IPv6 exists because the 32-bit IPv4 address space ran out: roughly 4.3 billion addresses was never going to…
TCP and UDP are the two transport protocols that carry almost all network traffic, and the choice between…
Two models describe how a network moves data: the seven-layer OSI model and the TCP/IP model that the…
You sit down at a brand-new router, type show ip interface brief, and every line says unassigned. Before…
Every IPv4 subnet mask, the usable host count it gives you, the wildcard mask, and the fastest way…
Carving a network into equal-size subnets wastes addresses. A point-to-point link with two routers does not need the…
Most people who struggle with the CCNA do not freeze on OSPF or VLANs. They freeze on a…
DNS turns names into addresses, so you can reach server1.lab.example.com without memorizing 10.0.0.1. A Cisco router handles names…
When the default gateway on a subnet dies, every host on it loses the path off the LAN…
Most of the time you spend on a Cisco router or switch is spent typing in the IOS…
Telnet sends your username and enable password across the wire in cleartext. SSH does not, and on a…
A factory-fresh Cisco router or switch trusts whoever reaches the console, answers to the generic name Router or…
