Network Address Translation is one of the most fundamental technologies in networking. It allows us to modify IP addresses as packets pass through a router. 1) Static NAT One-to-one mapping between a private and public IP. Used for: devices that must always be reachable. Config (on R2): 192.168.1.10 is always translated to 200.1.1.10 (Fixed mapping).…

When we design networks, we usually expect hosts to communicate with devices in other subnets through a default gateway. Each subnet is a separate broadcast domain, and ARP is only used for local communication. But what happens if hosts are misconfigured and don’t have a proper default gateway? This is where Proxy ARP comes into…

When engineers first learn IP SLA, they often start with ICMP echo, because it is simple and useful for checking basic reachability. But in production networks, just knowing that a device is reachable is often not enough. A server may still answer ping, while the actual service users need is already broken. That is where…

In modern networks, we usually separate Layer 2 switching and Layer 3 routing clearly. However, in some legacy or special scenarios, a router may need to do both bridging and routing at the same time. This is where Integrated Routing and Bridging (IRB) comes in. Integrated Routing and Bridging (IRB) allows a Cisco router to…

When we talk about First Hop Redundancy Protocols, many engineers immediately think about HSRP or VRRP. These protocols provide gateway redundancy, but they do not natively offer load balancing across multiple active gateways in the same way as GLBP. GLBP is a Cisco proprietary protocol that allows multiple routers to share the role of forwarding…