Monthly Archives: September 2026

Network / Routing

IS-IS Deep Dive: The Intermediate System to Intermediate System Routing Protocol

A complete guide to IS-IS: NSAP/NET addressing, Level-1/Level-2 hierarchy, PDUs and TLVs, adjacency formation, DIS election, LSP flooding, metrics, SPF/PRC, route leaking, authentication, IPv6 and multi-topology, modern extensions (TE, Segment Routing, Flex-Algo), an IS-IS vs OSPF comparison, and working configs for Cisco IOS-XE, IOS-XR and FRRouting.

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September 27, 2026
Network / Routing

BGP for CCNP ENCOR, Part 4: The Best Path Selection Algorithm

Part 4 of the BGP series for CCNP ENCOR 350-401 v1.2: the complete 13-step best path selection algorithm with a worked tie-break at every level, the two validity gates that run before step 1, the MED comparison rule that catches everyone, hot potato routing, multipath, and four hands-on labs.

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September 21, 2026
Network / Routing

BGP for CCNP ENCOR, Part 3: Advertising Routes and Path Attributes

Part 3 of the BGP series for CCNP ENCOR 350-401 v1.2: the four ways to originate a prefix, why the network statement needs an exact mask match, the iBGP next-hop problem and next-hop-self, the four path attribute categories, and how weight, local preference, AS_PATH, origin, MED and communities differ in scope — with four hands-on labs.

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September 20, 2026
Network / Routing

BGP for CCNP ENCOR, Part 2: Neighbor Relationships and the Finite State Machine

Part 2 of the BGP series for CCNP ENCOR 350-401 v1.2: TCP 179, the six-state finite state machine, the five message types, timer negotiation, eBGP multihop versus TTL security, MD5 authentication, and a four-layer troubleshooting method with four hands-on labs.

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September 19, 2026
Network / Routing

BGP for CCNP ENCOR, Part 1: Fundamentals, Autonomous Systems, and eBGP vs iBGP

Part 1 of a four-part BGP series for CCNP ENCOR 350-401 v1.2: why BGP is a policy protocol rather than a metric protocol, autonomous systems and ASN ranges, the rules that separate eBGP from iBGP, the iBGP full-mesh and next-hop problems, BGP's three tables, and four hands-on labs with answers.

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September 18, 2026