GoConqr hat ein neues Design! Sag uns, wie es dir gefällt.

Kostenlos registrieren

Karteikarten

DNS

Simon Perez Informatik Englisch 28 Karten

Karten in diesem Stapel (28)

  1. 1Why do we need DNS?DNS (Domain Name Server) is mainly used to convert human meaningful name (domain name) to computer meaningful name (IP address) in Internet. This is because computers can only recognise IP addresses.
  2. 2What is reverse DNS?everse DNS (rDNS) is a method of resolving an IP address into a domain name, just as the domain name system (DNS) resolves domain names into associated IP addresses. It uses PTR records in order to retrieve the information.
    One of the applications of reverse DNS is as a spam filter.
  3. 3What is a caching DNS server?ll DNS Servers cache the results of their queries. However, some DNS Servers are put into place to provide only this caching function. The Caching-only DNS server does not contain zone information or a zone database file. The Caching DNS server only contains information based on the results of queries that it has already performed. In this case, the cache takes the place of the zone database file.
    Caching DNS servers are valuable because:
    - They do not participate in zone transfer, and therefore there is no zone transfer traffic
    - They can be placed on the far side of a slow WAN link and provide host name resolution for remote offices that do not require a high level of host name resolution support
    - They can be implemented to provide secure host name resolution when configured as Forwarders
  4. 4What is the difference between a Primary and a Secondary DNS server?A primary server hosts the controlling zone file, which contains all the authoritative information for a domain (This means that it is trusted source for important information, such as the IP address of the domain). This includes important information such as the IP address of the domain and who is responsible for the administration of that domain. Primary servers get this information directly from local files. Changes to a zone’s DNS records can only be made on a primary server, which can then update secondary servers.
    Secondary servers contain read-only copies of the zone file, and they get their info from a primary server in a communication known as a zone transfer. Each zone can only have one primary DNS server, but it can have any number of secondary DNS servers. Changes to a zone’s DNS records cannot be made on a secondary server, but in some cases a secondary server can pass along change requests to a primary server.
  5. 5What is a root name server?It's the highest instance of DNS. The administration of the Domain Name System (DNS) is structured in a hierarchy using different managed areas or “zones”, with the root zone at the very top of that hierarchy. Root servers are DNS nameservers that operate in the root zone. These servers can directly answer queries for records stored or cached within the root zone, and they can also refer other requests to the appropriate Top Level Domain (TLD) server.
  6. 6What is the purpose of DNSSEC?The purpose of DNS Security Extensions, or DNSSEC, is to authenticate DNS responses with the major goal of preventing spoofing. DNSSEC is a backward-compatible protocol extension to DNS that brings authentication and a data integrity check; so, when a DNS message is received, the receiver can verify that this message originated from the “real” DNS server (not a spoofed one) and that the message content integrity is not compromised during transmission.
    DNSSEC is designed to protect from “man in the middle” and cache poisoning attacks, whereby hackers corrupt DNS data stored on recursive servers to redirect queries to fraudulent sites and unintended addresses.
  7. 7What is a glue record and why is it needed?In normal DNS resolution, when a resolver attempts to resolve a domain name, it first queries the root, which provides the top-level domain. Next, it queries the top-level domain servers, which provide the domain’s authoritative nameservers. Finally, it queries the authoritative nameservers for the domain to resolve the domain name. If the nameservers for a domain exist inside the domain itself, a glue record is needed to resolve the domain name.
    Glue records are DNS records created at the domain’s registrar. The record provides a complete answer when the TLD nameserver returns a reference for an authoritative nameserver for a domain. For example, the domain name “example.net” has nameservers “ns1.example.net” “ns2.example.net”. To resolve the domain name, the DNS would query in order: root, TLD nameserver, and authoritative nameserver. However, by having the authoritative nameservers inside the domain itself, these nameservers cannot be found without outside assistance. This is called a ‘circular reference’. Creating a glue record, an A record served by the TLD nameserver, avoids
  8. 8Name four DNS record types and explain for what purpose they are needed.A (Host address)
    AAAA (IPv6 host address)
    ALIAS (Auto resolved alias)
    CNAME (Canonical name for an alias)
    MX (Mail eXchange)
    NS (Name Server)
    PTR (Pointer)
    SOA (Start Of Authority)
    TXT (Text information for sources outside of your domain)
  9. 9At a minimum, how many DNS requests are needed to resolve search.google.com (starting with an empty cache)?1. Try to resolve the domain with the local DNS, if it's in the cache resolve it from there
    2. Otherwise iterative query via Root-TLD-Name Server
    3. Iterative query on NS for *.com
    4. Name Server to google → ns1.google.com
    5. Query for search.google.com on ns1.google.ch
  10. 10Can a secondary server be authoritative?The term authoritative refers to any DNS servers that has a complete copy of the domain's information, whether it was entered by an administrator or transferred from a primary server. Thus, a secondary server can and should be authoritative for any domain for which it performs secondary authoritative resolution.
    Any DNS server that contains a complete copy of the domain's zone file is considered to be authoritative for that domain only. A complete copy of a zone file must have:
    - A valid Start of Authority (SOA) record
    - Valid Name Server (NS) records for the domain
    - The listed NS records should match the servers listed in the SOA record. Servers listed in the zone file, but not in the SOA record are called lame servers.
    It is considered standard practice to have a primary authoritative DNS server AND a secondary authoritative DNS server.
  11. 11How many root name servers are there?There are 13 logical root name servers specified. These named authorities are listed alphabetically, from a.root-servers.net through m.root-servers.net.
    Number 13 comes from a technical design limitation because of limitations in the original DNS specification, which used only IPv4 containing 32 bytes. The IP addresses needed to fit into a single packet, which was limited to 512 bytes at that time. So, each of the IPv4 addresses is 32 bytes, and 13 of them come to 416 bytes, leaving the remaining 96 bytes for protocol information. So 13 is a practical maximum to the number of named authorities in the delegation data for the root zone.
  12. 12What happens if a domain does not support DNSSEC?It falls back to legacy DNS, unencrypted and no signature check.
  13. 13What are two disadvantages of DNSSEC?- DNSSEC can add significant load to DNS servers
    Legacy DNS: 100bytes
    DNSSEC: 650 bytes
    - “Bootstrap problem” – a minimum level of deployment is required before ANY users receive a benefit greater than their costs.
    - DNSSEC deployment requires software on BOTH the server and client side
    - DNSSEC adds complexity to a system that is intrinsically simple.
    - Very few top-level domains support DNSSEC
  14. 14Which are the 3 types of queries?- Recursive Query
    - Iterative Query
    - Non-Recursive Query
  15. 15Explain recursive queryIn a recursive query, a DNS client provides a hostname, and the DNS Resolver “must” provide an answer—it responds with either a relevant resource record, or an error message if it can't be found. The resolver starts a recursive query process, starting from the DNS Root Server, until it finds the Authoritative Name Server (for more on Authoritative Name Servers see DNS Server Types below) that holds the IP address and other information for the requested hostname.
  16. 16Explain iterative queryIn an iterative query, a DNS client provides a hostname, and the DNS Resolver returns the best answer it can. If the DNS resolver has the relevant DNS records in its cache, it returns them. If not, it refers the DNS client to the Root Server, or another Authoritative Name Server which is nearest to the required DNS zone. The DNS client must then repeat the query directly against the DNS server it was referred to.
  17. 17Explain non-recursive queryA non-recursive query is a query in which the DNS Resolver already knows the answer. It either immediately returns a DNS record because it already stores it in local cache, or queries a DNS Name Server which is authoritative for the record, meaning it definitely holds the correct IP for that hostname. In both cases, there is no need for additional rounds of queries (like in recursive or iterative queries). Rather, a response is immediately returned to the client.
  18. 18Name the most common types of DNS server- DNS resolver
    - DNS root server
    - Authoritative DNS server
  19. 19What is a A-record?DNS host record, stores a hostname and its corresponding IPv4 address.
  20. 20What is a AAAA-record?Stores a hostname and its corresponding IPv6 address.
  21. 21What is a CNAME-record?Can be used to alias a hostname to another hostname. When a DNS client requests a record that contains a CNAME, which points to another hostname, the DNS resolution process is repeated with the new hostname.
  22. 22What is a MX-record?Specifies an SMTP email server for the domain, used to route outgoing emails to an email server.
  23. 23What is a NS-record?Specifies that a DNS Zone, such as “example.com” is delegated to a specific Authoritative Name Server, and provides the address of the name server.
  24. 24What is a PTR-record?Allows a DNS resolver to provide an IP address and receive a hostname (reverse DNS lookup).
  25. 25What is a CERT-record?Stores encryption certificates—PKIX, SPKI, PGP, and so on.
  26. 26What is a SRV-record?A service location record, like MX but for other communication protocols.
  27. 27What is a TXT-record?Typically carries machine-readable data such as opportunistic encryption, sender policy framework, DKIM, DMARC, etc.
  28. 28What is a SOA-record?This record appears at the beginning of a DNS zone file, and indicates the Authoritative Name Server for the current DNS zone, contact details for the domain administrator, domain serial number, and information on how frequently DNS information for this zone should be refreshed.

Informationen

Beschreibung
Informatik Karteikarten am DNS, erstellt von Simon Perez am 05/12/2019.
Erstellt von
Simon Perez
Aufrufe
5
Bewertung

Mehr zu DNS zones, records and configuration

Feedback

Worum geht es?

Wie gefällt dir das neue Design?

Dein Eindruck