Administrative Distance (AD) is the trustworthiness ranking a router assigns to a routing source, lower being preferred, used to choose between protocols offering the same prefix. ENARSI covers troubleshooting AD across all routing protocols.
Administrative Distance (AD) is the trustworthiness ranking a router assigns to a routing source, lower being preferred, used to choose between protocols offering the same prefix.
Route Redistribution injects routes learned by one routing protocol into another, requiring care with metrics, tags, and loop prevention.
A Route Map is an ordered set of match/set clauses used to filter and manipulate routes or implement policy-based routing.
Policy-Based Routing (PBR) forwards packets based on a route map's criteria rather than the destination-based routing table.
EIGRP is Cisco's advanced distance-vector protocol using DUAL for loop-free paths and composite metrics.
OSPF is a link-state IGP that builds a topology database and runs SPF, organized into areas with LSAs.
Border Gateway Protocol (BGP) is the path-vector protocol that exchanges routing and reachability between autonomous systems using attributes for best-path selection.
VRF-Lite creates multiple isolated Layer 3 routing tables on a single router without MPLS, keeping customer traffic separated.
MPLS L3VPN (MPLS Layer 3 VPN) uses VRFs, MP-BGP, and label switching to carry isolated customer routes across a provider MPLS core.
Dynamic Multipoint VPN (DMVPN) builds on-demand spoke-to-spoke IPsec tunnels using multipoint GRE and NHRP for scalable hub-and-spoke VPNs.
IPsec is the suite that authenticates and encrypts IP traffic, used for site-to-site and remote tunnels including within DMVPN.
An Infrastructure ACL is an access control list that protects the network's core devices and control plane from unwanted traffic.
Control Plane Policing (CoPP) rate-limits traffic destined to the router's control plane to protect the CPU from attacks and overload.
uRPF (Unicast Reverse Path Forwarding) drops packets whose source address fails a reverse-path check: strict mode requires the source to be reachable via the receiving interface, while loose mode only requires a route to the source via any interface.
IP SLA generates synthetic probes to measure network performance (latency, jitter, reachability) and can trigger object tracking.