DHCP discover messages are L2 broadcasts - they do not cross routers. So when client and server are on different segments, you need DHCP relay (sometimes called "DHCP helper") to forward those broadcasts as unicasts to the server. The
NAT overload - usually called PAT (Port Address Translation) - shares a SINGLE outside IP across many inside hosts by tracking the source port. Each internal connection gets a unique source port from the perspective of the outside; the router maintains the
Dynamic NAT translates inside private addresses to a POOL of outside public addresses. Each inside host gets the next available public IP from the pool. No permanent mapping; each session may get a different public IP. This lab configures dynamic
VRRP (Virtual Router Redundancy Protocol, RFC 5798) is the open-standard equivalent of HSRP. Same idea: two or more routers share a virtual IP; one is the Master, others are Backup. The differences from HSRP are minor and mostly historical.
HSRP (Hot Standby Router Protocol) is Cisco's first-hop redundancy protocol. Two routers share a virtual IP address; one is Active, one is Standby. Hosts use the virtual IP as their default gateway. If the Active router dies,
Cisco IOS XE can act as a DHCP server, handing out IP addresses to clients on a LAN. Not as feature-rich as a dedicated DHCP server (no high availability, no DDNS, simpler reservation), but more than capable for small
HSRP and VRRP have one router actively forwarding for the virtual IP while the others sit idle. GLBP (Gateway Load Balancing Protocol) is different - it can use ALL routers in the group simultaneously. One router is the Active Virtual Gateway
A specific static route to a remote loopback is the simplest possible deterministic routing test. The loopback as the ping source proves end-to-end reachability with a stable address. This lab walks through configuring static routes across R1, R2,
By default, OSPF neighbors will form an adjacency with anyone speaking the protocol on the same segment. In a production network that is a security risk - anyone with link access can inject routing updates. OSPF authentication adds a shared secret
EIGRP's signature feature is sub-second convergence on common failure modes. The secret: DUAL (Diffusing Update Algorithm) precomputes loop-free backup paths called Feasible Successors (FS). When the primary path (Successor) fails, EIGRP instantly switches to the FS
EIGRP (Enhanced Interior Gateway Routing Protocol) is Cisco's dynamic routing protocol. It uses the DUAL algorithm (Diffusing Update Algorithm) and combines distance-vector simplicity with link-state-grade convergence. Originally Cisco-only; now an open IETF informational standard
Multi-area OSPF divides a network into smaller logical zones connected through Area 0 (the backbone). Each non-backbone area connects to Area 0 through an Area Border Router (ABR), which maintains the LSA databases for both areas and summarizes