CCNA Archives - InfoTech Ninja

Networking

Cisco IOS RIP Configuration: RIPv2, Authentication, Timers

Working reference for RIPv2 on Cisco IOS. The protocol basics (distance-vector, hop-count metric max 15, UDP 520, multicast 224.0.0.9, AD 120, 30s/180s/180s/240s timer model), why RIP is mostly retired (15-hop max, slow convergence, routing-by-rumor) and where it still fits (tiny stub networks, legacy gear). Basic configuration with the essential version 2 + no auto-summary commands, network statement (classful, no wildcard mask), passive-interface default + selective unpassive, default-information originate, MD5 authentication via key-chain, timer tuning. Loop prevention (split horizon, route poisoning, holddown), the no ip split-horizon trick on Frame Relay multipoint, RIPng per-interface enablement for IPv6. Pitfalls: forgetting version 2, no auto-summary, mismatched timers, MD5 key-id mismatch.

Networking

Cisco IOS Static and Default Routes: AD, Floating, Null0

Working reference for static routing on Cisco IOS. The three forms (recursive next-hop, interface-only for point-to-point, fully-specified for multi-access), default routes (0.0.0.0/0), administrative distance values across sources (Connected 0, Static 1, eBGP 20, EIGRP 90, OSPF 110, IS-IS 115, RIP 120, EIGRP-external 170, iBGP 200, Unknown 255), floating static routes for backup paths (AD set higher than protocol), the permanent keyword and why you usually shouldn't use it, the Null0 trick for black-holing and for keeping summary advertisements alive in BGP, ODR for hub-and-spoke. Pitfalls: ARP pressure from recursive routes on Ethernet, floating AD set too low, wrong default-route gateway, longest-prefix-match surprises.

Networking

Cisco IOS File Management & Maintenance: Backup, Archive, Rollback

Working reference for Cisco IOS file management. The running vs startup config distinction (RAM vs NVRAM) and copy run start as the most-forgotten command, backing up to TFTP / FTP / SCP including credential setup, the file system layout (flash, nvram, system, tftp:, scp:, usbflash0), running the router itself as a TFTP server, the archive feature for automatic config snapshots with path / write-memory / time-period, configure replace for non-disruptive rollback (it computes the diff vs copy which is additive only), archive log config for audit logging with hidekeys redaction, verify /md5 for IOS image integrity, and the pitfalls (TFTP file-must-exist trap, plaintext FTP creds, insufficient flash before image upgrade).

Networking

Cisco IOS Basic Configuration: Interfaces, Sub-interfaces, DHCP, CDP, and Banners

Working reference for baseline Cisco IOS configuration. The hostname / domain / no ip domain-lookup trio (the latter saves 20 seconds per typo), Layer 3 interfaces with description / ip address / no shutdown, sub-interfaces for router-on-a-stick with encapsulation dot1Q including the native keyword, loopback interfaces for management and router-id, the Null0 bit-bucket, clock rate / bandwidth on serial, full DHCP server config (excluded-address, pool, default-router, dns-server, lease) and ip helper-address for relay, CDP enable/disable per-interface, MOTD/login/exec banners, clock + NTP, disabling the HTTP server, and the baseline template every new router should start from.

Networking

Cisco IOS CLI & ROMMON: Modes, Shortcuts, and Password Recovery

Working reference for the Cisco IOS command-line. The mode hierarchy (User EXEC -> Privileged EXEC -> global config -> interface/router/line config), tab-complete and command abbreviation, the navigation shortcuts (Ctrl-A/E/W/U/R), output filtering with pipe (include / exclude / begin / section / redirect), the seven ping result codes, ROMMON access via terminal break sequence, and the standard four-step password recovery procedure (confreg 0x2142 - reset - copy startup to running - enable secret - config-register 0x2102). Pitfalls: forgetting to restore config-register, break sequence not transmitting, console baud-rate mismatches in ROMMON.

Networking

Configure EIGRP on Cisco IOS: Metrics, DUAL, Stub, and Authentication

Working reference for EIGRP on Cisco IOS. The composite metric (bandwidth + delay, with K-values), DUAL and the feasibility condition (Successor and Feasible Successor for sub-second convergence), basic configuration with no auto-summary and explicit router-id, passive-interface default + selective unpassive pattern, per-interface summarization, EIGRP stub for branch routers (bounding query scope and avoiding Stuck-In-Active), MD5 authentication via key-chain, the five verification commands, and the pitfalls (auto-summary trap, K-value mismatches, SIA, AS-number agreement).

Networking

Cisco IOS NAT and PAT: Static, Dynamic, and Overload Configuration

Working reference for the four NAT modes on Cisco IOS. The inside-local / inside-global / outside-global vocabulary that confuses everyone the first time, the ip nat inside / ip nat outside interface markings (most common cause of broken NAT), Static NAT with full IP and port-specific variants, Dynamic NAT with a public pool, PAT (overload) with the WAN interface IP and with a pool, the show ip nat translations and statistics commands, clear ip nat translation, and the pitfalls (missing markers, ACL gaps, PAT port exhaustion, NAT/IPsec interaction).

Networking

Cisco IOS Access Control Lists: Standard, Extended, Named, Reflexive, Time-Based

Working reference for the five Cisco IOS ACL types. How an ACL processes a packet (top-down, first-match-wins, implicit deny), where the order of operations relative to NAT matters (in: ACL before NAT, out: NAT before ACL), Standard vs Extended vs Named ACLs with full configuration examples, Reflexive ACLs for basic return-traffic state, Time-based ACLs with absolute and periodic schedules, application to interfaces vs VTY lines (ip access-group vs access-class), placement rules (Standard close to destination, Extended close to source), and the pitfalls (implicit deny, numbered-ACL edit gotcha, wildcard vs subnet mask, NAT-order trap, missing VTY restriction).

Networking

Configure OSPFv2 on Cisco IOS: From Single Area to Multi-Area

Working reference for OSPFv2 on Cisco IOS - the cost metric, hello/dead timers, the six LSA types, the five area types (Backbone, Normal, Stub, TSA, NSSA), router roles (ABR, ASBR, IR), basic configuration with both the network statement and ip ospf interface command, multi-area design, summarization at the ABR (area range vs summary-address), virtual links, MD5 authentication, the five verification commands, and the pitfalls (reference bandwidth mismatch, wildcard vs subnet mask, EXSTART MTU loops, implicit router-id changes).

Tag: CCNA