3 LAN Design Basics Computernetze 1 (CN1) Prof. Dr. Andreas Steffen Institute for Internet Technologies and Applications

Lesestoff im Ethernet Buch Kapitel 6 Ethernet Internals, Seiten 189-214 6.1 Längenbeschränkung im Ethernet Kapitel 8 Ethernet-Komponenten, Seiten 275-329 8.1 Netzwerkkarten 8.2 Repeater und Hubs 8.3 Switches 8.4 Medienwandler Selbststudium Erarbeiten Sie als Vorbereitung für die Übung 4 selbständig das Thema “Spanning Tree Protocol” mit Hilfe des Cisco Tutorials von Dan DiNicolo und des Kapitels 4 des CN1 Foliensatzes.

LAN and LAN Devices LANs make it possible for businesses that use computer technology to efficiently share such items as files and printers and to make possible communications such as e-mail. LANs are designed to do the following: operate within a limited geographic area or building allow many users to access high-bandwidth media provide full time connectivity to local services connect physically adjacent devices

The Beginning of LAN Design Initial idea: shared media LAN Bus structure; CSMA/CD was access method Coax cable; transmission rate up to 10 Mbit/s, half-duplex

Repeater

Repeater The purpose of a repeater is to amplify and retime network signals at the bit level. Repeaters can be single-port "in" and single-port "out" devices, though more often now, they are stackable (modular), or multi-port repeaters, better known as hubs. Repeaters are classified as layer 1 devices, in the OSI model, because they act only on the bit level and look at no other information.

Hub Used in 10BASE-T and 100BASE-T networks Is equivalent to a multi-port repeater Hubs come in three basic types: passive – no traffic and signal manipulation, used only to share the media active – amplifies the incoming signal intelligent – (smart hub) same function as an active hub, additionally includes a controller chip and diagnostic capabilities

Ethernet Strukturierung Collision Domain

Bridge The purpose of a bridge is to filter traffic on a LAN, to keep local traffic local, yet allows connectivity to other parts (segments) of the LAN for traffic that has been directed there. The bridge makes its decisions based on MAC addresses. The bridge is a layer 2 device.

MAC Layer Bridge (Transparent Bridge)

Bridge: Flooding or Filtering (destination address) Error-free frame received on port x no yes Destination address found in forwarding database? Forward frame to all ports (except port x) Is destination again on port x? no yes Forward frame to port y Discard frame Flooding Filtering 1

Bridge: Learning (source address) 1 no yes Source address found in forwarding database? Add address with port and age value to the forwarding database Update port and age value Learning end Typical address aging value: 300 s

Learning / Flooding LAN 1 LAN 3 p1 p1 MAC A MAC F MAC B MAC G bridge 1 SA DA A F L2 data A F L2 data LAN 1 LAN 3 learn A flood F p1 p1 MAC A MAC F MAC B MAC G bridge 1 bridge 2 MAC C p2 p2 flood F learn A LAN 2 A F L2 data table of bridge 1 table of bridge 2 p1 p2 p1 p2 A A

Learning / Filtering LAN 1 LAN 3 p1 p1 MAC A MAC F MAC B MAC G DA SA A L2 data LAN 1 LAN 3 learn F p1 p1 MAC A MAC F MAC B MAC G bridge 1 bridge 2 MAC C p2 p2 filter A LAN 2 table of bridge 1 table of bridge 2 p1 p2 p1 p2 A A F

Learning / Flooding LAN 1 LAN 3 p1 p1 MAC A MAC F MAC B MAC G bridge 1 data DA SA F G L2 data LAN 1 LAN 3 flood G p1 p1 MAC A MAC F MAC B MAC G bridge 1 bridge 2 MAC C p2 p2 flood G learn F LAN 2 F G L2 data table of bridge 1 table of bridge 2 p1 p2 p1 p2 A A F F

Learning / Forwarding LAN 1 LAN 3 p1 p1 MAC A MAC F MAC B MAC G data DA SA G F L2 data LAN 1 LAN 3 forward F learn G p1 p1 MAC A MAC F MAC B MAC G bridge 1 bridge 2 MAC C p2 p2 learn G forward F LAN 2 G F L2 data table of bridge 1 table of bridge 2 p1 p2 p1 p2 A G G A F F

Segmentation with Bridges Bridges split a LAN into several workgroups with smaller collision domains -> reduces whole LAN traffic One "broadcast domain" half-duplex collision domains

Switch The purpose of a switch is to concentrate connectivity, while guaranteeing bandwidth. It switches packets from incoming ports (interfaces) to outgoing ports, while providing each port with full bandwidth. The switch uses the MAC address to make its switching decisions. You might think of each port on a switch as a micro-bridge, which makes it a layer 2 device.

Ethernet Strukturierung Broadcast Domain (IP-Subnet)

Switch Forwarding Principles * * delays computed for 10 Mbit Ethernet

Switch Forwarding Principles Early-Cut only usable when finished learning forwards nearly all faulty frames Cut-Through reads destination and source address forwards many faulty frames Fast-Forward (Fragment Free) detects runts and collisions can filter specific Ethertypes Store-and-Forward detects CRC-errors can do filtering based on higher-layer Information

Switching Fabric cross-connect any two switch ports Port 1 Port 0

Non-Blocking Switching Fabric 10 Gbps 10 Gbps 10 Gbps 60 Gbps Fabric Brief overview on basic concept of non-blocking switches Anatomy of a switch, good or bad? Importance of buffers & queues Will learn more about how this is implemented per Cisco platform in our product sessions 10 Gbps Bandwidth of Fabric > Ingress + Egress

Blocking Switching Fabric 10 Gbps 10 Gbps 10 Gbps 20 Gbps Fabric Heart of a switch or router, must work or nothing will 10 Gbps Bandwidth of Fabric < Ingress + Egress

Shared Memory Architecture General Purpose CPU (CISC older or RISC newer) CPU Forwarding Tables Buffers Queues Pointers Headers IOS Image/Files Packet Memory CPU Memory System Buffers Processor Queues Data/Address/ Control Buses Interface Interface Interface Interface Interface Interface Interface Physical Media Interfaces (Fixed or Modular)

Cross Bar Switch Architecture CPU Memory (DRAM) CPU (C) Forwarding Table Multiple conflict free paths Typically higher bandwidth Signaling and scheduling is more complex CPU Interface Card (D) FT Packet Memory Tx Rx CPU Interface Card (D) FT Packet Memory Tx Rx CPU Interface Card (D) FT Packet Memory Tx CPU Interface Card (D) FT Packet Memory Rx Cross Bar ASIC

Router The purpose of a router is to examine incoming packets, choose the best path for them through the network, and then switch them to the proper port. Routers make their path selection decisions based on layer 3 information - the network addresses therefore they are considered layer 3 devices. Routers can connect different layer 2 tech-nologies, such as Ethernet, Token-ring, or FDDI.