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Find Out DNS Server IP Address Under MS-Windows

Click on Start button > Run > and Type command cmd > Press [enter] key

At DOS prompt type the command: C:\>ipconfig /all

You should DNS server IP address, and other information related to Windows networking:

OR

 You can Click on Start button > Settings > Network connections  Double click on Local Area Connection  Click on Properties button  Select Internet Protocol (TCP/IP)  Click on Properties button and Look for Preferred DNS Server:

The Domain Name System

The Domain Name System (DNS) is a hierarchical naming system built on a distributed database for computers, services, or any resource connected to the Internet or a private network.

It translates domain names meaningful to humans into the numerical identifiers associated with networking equipment for the purpose of locating and addressing these devices worldwide.

The Domain Name System assigns domain names and is independent of each entity’s physical location, e.g. Uniform Resource Locators (URLs) and e-mail addresses without having to know how the computer actually locates them.

The Domain Name System distributes the responsibility of assigning domain names and mapping those names to IP addresses by designating authoritative name servers for each domain. An authoritative name server can either be a master server or a slave server. A master server is a server that stores the original (master) copies of all zone records. A slave server uses an automatic updating mechanism of the DNS protocol in communication with its master to maintain an identical copy of the master records.

DNS resolvers (resolv.conf) The client-side of the DNS is called a DNS resolver. It is responsible for initiating and sequencing the queries that ultimately lead to a full resolution (translation) of the resource sought, e.g., translation of a domain name into an IP address.

Reverse Lookup

A reverse lookup is a query of the DNS for domain names when the IP address is known. Multiple domain names may be associated with an IP address. The DNS stores IP addresses in the form of domain names as specially formatted names in pointer (PTR) records within the infrastructure top-level domain arpa.

The Domain Name System is a distributed database of resource records (see [RFC1034]), associating many types of information (e.g. IP address, mail exchanger, etc.) with domain names. Similarly to the Unix file system, the structure of this database is a hierarchical inverted tree, with the root at the top. The whole tree is called the Domain Name Space. A domain is a subtree of the domain name space and takes the domain name of its top node. Each domain may have its own subtrees, called subdomains. Domains may also be referred to by level: a top-level (or first-level) domain is a child of the root; a second-level domain is a child of a first-level domain; and so on.

The hierarchical structure of the domain name system allows for the decentralization of its administration; in fact, an organization in charge of a domain can delegate, i.e. assign responsibility for, a subdomain to a different organization and only maintain information about the non-delegated part of the domain (called a zone).

Programs that store information about a zone are called domain name servers and are said to have authority for that zone. There are two types of name servers: primary master name servers, which read the data for the zone from a local file (called zone data file); secondary master name servers (or slaves), which get data from another name server that is authoritative for the zone (called master server) through a zone transfer; usually, but not necessarily, the master server is the zone's primary master. Having two types of name servers makes administration easier, by providing a single point of configuration, while allowing for redundancy, load sharing and responsiveness by having multiple authoritative name servers for a zone.

Forward Lookup and Reverse Lookup Forward DNS lookup is using an Internet domain name to find an IP address. Reverse DNS lookup is using an Internet IP address to find a domain name. www.sunysuffolk.edu -> (198.72.8.132) 198.72.8.132 -> www.sunysuffolk.edu

K:\>nslookup www.sunysuffolik.edu Server: ns1.bnl.gov Address: 130.199.1.1

Non-Authoritative answer: Name: www.sunysuffolk.edu Address: 198.72.8.132 Resource records Each node in the domain name space has a set of resource information (which may be empty) associated to it, composed of separate resource records (RRs). This information is contained in text form within the zone data files, while queries and zone transfers represent it in binary form. A resource record is made up of five fields: Name The domain name the resource record refers to Type The type of the resource record (see below) TTL The time to live of the RR, i.e. how long resolvers should keep it in cache before considering it outdated Class The type of network or software the record applies to; currently valid classes are Internet (IN), CHAOSnet (CH) and Hesiod (HS). We will discuss only the Internet class, which applies to all TCP/IP-based internets and is by far the most widespread RDATA The actual resource data associated with the domain name The main DNS record types are the following (see [RFC1035]): A (Address) A 32-bit host IP address AAAA (IPv6 Address) A host address in IPv6 format CNAME (Canonical Name) Specifies an alias for a domain name, i.e. a different FQDN that can be used to refer to the same host KEY The server's public key for TSIG and DNSSEC MX (Mail eXchanger) Specifies a list of mail servers to which to send mail for that domain name NS (Name Server) the authoritative name server for the domain PTR (Pointer) A pointer to another location in the domain name space; it is mostly used to associate a domain name with an IP address in the "in-addr.arpa" domain for reverse name resolution SOA (Start Of Authority) Identifies the start of a zone of authority TXT (Text) a text string containing arbitrary data (up to 255 bytes) associated with a name Zone File Format

The DNS system defines a number of Resource Records (RRs). The text representation of these records are stored in zone files.

Zone file example

Example of a “A” Record ; zone file for example.com $TTL 2d ; 172800 secs default TTL for zone $ORIGIN example.com. @ IN SOA ns1.example.com. hostmaster.example.com. ( 2003080800 ; se = serial number 12h ; ref = refresh 15m ; ret = update retry 3w ; ex = expiry 3h ; min = minimum ) IN NS ns1.example.com. IN MX 10 mail.example.net. joe IN A 192.168.254.3 www IN CNAME joe

Example of a “PTR” Record $TTL 2d ; 172800 secs $ORIGIN 23.168.192.IN-ADDR.ARPA. @ IN SOA ns1.example.com. hostmaster.example.com. ( 2003080800 ; serial number 12h ; refresh 15m ; update retry 3w ; expiry 3h ; minimum ) IN NS ns1.example.com. IN NS ns2.example.com. ; 2 below is actually an unqualified name and becomes ; 2.23.168.192.IN-ADDR.ARPA. 2 IN PTR joe.example.com. ; FDQN .... 15 IN PTR www.example.com. .... 17 IN PTR bill.example.com. .... 74 IN PTR fred.example.com. .... DHCP

Source Dest Source Dest Packet MAC addr MAC addr IP addr IP addr Description ------Client Broadcast 0.0.0.0 255.255.255.255 DHCP Discover DHCPSrvr Broadcast DHCPsrvr 255.255.255.255 DHCP Offer Client Broadcast 0.0.0.0 255.255.255.255 DHCP Request DHCPsrvr Broadcast DHCOsrvr 255.255.255.255 DHCP ACK

1. What is DHCP?

DHCP stands for "Dynamic Host Configuration Protocol".

2. What is DHCP's purpose?

DHCP's purpose is to enable individual computers on an IP network to extract their configurations from a server (the 'DHCP server') or servers

3. Can DHCP work with Appletalk or IPX?

DHCP does NOT work with Appletalk or IPX. DHCP is tied to IP.

4. How is it different than BOOTP or DHCP?

DHCP is based on BOOTP and maintains some backward compatibility. The main difference is that BOOTP was designed for manual pre-configuration of the host information in a server database, while DHCP allows for dynamic allocation of network addresses and configurations to newly attached hosts. Additionally, DHCP allows for recovery and reallocation of network addresses through a leasing mechanism.

5. What protocol and port does DHCP use?

DHCP, like BOOTP runs over UDP, utilizing ports 67 and 68.

6. What is a MAC address? (Media Access Control)

A MAC address (also called an Ethernet address or an IEEE MAC address) is a number (typically written as twelve hexadecimal digits, 0 through 9 and A through F, or as six hexadecimal numbers separated by periods or colons, i.e. 0080002012ef, 0:80:0:2:20:ef) which uniquely identifes a computer that has an Ethernet interface. Unlike the IP number, it includes no indication of where your computer is located. In DHCP's typical use, the server uses a requesting computer's MAC address to uniquely identify it.

7. What is a DHCP lease?

A DHCP lease is the amount of time that the DHCP server grants to the DHCP client permission to use a particular IP address. A typical server allows its administrator to set the lease time.

8. Can DHCP support statically defined addresses?

DHCP supports statically defined addresses.

9. How does DHCP and BOOTP handle multiple subnets?

DHCP and BOOTP handle multiple subnets. First of all, you can set up a seperate server on each subnet. Secondly, a feature of some routers known as "BOOTP forwarding" to forward DHCP or BOOTP requests to a server on another subnet and to forward the replies back to the client. The part of such a router (or server acting as a router) that does this is called a "BOOTP forwarding agent". Typically you have to enable it on the interface to the subnet to be served and have to configure it with the IP address of the DHCP or BOOTP server. On a Cisco router, the address is known as the "UDP Helper Address".

10.Can a BOOTP client boot from a DHCP server?

Only if the DHCP server is specifically written to also handle BOOTP queries.

11.Can a DHCP client boot from a BOOTP server?

Only if the DHCP client were specifically written to make use of the answer from a BOOTP server. It would presumably treat a BOOTP reply as an unending lease on the IP address.

In particular, the TCP/IP stack included with Windows 95 does not have this capability.

12.Is a DHCP server "supposed to" be able to support a BOOTP client?

The RFC on such interoperability (1534) is clear: "In summary, a DHC server:... MAY support BOOTP clients," (section 2). The word "MAY" indicates such support, however useful, is left as an option.

A source of confusion on this point is the following statement in section 1.5 of RFC 1541: "DHCP must provide service to existing BOOTP clients." However, this statement is one in a list of "general design goals for DHCP", i.e. what the designers of the DHCP protocol set as their own goals. It is not in a list of requirements for DHCP servers.

13.Is a DHCP client "supposed to" be able to use a BOOTP server?

The RFC on such interoperability (1534) is clear: "A DHCP client MAY use a reply from a BOOTP server if the configuration returned from the BOOTP server is acceptable to the DHCP client." (section 3). The word "MAY" indicates such support, however useful, is left as an option.

#dhcpd configure file to use as bootp server allow booting; allow bootp; #deny unknown-clients;

#dhcp address pool on 197.200-254 subnet 192.168.196.0 netmask 255.255.254.0 { # range 192.168.197.200 192.168.197.250; option broadcast-address 192.168.197.255; option ip-forwarding off; option subnet-mask 255.255.254.0; option ntp-servers 192.168.196.100; option domain-name "lsc.bnl.local"; option domain-name-servers 192.168.196.100; default-lease-time 86400; max-lease-time 86400; }

# x150 host xtrimm.lsc.bnl.local { filename "MICROS/vxWorks.xtrimm"; hardware ethernet 08:00:3e:26:30:c7; fixed-address 192.168.196.130; } # Example /etc/bootptab: database for bootp server (/etc/bootpd). #@(#) $Header: bootptab,v 1.2.109.1 91/11/21 11:48:22 kcs Exp $ # # Format: # nodename:tag=value:tag=value: ... :tag=value # # first field -- nodename (hostname) of terminal followed by colon # (should be full domain name) # # Blank lines and lines beginning with '#' are ignored. # Make sure you include a colon and a backslash to continue a line. # Don't put any spaces in the tag=value string. # The ht tag MUST precede the ha tag. # # The options listed below are useful for HP X Window terminals. # They are specified as tag=value and delimited by colons. # For a list of all possible options, see the bootpd.1m man page. # # ba -- broadcast bootp reply for testing with bootpquery # bf -- bootfile (for tftp download) # ds -- domain name server IP address # gw -- gateway IP address # ha -- hardware address (link level address) (hex) # hd -- home directory for bootfile (chrooted to tftp home directory) # hn -- send nodename (boolean flag, no "=value" needed) # ht -- hardware type (ether) (must precede the ha tag) # ip -- X terminal IP address # sm -- network subnet mask # tc -- template for common defaults (should be the first option listed) # vm -- vendor magic cookie selector (should be rfc1048) # T144 remote config file name (file name must be enclosed in "") # # x150 xtrimm.lsc.bnl.local:\ ba:\ ds=192.168.196.100:\ hd=/MICROS:\ hn:\ ht=ether:\ sm=255.255.254.0:\ # gw=192.168.196.254:\ bf=vxWorks.xtrimm:\ # ha=0x08003e253a44:\ ha=0x08003e2630c7:\ ip=192.168.196.130:\ vm=rfc1048

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