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Repeating Repeating Repeating Repeating Repeating, Bridging, Switching, and Routing Home 0 We Deliver For You Eric L. Michelsen Inductive Logic Visitor 63 Topics • • • • • • • • Simple Ethernet LAN Simple Repeating Repeated Repeaters Multiport Coax Repeaters Bridging Spanning Tree Switching Routing Inductive Logic 2/5/2002 2 Where in the Stack? 7. Application Application Gateway 7. Application 6. Presentation 6. Presentation 5. Session 5. Session 4. Transport 4. Transport 3. Network Router 3. Network 2. Link Bridge 2. Link 1. Physical Repeater 1. Physical Note: IP routers used to be called “gateways,” not to be confused with “application gateway.” We won’t be talking about application gateways. Inductive Logic 2/5/2002 3 Simple Ethernet LAN • Layer 2 interface to host, Layer 1 interface to medium • Each Ethernet interface has globally unique MAC address • Ethernet has restrictions: 10Base5 10Base2 10BaseT 100BaseT Layer 2 Cable Length Number of Interfaces node node node MAC MAC MAC 500m 185m 100m 100m 100 30 2 2 185 m Layer 1 10Base2 (coaxial) 7. Application 6. Presentation 5. Session 4. Transport 3. Network node node MAC 100 m Inductive Logic 10BaseT (2-pair UTP) MAC 2. Link 1. Physical 2/5/2002 4 Ethernet Services • Local addressing LAN: Local Area Network Despite globally unique MAC addresses, nodes can only reach local hosts (hosts on their LAN) • Datagram service One packet at a time • Best effort delivery Not guaranteed No acknowledgement • Other services (reliable delivery, 7. Application 6. Presentation 5. Session 4. Transport 3. Network 2. Link Local addressing Datagram Best effort Raw bits 1. Physical Wires, voltage, current global addressing) require Layer 3 and higher protocols Inductive Logic 2/5/2002 5 • • • • Simple Repeater Simplest and lowest overall network performance Repeats everything, including collisions Transparent to nodes All interfaces must run at the same speed (no buffering) node node node node node 10Base2 (coaxial) Repeater Segment 1, 185 m Segment 2, 185 m 370 m Repeating Hub node 100 m 100 m node Inductive Logic Repeating Hub 10BaseT 100 m node 100 m 100 m 100 m node node 10BaseT 100 m node 2/5/2002 6 Repeated Repeaters • Repeaters can be chained up to a limit: the 5-4-3 rule: Between any 2 nodes, no more than 5 segments 4 repeaters 3 coax segments Fun fact: 4-3-4 is also allowed (802.3 sec 13.3.f.3) Repeater 10BaseT Repeating Hub Inductive Logic noncoax Repeater Repeating Hub Repeater Repeating Hub noncoax Repeater Repeating Hub 2/5/2002 7 Multiport Coax Repeaters • Still follows the 5-4-3 rule • With all repeaters, broadcast domain and collision domain are the same coax Repeater noncoax Repeater Repeater noncoax Repeater Broadcast domain Collision domain Inductive Logic 2/5/2002 8 Bridging • • • • • • • • Yours is Yours, and Mines is Mines Bridges separate traffic as needed by segment Learn node MAC addresses dynamically (at least 4000) Flood unknown MAC addresses & broadcasts on all ports Bridge ports have no MAC addresses (transparent to nodes) Store and Forward delivery (typically) Each interface can run at an arbitrary speed (bridges have buffering) Standardized in IEEE-802.1d Collision domain is per segment, broadcast domain is all hosts on LAN node node node MAC MAC MAC No MAC node node node MAC MAC MAC Bridge Collision domain Simultaneous traffic Inductive Logic Collision domain Broadcast domain 2/5/2002 9 Spanning Tree Protocol (STP) • Bridge loops are catastrophic • Spanning Tree protocol disables redundant links, restores • • them dynamically as needed Suboptimal routing: minimum path along spanning tree Bridge as a whole has a MAC address (not its interfaces) node node node Bridge Bridge A MAC MAC Unknown or Broadcast packet crashes network Bridge MAC Inductive Logic X node Bridge B node node Disabled by spanning tree MAC X Chosen by spanning tree as root bridge Bridge C MAC Disabled by spanning tree. Frames from B to C go through bridge A 2/5/2002 10 Switching (3Com Link Switch 1000) A Bridge Too Far • Imagine a big bridge with lots of ports (LS-1000 has 24) • • • • Runs all interfaces simultaneously at (or near) wire speed Default path for unknown MAC addresses (not flooded) Broadcasts must still be flooded Cut through delivery (typically, but configurable) Optional spanning tree: just don’t do it Default Path Switching Hub Simultaneous traffic Broadcast domain Collision domains Inductive Logic 2/5/2002 11 Bridge/Switch Fun Facts • Addresses age out after configurable time • • • • • default 5 minutes on 802.1d bridge default 15 minutes on LS-1000 Lost address is more severe on a switch (no flooding) 802.1d bridge learns 4000 addresses, LS-1000 learns 500 No flow control (typically), discard overflow LS-1000 can invoke flow control by deliberately colliding with inbound frames it cannot handle LS-1000 has 3 forwarding modes: Cut Through: as fast as possible (propagates some collisions) Fragment-Free: cut through after collision time over (512 bits, propagates CRC errors) Store-and-Forward: maximum delay, forwards only good frames Inductive Logic 2/5/2002 12 Wireless LAN • Unlicensed National Information Infrastructure (U-NII) band, which spans 5.15 to 5.35 GHz and 5.725 to 5.825 GHz. The lower 200 MHz of the band is used for inbuilding applications; the upper 100 MHz is typically used for building-to-building or campus-bridging systems. • ISM bands (Industrial, Scientific and Medical) • 2.4 to 2.483 GHz, 802.11 specifies a total of 79 channels with 1-MHz spacing. data rates of 1, 2, 5.5, and 11 Mbps Inductive Logic 2/5/2002 13 Routing • A Cut Above Routing operates completely at Layer 3 (e.g., IP) repeating, bridging, switching are Layer 1/2 (e.g., Ethernet) Routing has nothing to do with Ethernet, FDDI, Token Ring, etc. • Each packet takes one route: no flooding • Routing protocols update topology • Arbitrary topology: loops allowed Nodes Router Frame Relay SONET Nodes Router Inductive Logic 7. Application Router Nodes 5. Session ATM Telephone modem Router 6. Presentation 4. Transport Nodes 3. Network 2. Link 1. Physical 2/5/2002 14 • • • • Routing: The Whole Truth Routers find least cost path Time To Live (TTL) kills looping packets Default routes minimize routing table size Each Layer 3 protocol requires 1 or more routing protocols IP uses RIP, RIP2, OSPF, EGP, GGP, ... IPX uses IPX RIP (not IP RIP) • Opaque to nodes: they must interact with routers IP uses ICMP IPX nodes listen to RIP Router 1 Router 2 node A node B Least cost path Router 3 Inductive Logic 2/5/2002 15 Side By Side Repeating Bridging Switching Routing Works at Layer... 1 2 2 3 Transparent? Yes Yes Yes No Performance worst ok high high delay Complexity low restricted, no loops medium high way-high arbitrary no loops arbitrary Topology broadcast & broadcast never (w/ default route) unknown Looping packet catastrophic catastrophic catastrophic TTL kills it flood or default or Unknown address flood default opt. discard discard Forwarding instant store & fwd cut thru (typ) store & fwd Packet Flooding always Topology learning none Inductive Logic STP opt. STP L3 protocol 2/5/2002 16 This slide intentionally left blank Inductive Logic 2/5/2002 17
