Question

Suppose that your department has a local DNS server for all computers in the department. You are an ordinary user (i.e., not a network/system administrator). Can you determine if an external Web site was likely accessed from a computer in your department a couple of seconds ago? Explain.

Short answer

No, as an ordinary user, you can't determine if an external site was accessed without checking the DNS cache, which requires special permissions.

Step-by-step solution

Understand DNS Servers

DNS Servers resolve domain names into IP addresses. A local DNS server caches recent DNS queries to efficiently resolve future requests from connected computers.

Observe DNS Cache Mechanism

When a computer attempts to access a web site, it sends a DNS query to the DNS server. The local DNS server checks if it has a cached record; if it doesn't, it queries an external DNS server.

Accessing the DNS Cache

As an ordinary user, you likely have restricted access to view the DNS cache directly unless you have the appropriate permissions on the system where the local DNS is running.

Consideration of Time Factor

Since the DNS cache only holds recent queries, if you had access and checked immediately, you might see the record of the DNS query if it was cached within the last few seconds.

Conclusion on Feasibility

Without administrator access to view the DNS cache, and considering the time-sensitive nature of DNS cache records, it is unlikely that you can determine if an external site was accessed.

Key concepts

DNS Cache

When you try to visit a website, your computer doesn't magically know where the site is located on the internet. It needs the help of a Domain Name System (DNS) server. A DNS cache plays a crucial role in this process. It temporarily stores (or "caches") DNS query results that translate website names, like www.example.com, into IP addresses that computers use to identify each other on the network.
Whenever your computer successfully queries a domain name, the result is stored in this DNS cache. This means that if you or someone else needs the same address again soon, your computer can skip asking a DNS server and fetch it directly from the cache—leading to faster browsing. However, this cache doesn't store results forever, and different records have varying time-to-live (TTL), meaning they expire after some time. Without explicit access to this data, ordinary users typically can't view the cache on a local DNS server.

DNS Queries

A DNS query is like a search question your computer asks when it needs to find the IP address of a domain name. There are two main types of DNS queries: recursive and iterative.

• A recursive DNS query compels the DNS server to respond with either the requested IP address or an error message, stating that the address can't be found.
• In contrast, an iterative DNS query allows the server to direct your computer elsewhere, providing only partial answers as it passes the buck to other DNS servers that might know the answer.

Each time a website is accessed, a DNS query starts this discovery process. If the local DNS server already has the answer in its cache, it will respond immediately, speeding things up considerably. But if not, it sends a query up the chain to external DNS servers. Understanding this helps us appreciate why checking recent queries may not always be possible for ordinary users without administrative privileges.

Local DNS Server

A local DNS server is like your neighborhood guide. It's one of the first stops for your computer when trying to find out where a website is located. Each department or organization typically has its own local DNS server. This server is closer to home, so it can speed up IP address lookups by storing recent DNS queries locally.

If you manage a computer network, you might configure a local DNS server to handle requests from all computers in the network, thereby reducing the number of external DNS queries and making the whole system more efficient. However, as an ordinary user, you can't directly interact with this server. Access to this local DNS cache typically requires special permissions that are usually only given to network administrators.

IP Addresses

Every device connected to the internet has a unique string of numbers known as an IP address. Think of it as a mailing address but for internet connections. Just as you need to know an address to send someone a letter, your computer needs the IP address of a website to send a query and receive data from it.

IP addresses come in two main versions: IPv4 and IPv6.

• IPv4: An older version, using a format like 192.0.2.1, which is running out of available addresses.
• IPv6: A newer format, expanding the number of possible addresses to accommodate the ever-growing number of devices, like 2001:0db8:85a3:0000:0000:8a2e:0370:7334.

Because IP addresses are difficult to remember, DNS servers translate human-friendly domain names into these numeric addresses. Understanding IPs helps emphasize the need for DNS systems to function smoothly during everyday browsing.

Network Permissions

Network permissions are like the keys to a restricted building. They allow or deny access to certain areas or functions of a computer network. Administrators set these to control who can view or change network settings.

For tasks involving DNS servers and caches, administrators typically handle permissions that manage who can directly access this information. Ordinary users generally have limited network permissions, preventing them from modifying or viewing details like DNS cache records. This is crucial to maintain network security and ensure that sensitive information, like a query history, isn't easily exposed. To view or alter DNS settings or caches, one would likely need specific administrative access.