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CS4231 Local Area Networks HW3 – Spanning Tree Algrithm

CS4231 Local Area Networks HW3 – Spanning Tree Algrithm. Overview. Overview. 區域網路 1. 埠 1. 埠 1. 橋接器 2. 橋接器 3. 埠 1. 埠 2. 埠 2. 橋接器 1. 區域網路 2. 埠 2. 埠 1. 橋接器 4. 埠 2. 區域網路 3. Spanning Tree Algorithm. Bridges Each bridge is assigned a unique identifier (8 octets):

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CS4231 Local Area Networks HW3 – Spanning Tree Algrithm

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  1. CS4231Local Area NetworksHW3 – Spanning Tree Algrithm

  2. Overview

  3. Overview 區域網路1 埠1 埠1 橋接器2 橋接器3 埠1 埠2 埠2 橋接器1 區域網路2 埠2 埠1 橋接器4 埠2 區域網路3

  4. Spanning Tree Algorithm • Bridges • Each bridge is assigned a unique identifier (8 octets): • Priority part (two octets): programmable • address part (six octets) • A special group MAC address for all bridges : 01-80-C2-00-00-00 (Multicast address) • Each port of a bridge has a unique port identifier.

  5. Spanning Tree Algorithm • Root Bridge: The bridge with the lowest value of bridge identifier. • Path Cost: For each port, the cost of transmitting a frame onto a LAN. • Root Port: For each bridge, the port on the minimum-cost path to the root bridge. • Root Path Cost: For each bridge, the cost of the path to the root bridge with minimum cost. • Designated Bridge: For each LAN, the bridge that provides the minimum cost path to the root bridge. The only bridge allowed to forward frames to and from the LAN. • Designated Port: The port of the designated bridge that attaches the bridge to the LAN. All internet traffic to and from the LAN pass through the designated port.

  6. Spanning Tree Algorithm • Three Steps: • 1. Determine the root bridge. • 2. Determine the root porton all other bridges. • 3. Determine the designated port on each LAN. • The port with the minimum root path cost. • In the case of two or more bridges with the same root path cost, the highest-priority bridge is selected. • If the designated bridge has two or more ports attached to this LAN, then the port with the lowest value of identifier is selected.

  7. Determine Root Bridge • 每個橋接器送出 BPDU 至所有與其相連之區網 • 將 ’根橋接器ID’ 設為自己的 ID; RPC 設為 0 • 當橋接器自埠 i 收到 BPDU • 若收到 BPDU 上之 ’根橋接器ID’ 比較小 • 認定 BPDU 上之 ‘根橋接器ID’ 方為正確 • 設定 i為根埠 • 更新 RPC 值 (=RPC(BPDU)+TC(i)) • 送出新的 BPDU 至除 i 外的所有埠 • 帶有更新後之 ‘根橋接器ID’ 與 RPC 值 • 否則，捨棄此BPDU • 在兩個 “轉送延遲時間” 內可確定是否為根橋接器

  8. Determine Designated Port • 橋接器 X設定埠 i為根埠後，將其 RPC 值送至除 i外之所有埠，測試是否可為代理埠 • 當 Y 由埠k收到 BPDU： • 若 RPC(X)<RPC(Y) 則放棄競爭.埠 k不為代理埠 • 若 RPC(X)>RPC(Y) 則將 RPC(Y) 送入埠 k • 若 RPC(X)=RPC(Y) 則以 ID 小的擁有代理權

  9. Spanning Tree Algorithm Example 9 RPC = 25 RPC = 20 5 埠 l 埠 i TC=5 RPC = 53, 根埠 = k 4 TC=15 RPC = 58, 根埠 = j 4 橋接器 Y 8 RPC = 40, 根埠 = k 橋接器 X 6 RPC = 35, 根埠 = i, D(W) = j 埠 k 10 RPC = 30, 根埠 = l, D(W) = k 埠 j TC=5 RPC = 35, 根埠 = i 12 TC=10 RPC = 35 7 11 RPC = 30 區域網路 Ｗ 3 RPC = 48 埠 m TC=10 RPC = 48, 根埠 = n, D(W) = m D(W): 區域網路W 的代理埠 橋接器 Z RPC = 45, 根埠 = m 埠 n RPC = 40, 根埠 = m TC=10 1 RPC = 38

  10. Spanning Tree Algorithm Example R R 埠l 埠i TC=5 TC=15 橋接器Y 橋接器X 埠k 埠j TC=5 TC=10 D 區域網路Ｗ R 埠 m TC=15 橋接器Z D: 代理埠 R: 根埠 埠n TC=10

  11. Bridge Port State Diagram 停滯狀態 被選為 代理埠或根埠 被取消為 代理埠或根埠 被取消為 代理埠或根埠 被取消為 代理埠或根埠 轉送狀態 學習狀態 傾聽狀態 經過一個轉送延遲時間 經過一個轉送延遲時間

  12. Bridge ProtocolData Unit 802.3:Ethernet 802.2: LLC

  13. Bridge ProtocolData Unit • http://www.banalyzer.de/ban/HTML/P_LAYER2/Eng/P_lay120.html

  14. Use libnet to send a BPDU • libnet_ptag_t libnet_build_stp_conf (u_int16_t id, u_int8_t version, u_int8_t bpdu_type, u_int8_t flags, u_int8_t * root_id, u_int32_t root_pc, u_int8_t * bridge_id, u_int16_t port_id, u_int16_t message_age, u_int16_t max_age, u_int16_t hello_time, u_int16_t f_delay, u_int8_t * payload, u_int32_t payload_s, libnet_t * l, libnet_ptag_t ptag) • libnet_ptag_t libnet_build_802_3 (u_int8_t * dst, u_int8_t * src, u_int16_t len, u_int8_t * payload, u_int32_t payload_s, libnet_t * l, libnet_ptag_t ptag) • libnet_ptag_t libnet_build_802_2 (u_int8_t dsap, u_int8_t ssap, u_int8_t control, u_int8_t * payload, u_int32_t payload_s, libnet_t * l, libnet_ptag_t ptag)

  15. Use libnet to send a BPDU u_int8_t root_id[8] = {0x80, 0x00, 0x00, 0x10, 0x14, 0x23, 0xA4, 0x08}, bridge_id[8] = {0x80, 0x00, 0x00, 0x10, 0x14, 0x23, 0xA4, 0x08}; u_int8_t payload[1] = {0x00}; libnet_build_stp_conf (0, 0, 0, 0, root_id, 0, bridge_id, 2, 0, 20, 2, 15, NULL, 0, l, 0); libnet_build_802_2 (0x42, 0x42, 0, NULL, 0, l, 0); libnet_build_802_3 (BPDU_MC, my_mac, 38, NULL, 0, l, 0);

  16. ABPDUPacket

  17. Requirement • 封包依建立的 Spanning Tree 傳送 frame • 想一個可以驗證建立的 Spanning Tree 是正確的方法 • 例如 show 出每一個 bridge 的收/送封包的狀況

  18. Grading • Correctness (60%) • Report (30%) • How to run your program. • What you’ve learned? • What are you suffer from this HW? • Any feedback? • Coding Style (10%)

  19. Hand in your program • Deadline: 2010/6/18 PM 23:59:59 • Demo: 2010/6/18 AM 10:00~12:00 at 資電326 • Write a simple report in text file. • Please tar/zip/rar your files (including code and report) named as 組別.tar (ex: group_1.tar) and login to • ftp:// 140.114.71.48:4231, cs4231/cs4231s10 Change directory to “Final Project” and create a directory named your 組別, then upload your file in this directory.

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