1 Dynamic DNS

2 Module - Dynamic DNS ♦ Overview The domain names and IP addresses of hosts and the devices may change for many reasons. This module focuses on different methods of resolving such dynamic host names and IP addresses. ♦ Lessons covered in this module ► Dynamic Domain Name System (DDNS) ► Remote Name Daemon Control Utility (rndc) ► Dynamic Host Configuration Protocol (DHCP)

3 Dynamic DNS Lesson 1 - Dynamic Domain Name System (DDNS) ♦ Introduction The changes to the DNS are difficult to be made manually in the current scenario of the lnternet. DDNS updates DNS file dynamically allocating domain names to IP addresses. ♦ Topics covered in this lesson ► DDNS and DHCP ► rndc and DHCP ► Advanced BIND Features

4 Dynamic DNS Topic 1 – DDNS and DHCP ♦ DNS file requires updation when host is added to a network, host is removed from a network, host is moved from one physical network to another or the IP address of a host is changed. DDNS updates primary DNS server dynamically. Then the primary server updates the secondary servers. ♦ Network client may need the network access for a limited duration due to many reasons. For example economic reasons or frequent change of locations. DHCP assigns dynamic IP addresses to the requesting client on a lease for a predetermined amount of time.

5 Dynamic DNS Topic 2 – rndc and DHCP ♦ rndc is a BIND utility enabling secure and remote management of running name server it is called by named to verify keys corresponding to localhost. rndc can also be called by a remote BIND, or DHCP server to dynamically "update" the local server's configuration. ♦ The DHCP server has a listing of IP addresses. When the client makes a request for an IP address, the DHCP server assigns a temporary IP address on a DHCP lease. The client can then access the network from the IP address assigned to him.

6 Dynamic DNS Topic 3 - Advanced BIND Features ♦ dig is the common query tool of choice, used in BIND. It is flexible, fast, and can he used to query anything from a DNS server. It can be used for debugging and obtaining other useful information. The syntax for dig is simple. dig (server) domain name (type) ♦ nslookup is a tool for checking nameserver setup. It can be used interactively or as a single common. It can be invoked as: nslookup hostname

7 Dynamic DNS Lesson 2 – rndc (Remote Name Daemon Control Utility) ♦ Introduction rndc is a BIND utility enabling secure and remote management of name server. It uses a shared secret key method to grant privileges to particular hosts. ♦ Topics covered in this lesson ► Access Control Lists ► rndc Utility ► Use of rndc

8 Dynamic DNS Topic 1 - Access Control Lists ♦ Access Control Lists (acl) are lists of IP Addresses, Network Prefixes or named address match lists, using semi-colons to separate. A named acl is a shortcut to specify a set of machines. acl directive can create a custom named acl. ♦ These are predefined named Access control lists: ► none - No IP addresses match ► any - All IP addresses match ► localhost - Any IP address of the Name server matches ► localnets - Any network with the Name server IP addresses matches

9 Dynamic DNS Topic 2 - rndc Utility ♦ While starting the BIND daemon named, rndc utility is also started. If the key for the designated "localhost" acl is missing, or does not match, named will not start. Similarly, to stop the named daemon, rndc is called to verify this key ♦ rndc Configuration Files ► /etc/named.conf – used to specify the key and execute rndc commands ► /etc/rndc.conf – contains three statements for rndc to use the ► specified key

10 Dynamic DNS Topic 3 - Use of rndc ♦ The matching configuration of /etc/named.conf and /etc/rndc.conf and secret key prevent unauthorized users from accessing the server. An rndc command takes the following form: rndc ♦ rndc commands can do the following: ► halt — Stops the named service. ► querylog — Turns on logging of queries to this nameserver. ► refresh — Refreshes the database. ► reload —Reloads the zone files and allows to edit them. ► stats — sends current named stats to /var/named/named.stats file. ► stop — Stops the server, saving updates and IXFR data.

11 Dynamic DNS Lesson 3 - DHCP ♦ Introduction DHCP assigns dynamic IP addresses to the requesting network client on a lease for a predetermined amount of time. The DHCP server should be configured for this purpose. ♦ Topics covered in this lesson ► DHCP Overview ► DHCP Client Configuration ► DHCP Server Set Up ► Diskless Networking

12 Dynamic DNS Topic 1 - DHCP Overview ♦ DHCP can ensure that every host on the network has a valid IP address, subnet mask, broadcast address, and gateway. Each host on the subnet should be configured as a DHCP client. ♦ The DHCP server has list of IP addresses assigned by the network administrator. These are assigned to the requesting client. When the DHCP receives a request for an IP address, it responds by issuing a DHCP lease.

13 Dynamic DNS Topic 2 - DHCP Client Configuration ♦ DHCP can set the hostname in two ways: ► Automatically – Default setting. The client’s system will obtain its IP address and other network information from DHCP server. ► Manually - For this option, there must be a hostname. If the client chooses DHCP, the network configuration is set automatically. ♦ To get IP address the command is : dhclient ► Then the daemon will reconfigure etho interface by assigning an IP address and also properly configuring the subnetting.

14 Dynamic DNS Topic 3 - DHCP Server Set Up ♦ The standard DHCP configuration is: vi /etc/dhcpd.conf vi /var/lib/dhcp/dhcpd.leases ♦ Common configuration options are : ► option domain-name, option domain-name-servers, default-lease-time, max-lease-time, fixed-address, hardware ethernet ► To configure server first verify that a BROADCAST address is specified in the network configuration using ifconfig. Then create the /etc/dhcpd.conf file.

15 Dynamic DNS Topic 4 - Diskless Networking ♦ It is possible to work on devices without a local storage. With a network card, the OS itself can be downloaded via the network from a properly configured server. This is known as diskless networking. ♦ The booting client runs the code in the bootrom or boot-floppy. Then it sends a broadcast with its MAC address and the unassigned IP address into the network. The DHCP server receives this request and sends the settings back with the command bootpc. ♦ Then it contacts the server and loads the kernel via the TFTP protocol from the assigned directory. The kernel is copied into the memory. When it is executed the OS boots.

16 Dynamic DNS ♦ Configuring DHCP server to assign a range of IP addresses. Lab Exercises

17 Dynamic DNS Conclusion ♦ Summary ► DDNS allows a Web or FTP server, to give a public name to users and updates DNS. DHCP temporarily assigns IP addresses to clients. rndc enables secure and remote management of name server. ► rndc is configured in /etc/named.conf and /etc/rndc.conf files. rndc has many commands and options to override the default settings. ► When there is no OS on the system it can be run from boot, using the OS on a server. This is known as diskless networking for which the DHCP server can be configured. ♦ Question and Answer Session