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Some Basic Databases Of DNS Service


For example:

- Service port.

- Target specifies the FQDN for the host supporting the service.


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_ftp._tcp.somecompany.com. IN SRV 0 0 21 ftpsvr1.somecompany.com.

_ftp._tcp.somecompany.com. IN SRV 10 0 21 ftpsvr2.somecompany.com


Figure 3.56: Information about RR SRV

f)MX (Mail Exchange)

DNS uses MX records to transfer mail on the Internet. Initially, the mail transfer function was based on two records: MD (mail destination) record and MF (mail forwarder) record. MD indicates the final destination of a mail message with a specific domain name. MF indicates the intermediate server that will forward the mail to the final destination server. However, this organization did not work well. Therefore, they were integrated into one record, MX. When receiving mail, the mail transfer program (mailer) will rely on the MX record to decide the route of the mail. The MX record indicates a mail exchanger for a domain - a mail exchanger is a processing server (transferring mail to a local mailbox or acting as a gateway to another mail transfer protocol such as UUCP) or forwarding mail to another mail exchanger (intermediary) closest to itself to reach the final destination server using the SMTP (Simple Mail Transfer Protocol) protocol.

To avoid duplicate mailings, the MX record has an additional value in addition to the mail exchanger domain name, a reference sequence number. This is a 16-bit unsigned integer value (0-65535) that indicates the priority of the mail exchangers.

MX record syntax:

[domain_name] IN MX [priority] [mail-host] Example of the following MX record:

t3h.com. IN MX 10 mailserver.t3h.com.

Indicates that the server mailserver.t3h.com is a mail exchanger for the domain t3h.com with reference number 10.

Note: these values ​​are only meant to be compared with each other. Example of declaring 2 records

MX:


t3h.com. IN MX 1 listo.t3h.com. t3h.com. IN MX 2 hep.t3h.com.

The mailer will try to deliver the message to the mail exchanger with the lowest reference number first. If the message cannot be delivered, the mail exchanger with the next highest value will be chosen. In case there are multiple mail exchangers with the same reference number, the mailer will randomly choose between them.

g) PTR (Pointer)

Record PTR (pointer) is used to map IP address to Hostname.

Syntax:

[Host-ID.{Reverse_Lookup_Zone}] IN PTR [computer-name]

For example:


PTR records for hosts in the 192.249.249 network: 1.14.29.172.in-addr.arpa. IN PTR server.t3h.com.

7) Install and configure DNS service

There are many ways to install DNS service on Windows environment such as: We can install DNS when we upgrade the server to domain controllers or install DNS on stand-alone Windows 2003 Server from Networking services option in Add/Remove Program component.

a) DNS settings

When installing DNS service on Windows 2003 Server, this machine must be provided with a static IP address. Here are some of the most basic steps to install DNS service on Windows 2003 stand-alone Server.

Select Start | Control Panel | Add/Remove Programs.

Select Add or Remove Windows Components in the Windows components dialog box.

From the dialog box in step 2, select Network Services then select the Details button.

Figure 3.57: Adding network services in Windows

Select Domain Name System(DNS), then select the OK button

Figure 3.58: Add DNS service

Select Next and the system will copy the necessary files to install the service (must ensure that there is a Windows 2003 CD ROM on the local machine or that this resource can be accessed from the network).

Select the Finish button to complete the installation process.

b) DNS configuration

Select Start Programs Administrative Tools DNS

Figure 3.59: DNS console

Event Viewer: This is a DNS service log event monitor, it will store information about: alerts, warnings, errors.

Forward Lookup Zones: Contains all forward zones of the DNS service, this zone is saved on the DNS Server.

Reverse Lookup Zones: Contains all reverse zones of the DNS service, this zone is saved on the DNS Server.

Create Forward Lookup Zones:Forward Lookup Zone to resolve hostname to IP address. To create this zone, follow these steps:

Select the Start Administrative Tools DNS button.

Select the DNS server name, then right-click and select New Zone. Select Next on the Welcome to New Zone Wizard dialog box.

Select Zone Type as Primary Zone Next.

Figure 3.60: Zone Type dialog box

Select Forward Lookup Zone Next.

Specify Zone Name to declare the Zone name (Example: csc.com), select Next.

Figure 3.61: Specifying zone name

From the Zone File dialog box, create a database file for the Zone (zonename.dns) and then select Next.

Dynamic Update dialog box to specify the zone to accept Secure Update, nonsecure Update or choose not to use Dynamic Update, select Next.

Figure 3.62: Specifying Dynamic Update

Select Finish to complete.

Create Reverse Lookup Zone:After we complete the process of creating a forward Zone, we will create a reverse Lookup Zone to support the mechanism of resolving IP addresses to hostnames.

To create a Reverse Lookup Zone, follow these steps: Select Start Programs Administrative Tools DNS.

Select the name of the DNS server, Right-click and select New Zone. Select Next on the Welcome to New Zone Wizard dialog box.

Select Zone Type as Primary Zone | Next. Select Reverse Lookup Zone | Next.

Enter the network address (NetID) portion of the IP address on the Name Server | Next.

Figure 3.63: Specifying the reverse zone

Create or use a database storage file for the reverse zone, then select

Next

Figure 3.64: Specifying zone file

Dynamic Update dialog box to specify the zone to accept Secure Update, nonsecure Update or choose not to use Dynamic Update, select Next.

Select Finish to complete.

Create Resource Record(RR):After we create the forward zone and reverse zone, the system will create two resource records NS and SOA by default.

Create RR A to create RR A to map hostname to computer name, to do this we click Forward Lookup Zone, then right click on Zone name | New Host, then we provide some information about Name, Ip address, then select Add Host.

Select Create associated pointer (PTR) record to create a PTR RR in the reverse zone.

Figure 3.65: Create Resource record A

Create RR CNAME:In case we want the DNS Server to have both the name server.csc.com and the name ftp.csc.com to reflect its function as a DNS Server, FTP server, etc. To create RR Alias, we do the following:

Click Forward Lookup Zone, then Right-click on the Zone name | New Alias ​​(CNAME) (refer to Figure 1.26), then we provide some information about:

Alias ​​Name: Specify the Alias ​​name (eg ftp).

Fully qualified domain name(FQDN) for target host: specify the host name to create Alias ​​(we can enter the host name in this field or select the Browse button then select the host name).

Figure 3.66: Create RR CNAME

Check DNS service operation: After we have completed the process of creating forward zone, reverse zone and describing some necessary RRs

Figure 3.67: Some basic databases of DNS service

To check the operation of the DNS service, perform the following steps: Declare Resolver:

To specify the DNS Client's DNS Server address to support domain name resolution.

To declare Resolver, select Start | Settings | Network Connections | Select Properties of Local Area Connection | Select Properties of Internet Control (TCP/IP) then specify two parameters.

Referenced DNS server: Address of the Primary DNS Server.

Alternate DNS server: Address of the backup or second DNS server.

Figure 3.68: Declare Resolver for workstation

Checking operation: We can use the nslookup tool to check the operation of the DNS service, resolve resource records or resolve domain names. To use the nslookup tool, go to Start | Run | nslookup.

Figure 3.69: DNS check

3.2.4. WWW and FTP Server Services

1) WWW Service

a) HTTP protocol

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