Wednesday, 16 April 2014

SAMBA Server Interview Questions and Answers for Linux.

Q-1: - Which SELinux security context used for SAMBA ?
Ans: - samba_share_t
Q-2: - On which ports SAMBA server works ?
Ans: -  UDP port 137 for netbios-ns, the NETBIOS Name Service
- UDP port 138 for netbios-dgm, the NETBIOS Datagram Service
- TCP port 139 for netbios-ssn, the NETBIOS session service
- TCP port 445 for microsoft-ds, the Microsoft Domain Service
Q-3: - What are the Secrity or Authentication Mode for SAMBA server?
Ans: - ADS
DOMAIN
SERVER
USER
SHARE
Q-4: - How to Manually Create Machine Trust Accounts ?Ans: - /usr/sbin/useradd -g machines -d /var/lib/nobody -c "machine nickname" -s /bin/false machine_name$
passwd -l machine_name$
Q-5: - What are the SAMBA server Types ?
Ans: - - Primary Domain Controller (PDC)
- Backup Domain Controller (BDC)
- ADS Domain Controller
Q-6: - Which protocol SAMBA server uses ?
Ans: - SMB, which stands for Server Message Block, is a protocol for sharing files, printers, serial ports, and communications abstractions such as named pipes and mail slots between computers.
Q-7: - How Does a Workstation find its Domain Controller?
Ans: - There are two different mechanisms to locate a domain controller: one
method is used when NetBIOS over TCP/IP is enabled and the other when
it has been disabled in the TCP/IP network configuration. Where NetBIOS over TCP/IP is disabled, all name resolution involves the use of DNS, broadcast messaging over UDP, as well as Active Directory communication technologies.
Q-8: - Can Samba Be a Backup Domain Controller to an NT4 PDC?
Ans: - No. The native NT4 SAM replication protocols have not yet been fully implemented.
Q-9: - How Do I Replicate the smbpasswd File?
Ans: - Replication of the smbpasswd file is sensitive. It has to be done whenever
changes to the SAM are made. Every user's password change is done in
the smbpasswd file and has to be replicated to the BDC. So replicating the
smbpasswd file very often is necessary.As the smbpasswd file contains plaintext password equivalents, it must not be sent unencrypted over the wire. The best way to set up smbpasswd replication from the PDC to the BDC is to use the utility rsync. rsync can use ssh as a transport. ssh itself can be set up to accept only rsync transfer without requiring the user to type a password.As said a few times before, use of this method is broken and awed. Machine trust accounts will go out of sync, resulting in a broken domain. This method is not recommended. Try using LDAP instead.
Q-10: - Can Samba fully replace my Windows NT server that is not a Primary Domain Controller (PDC)?
Ans: - Samba can completely serve files and printers to Windows, just as a Windows NT server would.
Q-11: - Can Samba replaces my Windows NT PDC?
Ans: - Not completely. Samba domain control capabilities for a Windows 9x client are
 solid and complete, and so these clients would probably never know the difference. The domain control support for Windows NT/2000 clients is still being developed. Currently, enough has been implemented to allow a Windows NT client to join a Samba-controlled domain, but there is more to domain control than that. The most conspicuous absence is the lack of support for Windows NT trust relationships and the SAM replication protocol used between NT PDCs and Backup Domain Controllers (BDCs).
Q-12: - What TCP and UDP ports required for NetBIOS over TCP/IP use?
Ans: - The NBT name service uses port 137/udp, the NBT session service uses port139/tcp, and the NBT datagram service uses port 138/udp.
Q-13: -  How SMB protocol works?
Ans: - There will be three stages in creating an SMB connection between a client and a specific share on a server.
The first stage in connecting to an SMB share is to negotiate the SMB protocol dialect to use. In the request packet, the client sends a text listing of all the SMB dialects that it understands. The server selects the most advanced protocol that it knows and responds to the client, specifying the protocol number from the list. At this point, the client and server have agreed that SMB commands can be used for the remainder of the conversation.
The second stage is to create a session connection between the client and server. To do this, the client issues a session setup request, which includes a sername and some proof of validity, such as a password. The server attempts to validate requesting user. If successful, the server then returns a session UID to client. This UID is unique for each session and has no relation to the server internal representation of users.
The third stage before access to files on a remote share is allowed is for the client to make a successful tree connection to the shared resource. The client sends to the server a tree connect request, which includes the UID previously issued by the server. At this stage the server verifies that the authenticated user is authorized to access the requested resource. If the user has sufficient privileges to access the share, the client is issued a tree connection ID (TID). The TID is used in all requests to access files contained in the resource to which the TID refers.

In this way SMB protocol works.
Q-14: - How man sections samba configuration file (smb.conf) contains?
Ans: - smb.conf file contains three sections.
1. [global] Contains settings that determine Samba overall behavior.
2. [homes] A default share for providing a home directory for all users.
3. [printers] A default share for exporting all printers on the host via CIFS.
Q-15: - If a netbios name is not defined in smb.conf, than what will be netbios name?
Ans: - If a netbios name is not defined, Samba will use the IP hostname of the server by default.
Q-16: -  I want to use User level security for my samba server than what i have to add in smb.conf file?
Ans: - security = user
Q-17: -  How you will verify that your smb.conf file doesn’t have any mistakes and misspellings?
Ans: - "testparm " tool that verifies the syntax of a configuration file(smb.conf). testparm -s smb.conf
Q-18: -  What is the use of "smbclient" command?
Ans: - "smbclient" is used to display the list of shares on your server. This verifies that smbd is running and functioning correctly. The -L option instructs smbclient to enumerate the shares on the server rather than actually connecting to one. The   -N switch instructs smbclient to use an anonymous login rather than the login name of the current user.
smbclient -L localhost -N
Antother use of "smbclient" command to connect the samba share.
smbclient //<server>/<share> -U <username>
Q-19: -  Explain "smbstatus" command?
Ans: - The smbstatus utility displays information about connected users and currently locked files.
Q-20: - Is it possible for Samba to share file systems that have been mounted using NFS?
Ans: - Yes. However, this can be problematic if the NFS server that provides the file system fails, causing the Samba server to hang. It is always safer to use Samba to share a local file system.
Q-21: - How many simultaneous connections can a Samba server support?
Ans: - In theory, there is no limit. In practice, the limit is determined by the server’s hardware, specifically the total amount of available RAM and the CPU power. It might also depend on the amount of activity from the smbd processes.
Q-22: - Can Samba be a member of more than one workgroup at the same time?
Ans: - No, Samba can be a member of only one workgroup.
Q-23: - What is SWAT?
Ans: - SWAT is GUI Based administration tool for samba server.
Q-24: - I am trying to use SWAT, but I keep getting the message There was no response. The server could be down or not responding. What is the problem?
Ans: - The most likely cause is that SWAT is not listening to connections, or you have used the wrong URL in trying to connect to SWAT. SWAT usually lives behind port 901, so the URL you should use is http://ID_ADDRESS_OF_SERVER:901/
Q-25: - Can i set empty password for samba user?
Ans: - yes, If you want to set the value to an empty password, you must change
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
to
NOPASSWORDXXXXXXXXXXXXXXXXXXXXX:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

in your smbpasswd file.
Note: - if you have edited the smbpasswd file by hand, make sure that the LAN Manager and NT password fields contain exactly 32 characters, no more and no fewer. If these fields do not have exactly 32 characters, Samba will not be able to correctly read the entry.
or You can modify by "smbpasswd" command.
smbpasswd -n USER_NAME
Also you have to set the null passwords parameter to yes in the [global] section of smb.conf:
null passwords = yes
Q-26: - Does Samba support PAM?
Ans: - Yes
Q-27: - What is role of "NTLM"?
Ans: - The challenge/response authentication protocol available to Windows clients and servers for validating connection requests.
Q-28: - Explain "force group" parameter used in smb.conf?
Ans: - It will define the group id to be used for all file access in the place of the user’s primary group.
Q-29: - Explain "force user" parameter used in smb.conf?
Ans: - It will define the user id to be used for all file access.
Q-30: - Explain "write list" parameter used in smb.conf?
Ans: - A list of users and/or groups that should be given write access even if the read only parameter has been enabled.
Q-31: - My clients are getting the error message that the Disk is Full when trying to print to my Samba server, but there is plenty of space. What is the problem?
Ans: - If smbd is unable to write the spooled file to the directory defined by the path parameter for a printer if the write permission were denied, for example it would respond to the client with the message, Disk is Full. Samba will also return this error message if the amount of free disk space in the spool directory has fallen below the value specified by the min print space parameter.
Q-32: - When I click on my Samba server in the network neighborhood, I am continually prompted for a password to the IPC$ share no matter what I enter.
Ans: - The Windows client is attempting to use encrypted passwords. However, the Samba server is configured to support only clear-text passwords. You should either enable encrypted passwords on the server or enable clear-text passwords on the Windows client.
Q-33: - Why is security = domain better than security = server?
Ans: - There are three reasons why security = domain is better. The first is because this method enables the Samba server to participate in domain trust relationships. This is impossible with server-level security. The second reason is that, under server-level security, each smbd process must keep an open connection with the authentication server. This can drain a Windows NT PDC quickly. Under domain-level security, this connection is maintained only long enough to perform the validation, thus conserving valuable resources. The final reason is that, as a domain member, the Samba server has access to much more information about user accounts, which can be used to automate the creation and deletion of user accounts upon demand.
Q-34: - what is nmbd daemon?
Ans: - This daemon handles all name registration and resolution requests. It is the primary vehicle involved in network browsing. It handles all UDP-based protocols. The nmbd daemon should be the first command started as part of the Samba startup process.
Q-35: - What is smdb daemon?
Ans: - This daemon handles all TCP/IP-based connection services for file- and print-based operations. It also manages local authentication. It should be started immediately following the startup of nmbd.
Q-36: - What is winbindd daemon?
Ans: - This daemon should be started when Samba is a member of a Windows NT4 or ADS domain. It is also needed when Samba has trust relationships with another domain. The winbindd daemon will check the smb.conf file for the presence of the idmap uid and idmap gid  parameters. If they are found, winbindd will use the values specified for UID and GID allocation. If these parameters are not specified, winbindd  will start but it will not be able to allocate UIDs or GIDs.
Q-37: - Explain the parameter "wins support = Yes" used in smb.conf?
Ans: - If the Samba server was configured to provide WINS support ("wins support = Yes"), then the WINS server is able to provide name resolution for all of the hosts that are not listed in the /etc/hosts file or within the DNS. Making this adjustment in the Name Service Switch configuration file (/etc/nsswitch.conf) allows the Linux system to query the WINS server for local name resolution. This saves manual adjustments to host files.
Q-38: - How to automate SMB share mounting during system startup?
Ans: - Add smb share entry in /etc/fstab file.
//IP_ADDRESS_OF_SERVER/Shared   /shared    smbfs    noauto,defaults  0  0
Q-39: - how to start and stop samba server?
Ans: - /etc/init.d/smb  restart
For any query please feel free to contact me my email id is sashwatkatore@gmail.com.

NFS Server Interview Questions and Answers for Linux.

Q-1: - Explain this entry /shared 192.168.1.0/255.255.255.0 (sync, rw)
Ans: - allows all systems with 192.168.1.* IP addresses read-write access to the /shared/ directory:
Q-2: - What will happened if a space is given in between allowed_hosts and (options)
Ans: - If a space is included, the options are applied to any and all IP addresses, which can be quite dangerous if write permission is granted. 
Q-3: - What is the role of "sync" option for NFS server
Ans: - If sync is specified, the server waits until the request is written to disk before responding to the client. The sync option is recommended because it follows the NFS protocol.
Q-4: - How to retrieve a list of clients connected to the NFS server ?
Ans: - To retrieve a list of clients connected to the NFS server, use the showmount command
from a shell prompt. To also show the directories the clients are connected to, use the
showmount -a command.
Q-5: - Name of Configuration file for NFS Server ?
Ans: - /etc/exports
Q-6: - What is meaning of "no_root_squash" option ?
Ans: - Treat remote root user as local root. Do not map requests from root to the anony-
mous user and group ID.
Q-7: - What is NFS ?
Ans: - NFS stands for Network File System. NFS was originally developed by Sun Microsystems in the 1980's. NFS allows remote hosts to mount file systems over a network and interact with those file systems as though they are mounted locally. 
Q-8: - Which NFS versions are available ?Ans: - 
NFS Version 2
NFS Version 3
NFS Version 4
Q-9: - What is different between NFS Version 2 & 3 ?
Ans: - nfs 2 default 8kb transfer rate,it did not check the authentication at the time connection.client wants to access unauthorized file it shows error messages like "write error","read error" nfs 3 32kb transfer rate. It check at the time connection- ACL Support
Q-10: - Can we grant access by Username and password for nfs share?
Ans: - No, access is granted only for IP address.
Q-11: - What is the role of "all_squash" option?
Ans: - Treat all client users as anonymous users. Map all user and group IDs to the anonymous user and group ID.
Q-12: - What is the role of "root_squash" option?
Ans: - All requests from the user root are translated or mapped as if they came from the user anonymous (default).
Q-13: - Explain option "all_squash"?
Ans: - The UID and GID of exported files are mapped to the user anonymous. It is good for public directories.
Q-14: - Explain "exportfs" command?
Ans: - The exportfs command is used to maintain the current table of exported file systems for NFS.
Q-15: - Explain command "/usr/sbin/exportfs -f"?
Ans: - It will flush everything out of the kernels export table. Any clients that are active will get new entries added by mountd when they make their next request.
Q-16: - Which option is used with exportfs command to display the current export list, also displays the list of export options?
Ans: - exportfs -v
Q-17: - Which option is used with exportfs command to re-export all directories?
Ans: - exportfs -r
Q-18: - How you will export directory (/data) to host 192.168.1.51, allowing asynchronous writes without adding the entry in /etc/exports file?
Ans: -  # exportfs -o async 192.168.1.51:/data
Q-19: - Is rpc.mountd daemon supports TCP_WRAPPERS?
Ans: - Yes, The rpc.mountd daemon is protected by the tcp_wrappers. You have to give the clients access to rpc.mountd if they should be allowed to use NFS Server.
Q-20: - Explain "nfsstat" command?
Ans: - The nfsstat command displays the statistics about NFS client and NFS server activity.
Q-21: - What do you understand by "nfsstat -o all -234" command?
Ans: - It will Show all information about all versions of NFS.
Q-22: - What do you understand by "nfsstat --nfs --server -3" command?
Ans: - It will show statistics for NFS version 3 server.
Q-23: - Can NFS share mounted on Window XP and Justify your answer?
Ans: - No, Window XP operating system doesn’t support nfs protocol.
Q-24: - 192.168.1.51:/data is exported by NFS Server and i want to add this NFS share to client /etc/fstab file. How you will add this entry in /etc/fstab file?
Ans: 
# device                      mount-point     fs-type     options      dump   fsckorder
192.168.1.51:/data            /mnt           nfs               rw              0         0
Q-25: - Explain "Soft Mounting" option at NFS Client?
Ans: - if a file request fails, the NFS client will report an error to the process on the client machine requesting the file access. if it cannot be satisfied (for example, the server is down), then it quits. This is called soft mounting.
Q-26: - Explain "Hard Mounting" option at NFS Client?
Ans: - If a file request fails, the NFS client will report an error to the process on the client machine requesting the file access. if it cannot be satisfied, then it will not quit until the request is satisfied. This is called Hard mounting.
Q-27: - What is "portmap"?
Ans: - The portmapper keeps a list of what services are running on what ports. This list is used by a connecting machine to see what ports it wants to talk to access certain services.
Q-28: - How you will check "portmap" service is running or not?
Ans: - rpcinfo -p
Q-29: - I am unable to mount a NFS share. How will you trace out the reason?
Ans: - Firstly, check that you have permissions to mount nfs share or not. Check /etc/exports file.
Secondly you can get RPC error: Program Not Registered (or another "RPC" error)
For this check your NFS server and portmap service running or not by "rpcinfo -p"
Q-30: - Can I modify export permissions without needing to remount clients in order to have them take effect?
Ans: - Yes. The safest thing to do is edit /etc/exports and run "exportfs -r".
For any query please feel free to contact me my email id is sashwatkatore@gmail.com.

FTP Server Interview Questions and Answers for Linux


Q-1: - How to deny specific users access to the FTP server ?

Ans: - To deny specific users access to the FTP server, add their usernames to the /etc/vsftpd/

ftpusers file. By default, system users such as root and nobody are included in this list.

Q-2: - Can we create logs for ftp authenticated sessions ?
Ans: - Yes, If the xferlog_enable directive in vsftpd.conf is set to YES, file transfers using the FTP protocol are logged to /var/log/xferlog. Information such as a time stamp, IP address of the client, the file being transferred, and the username of the person who authenticated the connection is included in the log entry.

Q-3: - What is meaning of max_clients parameter ?
Ans: - Maximum number of clients that can connect at one time.
If set to 0, the number of clients is unlimited.

Q-4: - On which port VSFTPD server works ?
Ans: - FTP uses two ports, 20 and 21. By default, the FTP server listens for requests on port 21.
After a connection is established, the client sends commands to the server on port 21.
However, port 20 is used when the server sends data back to the client.

Q-5: - How to restart VSFTPD server ?
Ans: - service vsftpd restart

Q-6: - How to allow Anonymous FTP ?
Ans: - Anonymous FTP is enabled by default by setting the anonymous_enable directive in
/etc/vsftpd/vsftpd.conf to YES.

Q-7: - What is FTP ?
Ans: - FTP stands for File Transfer Protocol. An FTP server allows clients to connect to it either
anonymously or with a username and password combination. After successful authentication, files can be transferred back and forth between the server and client. The files are neither encrypted nor compressed.

Q-8: - For Redhat Linux or Fedora which package is required for FTP service ?
Ans: - Red Hat Enterprise Linux 5 or FEDORA includes the vsftpd FTP service.
vsftpd-2.0.5-12.el5 (For Redhat)
Q-9: - Important Configuration file for vsftpd server ?


Ans: - The FTP server uses the /etc/vsftpd/vsftpd.conf configuration file. Using this file, you

can set options for displaying a custom banner message after users log in, setting the
default file permissions for uploaded files, and setting the port on which to listen for
incoming connections.
Q-10: - What is FTP ?
Ans: - FTP client connects to the FTP server by establishing an FTP control connection to port 21 of the server. Your commands such as 'ls' and 'get' are sent over this connection. Whenever the client requests data over the control connection, the server initiates data transfer connections back to the client. The source port of these data transfer connections is always port 20 on the server, and the destination port is a high port (greater than 1024) on the client.
Q-11: - What is Passive mode?
Ans: - Passive mode, like active mode, is initiated by the FTP client application. When requesting data from the server, the FTP client indicates it wants to access the data in passive mode and the server provides the IP address and a random, unprivileged port (greater than 1024) on the server. The client then connects to that port on the server to download the requested information.
Q-12: - Explain directive "session_support”?
Ans: - When enabled, vsftpd attempts to maintain login sessions for each user through Pluggable Authentication Modules (PAM).
Q-13: - Is there any way to monitor clients connected to vsftpd?
Ans: - Yes. We actually have two slightly different methods to monitor vsftpd clients. First, make sure you have enabled the config option, "setproctitle_enable=YES" like in our example above and restart your vsftpd server. Then run the command "watch ps -Cvsftpd -o user, pid, stime, cmd" to watch the processes including ip, username and actions like idle or data retrieval.
Q-14: - I want to copy multiple files with out prompting for any info, how can I do that one?
Ans: - ftp -i ftpserver
Q-15: - Local users cannot log in. How to resolve this issue?
Ans: - Check "local_enable=YES" in your /etc/vsftpd/vsftpd. conf to allow local users to log in.
Q-16: - How to change vsftpd default port?
Ans: - Set "listen_port" option in "vsftpd.conf"
Q-17: - How to restrict some IP's not use my FTP server?
Ans: - Use TCP_WRAPPERS
Q-18: - Does vsftpd support IPv6?
Ans: - Yes

For any query please feel free to contact me my email id is sashwatkatore@gmail.com.

DNS Server Interview Questions and Answers for Linux

Q-1: - which are the important configuration files for DNS server ?
Ans: - BIND uses /etc/named.conf as its main configuration file, the /etc/rndc.conf file as theconfiguration file for name server control utility rndc, and the /var/named/ directory for zone files and the like.
Q-2: - What is BIND ?
Ans: - BIND stands for Berkeley Internet Name Domain which is the most commonly used Domain Name System (DNS) server on the Internet.
Q-3: - On which version of bind u have worked ?
Ans: - BIND 9
Q-4: - What is the role of DNS ?
Ans: - A DNS server, or name server, is used to resolve an IP address to a hostname.
Q-5: - On which port DNS server works ?
Ans: - DNS servers use port 53 by default. Incoming and outgoing packets should be allowed on
port 53. Also allow connections on port 921 if you configure a lightweight resolver server.
The DNS control utility, rndc, connects to the DNS server with TCP port 953 by default. If
you are running rndc on the name server, connections on this TCP port from localhost
should be allowed. If you are running rndc on additional systems, allow connections to
port 953 (or whatever port you have chosen to configure) from these additional systems.
Q-6: - What is round robin DNS?
Ans: - Round robin DNS is usually used for balancing the load of geographically distributed Web servers. For example, a company has one domain name and three identical home pages residing on three servers with three different IP addresses. When one user accesses the home page it will be sent to the first IP address. The second user who accesses the home page will be sent to the next IP address, and the third user will be sent to the third IP address. In each case, once the IP address is given out, it goes to the end of the list. The fourth user, therefore, will be sent to the first IP address, and so forth. 
Q-7: - What is Name Server?
Ans: - A name server keeps information for the translation of domain names to IP addresses   and IP addresses to domain names. The name server is a program that performs the translation at the request of a resolver or another name server.
Q-8: - What is Primary name server or primary master server?
Ans: - Primary name server/primary master is the main data source for the zone. It is the authoritative server for the zone. This server acquires data about its zone from databases saved on a local disk. The primary server must be published as an authoritative name server for the domain in the SOA resource record, while the primary master server does not need to be published.
Q-9: - What is Secondary name server/slave name server?
Ans: - Secondary name server/slave name server acquires data about the zone by copying the data from the primary name server (respectively from the master server) at regular time intervals. It makes no sense to edit these databases on the secondary name servers, although they are saved on the local server disk because they will be rewritten during further copying.
Q-10: - what is Root name server?
Ans: - Root name server is an authoritative name server for the root domain (for the dot). Each root name server is a primary server, which differentiates it from other name servers.
Q-11: - what is Stealth name server?
Ans: - Stealth name server is a secret server. This type of name server is not published anywhere. It is only known to the servers that have its IP address statically listed in their configuration. It is an authoritative server. It acquires the data for the zone with the help of a zone transfer. It can be the main server for the zone. Stealth servers can be used as a local backup if the local servers are unavailable.
Q-12: - What do you mean by "Resource Records"?
Ans: - Information on domain names and their IP addresses, as well as all the other information distributed via DNS is stored in the memory of name servers as Resource Records (RR). 
Q-13: - Explain "TTL"? 
Ans: - Time to live. A 32-bit number indicating the time the particular RR can be kept valid in a server cache. When this time expires, the record has to be considered invalid. The value 0 keeps nonauthoritative servers from saving the RR to their cache memory.
Q-14: - Tell me 5 Types of DNS records?
Ans: - A, NS, CNAME, SOA, PTR, MX.
Q-15: - explain "SOA Record"?
Ans: - The Start of Authority (SOA) record determines the name server that is an authoritative source of information for the particular domain. There is always only one SOA record in the file, and it is placed at the beginning of the file of authoritative resource records. 
Q-16: - what is "A Record"
Ans: - A (Address) records assign IP addresses to domain names of computers. The IP address cannot have a dot at the end.
Q-17: - Explain "CNAME Record"?
Ans: - Synonyms to domain names can be created using CNAME records. This is often referred to as 'creating aliases for computer names'.
Q-18: - What are "HINFO and TXT Records"?
Ans: - HINFO and TXT records are for information only. An HINFO record has two items in its data part. The first item is information about hardware, and the second one is information about software. A TXT record contains a general data string in its data part.
Example :
test.com IN SOA ...
...
mail IN A 192.1.1.2
IN HINFO My_Server UNIX
IN TXT my server
Q-19: - what are "MX Records"?
Ans: - MX records specify the mailing server of the domain. An MX record shows to which computer a mail of a particular domain should be sent. The MX record also includes a priority number, which can be used to determine several computers where the mail for the domain can be sent. The first attempt is to deliver the mail to the computer with the highest priority (lowest value). If this attempt fails, the mail goes to the next computer (with a higher priority value), and so on.

test.com IN SOA ...

...

mail               IN        A         192.1.1.2
                       IN       HINFO    AlphaServer UNIX
                       IN        TXT       my  server
                       IN         MX   30    mail2.nextstep4it.com
                       IN         MX   20    mail3.nextstep4it.com
                       IN         MX   10    mail2.nextstep4it.com
Q-20: - Explain "PTR Records"?
Ans: - A Pointer Record (PTR) is used to translate an IP address into a domain name.
Q-21: - What is Dynamic DNS?
Ans: - Dynamic DNS a method of keeping a domain name linked to a changing IP address as not all computers use static IP addresses. Typically, when a user connects to the Internet, the user's ISP assigns an unused IP address from a pool of IP addresses, and this address is used only for the duration of that specific connection. This method of dynamically assigning addresses extends the usable pool of available IP addresses. A dynamic DNS service provider uses a special program that runs on the user's computer, contacting the DNS service each time the IP address provided by the ISP changes and subsequently updating the DNS database to reflect the change in IP address.
Q-22: - What is the role of "named-checkconf Utility"?
Ans: - The named-checkconf utility checks the syntax of the named.conf configuration file.
Syntax: named-checkconf    [-t directory] [filename] 
Q-23: - what is the role of "named-checkzone Utility"?
Ans: - The named-checkzone utility checks the syntax and consistency of the zone file.
Syntax:     named-checkzone [-dgv]   [-c class] zone   [filename]
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