Tag: Routing

Networking

Cisco IOS IPv6: Addressing, Routing Protocols, and Tunneling

Working reference for IPv6 on Cisco IOS. The 128-bit address format and compression rules, the five address scopes (loopback ::1/128, link-local fe80::/10 - automatic on every interface, ULA fc00::/7, GUA 2000::/3, multicast ff00::/8), the ipv6 unicast-routing global enable, three ways to set an interface address (manual, EUI-64 derived from MAC, SLAAC), static routing with ipv6 route, the four IPv6 routing protocols (OSPFv3 with the IPv4-format router-id quirk, EIGRPv6 which stays shutdown by default, RIPng, MP-BGP with its activate-in-address-family pattern), tunneling options (manual, GRE, 6to4, ISATAP), and the differences from IPv4 (no NAT, no ARP - replaced by NDP - no broadcast, multiple addresses per interface). Pitfalls: forgetting ipv6 unicast-routing, EIGRPv6 shutdown by default, missing BGP activate, routing protocols using link-locals you don't expect.

8 min read
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Networking

Configure BGP on Cisco IOS: Peering, Path Selection, and Route Manipulation

Working reference for BGP on Cisco IOS. eBGP vs iBGP and the iBGP full-mesh problem, peering setup over physical interfaces vs loopbacks (with update-source and next-hop-self), the network statement and its requirement that the prefix be in the IP routing table, the nine-step path-selection process (Weight - Local Pref - AS-Path - Origin - MED - eBGP/iBGP - IGP cost - Router ID), the four most-used manipulations (local-pref for outbound preference, AS-Path prepend for inbound, MED for same-peer multilink, communities for ISP-coordinated traffic engineering), prefix-list filtering on all neighbors, peer groups, soft vs hard reset, and pitfalls (missing IP route, iBGP next-hop, communities not sent, outbound prefix-list omitted).

9 min read
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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).

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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).

12 min read
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