09 - Naming

ucla | CS 118 | 2024-11-05

Table of Contents

Overview

Protocols

  • DHCP (Dynamic Host Configuration Protocol) - to get an IP addr
    • MAC -> IP (given MAC, provision IP)
    • any node can request from multicast DHCP server -> this means DHCP mac addr and IP begins with leading 1 (multicast)
  • DNS (Domain Name Server) - map domain names to IPs
    • domain name <-> IP
    • given from DNS, hierarchical until root DNS
    • root DNS (.com, .uk, etc.)
    • Top Level Domain (TLD) e.g. google, apple, etc.
    • sub domains - r.g., docs.google.com
  • NAT (Network Address Translation) - proxy a network (multiple users) through a single IP
    • Private IP <-> Public IP
    • simpelst is 1:1 mapping
    • stored on local/private router
  • ARP (Address Resolution Protocol) - map IP to MAC addr
    • IP -> MAC (given IP, reply with MAC)
    • every router has a ARP table for translations

Names

  • Domain/Host name - user readable, variable length, hierarchical
  • IP addr - 32 bit, topologically unique, hierarchical (subnetting)
  • MAC addr - 48 bit, fixed name, globally unique

DHCP

  • DHCP (Dynamic Host Configuration Protocol) - to get an IP addr
    • DHCP request

DNS

DNS (Domain Name Server) - map domain names to IPs

  • overview
  • radix tree structure for DNS hierarchy (almost always cached after 1t request to root)
  • DNS replicated to many servers, use UDP queries for robust requests, use exponential backoff for requests to the same server
  • SD-DNS e.g., Akami server store shortest paths as SDN/CDN and propagate (similar struture to other SD-WAN)

NAT

  • NAT (Network Address Translation) - proxy a network (multiple users) through a single IP
    • NApT - Network Address and Port translation
    • PAT - port address translation
    • NAT encompasses all
  • due to IP limits and flexibility to change ISP, local networks manage a private IP space using bogons
  • bogons - IPs with prefixes that indicate private IPs e.g., 192.168…, 176.1…
  • local routers (closest to private network) store private to public IP mappings in a table
    • route packets based on mapping
  • simplest case is 1-to-1 mapping, in some clever cases map set of private IPs to smaller set of public IPs
  • in some cases map all private IPs to 1 public IP
  • example NATed network
  • NApTed example
  • NATs may be layer-violating as they may change existing protocols like FTP to support private address mappings (e.g., when IP in application data)

The trick to Many:1

  • Mapping many private addresses to 1 public addr makes it impossible to anti-alias which actual device should receive the packet
  • Hack is to use the TCP Port => 32 bit IP + 32 TCP ports = 64 bit address space
  • enables port forwarding for private IP to be directly accessible over the internet
    • other forms of NAT traversal also possible