TCP/IP protocol has many types of applications, but all of them are forms of network utilities. All of them are important in a company to use the network. The network is there to be accessed and serve users, both from inside and outside. Servers are needed to serve applications, data and other resources. These servers can run on various types of hardware, from various vendors and also various types of operating systems. This chapter will explain the methods for accessing a source and application on a distributed network.
DNS Heirarchy
Substance:
- Domain Name System (DNS)
- Fully Qualified Domain Names (FQDN)
- Generic domain
- Country Domain
- Mapping Domain Names to IP Addresses
- Mapping IP Addresses to Domain Names -- pointer query
- Domain Name Distribution
- Domain Name Resolution
- Full domain name resolver
- Domain name stub resolver
- Domain Name Server Operations
- Resource Records from Domain Name System
- Transportation
- DNS Application
- Dynamic Domain Name System (DDNS)
- Network Information System (NIS)
1. Domain Name System (DNS)
DNS is described in the protocol standard with no STD 13. And is described in RFC 1034, and RFC 1035.
In the beginning of the internet, a user could only access the internet using an IP address. So users had to memorize various IP addresses like memorizing telephone numbers. For example, to access a server, users had to know the IP address of the server, by TELNET 202.154.187.5. Then a naming system was developed so that users could simply access the internet with a unique name, for example TELNET www. Where IP 202.154.187.5 is mapped with the name www.
Because the development of the internet is very fast, the Domain Name System (DNS) system was developed. Where it is enough for a host to map a name to an IP, so that other hosts simply access the host and ask for a name and the IP address is replied to the asking host. So the asking host does not need to have the mapping database.
Naming Hierarchy
Naming a domain is formed in a hierarchical tree form. Where this makes it easier to control a domain name. Example:
small.itso.raleigh.ibm.com
Small is the name of the host, itso.raleigh.ibm.com is the lowest level domain name, and is a subdomain of raleigh.ibm.com, and is also a subdomain of ibm.com, and is also a subdomain of the com domain which is also a top-level domain. This can be seen in the image below.
Naming Hierarchy
If you want to learn more about root domains, please check here:
http://www.root-servers.org/ (Root Server Map and Technical Operations Assn)
2. Fully Qualified Domain Names (FQDN)
When using DNS, users can access a site with only a small part of a domain. For example, to access the official campus website from the campus LAN network, users simply type www. In fact, the full name of the server is www.eepis-its.edu. The name www.eepis-its.edu is an FQDN.
3. Generic domain
The three characters of the top-level domain are also called generic domains or organizational domains. The table below shows examples of Top-Level Domains.
| Nama Domain | Arti |
|-------------|------------------------------------------|
| com | Organisasi komersial (company) |
| edu | Institusi edukasi atau pendidikan |
| gov | Institusi pemerintahan |
| int | Organisasi internasional |
| mil | Militer AS |
| net | Pusat layanan jaringan |
| org | Organisasi non-profit |
| ac | Institusi pendidikan tinggi |
| sch | Institusi pendidikan dasar-menengah-atas |
| Kode-negara | 2 digit kode negara |Since the Internet originated in the United States, most top-level domains are owned by US agencies. However, currently only gov and mil are used exclusively in the US.
4. Country Domain
Each country has its own domain using 2 letter characters which are the abbreviation of the country's name. The characters used are in accordance with ISO 3166. Example: Indonesia uses the .id domain.
5. Mapping Domain Names to IP Addresses
The one that controls the name mapping is the nameserver. The nameserver is a server program that holds the master or duplicate of the name mapping database to the IP address. The function of the nameserver is to answer requests from client programs about a domain name. The name of the client program is called the name resolver.
6. Mapping IP Addresses to Domain Names - pointer query
For mapping IP addresses to domain names, it is not in a hierarchical form but in the domain format in.addr-arpa (ARPA is used because the internet started from ARPAnet).
The use of in.addr-arpa is a reverse mapping of an IP address. Example: IP with address 129.34.139.30, in the database is written as 30.139.34.129.in-addr.arpa. Then search for a matching host name. This system is called a pointer query.
7. Domain Name Distribution
Setting a domain name can be done on a local network, this is because the way DNS works uses a zones of authority system or commonly abbreviated as zones. Where with this zones system a nameserver can delegate a domain name to another nameserver connected via internetworking.
On the root nameserver, the nameserver delegates a domain to a nameserver. Example: domain eepis-its.edu, where the .edu nameserver on eduacause.net delegates the name eepis-its to a nameserver on the PENS campus network. The domain name eepis-its is delegated to the nameservers ns1.eepis-its.edu (202.154.187.2) and ns2.eepis-its.edu (202.154.187.3). And on the nameservers ns1 and ns2 the host names of the eepis-its.edu network are recorded.
8. Domain Name Resolution
The processes involved in requesting a domain name include:
- A program uses gethostbyname().
- Resolver queries a nameserver
- The nameserver checks whether there is an answer in the local database or in temporary storage (cache). If not found, the nameserver will forward to another nameserver according to the domain name hierarchy.
- The user program receives a response in the form of an IP address or an error message if an error occurs.
- The above process is called Domain Name Resolution, which is a server-client based application. The client function is performed by the resolver transparently to the user. While the server function is performed by the Nameserver. This delivery uses UDP and TCP channels.
9. Full domain name resolver
It is said to be a full resolver if DNS resolution is performed from the user program, and is queried to a nameserver from the resolver program to be processed. The full resolver system is shown in the Figure below.
Using a full resolver for domain name resolution
10. Domain name stub resolver
A program equipped with a domain name processing subroutine and can query a nameserver is called a domain name stub resolver. Where in UNIX, stub resolver is done with the gethostbyname() and gethostbyaddr() subroutines. The stub resolver can be seen in the image below.
Using stub resolver for domain name resolution
11. Domain Name Server Operations
Types of nameservers include:
- Primary Nameserver uses zones from disk and has authorization over the entire zone.
- This Secondary Nameserver has authorization over the entire zone but the zone data is taken from the primary nameserver using the zones transfer process.
- Caching-only A nameserver that does not have authorization and zone data. But only forwards queries to a nameserver that has been recorded.
12. Resource Records from Domain Name System
The DNS database is called a resource record (RR), where it begins with Start of Authority (SOA), where SOA records the name of the domain. Then there is a nameserver (NS) appointment that will answer the name of the domain.
Resource record format:
DNS Resource Record Format
Information:
- Name: Name of the domain
- TTL : Time-to-live, the length of time a name will be in the cache. The unit used is seconds, for example 86400 is 1 day.
- Class : Identifies the protocol name, for example IN (Internet system)
- Type: Identifies the type of resource record.
RR (Resource Record) Type Table
| Tipe | Nilai | Arti |
|-------|-------|----------------------------------------------------------------------------------|
| A | 1 | Alamat host |
| CNAME | 5 | Canonical Name, nama alias dari suatu host |
| HINFO | 13 | CPU dan OS yang digunakan suatu host, bersifat komentar |
| MX | 15 | Mail Exchange untuk suatu domain |
| NS | 2 | Nameserver yang memiliki authority untuk suatu domain |
| PTR | 12 | Pointer untuk nama domain |
| SOA | 6 | Start of Authority |
| WKS | 11 | Well-Known Services, memberikan spesifik dari suatu layanan di jaringan tersebut |RData: the value depends on the type, for example:
- A IP Address
- CNAME domain name
- MX 16 bit priority followed by domain name
- NS host name
- PTR domain name
13. Transportation
DNS messages are sent via UDP and TCP
- UDP: port 53, Used for zone transfer between nameservers, with a message length of 512 bytes.
- TCP : port 53, Total frame length of the message
14. DNS Application
DNS is implemented on:
- host Get IP address from a hostname or get hostname from an IP address
- nslookup Looks up information about network nodes, and examines the contents of the nameserver database.
- dig Search for more complete information about a domain name. DIG stands for Domain Internet Groper
- Bind Application nameserver
15. Dynamic Domain Name System (DDNS)
DDNS is used on clients that use the DHCP system, where the DHCP server sends a message to the nameserver to record the IP and host name. How DDNS works can be seen in the Figure below.
DDNS
Information:
- Client gets IP address from DHCP server
- The client sends the host name with the IP address to the DHCP server.
- Sending update requests during DHCP process
- Registering PTR RR IP address to hostname
16. Network Information System (NIS)
NIS is not an internet standard. NIS is used to share information in a unix environment. Information that can be shared includes /etc/passwd, /etc/group and /etc/hosts.
NIS has advantages including:
- Provides consistency of user IDs and group IDs on large networks.
- Shortens the time to manage user IDs, group IDs and NFS ownership by both users themselves and system administrators.
The NIS system consists of:
- NIS master server, Manages a map or database of user passwords
- NIS slave server, Backup from NIS master server
- NIS client system, which is served by the NIS server