Understanding 802.11 Frame Types
Understanding 802.11 Frame Types Client associate AP, 然後收接frame都經AP 或client p2p 都靠AP, 用802.11z Direct Link Setup DLS ※ Distributed Coordination Function (DCF) ※ 大家wireless device合作, 不要collision.
IT Networking
Wireless LAN Topologies
Wireless LAN Topologies
Understanding Antennas
Understanding Antennas 0dB 為Antenna最強可達位 Antenna gain 即是集中RF能力 理論天線為一點, Gain為0 dBi, 沒RF集中能力 Beamwidth: 在-3dBm畫線, 計角度 Polarization: Tx 及 Rx 要parallel傳接
RF Signal in the Real World
RF Signal in the Real World
RF Standard
RF Standard FCC EIRP Limit (Point-to-multipoint links): FCC EIRP Limit (Point-to-point links): ※ IEEE 802.11 Channel Layout ※ IEEE 802.11 Channel Layout in 2.4-GHz Band: IEEE 802.11 Channel Layout in 5-GHz Band: ※ IEEE 802.11 ※ 802.11b 802.11g 802.11a 802.11n 802.11ac (802.11n加強) Data Rate 802.11ac (802.11n加強) Reliability Rate Other Frequency Band
RF Signals & Modulation
RF Signals & Modulation ※ RF Signals ※ Absolute Value Formula: Compare Formula: For example:mW = 200 x 2 x 2 x 10dB = 23 = 7 + 3 + 3 + 10 Rx Signal: EIGP: Transmitter: EIRP (100mW to 1mW) (+20dBm to 0dBm)Receiver: RSSI (1mW to 0mW) (0dBm to -100dBm)Signal to Noise Ratio in …
MPLS
MPLS 在L3及L2 header之間插入Label。32-bit Label 中的 20-bit Label值用作決定Next hop。避免用recursive routing。LSR之間是LDP neighbor. ※ Router Role ※ ※ 設定MPLS ※ R2(config)#int e0/0R2(config-if)#mpls ip Untagged 指此Router把所有Label除去, 因R1不屬於MPLS範圍。Pop 指把Label的外層除去, 因R2知道R3擁有網段:192.168.34.0/24。提早一hop便Pop掉, 稱作PHP 或implicit null. 如想把label留到最後一hop, 要enable explicit null, 以保留QoS值。 R3(config)#mpls ldp explicit-null ※ Label Range ※ Default Label Range: 16 – 1,048,575 R2(config)#mpls label range 50 100 ※ TDP ※ Cisco …
EIGRP
EIGRP ※ Why EIGRP? ※ 因為上一代用IGRP太慢,而BGP不會auto-summary route, 又不會快速搵alternate path. ※ Metric ※ Metric = [K1*BW*256+(K2*BW)/(256-load)+K3*delay*256]*[K5/(realiability+K4)]where BW = 107 Kbit / interface_bandwidth(Kbit), 請選取Path中最小BWwhere delay = interface_delay(usec) / 10, 請選取Path中delay總和 Default K Value: K1=1, K2=0, K3=1, K4=0, K5=0 R1(config-router)#metric weights 0 5 2 1 10 1 //0,K1,K2,K3,K4,K5 Default Metric =BW*256+delay*256 Wide Metric = [K1*BW*256+(K2*BW)/(256-load)+K3*delay*256+K6*Extended_Attributes]*[K5/(realiability+K4)]where BW = 107 …
OSPF
OSPF ※ Router Role ※ ※ Neighbour & Adjacency ※ Down 沒發Hello Init 剛向對方發Hello 2-Way (Neighbor) DROTHER終點, 選DR/BDR ExStart 預備交換Link State ExChange 給對方LSA Menu(DBD) Loading 正在交換LSA Full (Adjacency) 同Area的Topo是一樣 ※ LSA ※ LSA 1 (From/To: 同Area所有Router) 自己的 (neighbor+Cost) LSA 2 (From: DR, To: non-DR) DR的 (neighbor+Cost) LSA 3 (From: ABR, To: 同Area所有Router) ABR的 (network+Cost) LSA …
IPsec
IPsec ※ 基本要點 ※ Integrity (完整性): 訊息收發一致 [MD5, SHA]Authentication (身份認證): 證明對方身份 [PSK, RSA, Key Management]Confidentiality (加密): 隱藏訊息 [DES, 3DES, AES, SEAL] IKEv1還是IKEv2?IKEv1: Phase I 可選Main/Aggregate Mode,IKEv2: Phase I 只有4 msg, 同時支援NAT-T,AES加密, EAP認證 ※ IKEv1 Phase I ※ IKEv1 Phase I (Phase I 建立加密管道)(金鑰交換), udp500/4500:設定IKE SA, SADB 想用Main Mode 定 Aggregate Mode?Main Mode: 可以加密對家身份. 但6-ways handshakeAggregate …