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Networking

  • dotted quad (format of IPv4 address): 4-bytes.4-bytes.4-bytes.4-bytes; 32-bits
  • host: devices on a network
  • subnet: sub-network; ISP Sub-nets to Customers; Customers sub-nets into private/home network
    • Network prefix: Class A, B, C, D; ISP owns 192.0.0.0 vs 192.168.0.0 vs 192.168.1.0
    • Subnet mask: 255.255.255.255
    • CIDR notation (substitute for long form subnet mask) 255.255.255.0/8
  • gateway: a node (router) in a computer network, a key stopping point for data on its way to or from other networks.
  • Default Gateway - bounded IP data sent to when outside network
  • routing
    • Read a routing table for where traffic will be routed
      • Destination 10.0.0.x with netmask 255.255.255.0 will talk to all devices on 10.0.0.x network
    • MAC addresses: Media Access Control/Manufacturer based ID
    • arp table associates MAC with IP
  • Hardware interface names (common)
    • eth0, wifi0 / wlan0, lo
  • DNS: www.google.com vs 8.8.8.8
    • Local hostname resolution
      • Role of /etc/hosts: a static lookup method/mapping for resolution, locally used in sys admin purposes
      • Role of /etc/resolv.conf: lists nameservers that are used by your host for DNS resolution.
  • Ports (common)
    • 22 (SSH), 80 (HTTP), 443 (HTTPS)
    • Read output of netstat with flags (-n -t -l)
  • What an IP address tells you about the network:
    • Private network prefixes:
      • 10.0.0.0/8
      • 192.168.0.0/16
      • 172.16.0.0/12
    • Local network prefixes:
      • 127.0.0.0/8
  • Router (as separate hardware):
    • NAT: Network Address Translation: Private to Public translation
    • DHCP: Dynamic Host Configuration Protocol: assigns IP addresses to hosts in a private network
  • Firewall
    • INPUT, OUTPUT, FORWARD chains
    • Can be managed at router level or host level
    • Host level management in Linux: iptables
    • Packet is blocked by first rule that matches in chain
  • Forward proxy vs VPN
  • Reverse proxies:
    • Caching
    • Load balancing (web servers): Round Robin, Weighted Round Robin, Least Connections, Least Response Time
      • Round Robin: Prioritize First In to Bottom of List, looping
      • Weighted Round Robin: Factoring in X where X can be other connections still in load balancer, etc etc
      • Least Connections: Systems who have lowest connections are priority
      • Least Response Time: Systems who have faster response time are priority
      • Monitor services?
      • Allocation strategies
      • Connection maintainence
      • Session persistence