. These network identifiers match the netconfig network ID field and are used as links to the records in the netconfig file. The Network Selection application programming interface consists of a set of network configuration database access routines. One group of these library routines accesses only the netconfig entries identified by the NETPATH environment variable; another group of routines accesses netconfig directly. The first group is also described in detail in getnetpath(3N). The second group is described in getnetconfig(3N). Applications should use the routines that access NETPATH. These routines allow users to influence the selection of transports used by the application. If an application does not want the user to influence its decision, then the routines that access the netconfig data- base directly should be used. The netconfig file, on which the Network Selection library routines depend, is maintained by the system administrator. The NETPATH environment variable is typically set or modified by application programmers and users, depending on the needs of their applications, but it may also be set by the system administrator in response to the needs of administrative applications. 2-2Administering Network Selection The /etc/netconfig File 2 The system administrator is responsible for maintaining the network configuration data- base file /etc/netconfig. Entries in the netconfig file contain the following fields in the order shown. A sample netconfig file is shown in Table 2-2. Table 2-2. Fields in netconfig Entries network_id semantics flags protofamily protoname device nametoaddr_libs The fields correspond to elements of the netconfig structure. Pointers returned by Net- work Selection library routines are pointers to netconfig entries in netconfig format. See netconfig(4) for more information. The netconfig(4) manual page also describes the elements of the struct netconfig structure. All symbolic names, structure definitions, and constant values for the Network Selection feature are defined in the header files /usr/include/netconfig.h, /usr/include/sys/ netconfig.h, and /usr/include/netdir.h. netconfig fields are defined as follows: network_id A string used to identify a transport provider. network_id consists of non-NULL characters, and has a length of at least 1. No maximum length is specified. This name space is locally significant and the local system administrator is the naming authority responsible for ensuring that all network_ids on a system are unique. semantics A string that identifies the “semantics” of the transport provider, that is, the set of services it supports, by identifying the service interface it provides. This is closely related to, but not identical with, the API (Application Programming Interface) with which applications are “supposed” to access the network. Typically, an application will specify its API by pushing an appropriate STREAMS module (such as timod) and using an appropriate user-level library (such as the TLI library). The semantics field is mandatory. The following semantics are recognized. tpi_clts Transport Provider Interface, connection- less tpi_cots Transport Provider Interface, connection- oriented tpi_cots_ord Transport Provider Interface, connection- oriented and supports orderly release tpi_raw Transport Provider Interface, raw flags The flags field contains two-valued (“true” and “false”) attributes of transport providers. flags is a string of characters, each of which specifies the value of the corresponding attribute. If the character is present, the attribute is “true.” If the character is absent, the 2-3Network Administration attribute is “false.” A hyphen (-) indicates no attributes are present. The characters currently recognized are: v Visible network. Used to establish a default list of net- works to search when the environment variable NET- PATH is unset. See the section entitled “The NET- PATH Environment Variable” on page 2-6 for a description of how the v flag is used. b Enable RPC broadcast. Used by rpc_broadcast() see rpc_clnt_calls(3N). protofamily The protofamily and protoname fields are provided for protocol- specific applications. The protofamily field contains a string that identifies a protocol family. The protofamily identifier follows the rules for network_ids: It is a string of non-NULL characters with a length of at least 1. No maximum length is specified. A hyphen (-) in the protofamily field indicates that none of the available protocol family identifiers applies, that is, the transport provider is experimental. An application that wants to have family characteristics can match on the protofamily field when selecting a network. (For example, an application can search for an “osi” family.) In this case, the application is not protocol independent, since it has searched only for OSI entries. The following are examples of protocol family identifiers: loopback Loopback (local to host) inet Internetwork: UDP, TCP, and so on. implink ARPANET imp addresses pup PUP protocols: for example, BSP chaos MIT CHAOS protocols ns XEROX NS protocols nbs National Bureau of Standards (NBS) protocols ecma European Computer Manufacturers Association datakit Datakit protocols ccitt CCITT protocols, X.25, and so on. sna IBM SNA decnet DECNET dli Direct data link interface lat LAT hylink NSC Hyperchannel 2-4Administering Network Selection appletalk Apple Talk nit Network Interface Tap ieee802 IEEE 802.2; also ISO 8802 osi Umbrella for all families used by OSI x25 CCITT X.25 in particular osinet AFI = 47, IDI = 4 gosip U.S. Government OSI protoname The protoname field contains a string that identifies a protocol. This field is currently used only for the inet family. For any other family, the protocol name field contains a hyphen (-). The protoname identifier follows the same rules as network_ids: The string consists of non-NULL characters and has a length of at least 1. No maximum length is specified. The protoname field may contain: icmp Internet Control Message Protocol tcp Transmission Control Protocol udp User Datagram Protocol device The device is the full pathname of the device used to connect to the remote machine via the transport provider. Typically, this device will be in the /dev directory. The device must be specified. nametoaddr_libs The nametoaddr_libs support a “directory service” (that is, a Name-to-Address Mapping service) for the network. This service is implemented by the Name-to-Address Mapping feature. If a transport is not provided with such a library, that is, if the nametoaddr_libs field in the netconfig file contains only a hyphen, the Network Selection request will fail. The nametoaddr_libs field consists of a comma-separated list of full pathnames to dynamically linked libraries. Literal commas may be embedded as “\,”; backslashes as “\\.” Lines in /etc/ netconfig that begin with a pound sign () in the first column are comments. The system administrator determines the order of the entries in the netconfig data- base. Because the Network Selection library routines that access netconfig directly return entries in order, beginning at the top of the /etc/netconfig file, the order in which networks are entered in the file by the system administrator becomes the default search path for applications choosing networks to which they will connect. 2-5Network Administration network_id semantics flags protofamily protoname device nametoaddr_libs ticlts tpi_clts v loopback - /dev/ticlts /usr/lib/straddr.so ticots tpi_cots v loopback - /dev/ticots /usr/lib/straddr.so ticotsord tpi_cots_ord v loopback - /dev/ticotsord /usr/lib/straddr.so tcp tpi_cots_ord v inet tcp /dev/tcp /usr/lib/tcpip.so,\ /usr/lib/resolv.so udp tpi_clts v inet udp /dev/udp /usr/lib/tcpip.so,\ /usr/lib/resolv.so icmp tpi_raw - inet icmp /dev/icmp /usr/lib/tcpip.so,\ /usr/lib/resolv.so rawip tpi_raw - inet - /dev/rawip /usr/lib/tcpip.so,\ /usr/lib/resolv.so Screen 2-2. Sample netconfig File The NETPATH Environment Variable 2 In most cases a user isn't interested in which transport provider handles a network operation, and the default network search path established by the system administrator (the netconfig file) is used to locate a transport provider available for connection. However, if a user or the system administrator wants to influence the choices made by applications, the search path can be modified using a new standard shell variable, NET- PATH. NETPATH is similar to the PATH variable. NETPATH consists of a colon-separated list of network IDs. Each network ID corresponds to the network_id field of a record in the netconfig database. A literal colon can be embedded as “\:” and a literal backslash as “\\.” An empty component in NETPATH (signified by a beginning colon, an ending colon, or two successive colons) is not a valid entry because the empty string is not a valid network ID. NETPATH is described in environ(5). The NETPATH environment variable is not set in /etc/profile. It can, however, be set in a user's HOME/.profile. Both users and system administrators should be aware that the set of “default” networks is different for routines that access netconfig directly and routines that access netconfig via the NETPATH environment variable. For routines that access netconfig directly see getnetconfig(3N), the set of default networks is the entire netconfig file; the set of “default” networks for the routines that access netconfig via NETPATH is the visible networks in the netconfig file see getnetpath(3N). A network is “visible” if the system administrator has included a v flag in the flag field. If NETPATH is unset, these visible networks are the default search path for this second group of access routines. 2-63 Administering Name-to-Address Mapping Introduction to Name-to-Address Mapping Administration . . . . . . . . . . . . . . . . . . . 3-1 The tcpip.so Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2 The tcip_nis.so Library. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3 The resolv.so Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3 The straddr.so Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3Network Administration

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