Given that an intranet is well managed, its networking reliability should easily exceed that of the Internet, as a whole. This is easy to understand, as there are many routers and pathways between two hosts on the Internet. Although the IP (Internet Protocol) finds alternate paths in the network if any path is broken, there are critical nodes on the Internet. If a critical node stops functioning, communication between many hosts can be broken.
Furthermore, hosts on the Internet are more prone to denial-of-service (DOS) attacks. The spreading of virsues, worms and spyware also directly impact the reliability of the Internet. Even though two hosts on the Internet may not get infected, the communication between them can still be impacted by all the extra traffic on the Internet.
However, the reliability of an intranet does depend on many factors. The most important part is the administration and maintenance of related networking equipment and resources. In the internet, there is a great deal of redundancy of routers and other networking equipment, and most are maintained by communication corporations that rely on networking for their profits. As a result, it is important for these corporations to keep their networking equipment operational.
Smaller organizations, on the other hand, often do not have the necessary resources to maintain intranetworking infrastructure. As a result, reliability is negatively impacted.