AP Networking Unit 2单词卡 | Quizlet

ARP: Reply destination MAC

The requestor's MAC (unicast to you).

Front

Back

Core truth: Frames vs packets

Frames (L2) are local hop-by-hop; packets (L3) go end-to-end. First hop to Internet uses gateway's MAC.

Core truth: Presentation layer duty

OSI Layer 6 (Presentation) handles encryption, compression, and data formatting.

Core truth: Which layer adds IP? Which adds MAC+FCS?

Network (L3) adds IP addresses; Data Link (L2) adds MAC addresses and FCS.

Core truth: TCP/IP to OSI mapping (Internet, Network Access)

TCP/IP Internet ≈ OSI Network (L3); TCP/IP Network Access (Link) ≈ OSI L2/L1.

Core truth: Hex and MAC quick facts

1 hex digit = 4 bits; MAC address = 48 bits (OUI 24 + NIC 24).

Core truth: ARP request vs reply

ARP Request is broadcast; ARP Reply is unicast; replies populate the ARP cache.

Wireshark: 6-step workflow (summary)

1) Find NIC/IP/MAC 2) Start capture 3) Filter (arp or icmp) 4) ping 5) Stop 6) Inspect Ethernet II → IPv4 → ICMP.

Wireshark: display filter for ARP only

arp

Wireshark: display filter for only pings

icmp

Wireshark: display filter for a specific IP address

ip.addr == x.x.x.x (or ip.src / ip.dst)

Wireshark: display filter for a MAC address

eth.addr == aa:bb:cc:dd:ee:ff (or eth.src / eth.dst)

Wireshark: display filter for a TCP/UDP port

tcp.port == 443 (or udp.port == 53)

Wireshark: What are the three panes called?

Packet List (top), Packet Details (middle), Packet Bytes (bottom).

Wireshark: Why do Internet pings use the gateway's MAC as destination?

Frames are L2 and hop-by-hop. Your host frames to the default gateway's MAC; routers re-frame per hop.

ARP: Purpose

Map a Layer 3 IPv4 address to a Layer 2 MAC address.

ARP: Request destination MAC

ff:ff:ff:ff:ff:ff (broadcast).

ARP: Windows command to view cache

arp -a

ARP: Windows command to delete one entry

arp -d

ARP: Windows command to delete all dynamic entries

arp -d * (requires admin)

ARP cache: Why keep entries?

Avoids repeated broadcasts and speeds delivery to frequent peers.

Ethernet II: fields and sizes (in order)

Preamble+SFD (8B) | Destination MAC (6B) | Source MAC (6B) | Type (2B) | Data (46-1500B) | FCS (4B).

Ethernet II: EtherType for IPv4

0x0800

Ethernet II: EtherType for ARP

0x0806

Ethernet II: broadcast MAC address

ff:ff:ff:ff:ff:ff

Ethernet II: Which fields are often hidden in captures?

Preamble/SFD and FCS are handled by NICs and may not appear in capture.

OSI vs TCP/IP: layer correspondence

OSI L7-L5 ↔ TCP/IP Application; OSI L4 ↔ TCP/IP Transport; OSI L3 ↔ TCP/IP Internet; OSI L2/L1 ↔ TCP/IP Network Access.

Which OSI layer adds IP addresses?

Network (Layer 3).

Which OSI layer adds MAC + FCS?

Data Link (Layer 2).

Which OSI layer does reliable delivery with ACKs?

Transport (Layer 4) via TCP.

OSI mnemonic (L7→L1)

All People Seem To Need Data Processing.

Windows: show IP, MAC, gateway

ipconfig /all

Windows: ping

ping

Windows: traceroute

tracert

Windows: routing table

route print

Windows: ARP cache view

arp -a

Windows: ARP help

arp /?

Linux: show IP and MAC

ip addr (legacy: ifconfig)

Linux: show routes/default gateway

ip route (or netstat -rn)

Linux: ping

ping (Ctrl-C to stop)

Linux: traceroute

traceroute

Linux: neighbor/ARP table

ip neigh show (or arp -a)

macOS: show IP and MAC

ifconfig

macOS: routing table

netstat -rn

macOS: traceroute

traceroute

macOS: ARP table

arp -a

Hex fact: bits per hex digit

4 bits (a nibble).

Hex fact: why hex in networking

Compact shorthand for binary; maps 1:1 to nibbles; great for MACs and headers.

Binary anchors (byte weights)

128, 64, 32, 16, 8, 4, 2, 1.

Hex place values

..., 4096 (16^3), 256 (16^2), 16 (16^1), 1 (16^0).

Nibble map (hex→binary)

0=0000 1=0001 2=0010 3=0011 4=0100 5=0101 6=0110 7=0111 8=1000 9=1001 A=1010 B=1011 C=1100 D=1101 E=1110 F=1111

Convert 168₁₀ to hex and binary

0xA8; 1010 1000₂.

Convert 0x3A to decimal and binary

58₁₀; 0011 1010₂.

Hex shift trick

Shift left one hex digit = ×16; right one hex digit = ÷16.

ASCII anchors (for payload reading)

'0'=48, 'A'=65, 'a'=97.

Define: 802.11

IEEE Wi‑Fi standards at PHY/MAC layers.

Define: Access Point (AP)

Bridges wireless clients to wired LAN; manages channel/security/associations.

Define: Ad-hoc

Peer-to-peer Wi‑Fi (no AP).

Define: Bandwidth

Max theoretical capacity of a link/channel.

Define: Beamforming

AP steers RF energy toward client to improve SNR/throughput.

Define: BSSID

AP radio's MAC address (BSS identifier).

Define: Channel

Specific RF sub‑band used by Wi‑Fi (e.g., 1/6/11 in 2.4 GHz).

Define: Frequency Bands

2.4 GHz, 5 GHz, 6 GHz (Wi‑Fi 6E/7).

Define: Hotspot

Public AP offering Internet access.

Define: Interference

Unwanted RF energy degrading Wi‑Fi (microwaves, BT, neighbor APs).

Define: Latency

Delay (often measured as RTT).

Define: MAC Filtering

Allow/deny clients by MAC; weak (MACs can be spoofed).

Define: Mesh (Wi‑Fi)

APs relay/backhaul wirelessly for coverage/redundancy.

Define: MIMO

Multiple antennas/streams for higher capacity/robustness.

Define: Roaming

Client moves between APs within one ESS.

Define: Router

Layer‑3 device forwarding between IP networks/subnets.

Define: SSID

Wi‑Fi network name.

Define: Throughput

Actual measured data rate (lower than bandwidth).

Define: WEP

Legacy encryption; insecure—do not use.

Define: WPA/WPA2/WPA3

Wi‑Fi security suites; WPA3 is current best practice.

Define: Wi‑Fi

WLAN technology based on IEEE 802.11.

Define: Frame (Ethernet II)

L2 PDU: Dst MAC | Src MAC | EtherType | Payload | FCS (CRC-32).

Define: CAM (MAC Address Table)

Switch mapping MAC→port, learned from SOURCE MACs.

Define: Broadcast

One-to-all in a VLAN/broadcast domain (ff:ff:ff:ff:ff:ff).

Define: Multicast

One-to-many to a subscribed group.

Define: Unicast

One-to-one delivery.

Define: STP (Spanning Tree Protocol)

Prevents L2 loops by blocking redundant paths.

Define: VLAN

L2 segmentation: separate broadcast domains on one switch fabric.

Define: LACP

Link aggregation; bundles links for more bandwidth and redundancy.

Define: QoS

Prioritize traffic classes (voice/video) to control delay/jitter/loss.

Define: Hub

Physical-layer repeater; floods bits to all ports (legacy).

Define: Layer 2 Switch

Forwards using CAM table; no routing between subnets.

Define: Layer 3 Switch

Adds routing (e.g., inter‑VLAN routing).

Define: ACL

Per-interface rules permitting/denying traffic.

Define: PoE

Power over Ethernet to APs/phones/cameras.

Define: Port

Physical interface on a switch.

Define: Preamble

Sync pattern before frame; not shown in captures.

Define: Segmentation

Dividing a network into smaller domains (e.g., via VLANs).

Define: Topology

Physical/logical arrangement of links and nodes.

Define: PAN

Personal Area Network (very short range; e.g., Bluetooth headphones).

Define: LAN

Local Area Network (single site like home/office).

Define: CAN

Campus Area Network (multiple buildings).

Define: MAN

Metropolitan Area Network (city/metro).

Define: WAN

Wide Area Network (connects multiple LANs across distance).