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

Cisco ENNA 300-445: Network Fundamentals

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

All guide sections

Network Fundamentals

Network Fundamentals

This domain tests how data moves from an application to the wire and back: OSI and TCP/IP layering, Ethernet media and framing, IPv4/IPv6 addressing and subnetting, switching logic, wireless principles, virtualization, and common topology architectures. Expect questions that ask you to choose the correct layer, media, address, or forwarding decision rather than recite definitions.

Core rules

  • Encapsulation proceeds top-down; decapsulation bottom-up. A switch forwards at Layer 2 by destination MAC; a router forwards at Layer 3 by destination IP.
  • Ethernet II frame fields: preamble/SFD, destination MAC, source MAC, EtherType, payload, FCS. Minimum frame 64 bytes; maximum standard payload 1500 bytes (MTU), so a 1500-byte IP packet becomes a 1518-byte frame before tags.
  • IPv4 private ranges: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16; loopback 127.0.0.0/8; link-local 169.254.0.0/16. IPv6: global unicast 2000::/3, unique local fc00::/7, link-local fe80::/10, multicast ff00::/8.
  • Subnetting: borrow host bits for network bits. Usable hosts = 2^h - 2 for traditional IPv4 subnets; prefix length /n has 2^(32-n) addresses.
  • Wireless: 802.11 uses CSMA/CA, not CSMA/CD; 2.4 GHz has 3 non-overlapping channels (1, 6, 11 in North America), 5 GHz has more; SSID identifies the WLAN, BSSID identifies the AP radio.
  • Virtualization: a hypervisor abstracts hardware; a virtual switch provides Layer 2 connectivity between VMs and physical NICs; overlay networks encapsulate traffic such as VXLAN.

Worked example

A host is 192.168.10.130/26. Find network, broadcast, and usable range. /26 = 255.255.255.192; block size 64. Networks: .0, .64, .128, .192. .130 falls in .128. Network 192.168.10.128, broadcast .191, usable .129-.190. This is why a /26 gives 62 usable hosts, not 64.

Traps

  • Confusing collision and broadcast domains: a switch port is one collision domain; a VLAN is one broadcast domain.
  • Forgetting that a router drops a packet when destination is on a different subnet and no route exists.
  • Mixing up MAC address table (Layer 2) and ARP table (IPv4-to-MAC).
  • Assuming all 2.4 GHz channels overlap equally; channel width changes overlap.