9. The Application of Cybersecurity: Principles and Practices 247 when devices are able to access the Internet. Advanced firewall rules can be created to allow applications to only access certain computers on the network. Routers can also be configured to provide firewall-like functionality through a service called DNS filtering. DNS filtering prevents access to blacklisted websites and is enabled by pointing a router’s DNS servers to a DNS filtering service (see Section 2.4.3 for more info on DNS). When computers on the network request the IP address of a blacklisted site, the DNS server will not respond with the correct IP address. Therefore, the computer cannot initiate the connection to the website because it is unable to determine what “number to dial.” It is as-if the website does not exist. DNS filtering is a free service provided by third parties, and it is a cheap and easy way to perform content filtering on a home network. DNS filters are helpful for blocking known malicious websites and offensive content such as pornography, but they are not perfect systems. Some sites that should be blocked may not be, and determined users can find workarounds to access forbidden websites. 9.2.4.2 Secure Wireless Networks The SSID (service set identifier) of a wireless network is the network name seen by users when they scan for available wireless networks. Wireless routers come with a default SSID that typically includes the device manufacturer’s name. The default SSID should be changed to something unique, but one that does not reveal any personally identifiable or sensitive information such as an address or name. Many wireless routers allow users to create separate SSIDs for guests and this is a best practice. It creates a barrier between the wireless network that guests use and the devices in the home. Both the home and guest network need to be protected with strong passwords because wireless networks are susceptible to brute-force password guessing attacks. Depending on how many guests use the guest network and how frequently, it may be prudent to change the guest network password periodically to prevent previous guests from continuing to connect to the network without authorization. Once connected to a wireless network, users with login credentials can gain administrative access to the router using their web browser via the default gateway’s IP address. As illustrated in Figure 9.12, this IP address is readily available to anybody that is connected to the network. It used to be common for wireless routers to use a model-wide default username and password, and lists of these default credentials were widely available on the Internet. Fortunately, most wireless routers today ship with unique default administrator passwords. However, they are typically printed on the bottom of the router and could be observed by bad actors. Therefore, either way, people that connect to a wireless network may be able to determine the default password of the router and gain administrative access. Therefore, it is important to change the default administrator password to a unique strong password—definitely one that is different from the wireless network password!
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