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HSRP Object Tracking Interface Posted in: IP Services - HSRP Object Tracking Interface monitors the operational state of a specific interface and automatically adjusts the priority of a Hot Standby Router Protocol (HSRP) router when that interface goes down, triggering a failover to the standby router. This is useful because without it, it's possible that your router has no upstream path but remains the… ... Continue Reading
Cisco Discovery Protocol (CDP) Packet Header Posted in: CCIE Enterprise Infrastructure, Network Fundamentals - The CDP packet header is a fixed-format 4-byte structure that is used for all Cisco Discovery Protocol (CDP) messages. CDP operates at Layer 2 and is technically a frame, not a packet. In this lesson, we'll take a look at the purpose of each CDP header and how version compatibility, hop limiting, error detection, and… ... Continue Reading
HSRP BFD Peering Posted in: IP Services - HSRP BFD Peering combines Hot Standby Router Protocol (HSRP) with Bidirectional Forwarding Detection (BFD) to reduce gateway failover time. By default, HSRP detects a peer failure only after the hold timer expires, which can take up to 10 seconds by default. BFD allows sub-second detection and notifies HSRP immediately when the router on the other… ... Continue Reading
HSRP Preemption Posted in: IP Services - Hot Standby Router Protocol (HSRP) preemption allows a higher-priority router to take back the active role when it returns to the network. Without preemption, whichever router becomes active first stays active. Even if a higher-priority router comes back online later. In this lesson, we demonstrate exactly that difference. First, we run through the scenario without… ... Continue Reading
IPv6 Device Tracking Posted in: CCIE Enterprise Infrastructure, IPv6 - IPv6 ND has no built-in authentication. Any device can send Neighbor Advertisements (NA) claiming any IPv6 address. Luckily, there is something we can do about this. IPv6 Device Tracking is part of the IPv6 First Hop Security feature set and the modern name for what used to be configured with the legacy IPv6 first-hop security… ... Continue Reading