http://www.checkdomain.com/
Monday, 17 October 2011
Monday, 3 October 2011
DNS (Domain Name System), is the service which translates between Internet names and Internet addresses. Internet names are the names which we use to refer to hosts on the Internet, such as www.debianhelp.co.uk. Internet addresses are the numbers which routers use to move traffic across the Internet, such as 211.1.13.115 and What are DNS Records ? DNS records or Zone files are used for mapping URLs to an IPs. Located on servers called the DNS servers, these records are typically the connection of your website with the outside world. Requests for your website are forwarded to your DNS servers and then get pointed to the WebServers that serve the website or to Email servers that handle the incoming email. Different Types of DNS Records With Syntax and Examples Types of DNS Records A AAAA CNAME MX PTR NS SOA SRV TXT NAPTR The above DNS records are mostly used in all DNS Configurations. Now we will see each one with examples. A Record An A record or address record. Address Record, assigns an IP address to a domain or subdomain name. When the domain name system was designed it was recommended that no two A records refer to the same IP address. Suppose you have the somedomain.tld domain and want to assign 10.10.0.1 IP address to your web server, then you should create an A record with "www.somedomain.tld" as Fully Qualified Domain Name and "10.10.0.1" in the value field. From now on, all the requests for www.somedomain.tld will be sent to a server with that IP. Basically is useful to use an A record when you have subdomains residing on various systems. Usefultip: you might use a "*.somedomain.tld" A record to allow WHATEVER.somedomain.tld to be resolved to your IP, though a wildcard CNAME record is often better than a wildcard A record. Example of A Record with Syntax example.com. IN A 69.9.64.11 Where IN indicates Internet A indicates the Address record. The above example indicate that the IP Address for the domain example.com is 69.9.64.11 AAAA Record An AAAA record or IPv6 address record maps a hostname to a 128-bit IPv6 address. The regular DNS Address resource record is defined for a 32-bit IPv4 address, so a new one was created to allow a domain name to be associated with a 128-bit IPv6 address. The four “A”s (“AAAA”) are a mnemonic to indicate that the IPv6 address is four times the size of the IPv4 address. The AAAA record is structured in very much the same way as the A record in both binary and master file formats; it is just much larger. The DNS resource record Type value for AAAA is 28. Example of AAAA Record with Syntax The AAAA record is to help transition and coexistence between IPv4 and IPv6 networks.An IPv4 nameserver can provide IPv6 addresses: linux aaaa 3ffe:1900:4545:2:02d0:09ff:fef7:6d2c CNAME Record A CNAME record or canonical name record makes one domain name an alias of another. The aliased domain gets all the subdomains and DNS records of the original. You should use a CNAME record whenever you want associate a new subdomain to an already existing A record; i.e. you can make "www.somedomain.tld" to "somedomain.tld", which should already have been assigned an IP with an A record. This allows you to have as many subdomains as you wish without having to specify the IP for every record. Use a CNAME if you have more services pointing to the same IP. This way you will have to update only one record in the convenience of a change of IP address. Example of a CNAME record: "stuff.everybox.com CNAME www.everybox.com" where 'www.everybox.com' is an A record listing an IP address, and 'stuff.everybox.com' points to 'www.everybox.com'. It will NOT allow you to foward a domain to a specific web page. Use a webhop for that. Port numbers can be changed with webhops, as well; CNAMEs cannot change the HTTP default of 80 to any other port number. Do not use CNAME defined hostnames in MX records. For example, this is not recommended Example Of CNAME With syntax mail.example.com IN CNAME mail.example.net where IN indicates Internet CNAME indicates CNAME record. MX Record An MX record or mail exchange record maps a domain name to a list of mail exchange servers for that domain. Example with MX Record Syntax - Single mail servers mydomain.com. 14400 IN MX 0 mydomain.com. The MX record shows that all emails @ mydomain.com should be routed to the mail server at mydomain.com. The DNS record shows that mydomain.com is located at 26.34.9.14. This means that email meant for test@mydomain.com will be routed to the email server at 26.34.9.14. This finishes the task of the MX record. The email server on that server then takes over, collects the email and then proceeds to distribute it to the user ``test''. It is important that there be a dot(``.'') after the domain name in the MX record. If the dot is absent, it routes to ``mydomain.com.mydomain.com''. The number 0, indicates Preferance number. Mail is always routed to the server which has the lowest Preferance number. If there is only one mail server, it is safe to mark it 0. Using Multiple mail servers If you want to use multiple mail servers you have to use MX record preferences.The MX record preference values indicate which mail server to use and in which order to try them when they fail or don't respond. A larger preference number is less preferred. Thus, a mail exchanger with a preference of zero (0) is always preferred over all other mail exchangers. Setting preference values to equal numbers makes mail servers equally preferred. Example with MX Record Syntax - Multiple mail servers mydomain.com. 14400 IN MX 0 mydomain.com. mydomain.com. 14400 IN MX 30 server2.mydomain.com You can have unlimited MX entries for Fallback or backup purpose.If all the MX records are equal Preference numbers, the client simply attempts all equal Preference servers in random order, and then goes to MX record with the next highest Preference number. PTR Record A PTR record or pointer record maps an IPv4 address to the canonical name for that host. Setting up a PTR record for a hostname in the in-addr.arpa domain that corresponds to an IP address implements reverse DNS lookup for that address. For example www.name.net has the IP address 122.0.3.16, but a PTR record maps 16.3.0.122.in-addr.arpa. Example of PTR Record with syntax 16.3.0.122.in-addr.arpa. IN PTR name.net Here as you see the IP Address is reversed and added with in-addr.arpa and this has come to the left side while the actual domain name has gone to right side of IN PTR. This is mostly used as a security and an anti-spam measure wherein most of the webservers or the email servers do a reverse DNS lookup to check if the host is actually coming from where it claims to come from. It is always advisable to have a proper reverse DNS record (PTR) is been setup for your servers especially when you are running a mail / smtp server. NS Record An NS record or name server record maps a domain name to a list of DNS servers authoritative for that domain. Delegations depend on NS records. NS Record Name Server Record which indicates the Authoritative Name Servers for a particular Domain. The NS records of the Authoritative Name Server for any given Domain will be listed on the Parent Server. These are called as the Delegation Records as these records on the Parent Server indicates the delegation of the domain to the Authoritative servers. The NS record will also be listed in the Zone records of the Authoritative Name Server itself. These records are called as the Authoritative Records. The NS records found on the Parent Server should match the NS records on the Authoritative Server as well. However, you can have NS records listed on the Authoritative server that is not listed in the Parent Server. This arrangement is normally used to configure Stealth Name Servers. Example of NS Record With syntax example.com. IN NS ns1.live.secure.com. where IN indicates the Internet NS indicates the type of record which Name Server record The above indicates that the ns1.live.secure.com is the authoritative server for the domain example.com SOA Record An SOA record or start of authority record specifies the DNS server providing authoritative information about an Internet domain, the email of the domain administrator, the domain serial number, and several timers relating to refreshing the zone. An SOA(State of Authority) Record is the most essential part of a Zone file. The SOA record is a way for the Domain Administrator to give out simple information about the domain like, how often it is updated, when it was last updated, when to check back for more info, what is the admins email address and so on. A Zone file can contain only one SOA Record. A properly optimized and updated SOA record can reduce bandwidth between nameservers, increase the speed of website access and ensure the site is alive even when the primary DNS server is down. Example of SOA Record with syntax Here is the SOA record. Notice the starting bracket ``(``. This has to be on the same line, otherwise the record gets broken. ; name TTL class rr Nameserver email-address mydomain.com. 14400 IN SOA ns.mynameserver.com. root.ns.mynameserver.com. ( 2004123001 ; Serial number 86000 ; Refresh rate in seconds 7200 ; Update Retry in seconds 3600000 ; Expiry in seconds 600 ; minimum in seconds ) name - mydomain.com is the main name in this zone. TTL - 14400 - TTL defines the duration in seconds that the record may be cached by client side programs. If it is set as 0, it indicates that the record should not be cached. The range is defined to be between 0 to 2147483647 (close to 68 years !) . Class - IN - The class shows the type of record. IN equates to Internet. Other options are all historic. So as long as your DNS is on the Internet or Intranet, you must use IN. Nameserver - ns.nameserver.com. - The nameserver is the server which holds the zone files. It can be either an external server in which case, the entire domain name must be specified followed by a dot. In case it is defined in this zone file, then it can be written as ``ns'' . Email address - root.ns.nameserver.com. - This is the email of the domain name administrator. Now, this is really confusing, because people expect an @ to be in an email address. However in this case, email is sent to root@ns.nameserver.com, but written as root.ns.nameserver.com . And yes, remember to put the dot behind the domain name. Serial number - 2004123001 - This is a sort of a revision numbering system to show the changes made to the DNS Zone. This number has to increment , whenever any change is made to the Zone file. The standard convention is to use the date of update YYYYMMDDnn, where nn is a revision number in case more than one updates are done in a day. So if the first update done today would be 2005301200 and second update would be 2005301201. Refresh - 86000 - This is time(in seconds) when the slave DNS server will refresh from the master. This value represents how often a secondary will poll the primary server to see if the serial number for the zone has increased (so it knows to request a new copy of the data for the zone). It can be written as ``23h88M'' indicating 23 hours and 88 minutes. If you have a regular Internet server, you can keep it between 6 to 24 hours. Retry - 7200 - Now assume that a slave tried to contact the master server and failed to contact it because it was down. The Retry value (time in seconds) will tell it when to get back. This value is not very important and can be a fraction of the refresh value. Expiry - 3600000 - This is the time (in seconds) that a slave server will keep a cached zone file as valid, if it can't contact the primary server. If this value were set to say 2 weeks ( in seconds), what it means is that a slave would still be able to give out domain information from its cached zone file for 2 weeks, without anyone knowing the difference. The recommended value is between 2 to 4 weeks. Minimum - 600 - This is the default time(in seconds) that the slave servers should cache the Zone file. This is the most important time field in the SOA Record. If your DNS information keeps changing, keep it down to a day or less. Otherwise if your DNS record doesn't change regularly, step it up between 1 to 5 days. The benefit of keeping this value high, is that your website speeds increase drastically as a result of reduced lookups. Caching servers around the globe would cache your records and this improves site performance. SRV Record The theory behind SRV is that given a known domain name e.g. example.com, a given service e.g. web (http) which runs on tcp in this case, a DNS query may be issued to find the host name that provides such on behalf of the domain - and which may or may not be within the domain. Example of SRV Record with syntax srvce.prot.name ttl class rr pri weight port target _http._tcp.example.com. IN SRV 0 5 80 www.example.com. srvce Defines the symbolic service name (see IANA port-numbers) prepended with a '_' (underscore). Case insensitive. Common values are: _http - web service _ftp - file transfer service _ldap - LDAP service prot Defines the protocol name (see IANA service-names) prepended with a '_' (underscore). Case insensitive. Common values are _tcp - TCP protocol _udp - UDP protocol name Incomprehensible description in RFC 2782. Leaving the entry blank (without a dot) will substitute the current zone root (the $ORIGIN), or you can explicitly add it as in the above _http._tcp.example.com. (with a dot). ttl Standard TTL parameter. For more information about TTL values. pri The relative Priority of this service (range 0 - 65535). Lowest is highest priority. weight Used when more than one service with same priority. A 16 bit unsigned integer in the range 0 - 65535. The value 0 indicates no weighting should be applied. If the weight is 1 or greater it is a relative number in which the highest is most frequently delivered i.e. given two SRV records both with Priority = 0, one with weight = 1 the other weight = 6, the one with weight 6 will have its RR delivered first 6 times out of 7 by the name server. port Normally the port number assigned to the symbolic service but does this is not a requirement e.g. it is permissible to define a _http service with a port number of 8100 rather than the more normal port 80. target The name of the host that will provide this service. Does not have to be in the same zone (domain). TXT Record A TXT record allows an administrator to insert arbitrary text into a DNS record. For example, this record is used to implement the Sender Policy Framework specification. Example of TXT Record with syntax SPF domains have to publish at least two directives: a version identifier and a default mechanism. mydomain.com. TXT "v=spf1 -all" This is the simplest possible SPF record: it means your domain mydomain.com never sends mail. It makes sense to do this when a domain is only used for web services and doesn't do email. MX servers send mail, designate them. mydomain.com. TXT "v=spf1 mx -all" Let's pretend mydomain.com has two MX servers, mx01 and mx02. They would both be allowed to send mail from mydomain.com. other machines in the domain also send mail, designate them. mydomain.com. TXT "v=spf1 mx ptr -all" This designates all the hosts whose PTR hostname match mydomain.com. any other machines not in the domain also send mail from that domain, designate them. mydomain.com. TXT "v=spf1 a:mydomain.com mx ptr -all" mydomain.com's IP address doesn't show up in its list of MX servers. So we add an "a" mechanism to the directive set to match it. mydomain.com. TXT "v=spf1 a mx ptr -all" This is shorthand for the same thing. Each of your mail servers should have an SPF record also.When your mail servers create a bounce message, they will send it using a blank envelope sender: <>. When an SPF MTA sees a blank envelope sender, it will perform the lookup using the HELO domain name instead. These records take care of that scenario. amx.mail.net. TXT "v=spf1 a -all" mx.mail.net. TXT "v=spf1 a -all" NAPTR Record NAPTR records (NAPTR stands for "Naming Authority Pointer") are a newer type of DNS record that support regular expression based rewriting. Example of NAPTR Record with syntax $ORIGIN 3.8.0.0.6.9.2.3.6.1.4.4.e164.arpa. NAPTR 10 100 "u" "E2U+sip" "!^.*$!sip:info@example.com!" . NAPTR 10 101 "u" "E2U+h323" "!^.*$!h323:info@example.com!" . NAPTR 10 102 "u" "E2U+msg" "!^.*$!mailto:info@example.com!" . This record set maps the phone number +441632960083 onto three possible identically ordered URIs, with a preference for SIP, then H323, and finally email. In each case, the regular expression matches the full AUS (^.$), and replaces it with a URI (e.g., sip:info@example.com). As this is a terminal record, this URI is returned to the client.Though most NAPTR records replace the full AUS, it is possible for the regular expression to back-reference part of the AUS, to grab an extension number, say: $ORIGIN 0.6.9.2.3.6.1.4.4.e164.arpa. * NAPTR 10 100 "u" "E2U+sip""!^+441632960(.*)$!sip:\1@example.com!" . Once the client has the URI it must be resolved using DNS, but this is no longer part of the DDDS algorithm.. wildcard DNS record A wildcard DNS record is a record in a DNS zone file that will match all requests for non-existent domain names, i.e. domain names for which there are no records at all.
http://who.is Ex:http://who.is/dns/kapilhomes.com/ To check the DNS What's My DNS? whatsmydns.net is an online service that allows you to instantly perform a DNS lookup to check a hostnames current IP Address and other DNS information against a selection of random name servers around the world. This is especially useful to check the current state of DNS propagation after making changes to your domains zones. http://www.whatsmydns.net/#CNAME/mail.kapilhomes.com To check all the records propagation.
Thursday, 29 September 2011
Snapshot - Remote Backup -------------------------------------------------------------------------------- As a System administrator, keeping disk images for many computers current can be quite time consuming. Due to Drive Snapshot's easy command line interface, this can be done much more easily. Using RLOGIN/RCONSOLE from the Windows NT Resource pack, or the ingenious PSEXEC utility from Sysinternals, you can easily automate this process, or control it from your own working place. Example for PSEXEC: C::\>PSEXEC \\userComputer -u administrator -p AdminPasswd -c -f -h c:\Programme\snapshot\Snapshot.exe C: \\Server\Backup\user\C-drive.SNA This will: login to the computer 'Usercomputer' as an administrator (required); copy Snapshot.exe to the other computer, and start a backup of the C:-drive to some space on your \\Server. Please see PSEXEC documentation for more details. Note: when backing up a Vista or Windows 7 computer, please use -h If the target system is Vista or higher, has the process run with the account's elevated token, if available. Otherwise you will get a UAC (User Account Control) prompt that no one is able to answer.
Snapshot Backup - FAQ How can I verify that Snapshot did what it claimed - backup all my data The easiest and fastest way: Backup a drive. Map the drive as virtual drive. Use WINDIFF or similar file compare tools to compare the two drives; they should be identical. You will see differences, because WINDIFF will not be able to open the PAGEFILE or registry files on the original drive; but that's not SNAPSHOT's fault. For these files you have to trust us (of course we tested this, using slightly more complicated setup's) Do I have to shut down all Windows programs (highly recommended) No. It's probably a good idea to save your open files before starting Snapshot Backup. Otherwise you would eventually get outdated data on your disk. After Snapshot has started you may continue to work normally, the image will reflect the data at start time. May I install a new VIRUS, while Snapshot is running? Yes. It won't make you happy, but Snapshot won't care. The created image will not contain any sign of a virus, ready to be restored. May I FORMAT/FDISK the disk that is currently being Snapshot'ed? No. It is not possible to run programs that access the disk directly while Snapshot is running. What File systems does Snapshot support? SnapShot relies mostly on the operating system to support a drive. All file systems known to Windows(FAT16, FAT32, NTFS) are supported; additionally some LINUX file systems (EXT2,EXT3,Reiser) are 'manually' supported. Other file system are stored completely, ignoring any free space information. Does Snapshot support enhanced NTFS features like encryption, security, hard and symbolic links, mount points, multiple data streams, extended attributes,quota,... Yes. Snapshot is sector-oriented. Snapshot will backup all sectors relevant for the file system, and restore them exactly the same way. Snapshot never interprets these data on its own, the interpretation of these data is up to the file system. Snapshot only provides the necessary data. The same is true for the Image Viewer. --------------------------------------------------------------------------------
Snapshot - Restoring a volume from Dos Quick steps Boot your system from a DOS boot disk. Below it is assumed that your image data are accessible as drive W:\C-DRIVE.SNA. If you want to (or have to) repartition your drive, because it is new or completely damaged, enter: A:>SNAPSHOT RESTORE HD1 partitionstructure W:\C-DRIVE.SNA -Y This will partition the whole drive (HD1) in exactly the same way as your original drive. You don't need to do that, and shouldn't do it, if you only want to restore a single, damaged volume. A:>SNAPSHOT RESTORE HD1 auto W:\C-DRIVE.SNA -Y -V This restores all data in the automatically selected partition from the image saved on C-drive, will not ask for confirmation (-Y), and will verify that all data were indeed written correctly (-V). Details Boot your system (from a DOS bootdisk) If you don't have a DOS bootdisk available, here is more information on how to create one. When restoring a partition, all data on it will be deleted and replaced by the data at the time of the backup. If you think you need some of the data, you have to copy them to somewhere else before restoring the image. After the restore, the system will be identical to the time you created the image. To restore an image, the imagefile must be accessible to DOS (you must be able to say C:>DIR); for more information about how to access a file on CDROM, Network, or local NTFS click here. actions to be performed show information about the hard disk's partition structure show information about the Image file restore the partition structure restore the partition data test image file for internal consistency (optional) restore Master Boot Sector (MBR) (rarely needed) show information about the hard disk's partition structure snapshot.exe show [HDx] [HDx]: number of hard disk, HD1 is the first hard disk A:>SNAPSHOT SHOW HD1 SNAPSHOT for DOS V1.21 [Feb 27 2003] Copyright (c) tom ehlert 1 hard disk(s) detected disk 1 - 1022 cylinders, 255 heads, 63 sectors, 512 byte total physical size 29314 MB Primary partitions start - end : start, size 1:06 FAT16 CHS 0 1 1- 129 254 63 : 0MB, 1020MB 2:05 extended Part. CHS 130 0 1- 2 254 63 : 1019MB, 7037MB 3:07 NTFS inst FS CHS 3 0 1- 249 254 63 : 8056MB, 18003MB 4:0C FAT32 LBA CHS 250 0 1- 663 254 63 : 26058MB, 3248MB Logical partitions 1:06 FAT16 CHS 130 1 1- 194 254 63 : 1019MB, 510MB 2:06 FAT16 CHS 195 1 1- 324 254 63 : 1529MB, 1020MB 3:06 FAT16 CHS 439 1 1- 568 254 63 : 3443MB, 1020MB 4:07 NTFS inst FS CHS 569 1 1-1014 254 63 : 4463MB, 3499MB 5:07 NTFS inst FS CHS 1015 1 1-1015 254 63 : 7961MB, 8MB 6:04 FAT16 < 32MB CHS 1016 1 1-1019 254 63 : 7969MB, 32MB highest used sector on disk 60018840 (29307 MB) show information about the Image file snapshot.exe show imagefile imagefile: path and name of the image file This shows information about the saved volume as it was stored at backup time. Additionally, the partition structure of the original disk is shown. A:>snapshot show x:\c-drive.sna Information about the saved volume from Computer 'TP', drive C:, Label 'C-TP ', Filesystem FAT (06) Hard disk 1 Primary Partition 1- size 2.097.393.664 =1999MB total size 1999 MB - 420 MB free - 32768 Bytes per cluster disk 1 - 1222 cylinders, 255 heads, 63 sectors, 512 byte total physical size 9585 MB Primary partitions start - end : start, size 1:06 FAT16 CHS 0 1 1- 254 254 63 : 0MB, 2001MB 2:0F extended Part CHS 255 0 1-1023 254 63 : 2000MB, 7586MB Logical partitions 1:07 NTFS inst FS CHS 255 1 1- 514 254 63 : 2000MB, 2040MB 2:06 FAT16 CHS 515 1 1- 641 254 63 : 4039MB, 997MB 3:07 NTFS inst FS CHS 642 1 1-1023 254 63 : 5036MB, 2997MB 4:07 NTFS inst FS CHS 1023 1 1-1023 254 63 : 8032MB, 1554MB highest used sector on disk 19631430 (9586 MB) restore the partition structure This is required, if your disk is new (not partitioned), or partitioned differently. Snapshot will restore the exact partitioning of the original disk. The necessary information is available in each Snapshot image file. If for some reason you want to partition the disk in a different way, you have to use FDISK or similar tools. Note: for this to work it is necessary, that the new disk is at least as large as the partitioned area on the original disk; Snapshot will not modify the partition information in any way. A:>snapshot restore [HDx] partitionstructure imagefile [HDx]: Number of hard disk, starting with HD1 [imagefile]: Path and name of Image file restore the partition data The real restore action. This will overwrite all data on this partition and replace it with the original data. After that, the partition is identical to the original state. snapshot.exe restore [HDx] {auto/primary#/logical#} imagefile [HDx]: Number of hard disk {auto/primary#/logical#}: automatically select the destination partition, or force a primary or logical partition to be restored [imagefile]: Path and name of image file AUTO - PRIMARY1 - LOGICAL5 Snapshot knows which partition is contained in the image file; option 'AUTO' will use this partition as the destination. Should you want to restore a different partition, you may select this by PRIMARY1 or LOGICAL2. Please use the SHOW command first to verify what partition you want to restore. option -V ( Verify) this will cause a verification run after the restore is completed, to verify that all data are readable and correct. You may abort the verification at any time by pressing Ctrl-C. Parameter -Y (Yes) -Y (YES) will skip the 'are you really sure' question. the command to automatically restore the C-drive from network drive W: should look similar to: A:\>snapshot.exe restore HD1 auto W:\c.drive.sna -Y -V test image file for internal consistency A:>snapshot test X:C-DRIVE.SNA this reads the complete image file, and verifies readability and consistency. This is useful, if you want to make sure, for example, that all your CDROM is readable before starting the restore. restore Master Boot Sector (MBR) This is rarely needed, but useful if some software installed a different boot loader in the MBR. It will restore the very first sector on the disk. A:>snapshot.exe restore HD1 MBR W:\c.drive.sna
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