1. Networking and Internet Domain Name System,
Dynamic Host Configuration protocol
Prepared by Žymantas Valacka

2. 1.7 Relations with Windows API
1. DNS & DHCP
1.1 Definition
1.2 History
1.3 Architecture
1.4 Working mechanism
1.5 Features
1.6 Pros and cons
1.7 Relations with Windows API
1.8 DNS-DHCP comparison
2. Conclusions
Contents

4. DNS
The Domain Name System (DNS) is a hierarchical decentralized naming system for computers, services or other resources connected to the Internet, or a private network. It associates various information with domain names assigned to each of the participating entities.

5. DNS history ARPANET utilized a central file HOSTS.TXT
Contains names to addresses mapping
Maintained by SRI’s NIC (Stanford-Research-Institute: Network-Information-Center)
Administrators changes to NIC
NIC updates HOSTS.TXT periodically
Administrators FTP (download) HOSTS.TXT
In 1984, Paul Mockapetris released the first version (RFCs 882 and 883, superseded by 1034 and 1035 …)

6. Main function of DNS The primary function of DNS is name resolution.
It’s an architecture that maps names to addresses so that when a user tries to access another computer on a network, it directs him there. For example, when you type in a web address, e.g.,  Internet Service Provider views the DNS associated with the domain name, translates it into a machine-friendly IP address (for example is the IP for  directs your Internet connection to the correct website.

7. DSN components
Name Space
Name Servers
Resolvers

8. Domain name space
The domain name space consists of a tree data structure . Each node or leaf in the tree has a label and zero or more resource records (RR), which hold information associated with the domain name. The domain name itself consists of the label, possibly concatenated with the name of its parent node on the right, separated by a dot.

10. Domain name
Domain names are the unique, human-readable Internet addresses of websites. They are made up of three parts: a top-level domain (sometimes called an extension or domain suffix), a domain name (or IP address), and an optional subdomain. There are several domain names available; some of them are generic such as com, edu, gov, net etc., while some country level domain names such as au, in, za, us etc.

12. Nameservers
The Domain Name System is maintained by a disributed database system, which uses the client–server model. The nodes of this database are the name servers. Each domain has at least one authoritative DNS server that publishes information about that domain and the name servers of any domains subordinate to it. The top of the hierarchy is served by the root name servers, the servers to query when looking up (resolving) a TLD.

13. Nameservers ROOT SERVER
Root Server is the top level server which consists of the entire DNS tree. It does not contain the information about domains but delegates the authority to the other server
PRIMARY SERVERS
Primary Server stores a file about its zone. It has authority to create, maintain, and update the zone file.
SECONDARY SERVER
Secondary Server transfers complete information about a zone from another server which may be primary or secondary server. The secondary server does not have authority to create or update a zone file.
Authoritative name server

14. Zones

15. Authoritative name server
An authoritative name server is a name server that only gives answers to DNS queries from data that has been configured by an original source, for example, the domain administrator or by dynamic DNS methods, in contrast to answers obtained via a query to another name server that only maintains a cache of data.
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 a special automatic updating mechanism in the DNS protocol in communication with its master to maintain an identical copy of the master records.

16. Iterative vs Recursive Name Servers
Serve two very different functions
Shouldn’t mix the two
Generally the DNS your computer points to is recursive
Zones are hosted in iterative name servers
Iterative servers can only answer information they know or have cached
Recursive know how to ask others for information

17. Resolvers
A Domain Name System (DNS) resolver, more commonly referred to as a “DNS lookup” tool, resolves an individual host name to an IP address. This type of resolve command helps to figure out how Web services are hosted, how a domain name is supported and how various hardware devices correspond to particular servers and vendors or to their client companies.

18. How does DNS work?

19. Features of DNS Global distribution Scalability Dynamicity Reliability
Loose coherency

20. Global distribution
Data is maintained locally, but retrievable globally.
No single computer has all DNS data.
DNS lookups can be performed by any device.
Remote DNS data is locally catchable to improve performance.

21. Scalability No limit to the size of the database.
One server has over names.
No limit to the number of queries.
24000 queries per second handled easily.
Queries distributed among masters, slaves and caches.

22. Dynamicity Database can be updated dynamically:
Add/delete/modify of any record
Modification of the master database triggers replication
Only master can be dynamically update:
Creates a single point of failure

23. Reliability Data is replicated:
Data from master is copied to multiple slaves
Clients can query:
Master server
Any of the copies at slave servers
Clients will typically query local caches
DNS protocols can use either UDP or TCP:
If UDP, DNS protocol handles retransmission, sequencing, etc.

24. Loose of coherency
The database is always internally consistent, each version of a subset of the database has a serial number.
The serial number is incremented on each database change.
Changes to the master copy of the database are replicated according to timing set by the zone administrator, Cached data expires according to timeout set by zone administrator.

25. Advantages of DNS
Generally DNS is the only system in the entire world that can help you browse the internet.
No need for memorizing IP addresses -DNS servers provide a nifty solution of converting domain or sub domain names to IP addresses. 
Security enhancement -DNS servers are an important component for the security of your home or work connections.
DNS servers have fast internet connections.

26. Disadvantages of DNS
One of the main disadvantages of the DNS is the fact that its registry can only be controlled ICAAN, a non-profit organisation with roots tied in one country. 
DNS queries usually don’t carry any information about the clients who initiated it.
DNS servers are based on the principle of a slave- master relationship.

27. DNS in Windows API
Domain Name System (DNS), a locator service in Microsoft Windows, is an industry-standard protocol that locates computers on an IP-based network. IP networks, such as the Internet and Windows networks, rely on number-based addresses to process data. Users however, can more easily remember name addresses, so it is necessary to translate user-friendly names (such as  into addresses that the network can recognize (such as ).

28. DNS functions in API
The DNS_QUERY_COMPLETION_ROUTINE callback is used to asynchronously return the results of a DNS query.
Syntax:
DNS_QUERY_COMPLETION_ROUTINE DnsQueryCompletionRoutine;
void DnsQueryCompletionRoutine(
PVOID pQueryContext,
PDNS_QUERY_RESULT pQueryResults )
{...}

29. Some DNS API functions DnsAcquireContextHandle DnsCancelQuery
DnsModifyRecordsInSet
DnsNameCompare
DnsQuery
DnsQueryConfig
DnsRecordCompare
DnsRecordSetCompare
DnsValidateName
DnsValidateServerStatus

30. DNS API structures DNS_ADDR DNS_ADDR_ARRAY DNS_HEADER
DNS_MESSAGE_BUFFER
DNS_PROXY_INFORMATION
DNS_QUERY_REQUEST
DNS_RECORD
DNS_RECORD_FLAGS
IP4_ARRAY
IP6_ADDRESS

31. DHCP
DHCP (Dynamic Host Configuration Protocol) is a network management protocol used to dynamically assign an Internet Protocol (IP) address to any device, or node, on a network so they can communicate using IP. DHCP automates and centrally manages these configurations rather than requiring network administrators to manually assign IP addresses to all network devices. 

32. DHCP history
DHCP was used for the first time in It was built on the Bootstrap Protocol (BOOTP) of The definition of the Dynamic Host Configuration Protocol is in RFC 2131 and can be found under the UDP port numbers 67 and 68.

33. DHCP characteristics Centralized IP address adminstration
Supports multiple servers
Provides dynamic assignment
Allows static assignment
Doesn‘t interact with domain name service(DNS)

34. DHCP entities
DHCP server: It automatically provides network information(IPaddress, subnet mask, gateway address) on lease. Once the duration is expired, that network information can be assigned to other machine.  It also maintains the data storage which stores the available IP addresses.
DHCP client: Any node which request an IP address allocation to a network is considered as DHCP client.
DHCP Relay Agent: In case, we have only one DHCP server for multiple LAN’s then this Agent which presents in every network forwards the DHCP request to DHCP server. So, using DHCP Relay Agent we can configure multiple LAN’s with single server.

35. How does DHCP work?

36. DHCP messages

37. DHCP Address Allocation Methods
Automatic allocation— the DHCP server assigns a permanent IP address to a client from its IP Pools. On the firewall, a Lease specified as Unlimited means the allocation is permanent.
Dynamic allocation—the DHCP server assigns a reusable IP address from IP Pools of addresses to a client for a maximum period of time, known as a lease. This method of address allocation is useful when the customer has a limited number of IP addresses; they can be assigned to clients who need only temporary access to the network.
Static allocation—the network administrator chooses the IP address to assign to the client and the DHCP server sends it to the client. A static DHCP allocation is permanent; it is done by configuring a DHCP server and choosing a Reserved Address to correspond to the MAC Address of the client device. The DHCP assignment remains in place even if the client logs off, reboots, has a power outage, etc.

38. DHCP advantages
DHCP is included with popular server packages: To implement DHCP requires no additional costs.
Centralized, simpler management of IP addressing: You can manage IP addressing from a central location.
DHCP also provides for the simple deployment of other configuration options, such as default gateway and DNS suffix.
Because the system assigns IP addresses, it leads to less incorrect configurations of IP addresses. Duplicated IP addresses are prevented
DHCP service supports clustering. This enables you to set up high availability DHCP servers.

39. DHCP disadvantages
The DHCP server can be a single point of failure in networking environments that only have one DHCP server.
If your network has multiple segments, you have to perform either of the following additional configurations:
Place a DHCP server on each segment
Place a DHCP relay agent on each segment
Configure routers to forward Bootstrap Protocol (BootP) broadcasts.
All incorrectly defined configuration information will automatically be propagated to your DHCP clients.

40. DHCP API
The DhcpRegisterParamChange function enables clients to register for notification of changes in DHCP configuration parameters. DWORD DhcpRegisterParamChange( IN DWORD Flags, LPVOID Reserved, LPWSTR AdapterName, IN LPDHCPCAPI_CLASSID ClassId, IN DHCPCAPI_PARAMS_ARRAY Params, IN OUT LPVOID Handle );

41. DHCP API functions
DhcpAddServer - function attempts to add a new server to the existing list of DHCP servers maintained in the domain directory service. If the specified DHCP server already exists in the directory service, an error is returned.
DhcpGetAlloptions - returns an array that contains all options defined on the DHCP server.
DhcpScanDatabase -enumerates the leased DHCPv4 client IPv4 addresses that are not synchronized between the in-memory cache and the server database.

42. Comparison of DHCP and DNS
Parameters
DHCP
DNS
Basic
A protocol for assigning IP address to the host statically or dynamically.
An address resolving mechanism.
Related protocols
UDP
UDP and TCP
Server
DHCP server is responsible for allocating the temporary addresses to the client computer for a lease time, and then extending the lease according to the requirement.
DNS server is responsible for accepting the queries through client and responding back with the results.
Working methodology
Centralized
Decentralized
Features
1. Provide additional information such as IP addresses of the host and Subnet mask of the computer. 2. Assigns IP to host for a particular lease time.
1. Coverts symbolic names into IP address and vice-versa. 2. Used for locating active directory domain servers.
Advantage
Reliable IP address configuration and reduced network administration.
Eliminate the need to remember the IP address; instead, the domain name is used for the web address.

43. Conclusions
It is true that with these dynamic addressing capabilities, Network Managers save money, time and make their networks more robust and adaptable.
DHCP has grown from a tool to simply apply IP addresses to a link-local interface to a multifaceted networking tool, invaluable for maintaining large-scale networks. 
DNS is integral part in most protocols used on the internet.
DNS is the world largest distributed database system.
DNS makes the internet human friendly for us all.

44. References https://computer.howstuffworks.com/dns.htm
system-dns-uses-features-advantages-and-disadvantages/
features-of-dns-write-so-1/
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about-dhcp-as-a-systems-administrator