SysAdmin Flashcards
Microsoft IIS, Apache, nginx
A few of the most popular web servers
DNS
Domain name system
Network service that converts a webpage’s domain name into its IP address
Allows a company to host multiple servers around the world with the same domain name, or to change IP addresses without affecting customers
4 things you need to connect a network to the internet
IP address, subnet mask, gateway router, and DNS
not totally sure about this one!
5 types of DNS servers
Caching, recursive, root, TLD (top level domain), authoritative
(good diagram of how they work together in Course 2 notes p 15)
Caching name server
DNS server that simply stores known domain names for a certain amount of time
Usually provided by your ISP; most are also recursive servers
Recursive name server
DNS server that performs full DNS resolution requests
Usually provided by your ISP
Root name server
DNS server that is the first stop when your caching/recursive name server needs to find an IP address
Includes 13 authorities, and your request can go to any of them
TLD (top-level domain) name server
Top-level domain is the .com or .edu (for example) part of a domain name
Each TLD has a server, which is really a series of Anycast servers
Authoritative name server
DNS server that provides the IP address requested
This is usually a server controlled by the organization that runs the website in question
Anycast
Technique that routes traffic to different internet destinations based on location, traffic, and other factors
Allows for multiple servers, frequently spread across the globe, to function as one server
DNS time to live (TTL)
How long (in seconds) a DNS server can cache an entry; set by the owner of the domain name
Usually a few minutes to a few hours
A record
Connects a certain domain name to a certain IPv4 address
A busy domain name (ex: google.com or facebook.com) will have multiple IP addresses and an A record for each
Quad A (AAAA) record
Connects a certain domain name to a certain IPv6 address
CNAME record
canonical name record
Directs traffic from one domain name to another
ex: weather.com to www.weather.com
Fully qualified domain name (FQDN)
Includes subdomain (www), domain (palmbeachzoo), and top-level domain (.org)
DNS zones
Part of a large company served by a particular authoritative name server
Ex: a company with business centers in LA, Shanghai and Paris might have 4 authoritative servers, one for company.com, and one for each subdomain (la.company.com, etc.)
DNS zone files
Simple configuration files that list all resource records (ex: A and Quad A records) for a particular zone
DHCP
Dynamic Host Configuration Protocol
Application layer protocol that assigns IP addresses to devices in a network
Good for clients, but servers should have a fixed IP address
DHCP allocation options (dynamic, automatic, fixed)
Dynamic allocation - DNS server issues a random IP address from its range each time a device connects; most common
Auto allocation - DNS server keeps track of devices’ last IP address, and gives the same one back if possible
Fixed allocation - can be a security feature to disable dynamic/auto allocation (a device that hasn’t been assigned a fixed IP address won’t be able to connect)
NTP
Network time protocol
NTP server keeps all computers on your network synchronized
DHCP usually handles this
DHCP discovery
Process a client devices uses to “ask for” an IP address and the other info (such as gateway IP and subnet mask) it needs to connect to the network
DHCP lease
Temporary IP address assigned to a client by a DNS server
Can be good for a few days or just a short time
NAT
Network Address Translation
Technology that allows a gateway (usually a router or firewall) to rewrite the source IP of an outgoing IP datagram, and send the response back to the correct device
Allows most of a network’s computers to use non-routable IP addresses
IP masquerading
Hiding a computer’s IP address (usually through Network Address Translation)
Prevents unauthorized devices from connecting to the computer
