Repeating Repeating Bridging Switching and Routing Home 0

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 Gateway 7. Application 6. Presentation 5. Session 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: 10 Base 5 10 Base 2 10 Base. T 100 Base. T u u Layer 2 Cable Length Number of Interfaces node MAC MAC ··· Layer 1 500 m 185 m 100 m 100 30 2 2 185 m 10 Base 2 (coaxial) 7. Application 6. Presentation 5. Session 4. Transport node MAC 100 m Inductive Logic 10 Base. T (2 -pair UTP) MAC 3. Network 2. Link 1. Physical 2/5/2002 4

Ethernet Services • Local addressing u u LAN: Local Area Network Despite globally unique MAC addresses, nodes can only reach local hosts (hosts on their LAN) • Datagram service u One packet at a time • Best effort delivery u u 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 ··· 10 Base 2 (coaxial) Repeater Segment 1, 185 m Segment 2, 185 m 370 m Repeating Hub node 100 m node Inductive Logic Repeating Hub 10 Base. T 100 m node 100 m node 10 Base. T 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 u u 5 segments 4 repeaters 3 coax segments Fun fact: 4 -3 -4 is also allowed (802. 3 sec 13. 3. f. 3) Repeater 10 Base. T Repeating Hub Inductive Logic 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 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. 1 d Collision domain is per segment, broadcast domain is all hosts on LAN node MAC MAC No MAC node 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 Bridge A MAC Unknown or Broadcast packet crashes network Bridge MAC Inductive Logic X node Disabled by spanning tree Bridge B 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 (3 Com Link Switch 1000) • A Bridge Too Far Imagine a big bridge with lots of ports (LS-1000 has 24) u • • 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 u u • • • default 5 minutes on 802. 1 d bridge default 15 minutes on LS-1000 Lost address is more severe on a switch (no flooding) 802. 1 d 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: u u u 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) u u 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 u u IP uses RIP, RIP 2, OSPF, EGP, GGP, . . . IPX uses IPX RIP (not IP RIP) • Opaque to nodes: they must interact with routers u u 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 No Performance worst ok high delay Complexity low restricted, no loops medium high way-high arbitrary no loops arbitrary Topology broadcast & broadcast never unknown (w/ default route) Looping packet catastrophic TTL kills it default or flood or Unknown address flood default discard opt. discard Forwarding instant store & fwd cut thru (typ) store & fwd Packet Flooding always Topology learning none Inductive Logic STP opt. STP L 3 protocol 2/5/2002 16

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