- Relate names to values (possibly with a context)
    - Context: extra data to help find a name's binding
- Naming examples
    - Filesystem: file name -> inode (context: working directory)
    - Memory management: virtual address -> physical address (context: address
      space)
    - Data storage: block number -> block; physical address -> memory cell;
      etc.
    - DNS: hostname -> IP address (context: search path)
- DNS
    - Absolute name: ends with a dot
    - Divide into components at the dot
    - Two kinds of resolvers
        - Stub resolver: forwards all queries to a single DNS server, which
          gives a result back
        - Recursive resolver: does the full lookup process
            - Each one knows ten root nameservers
            - Connect to that nameserver; if it doesn't know it'll return a
              referal (the nameserver of the next lower-level domain)
            - Connect to that nameserver & repeat
            - At the end, the nameserver for a domain will return a response
              with an IP address (or a CNAME record, etc.)
            - Generally does caching, so can short-circuit the first several
              lookups
    - CNAME record: indirect name
    - Without a final dot, will use a search path --- so looking up
      "google.com" would first look up "google.com.mit.edu.", and then try
      "google.com."
    - Applications
        - Finding a service
        - Load balancing
            - Have five servers of some content
            - When you get a lookup, the DNS server randomly picks one (or
              randomly picks the least loaded) to return first
        - CDN (Akamai)
            - Does load balancing
            - Rather than randomly picking one server, will consider where the
              DNS resolver is and pick one nearby
            - Issue: resolver will be a recursive resolver (in the ISP's data
              center, or with Google), so may have different location than the
              client machine that's trying to establish an HTTP connection
- Sample questions
    - 2012, Section III
    - 2007, Section III