Infrastructure, Systems, and Connectivity
The iBGP full-mesh requirement, briefly mentioned earlier in this series, becomes a serious scaling problem as an autonomous system grows, requiring a number of sessions that increases quadratically with router count. This article explains exactly why full mesh does not scale, walks through how route reflectors solve this by relaxing BGP's normal route-propagation rules, and covers confederations as an alternative approach that divides a single AS into smaller sub-autonomous systems.
Traditional IP routing requires every router along a path to perform a full routing table lookup on every packet, but MPLS takes a fundamentally different approach by making that forwarding decision once and attaching a simple label that every subsequent router can use instead. This article explains the core label-switching concept, walks through how the Label Distribution Protocol builds the label forwarding tables that make this possible, and covers the practical benefits MPLS provides in real provider networks.
Connecting two sites across the public internet exposes traffic to interception unless it is properly encrypted, and IPsec provides the standard framework for building secure, authenticated tunnels between sites. This article explains the two-phase IKE negotiation process, covers the distinction between AH and ESP protocols, walks through configuring a basic site-to-site IPsec VPN, and covers essential verification commands.
The REST APIs and JSON/YAML formats covered earlier in this series represent one approach to network automation, but NETCONF and YANG provide a more structured, standards-based alternative purpose-built for network device configuration. This article explains what distinguishes NETCONF from a simple REST API, covers how YANG models define exactly what configuration data looks like, and walks through using Python to programmatically interact with network devices.
Every protocol and technology covered throughout this series is only useful if a problem involving it can actually be diagnosed and fixed efficiently under real-world pressure. This article presents a systematic troubleshooting methodology built around the OSI layers, walks through applying it to a realistic connectivity problem, and shows how the specific verification commands covered throughout this entire series fit into a structured diagnostic process.
This hands-on lab walks through assigning IPv4 addresses to router interfaces, verifying that addressing with essential show commands, and correcting a deliberately introduced configuration error. Students will practice the core interface configuration workflow every Cisco engineer uses daily.
This hands-on lab covers assigning global unicast IPv6 addresses to router interfaces, confirming the automatically generated link-local address, and verifying reachability between two routers using IPv6-specific commands.
This hands-on lab demonstrates how a router can automatically generate its own IPv6 global unicast address using stateless address autoconfiguration, based on a prefix advertised by a neighboring router, eliminating the need to manually type every address.
This hands-on lab demonstrates how a device resolves an IP address to a MAC address using ARP, and shows how Proxy ARP allows a router to answer ARP requests on behalf of a device on a different subnet, sometimes masking a missing default gateway configuration.
This hands-on lab covers connecting two routers directly via a serial cable without any intermediate WAN provider, correctly identifying and configuring the DCE and DTE ends, and verifying the resulting point-to-point link.
This hands-on lab confirms that Cisco HDLC is the default WAN encapsulation on serial interfaces, demonstrates what happens when the two ends of a link use mismatched encapsulation, and covers the verification commands used to diagnose this common WAN connectivity problem.
This hands-on lab covers replacing the default Cisco HDLC encapsulation with the open-standard PPP protocol on a serial link, verifying the LCP and NCP negotiation phases, and confirming the link functions correctly.
