Tag: CCNP

Networking

Cisco IOS IS-IS Configuration: NET, Levels, and Backbone Routing

Working reference for IS-IS on Cisco IOS. What makes IS-IS different (runs on Layer 2 / CLNS not IP, doesn't need IP addresses to form adjacencies, carries multiple address families in one process). The NET address breakdown (AFI, area, system-id, SEL) and convention of deriving System ID from loopback. Levels: L1 intra-area, L2 backbone, L1/L2 ABR-equivalent routers, with circuit-type per-interface control. Basic configuration (net, is-type, ip router isis on interface), loopback inclusion for /32 propagation, default cost of 10 and metric-style wide for headroom, MD5 authentication. Verification (show isis neighbors / topology / database, show clns commands). IS-IS vs OSPF comparison. Pitfalls: wrong NET, circuit-type mismatch, narrow metric overflow, missing ip router isis, discontiguous L2 backbone.

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Networking

Cisco IOS Route Filtering: Distribution Lists, Prefix Lists, Route-Maps

Working reference for the three Cisco IOS route-filtering tools. Distribution lists with ACL or prefix-list reference for inbound/outbound filtering at the routing process boundary. Prefix lists with ge/le qualifiers for prefix-length range matching, common patterns (default route only, any prefix, host routes, /24-/28 of a /8). Route-maps with sequenced clauses, the implicit final deny and the explicit permit-anything-else fallthrough, the menu of match conditions (ip address, next-hop, route-source, interface, metric, tag, as-path, community) and set actions (next-hop, metric, local-preference, community, as-path prepend, tag, weight). Where route-maps plug in: BGP neighbors, redistribution, PBR. Route tags as the glue between protocols to prevent redistribution loops. Pitfalls: missing fallthrough, prefix-list ge/le defaults, OSPF flood-can't-be-filtered, redistribution loops without tags.

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Networking

Cisco IOS Path Control: PBR, IP SLA, and Offset Lists

Working reference for Cisco IOS path-control. Policy-Based Routing (PBR) with route-maps and ACLs to override the routing table for specific traffic on inbound interfaces, locally-originated PBR via ip local policy. IP SLA active measurement with icmp-echo / tcp-connect / http probes plus the schedule command. Track objects bound to IP SLA reachability or interface line-protocol, with delay debouncing to prevent flapping. Tying a static route to a track for automatic dual-WAN failover. Offset lists to add/subtract from routing protocol metrics. The combined PBR + IP SLA + floating static pattern for resilient dual-WAN. Pitfalls: PBR applied outbound, missing fallthrough, IP SLA without schedule, track delay too short, set ip next-hop without verify-availability.

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Networking

Cisco IOS Logging, SNMP, and EEM: Syslog Levels, Traps, and Automation

Working reference for Cisco IOS visibility and automation. The 8 syslog severity levels (Emergency 0 through Debug 7) and how to threshold each destination, syslog config (buffered / console / host / source-interface Loopback0 for stable identity), service timestamps log datetime msec for correlation, SNMP v2c with ACL-restricted community strings vs SNMPv3 with auth+priv security level, EEM applets for event-driven automation (syslog pattern matching, time-based cron schedules, counters), example applets for interface-down alerting and auto-saving config, and the pitfalls (console at debug, missing source-interface, community without ACL, EEM runaway loops, no timestamps).

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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.

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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).

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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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