네트워크 기초
OSI L1~L7 + 장비·토폴로지

Session 4 · Day 1 — TA가 알아야 할 네트워크 전 계층 한 권

본문 108 슬라이드 · 강의 시간 약 150분 · TA(Technical Architect) 양성 과정

강사 박수현 · 🚀 젠아이랩스(GenAI Labs)

🎨 이미지 프롬프트: "Editorial wide cinematic illustration on dark navy background — a large wooden desk overhead view; on the desk sit thick coiled Cat 6a U/FTP cables in teal jacket (with a small printed label 'Cat 6a U/FTP · 10GBASE-T · 100m · 802.3an') and a coil of OS2 SM 9/125µm yellow fiber patch cords plus an aqua OM4 MM 50/125µm duplex; a tray of pluggable optical modules glinting under warm lamplight — 'Cisco SFP-10G-SR', 'Finisar QSFP28-100G-SR4', 'Arista QSFP-DD-400G-DR4', 'OSFP-800G 2×400GBASE-DR4' — each with a tiny printed PN sticker and matching DOM label; a printed OSI 7-layer cheat sheet next to an IEEE 802.3 timeline (802.3ae 10G · 802.3by 25G · 802.3bs 200/400G · 802.3df 800G); a folded network topology blueprint showing Core / Aggregation / Access (Catalyst 9500 · 9400 · 9300-48P) and Spine-Leaf (Nexus 9336C-FX2 · Arista 7050X3) side by side with port-channel and ECMP annotations; a small toy-sized 1RU rack switch labeled 'Cisco Catalyst 9300-48P' with blinking green/amber link LEDs and a console RJ45 dongle; a 1m SFP28 Twinax DAC coiled beside an LC duplex pair; a protocol-stack notepad with a hand-drawn TCP 3-way handshake (SYN / SYN-ACK / ACK) plus a sticky note showing Switch# show ip interface brief output; soft cinematic light, teal #00b894 and purple #6c5ce7 accents, 16:9"

Session 4 · Day 1 — TA가 알아야 할 네트워크 전 계층 한 권

세션 4 — 회차 메타데이터

강의 지도 — 세션 4 본문 10개 PART

PART A

OSI 7 Layer + TCP/IP — 모든 네트워크의 공통 어휘

7개 계층의 약속이 모여 우리가 보는 모든 통신이 된다.

OSI 7 Layer — 7개 계층의 책임

암기 트릭: "All People Seem To Need Data Processing" (위→아래) — Please Do Not Touch Steve's Pet Alligator (아래→위).

OSI 7 Layer 스택 (삽화)

TCP/IP 4 Layer — 실제 구현 모델

패킷 캡슐화 (Encapsulation) — 송신 시 위→아래

디캡슐화 (Decapsulation) — 수신 시 아래→위

계층별 장비 매핑 — 어느 계층에서 일하는가

PART B

L1 물리 계층 — 케이블·광·SFP의 세계

물리 표준이 잘못되면 그 위의 모든 계층이 무너진다.

동선 표준 — Cat 5e · 6 · 6a · 7 · 8 비교

차폐 구조 — UTP · FTP · STP · S/FTP

🎨 이미지 프롬프트: "Editorial cross-section comparison illustration on dark navy background — four labeled cable cutaway panels in a 2x2 grid showing twisted-pair shielding constructions: (1) 'UTP' Cat 6 with 4 unshielded twisted copper pairs in colored insulation (blue, orange, green, brown) wrapped in a thin gray PVC jacket; (2) 'F/UTP (FTP)' Cat 6a with the same 4 pairs wrapped together by a single aluminum foil sheath and a thin drain wire, teal outer jacket; (3) 'S/UTP (STP)' showing 4 pairs encased in a braided copper shield mesh, black jacket; (4) 'S/FTP' Cat 7 — each individual twisted pair wrapped in its own aluminum foil, all four foil-wrapped pairs then enclosed by an outer braided copper shield, LSZH purple jacket. Each panel shows a clean engineering cutaway with thin callout lines labeling 'Conductor 23 AWG', 'Pair Foil', 'Overall Braid Shield', 'Drain Wire', 'Outer Jacket'. Bottom strip lists 'IEC 61156 / ISO/IEC 11801' and EMI rejection bars (UTP low → S/FTP high). Soft technical lighting, monospaced labels, teal #00b894 and purple #6c5ce7 accents, 16:9"

차폐 구조 — UTP · FTP · STP · S/FTP

광 케이블 — Single-Mode vs Multi-Mode

MM 등급 — OM1 · OM2 · OM3 · OM4 · OM5

🎨 이미지 프롬프트: "Editorial fiber-optic cross-section illustration on dark navy background — split into two large side-by-side cutaway panels. Left panel 'Single-Mode (OS2)': yellow LSZH outer jacket with a 9µm glass core / 125µm cladding cross-section magnified in an inset circle; a horizontal ray-trace shows a single laser mode traveling in a nearly straight line down the core with label '1310 / 1550 nm Laser · DFB', tagged 'Reach 10 km — 80 km+ · 100G/400G/800G long-haul'. Right panel 'Multi-Mode (OM3 / OM4 / OM5)': aqua jacket (with a lime-green OM5 stripe) showing 50µm core / 125µm cladding; ray-trace shows multiple bouncing light modes reflecting off the core-cladding boundary at varying angles ('Modal dispersion'), labeled '850 nm VCSEL', tagged 'OM3 300m · OM4 400m · OM5 550m @ 10G · DC short-reach'. Below each panel small color swatches: yellow jacket vs aqua/lime jacket. Center divider lists IEC 60793-2 / ITU-T G.652 (SM) and G.651.1 (MM). Clean technical editorial style, thin callout lines, monospaced labels, teal #00b894 and purple #6c5ce7 accents, 16:9"

광 케이블 — Single-Mode vs Multi-Mode

광 모듈 라인업 (삽화)

광 모듈 — SFP · SFP+ · SFP28 · QSFP 계열 · OSFP

광 거리 표준 — SR · LR · ER · ZR

100G/400G 표준 (IEEE 802.3) 예시

케이블 결정 매트릭스 — Cat 6a · Cat 8 · 광 SR·LR

PART C

WiFi — 802.11 표준의 진화

무선은 유선의 보조가 아니라, 사무실·캠퍼스의 1차 액세스 매체다.

802.11 진화 — a/b/g/n/ac/ax/be

주파수 대역 — 2.4 · 5 · 6 GHz 비교

채널 폭 — 20·40·80·160·320 MHz

WiFi 주파수·채널 (삽화)

WiFi 보안 — WEP · WPA · WPA2 · WPA3 + EAP

AP 배치 원칙 — 간격 · 간섭 · 채널 계획

🎨 이미지 프롬프트: "Editorial top-down office floor plan illustration on dark navy background — a wide rectangular open-plan office layout viewed from above showing desk clusters, meeting rooms, restrooms and a central corridor; 6 ceiling-mounted Wi-Fi access points (small white disc icons labeled 'AP-01' through 'AP-06') distributed evenly across the ceiling grid at roughly 12 m spacing with a thin annotation '≈ 12 m between APs'. Each AP radiates a soft circular Wi-Fi heatmap contour — bright teal core fading through cyan to dim purple at the edges, with overlapping coverage zones around the corridor; signal-strength legend at bottom-right shows '-50 dBm (strong) · -65 dBm · -75 dBm (weak)'. Channel labels above each AP follow the 2.4 GHz non-overlapping plan: 'CH 1', 'CH 6', 'CH 11', 'CH 1', 'CH 6', 'CH 11' arranged so no two adjacent APs share a channel. A small side panel notes 'Wi-Fi 6/6E · PoE++ · WPA3-Enterprise · 802.11k/v/r roaming'. Clean architectural editorial style, thin white grid lines, monospaced English labels, teal #00b894 and purple #6c5ce7 accents, 16:9"

AP 배치 원칙 — 간격 · 간섭 · 채널 계획

PART D

L2 데이터링크 — Ethernet · MAC · ARP · STP · VLAN

L2는 같은 브로드캐스트 도메인 안의 약속. 여기서 사고는 곧 폭풍이 된다.

Ethernet 프레임 구조 — 바이트 단위

┌─────────┬─────────┬─────────┬──────┬─────────────┬──────┐
│Preamble │  Dst    │  Src    │ Type │   Payload   │ FCS  │
│  + SFD  │  MAC    │  MAC    │      │ 46~1500 B   │  4B  │
│   8 B   │  6 B    │  6 B    │ 2 B  │             │      │
└─────────┴─────────┴─────────┴──────┴─────────────┴──────┘

MAC 주소 — 48bit + OUI

00:50:56:AB:CD:EF
└──────┘└──────┘
   OUI    NIC
 24bit   24bit

L2 스위치 동작 — 학습 · 플러딩 · 포워딩

충돌 도메인 vs 브로드캐스트 도메인

L2 스위치 토폴로지 — MAC Table 학습 흐름

ARP 패밀리 — ARP · RARP · GARP · Proxy ARP

ARP 동작 흐름

PC1 (10.0.0.1) → 브로드캐스트: "Who has 10.0.0.5?"
                        ↓
PC2 (10.0.0.5) → 유니캐스트 응답: "I am 10.0.0.5, MAC=BB:..."
                        ↓
PC1 ARP 캐시에 (10.0.0.5, BB:...) 저장 (TTL 약 4시간)

STP (Spanning Tree Protocol) — 802.1D · 루프 방지

STP — Port Role · State · 수렴 시간

Port Role (역할)

Port State (802.1D 기준 — 느림)

STP 토폴로지 (삽화)

LACP (Link Aggregation) — 802.3ad

VLAN — 802.1Q 태깅

일반 Ethernet 프레임:
[ Dst MAC | Src MAC | Type=0x0800(IPv4) | Payload | FCS ]

VLAN 태그가 추가된 802.1Q 프레임:
[ Dst MAC | Src MAC | Type=0x8100(VLAN) | VLAN ID(12bit) + PCP(3bit) + DEI(1bit) | Type=0x0800 | Payload | FCS ]
                                          └────────────────── 4 bytes ──────────────────┘

Cisco IOS CLI — VLAN·Trunk 실제 명령

! ── 액세스 SW: VLAN 10 (Sales) / VLAN 20 (Engineer) 생성 ──
Switch> enable
Switch# configure terminal
Switch(config)# vlan 10
Switch(config-vlan)#  name SALES
Switch(config-vlan)# exit
Switch(config)# vlan 20
Switch(config-vlan)#  name ENG
Switch(config-vlan)# exit

! ── 단말 포트 (Gi1/0/1) 를 VLAN 10 액세스 포트로 ──
Switch(config)# interface GigabitEthernet1/0/1
Switch(config-if)#  switchport mode access
Switch(config-if)#  switchport access vlan 10
Switch(config-if)#  spanning-tree portfast
Switch(config-if)#  spanning-tree bpduguard enable
Switch(config-if)# exit

! ── 업링크 (Gi1/0/24) Trunk + Native VLAN 999 ──
Switch(config)# interface GigabitEthernet1/0/24
Switch(config-if)#  switchport mode trunk
Switch(config-if)#  switchport trunk encapsulation dot1q
Switch(config-if)#  switchport trunk allowed vlan 10,20,30
Switch(config-if)#  switchport trunk native vlan 999
Switch(config-if)# end

! ── 확인 명령 ──
Switch# show vlan brief
Switch# show interface trunk
Switch# show interface GigabitEthernet1/0/1 switchport
Switch# show mac addres6-table dynamic vlan 10
Switch# write memory     ! startup-config 저장

🎨 이미지 프롬프트: "Editorial terminal screenshot mockup on dark navy background — a wide retro green-on-black CRT-style PuTTY/iTerm window with a Cisco IOS XE prompt 'Switch(config)#' visible; window shows the configuration session creating VLAN 10 (name SALES) and VLAN 20 (name ENG), then descending into 'interface GigabitEthernet1/0/1' to set 'switchport mode access / switchport access vlan 10 / spanning-tree portfast / spanning-tree bpduguard enable', then into 'interface GigabitEthernet1/0/24' to set 'switchport mode trunk / switchport trunk encapsulation dot1q / switchport trunk allowed vlan 10,20,30 / switchport trunk native vlan 999', followed by a 'Switch# show vlan brief' output table with columns 'VLAN | Name | Status | Ports' filled with realistic values ('10 SALES active Gi1/0/1-12 / 20 ENG active Gi1/0/13-23 / 999 NATIVE-BLACKHOLE active —'), and a 'Switch# show interfaces trunk' snippet below showing Port Gi1/0/24, Mode on, Encapsulation 802.1q, Status trunking, Native vlan 999, Vlans allowed 10,20,30. Soft glow on the cursor, subtle scanlines, monospaced Consolas/Menlo font, a small terminal header bar reading 'ta@bastion: ~ — SSH 22 — Catalyst 9300-48P · IOS XE 17.9.4 (Cupertino)' (no vendor logo). A side post-it labeled '☑ portfast + bpduguard, Native VLAN 999 (VLAN Hopping 방어)'. Clean editorial mockup, teal #00b894 accents around the window frame, 16:9"

Cisco IOS CLI — VLAN·Trunk 실제 명령

L2 보안 — Port Security · DHCP Snooping · DAI

PART E

L3 네트워크 — IP · CIDR · 라우팅의 세계

L3는 다른 네트워크를 잇는 약속. TA의 가장 큰 설계 결정이 여기 모인다.

IPv4 패킷 헤더 — 20 bytes

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ver|IHL|   ToS   |          Total Length                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|         Identification        |Flags|     Fragment Offset     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     TTL       |    Protocol   |          Header Checksum      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       Source IP Address                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                    Destination IP Address                     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                    Options (optional)                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

IPv4 — 클래스풀 → CIDR / VLSM

옛 클래스풀 (참고)

현재 = CIDR (Classless Inter-Domain Routing)

• 마스크를 /8 ~ /32 자유롭게 사용
• 예: 10.0.0.0/22 = 4개 /24 = 1024 IP

VLSM (Variable Length Subnet Mask)

• 같은 큰 블록 안에서 서브넷마다 다른 크기
• 효율적 IP 분배 — /24·/26·/30 혼합 가능

사설 IP + 특수 주소 — RFC 1918 외

특수 주소 예시

서브넷 계산 — 분할 · 집약

표기 변환

분할 예시

10.0.0.0/22 (1024 IP) → 4개 /24
  10.0.0.0/24
  10.0.1.0/24
  10.0.2.0/24
  10.0.3.0/24

10.0.0.0/24 → 4개 /26
  10.0.0.0/26   (0~63)
  10.0.0.64/26  (64~127)
  10.0.0.128/26 (128~191)
  10.0.0.192/26 (192~255)

라우팅 기본 — Static vs Dynamic · 라우팅 테이블

Destination  Next Hop      Interface  Metric  Protocol
10.0.0.0/24  Connected     eth0       0       Direct
10.0.1.0/24  10.0.0.254    eth0       1       Static
172.16.0.0/16 10.0.0.254   eth0       110     OSPF
0.0.0.0/0    10.0.0.254    eth0       1       Static (Default)

라우팅 프로토콜 — Distance Vector vs Link State

IGP vs EGP

Administrative Distance (Cisco 기준)

OSPF — Open Shortest Path First (RFC 2328)

OSPF Area 다이어그램 (삽화)

OSPF·BGP 콘솔 — Cisco IOS 실제 명령

! ────────── OSPF 설정 (Area 0 Backbone) ──────────
R1# configure terminal
R1(config)# router ospf 1
R1(config-router)#  router-id 1.1.1.1
R1(config-router)#  network 10.0.0.0  0.0.0.255  area 0
R1(config-router)#  network 10.0.1.0  0.0.0.255  area 0
R1(config-router)#  passive-interface default
R1(config-router)#  no passive-interface GigabitEthernet0/0
R1(config-router)#  auto-cost reference-bandwidth 100000
R1(config-router)# exit

! 확인
R1# show ip ospf neighbor
R1# show ip ospf interface brief
R1# show ip route ospf

! ────────── BGP 설정 (eBGP + iBGP) ──────────
R1(config)# router bgp 65001
R1(config-router)#  bgp router-id 1.1.1.1
R1(config-router)#  neighbor 1.1.1.2  remote-as 65002      ! eBGP (KT)
R1(config-router)#  neighbor 1.1.1.2  description "KT-Edge"
R1(config-router)#  neighbor 10.0.0.2 remote-as 65001      ! iBGP
R1(config-router)#  neighbor 10.0.0.2 update-source Loopback0
R1(config-router)#  addres6-family ipv4 unicast
R1(config-router-af)#   network 203.0.113.0 mask 255.255.255.0
R1(config-router-af)#   neighbor 1.1.1.2  route-map IN-FROM-KT in
R1(config-router-af)#   neighbor 1.1.1.2  route-map OUT-TO-KT  out
R1(config-router-af)#   maximum-paths 4                    ! ECMP
R1(config-router-af)# end

! 확인
R1# show ip bgp summary
R1# show ip bgp neighbors 1.1.1.2 advertised-routes
R1# show ip bgp 0.0.0.0/0
R1# show ip route bgp

🎨 이미지 프롬프트: "Editorial terminal mockup on dark navy background — a wide green-on-black tmux/iTerm window split vertically with a Cisco IOS XR prompt 'RP/0/RSP0/CPU0:R1(config-router)#'; LEFT pane shows OSPFv2/v3 configuration on R1 ('router ospf 1 / router-id 1.1.1.1 / network 10.0.0.0 0.0.0.255 area 0 / passive-interface default / no passive-interface GigabitEthernet0/0/0 / auto-cost reference-bandwidth 100000') with syntax-highlighted keywords; RIGHT pane shows BGP-4 + MP-BGP configuration ('router bgp 65001 / bgp router-id 1.1.1.1 / neighbor 1.1.1.2 remote-as 4766 description \"KT-EDGE\" / neighbor 10.0.0.2 remote-as 65001 update-source Loopback0 / addres6-family ipv4 unicast / network 203.0.113.0/24 / maximum-paths 4'). At the bottom a stacked output: R1# show ip ospf neighbor table with rows 'Neighbor ID Pri State Dead Time Address Interface / 2.2.2.2 1 FULL/BDR 00:00:35 10.0.0.2 Gi0/0/0', and R1# show ip bgp summary table with rows 'Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd / 1.1.1.2 4 4766 1842 1851 47 0 0 02:14:01 Established 943125 / 10.0.0.2 4 65001 412 415 47 0 0 01:08:33 Established 27'. A small bottom-right inset shows R1# show ip route bgp summary 'B* 0.0.0.0/0 [20/0] via 1.1.1.2 (eBGP)'. Subtle scanlines, monospaced font, header bar 'ta@bastion → R1 — SSH 22 — Cisco ASR 9000 · IOS XR 7.10.2' (no vendor logo). Teal #00b894 frame accents, 16:9"

OSPF·BGP 콘솔 — Cisco IOS 실제 명령

BGP — Border Gateway Protocol (RFC 4271)

BGP AS 토폴로지 (삽화)

ECMP · PBR — 경로 다중화·정책 라우팅

라우팅 결정 매트릭스 — 언제 무엇을 쓸 것인가

PART F

L4 전송 — TCP · UDP · QUIC

신뢰의 약속(TCP)과 속도의 선택(UDP), 그리고 차세대(QUIC).

TCP · UDP — 두 가지 전송 약속

TCP 3-Way Handshake — 연결 수립

TCP 3-Way Handshake — Sequence Diagram (시간 흐름)

TCP 3-Way Handshake (삽화)

TCP 4-Way Termination — 연결 종료

Sliding Window · Congestion Control

UDP — 비연결·저지연 표준

[ Src Port | Dst Port | Length | Checksum ]
   2 B       2 B        2 B      2 B

QUIC — Quick UDP Internet Connections (RFC 9000)

포트 분류 — Well-Known · Registered · Dynamic

자주 보는 포트 (Well-Known + 운영)

PART G

L5~L7 응용 프로토콜 — DNS · HTTP · TLS · 그 외

사용자가 직접 만나는 모든 서비스는 여기서 산다.

DNS — Domain Name System (RFC 1034/1035)

DHCP — Relay + Option (DORA 개요)

DHCP DORA — 시간 흐름

HTTP — 1.1 · 2 · 3 진화

HTTPS / TLS — 1.2 vs 1.3 핸드셰이크

TLS 1.2 — 2-RTT 핸드셰이크

이메일 — SMTP · POP3 · IMAP

파일 전송 — FTP · SFTP · FTPS · NFS · SMB

SSH — Secure Shell (RFC 4251)

운영 프로토콜 — SNMP · NTP · Syslog · LDAP

PART H

네트워크 장비 — Hub부터 WAF까지

계층별로 살펴본 장비들을 한 번에 정리.

L1·L2 장비 — Hub · Bridge · L2 Switch

L2 vs L3 스위치 (삽화)

L3 Switch vs Router — 언제 무엇을 쓸 것인가

보안 장비 — FW · NGFW · WAF · IPS · VPN · Anti-DDoS

LB / ADC — L4 vs L7 한 줄, 본문은 Session 5

LB = L4(5-Tuple로 IP/Port 분배) · L7(URL/Cookie/Header 분배), ADC = LB + SSL 종단 + WAF + Caching. 보안 장비(WAF·NGFW) 바로 옆 — 트래픽의 마지막 분기점이다.

PART I

토폴로지 — Star · Mesh · 3-Tier · Spine-Leaf

토폴로지는 곧 가용성·확장성·비용을 결정한다.

기본 토폴로지 — Bus · Ring · Star · Mesh · Tree · Hybrid

기본 토폴로지 6종 — 형태 비교

🎨 이미지 프롬프트: "Editorial network topology illustration on dark navy #0f1722 background showing six classic LAN topology shapes arranged in a clean 3x2 grid. Each cell contains one topology with a small English title above it: 'BUS' — a single horizontal cable with 4 nodes hanging off it; 'RING' — 5 nodes connected in a circular loop with directional arrows; 'STAR' — one central hub with 5 spoke nodes radiating outward; 'MESH' — 5 nodes all directly interconnected (full mesh); 'TREE' — a hierarchical 3-level tree with one root, 2 mid-tier, 4 leaf nodes; 'HYBRID' — a small mesh core connected to multiple star clusters. Nodes are small white circles or rounded squares, links are thin teal #00b894 or purple #6c5ce7 lines. Each cell separated by faint white grid lines. Clean editorial illustration style, monospaced English labels only, teal and purple accents, 16:9. CRITICAL: All visible text MUST be in English ONLY (no Korean characters). Each label appears EXACTLY ONCE — no duplicates. No mirrored or reversed text."

3-Tier 아키텍처 — Core · Aggregation · Access

🎯 3-Tier 사용 위상

• 현장 표준: 캠퍼스 LAN·엔터프라이즈 빌딩 (사용자 → 액세스 → 어그리게이션 → 코어)
• 트래픽 패턴: North-South 중심 (사용자 ↔ 서버·인터넷)
• 한계: 데이터센터 East-West 트래픽 폭증 → Spine-Leaf로 대체

3-Tier 아키텍처 — Tier 배치 일러스트

🎨 이미지 프롬프트: "Editorial 3-tier enterprise network architecture illustration on dark navy #0f1722 background. Three horizontal tiers stacked top-to-bottom with clean spacing. Top tier labeled 'CORE' contains 2 large rounded square nodes (Core SW 1, Core SW 2) drawn in purple #6c5ce7 with thicker borders. Middle tier labeled 'AGGREGATION' (also 'DISTRIBUTION') contains 4 medium rounded nodes (Agg SW 1~4) in teal #00b894. Bottom tier labeled 'ACCESS' contains 6 smaller nodes (Access SW with small PC and phone icons hanging below). Each Core node connects to all Aggregation nodes (full mesh between tier 1 and 2) with thin teal lines; each Aggregation node connects to 2-3 Access nodes with thinner lines. Subtle horizontal dividers separate the tiers. Small annotations on the right: 'North-South traffic dominant', 'L3 boundary at Aggregation', 'PoE / VoIP at Access'. Clean editorial illustration style, monospaced English labels only, teal #00b894 and purple #6c5ce7 accents, 16:9. CRITICAL: All visible text MUST be in English ONLY (no Korean characters). Each label appears EXACTLY ONCE — no duplicates. No mirrored or reversed text."

3-Tier 토폴로지 — Core · Aggregation · Access 연결 도식

Spine-Leaf (Clos) — 현대 데이터센터 표준

Spine-Leaf (Clos) — Full Mesh 패브릭 일러스트

🎨 이미지 프롬프트: "Editorial Spine-Leaf (Clos) data center fabric illustration on dark navy #0f1722 background. Two horizontal tiers: top row labeled 'SPINE' contains 4 large rounded square nodes (Spine 1~4) in purple #6c5ce7; bottom row labeled 'LEAF (ToR)' contains 6 rounded square nodes (Leaf 1~6) in teal #00b894 with small server rack icons hanging below each leaf. EVERY leaf is connected to EVERY spine with thin teal lines (full bipartite mesh — 4 spines × 6 leaves = 24 links visible), demonstrating ECMP. Small server icons (3 per leaf) labeled with tiny 'SRV' text show the workload layer. Annotations on the right side: 'ECMP equal-cost paths', 'East-West optimized', 'BGP unnumbered Underlay', 'VXLAN-EVPN Overlay'. Bottom-right corner: tiny comparison icon 'No STP'. Clean editorial illustration style, monospaced English labels only, teal #00b894 and purple #6c5ce7 accents, 16:9. CRITICAL: All visible text MUST be in English ONLY (no Korean characters). Each label appears EXACTLY ONCE — no duplicates. No mirrored or reversed text."

Spine-Leaf 토폴로지 — Full Mesh 연결 도식

3-Tier vs Spine-Leaf (삽화)

WAN 토폴로지 — Hub-and-Spoke · Full-Mesh · SD-WAN

🎨 이미지 프롬프트: "Editorial WAN topology comparison illustration on dark navy background — three side-by-side network diagrams in panels labeled 'Hub-and-Spoke', 'Partial Mesh', and 'Full Mesh'. Left 'Hub-and-Spoke': a central building icon 'HQ Seoul (Hub)' connected by solid teal lines to 5 surrounding nodes labeled 'Branch Busan', 'Branch Daegu', 'Branch Gwangju', 'Branch Daejeon', 'DR Site Cheonan' — every spoke routes through the hub; small tag 'MPLS L3VPN · KT/LG U+'. Middle 'Partial Mesh': same HQ + 4 branches + 1 DR site, with HQ-to-all-spokes plus selective direct links between high-traffic branches (HQ↔DR, HQ↔Busan↔Daegu) drawn with dashed purple lines, label 'DMVPN · selective direct'. Right 'Full Mesh': all 6 sites fully interconnected, every node-to-node line drawn in thin teal, with annotation 'Links = N(N-1)/2 = 15' and tag 'SD-WAN overlay · multi-carrier'. Each node rendered as a small clean isometric building icon (HQ taller, DR with a shield icon, branches small) with monospaced English labels and IP-cloud icons in the link space ('MPLS', 'Internet', 'LTE/5G'). Clean technical editorial style, thin connection lines with small bandwidth/latency tags, teal #00b894 and purple #6c5ce7 accents, 16:9"

WAN 토폴로지 — Hub-and-Spoke · Full-Mesh · SD-WAN

토폴로지 비교 매트릭스 — 장단점·비용·확장성

Out-of-Band (OOB) 관리 — 별도 NW로 장비 관리

PART J

TA의 네트워크 결정 · 산출물 · 정리

7계층·100+ 프로토콜·수십 가지 장비를 결정의 언어로 옮긴다.

데이터센터 NW 구성도 (삽화)

TA가 네트워크 설계에서 결정해야 할 10가지

TA의 네트워크 산출물 — 6종 표준

추가 보조 산출물

• 방화벽 정책표 — Src/Dst/Port/Action/Justification
• 케이블 라벨링 표준 — 양 끝 라벨·도면 ID
• 점검 체크리스트 — 일/주/월/분기
• 변경관리 (CR) — 변경 영향·롤백 절차

결정 의사결정 트리 — 케이블·라우팅·토폴로지

거리 < 5m, 25G+
  → DAC (저렴·저전력)
거리 < 30m, 25/40G
  → Cat 8 또는 SFP28 DAC
거리 < 100m, 1G/10G
  → Cat 6a
거리 100m~500m, 10/40/100G
  → MM (OM4) + SR
거리 > 500m, 100G+
  → SM + LR
거리 > 10km
  → SM + ER/ZR 또는 통신사 회선

지점 1~3개·변경 없음
  → Static
단일 캠퍼스·동일 벤더
  → OSPF Single Area
다중 캠퍼스
  → OSPF Multi-Area
Cisco 단일·중소
  → EIGRP (선택)
인터넷 연결·멀티 ISP
  → BGP (필수)
DC 내부 Spine-Leaf
  → BGP (RFC 7938)
ISP·캐리어 백본
  → IS-IS

Linux 네트워크 CLI — ip · ss · tcpdump · dig

# ────────── ip 명령 (iproute2 — net-tools 대체) ──────────
$ ip -br addr                                # 인터페이스 + IP 요약
$ ip addr add 10.0.0.10/24 dev eth0          # IP 추가
$ ip link set eth0 mtu 9000                  # Jumbo MTU
$ ip link set eth0 up                        # 인터페이스 UP
$ ip route                                   # 라우팅 테이블
$ ip route add 192.168.1.0/24 via 10.0.0.1   # Static Route 추가
$ ip route add default via 10.0.0.254
$ ip neigh                                   # ARP 테이블 (ip neighbour)
$ ip -s link show eth0                       # 인터페이스 통계

# ────────── ss — netstat 대체 ──────────
$ ss -tnp        # TCP LISTEN+ESTABLISHED + 프로세스
$ ss -tan state established
$ ss -s          # 요약 (TCP/UDP/Total)

# ────────── tcpdump — 패킷 캡처 ──────────
$ sudo tcpdump -i eth0 -nn  host 10.0.0.5 and port 443
$ sudo tcpdump -i any -nn   'tcp[tcpflags] & (tcp-syn|tcp-rst) != 0'
$ sudo tcpdump -i eth0 -w /tmp/capture.pcap  port 53
$ sudo tcpdump -r /tmp/capture.pcap -nn -A | less

# ────────── DNS·TLS·HTTP 디버그 ──────────
$ dig +short A   www.example.com  @8.8.8.8
$ dig +trace     www.example.com           # 루트→TLD→권한 추적
$ openssl s_client -connect example.com:443 -servername example.com </dev/null
$ curl -v -o /dev/null  https://example.com
$ mtr -rwbzc 100  8.8.8.8                  # ping + traceroute + 통계

🎨 이미지 프롬프트: "Editorial Linux terminal mockup on dark navy background — a wide tmux-style terminal split into 4 panes on a RHEL 9.4 / Ubuntu 24.04 LTS host; TOP-LEFT pane runs [root@ta-jump01 ~]# ip -br addr showing rows 'lo UNKNOWN 127.0.0.1/8 ::1/128 / eth0 UP 10.0.0.10/24 fe80::250:56ff:feaa:bb01/64 / eth1 UP 10.255.0.10/24 (OOB) / bond0 UP 10.0.100.10/24 (mode=802.3ad)' followed by # ip link set eth0 mtu 9000 and # ip -s link show eth0 with RX/TX byte counters and 0 errors/drops; TOP-RIGHT pane runs [root@ta-jump01 ~]# ip route showing 'default via 10.0.0.254 dev eth0 proto static metric 100 / 10.0.0.0/24 dev eth0 proto kernel scope link src 10.0.0.10 / 10.0.1.0/24 via 10.0.0.254 dev eth0 proto ospf metric 110 / 192.168.1.0/24 via 10.0.0.254 dev eth0 proto static' and below # ss -tnlp showing 'LISTEN 0 128 0.0.0.0:22 sshd / LISTEN 0 511 :443 nginx / ESTAB 0 0 10.0.0.10:51234 203.0.113.5:443'; BOTTOM-LEFT pane runs [root@ta-jump01 ~]# tcpdump -i eth0 -nn -vv 'tcp port 443 and tcp[tcpflags] & (tcp-syn|tcp-ack) != 0' with several live packet capture lines streaming '14:02:11.123456 IP 10.0.0.10.51234 > 203.0.113.5.443: Flags [S], seq 1842..., win 64240, options [mss 1460,sackOK,TS val..., wscale 7], length 0 / 14:02:11.135789 IP 203.0.113.5.443 > 10.0.0.10.51234: Flags [S.], seq 9281..., ack 1843..., win 65535 / 14:02:11.135999 IP 10.0.0.10.51234 > 203.0.113.5.443: Flags [.], ack 1, win 502 / Flags [P.] length 517 (TLS ClientHello)'; BOTTOM-RIGHT pane runs [root@ta-jump01 ~]# dig +short A www.example.com @8.8.8.8 returning '93.184.215.14' then # dig +trace www.example.com (truncated root→TLD→authoritative chain), then # curl -v --resolve www.example.com:443:93.184.215.14 https://www.example.com showing TLS 1.3 handshake details (' SSL connection using TLSv1.3 / ALPN: server accepted h2 / * issuer: C=US; O=DigiCert Inc... / > GET / HTTP/2 / < HTTP/2 200'). Monospaced Source Code Pro font, soft glow on the tmux status bar showing hostname '[ta-jump01] · CPU 0.42 · 4 panes · Bastion · OOB 10.255.0.10', subtle scanlines. Teal #00b894 prompt accents on each # symbol, 16:9"

Linux 네트워크 CLI — ip · ss · tcpdump · dig

트러블슈팅 체크리스트 — Bottom-up 7단계

세션 4 핵심 키워드 — 암기 카탈로그

Q&A — 세션 4 자주 묻는 질문

마무리 — 7계층, 한 권의 통일

네트워크는 7개 계층의 약속, 100여 개의 프로토콜, 수십 가지 장비의 종합 예술.

TA는 이 약속을 도면 · 표 · 결정 매트릭스 · 산출물로 풀어낸다.