NetworkPuzzles

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…

Normally, when we think about DNS, we think about dedicated DNS servers. But Cisco IOS routers can also provide useful DNS features. In this scenario, I built a small lab to test how a router can act as: The lab contains two DNS servers and two clients. One of the clients also works as a…

In this lab, I wanted to analyze a very specific use case: How can a router connected over a PPP serial link receive its IP address dynamically from a DHCP server that is not directly attached? What makes this lab interesting is that the DHCP client is connected through a PPP serial interface, not through…