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1.6 network services

Dec 03, 20245 min read

1.6 Explain the use and purpose of network services.

  • DHCP (Dynamic Host Configuration Protocol)

    • DHCP is a network management protocol used to dynamically assign IP addresses to devices, allowing them to communicate on the network without needing manual IP configuration.

  • Scope

    • A DHCP scope defines a range of IP addresses that can be assigned to clients on a specific subnet.

  • Exclusion Ranges

    • Exclusion ranges define specific IP addresses within a DHCP scope that should not be assigned to any client, often reserved for servers, printers, or other fixed devices.

  • Reservation

    • A reservation is a pre-defined IP address within the scope that is always assigned to a specific device, identified by its MAC address.

  • Dynamic Assignment

    • Dynamic assignment is the default DHCP mode where available IP addresses are assigned to clients as they connect to the network.

  • Static Assignment

    • Static assignment (or manual assignment) is when IP addresses are manually configured on the device itself, rather than assigned by the DHCP server.

  • Lease Time

    • The lease time specifies how long a device can use an IP address before needing to renew it. After expiration, the address may be reassigned if not renewed.

  • Scope Options

    • Scope options allow DHCP servers to send additional configuration settings (like default gateway, DNS server, etc.) to clients along with the IP address.

  • Available Leases

    • This refers to the number of IP addresses left in the DHCP scope that can still be assigned to clients.

  • DHCP Relay

    • DHCP relay enables devices on different subnets to obtain IP addresses from a central DHCP server, forwarding DHCP requests between clients and the server.

  • IP Helper/UDP Forwarding

    • IP helper addresses are configured on routers to forward DHCP requests (or other UDP broadcasts) to a remote DHCP server.

  • DNS (Domain Name System)

    • DNS is a hierarchical system that translates human-readable domain names into IP addresses, allowing users to reach websites and services by entering familiar names.

  • Record Types

    • Different types of DNS records store various pieces of information:
      • A vs. AAAA: ‘A’ records map a domain to an IPv4 address, while ‘AAAA’ records map a domain to an IPv6 address.
      • CNAME (Canonical Name): CNAME records create an alias for another domain name, pointing one domain name to another.
      • MX (Mail Exchange): MX records specify the mail servers responsible for receiving email for a domain.
      • SOA (Start of Authority): SOA records contain administrative information about a DNS zone, including the primary name server and zone serial number.
      • PTR (Pointer): PTR records map IP addresses to domain names, used in reverse DNS lookups.
      • TXT (Text): TXT records contain text information and are often used for security and verification, like SPF or DKIM records for email.
      • SRV (Service): SRV records indicate the location of specific services, often used for applications like SIP or LDAP.
      • NS (Name Server): NS records specify the authoritative DNS servers for a domain.

  • Global Hierarchy

    • The DNS system has a hierarchical structure:
      • Root DNS Servers: Root DNS servers are at the top of the DNS hierarchy and direct requests to the appropriate top-level domain (TLD) servers, like .com or .org.

  • Internal vs. External

    • Internal DNS servers resolve names within a private network, while external DNS servers provide public name resolution for domains on the internet.

  • Zone Transfers

    • Zone transfers are used to replicate DNS records from a primary DNS server to secondary servers, ensuring redundancy and consistency.

  • Authoritative Name Servers

    • Authoritative name servers provide definitive answers to DNS queries for specific domains, storing the actual DNS records for a domain.

  • Time to Live (TTL)

    • TTL defines the duration that a DNS record is cached by clients or DNS resolvers, after which a new query is required.

  • DNS Caching

    • DNS caching temporarily stores DNS query results to speed up future queries for the same domain.

  • Reverse DNS/Reverse Lookup/Forward Lookup

    • Forward lookup translates domain names to IP addresses. Reverse DNS (rDNS) does the opposite, translating IP addresses to domain names using PTR records.

  • Recursive Lookup/Iterative Lookup

    • In recursive lookups, a DNS resolver takes full responsibility for returning the answer to a DNS query, querying multiple servers if necessary. Iterative lookup involves the resolver returning a referral to another DNS server if it doesn’t have the answer, requiring the client to continue the query.

  • NTP (Network Time Protocol)

    • NTP is used to synchronize the clocks of computers and devices on a network, ensuring consistent time across the organization.
      • Stratum
        • NTP uses a hierarchical system to indicate clock accuracy. Stratum 1 is the highest accuracy level, connected directly to a time source like a GPS clock. Lower stratum levels sync with higher strata, where stratum 2 devices sync to stratum 1, and so on.
      • Clients
        • NTP clients are devices that receive time information from an NTP server to keep their clocks in sync with the network.
      • Servers
        • NTP servers provide the accurate time source to NTP clients and other servers, either synced to a primary time source (like GPS) or to another NTP server in the hierarchy.

Links to Videos and Additional reading

Professor Messer - 1.6 – Network Services

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