I85PREP
⌘ K
Cisco ENNA 300-445 study materials
Cisco ENNA 300-445 study resources

Cisco ENNA 300-445: IP Connectivity

Cisco ENNA 300-445 · Work through your exam, one topic at a time.

All guide sections

IP Connectivity

IP Connectivity

This domain tests the forwarding plane and control plane for IPv4 and IPv6: reading the routing table, static routing, OSPFv2/v3, and first-hop redundancy. Expect route-selection and neighbor-adjacency scenarios.

Core rules

  • Routers choose the longest prefix match first, then the lowest administrative distance, then the lowest metric. Connected = 0, static = 1, eBGP = 20, EIGRP = 90, OSPF = 110, RIP = 120, iBGP = 200.
  • A static route uses ip route network mask next-hop|exit-interface [distance]. A floating static sets a distance above the dynamic protocol so it is a backup.
  • OSPF establishes neighbors through Hello packets. On Ethernet, Hello = 10 s and Dead = 40 s by default; both must match. OSPF cost = reference bandwidth / interface bandwidth, with reference default 100 Mbps. A DR/BDR is elected on multiaccess networks by highest priority, then highest router ID; there is no preemption.
  • OSPFv2 multicasts to 224.0.0.5 (all OSPF routers) and 224.0.0.6 (DR/BDR). OSPFv3 uses FF02::5 and FF02::6. Passive interfaces suppress Hellos but still advertise the connected network.
  • FHRP: HSRP uses a virtual IP and virtual MAC 0000.0c9f.fxxx; VRRP uses 0000.5e00.01xx; GLBP provides load sharing. HSRP priority (higher wins) and preemption must be configured to take over after recovery.

Worked example

A router has these routes to 10.10.10.0/24: a static route with distance 1, an OSPF route with cost 20, and an EIGRP route with metric 100. The static route is installed because AD 1 is lowest. If the static is removed, EIGRP (90) beats OSPF (110) even though OSPF cost is lower. If the static were configured with distance 130, it would be a floating static and OSPF would win.

Traps

  • Comparing OSPF cost across routes before comparing administrative distance.
  • Using a subnet mask instead of a wildcard in network statements; OSPF expects wildcard bits.
  • Expecting a DR to be replaced as soon as a new router with higher priority appears; OSPF DR election is not preemptive.
  • Forgetting that an interface can be passive and still have its network in OSPF.