9. DHCP relay: A feature that allows DHCP clients on different subnets to communicate with a DHCP server located on another subnet.
10. IP helper/UDP forwarding: A feature that allows the forwarding of broadcast DHCP requests from one subnet to another subnet where a DHCP server is located. This is also known as IP helper or UDP forwarding.
Explain the following in reference to DNS
DNS is a distributed database that maps domain names to IP addresses and other resources, and provides other information needed to route and deliver email and other Internet traffic. In DNS, the following are some common record types:
Record types:
1. Address (A vs. AAAA): The A record maps a domain name to an IPv4 address, while the AAAA record maps a domain name to an IPv6 address.
2. Canonical name (CNAME): A CNAME record maps an alias name to its real (canonical) name. The CNAME record is often used to map a subdomain name to a domain name, but it can also be used to map a domain name to another domain name.
3. Mail exchange (MX): An MX record maps a domain name to a list of mail servers for that domain. When a mail client wants to deliver mail to a recipient in a particular domain, it first looks up the MX record for that domain to find the mail servers for that domain.
4. Start of authority (SOA): The SOA record defines the start of a zone of authority in the DNS namespace. Every zone must have a SOA record, and it must appear at the beginning of the zone file. The SOA record specifies the name of the primary name server for the zone, the email address of the person responsible for the zone, and various time intervals and other parameters related to the zone.
5. Pointer (PTR): A PTR record maps an IP address to a domain name. PTR records are used for reverse DNS lookups, which translate IP addresses to domain names.
6. Text (TXT): A TXT record is used to associate text data with a domain name. TXT records are often used to store information such as SPF information, domain-based message authentication, reporting and conformity (DMARC) information, and other data.
7. Service (SRV): An SRV record is used to specify the host and port number of a service provided by a domain. SRV records are used to discover services such as SIP, LDAP, and XMPP servers.
8. Name server (NS): An NS record maps a domain name to the name servers that are authoritative for that domain. NS records are used to delegate subdomains to different name servers, and to specify the name servers for a top-level domain.
1. Global hierarchy
The global hierarchy of the Domain Name System (DNS) is the hierarchical structure of the domain names in the DNS and the way they are organized. It consists of multiple levels, each of which serves a specific purpose in organizing domain names.
At the top level of the hierarchy is the root domain, represented by a dot (.) symbol. The root domain does not have an IP address and serves as the starting point for all domain names in the DNS. The root domain delegates responsibility for different parts of the domain name space to top-level domains (TLDs), such as .com, .org, .net, .gov, and others.
Root DNS servers are the servers that hold the authoritative information for the root domain. There are 13 root DNS servers in operation, and they are maintained by organizations from around the world. These servers are critical to the operation of the Internet, as they provide the starting point for all DNS resolution. The root DNS servers hold the information that maps TLDs to the authoritative DNS servers responsible for each TLD.
2. Internal vs. external
An internal DNS server is one that is located within an organization's network and is used to resolve domain names for hosts within that network. An external DNS server is one that is located outside of the organization's network and is used to resolve domain names for hosts on the internet.
3. Zone transfers
A zone transfer is the process of copying the DNS data from one DNS server to another. This allows multiple DNS servers to share information about a particular domain and provide redundancy and improved performance.
4. Authoritative name servers
These are the DNS servers that are responsible for providing the actual data for a specific domain. They are the final source of information for a particular domain, and other DNS servers query them for information.
5. Time to live (TTL)
The TTL is a value in a DNS record that determines how long a DNS server should cache the record before it is discarded. A low TTL value means that the record will be discarded more frequently, while a high TTL value means that the record will be cached for a longer period of time.
6. DNS caching
DNS caching refers to the temporary storage of DNS records by a DNS server or client. This allows for faster resolution of domain names, as the cached information can be reused instead of having to be retrieved from the authoritative name server every time a request is made.
7. Reverse DNS/reverse lookup/forward lookup
A reverse DNS lookup is the process of mapping an IP address to a domain name, while a forward lookup is the process of mapping a domain name to an IP address. A reverse DNS lookup is also known as a reverse lookup.
8. Recursive lookup/iterative lookup
A recursive lookup is a type of DNS query in which the DNS server will perform all of the necessary lookups to resolve a domain name and return the final result to the client. An iterative lookup is a type of DNS query in which the DNS server returns the best information it has, but may not be the final result. The client can then make additional queries to resolve the domain name.
Explain the following with reference to NTP
Network Time Protocol (NTP) is a protocol for synchronizing the clocks of computers in a network to a common, accurate time source. The following concepts are important to understand with respect to NTP:
Stratum: The NTP hierarchy is divided into a series of levels, called strata, that are numbered from 0 to 15. Stratum 0 refers to the most accurate time sources, such as GPS or atomic clocks. Stratum 1 servers receive their time directly from these sources and pass it on to other NTP servers on the network. The higher the stratum number, the further away the server is from an accurate time source.
Clients: Clients are computers or devices that use NTP to synchronize their clocks with a time source. They send requests to NTP servers for the current time and adjust their clocks based on the response.
Servers: Servers are computers or devices that provide time information to NTP clients. They receive time information from other NTP servers and pass it on to their clients. In large networks, it is common to have multiple NTP servers to ensure high availability and reliability.
