switchroute1

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Published on January 1, 2008

Author: Woofer

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Link Layer Switching:  Link Layer Switching Connecting local networks Bridges Repeaters, Hubs, Bridges, Switches, Routers, Gateways Virtual LANs Ethernet:  Ethernet 50  thick: 500 m 50  thinn: 185 m max 4 repeaters traffic on one segment means traffic on all other segments CSMA/CD (IEEE 802.3):  CSMA/CD (IEEE 802.3) A-MAC Phys. A B-MAC Phys. B C-MAC Phys. C Logical Link Control Physical Link Bridges:  Bridges Connection on link layer: forwarding based on MAC addresses self-learning bridges operation Advantages and limitations Spanning-tree bridges operation Advantages and limitations Self-learning Bridge:  Self-learning Bridge MAC_1 Phys_1 MAC_2 Phys_2 Forwarder Bridge routing table Network 1 Network 2 Self-learning Bridge:  Self-learning Bridge Driver interface 1 . Driver interfaec 3 . Driver interface 2 . LAN 1 LAN 2 LAN 3 Learning & routing Routing table MAC-adr . Interface . time Mac-1 - - - - - Mac-2 2 - - 3 - - - - - -   Self-learning Bridge:  Self-learning Bridge Extract Sender and receiver MAC-adresser Update interface # and timer New entry MAC-addr interface # and timer Start Sender known? Yes No Look up in Routing table Broadcast frame, except on receiving interface Put frame into correct outgoing queue End Learning phase Forwarding phase Look up in Routing table Link Layer Switching:  Link Layer Switching Multiple LANs connected by a backbone to handle a total load higher than the capacity of a single LAN. Bridge from 802.x to 802.y:  Bridge from 802.x to 802.y IEEE 802 frame formats Bridges from 802.x to 802.y:  Bridges from 802.x to 802.y Operation of a LAN bridge from 802.11 to 802.3. Local “Internetworking”:  Local “Internetworking” A configuration with four LANs and two bridges. Problem with standard bridge:  Problem with standard bridge Two parallel transparent bridges. Spanning tree:  Spanning tree Goal: each bridge should identify the interfaes for forwarding traffic Build a spanning tree From on root node Self-configuring To all nodes Only these interfaces in the spanning tree can forward traffic Provides the shortest path for all traffic Spanning Tree Algorithm:  Spanning Tree Algorithm Configuration phase: Each nodes sends out: Its own identity (ID) (MAC-address) ID to the root-bridge Number of hops to root-bridge In this way, building up a spanning tree, bridge with lowest ID become root node Start forwarding frames Spanning Tree Bridges:  Spanning Tree Bridges (a) Interconnected LANs. (b) A spanning tree covering the LANs. The dotted lines are not part of the spanning tree. Remote Bridges:  Remote Bridges Bridges can be used to connection physically distant local networks Repeaters, Hubs, Bridges, Switches, Routers and Gateways:  Repeaters, Hubs, Bridges, Switches, Routers and Gateways (a) Which device is in which layer. (b) Frames, packets, and headers. Hub (Nav):  Hub (Nav) < 100 m Transceiver Repeaters, Hubs, Bridges, Switches, Routers and Gateways:  Repeaters, Hubs, Bridges, Switches, Routers and Gateways (a) A hub. (b) A bridge. (c) a switch. Switched Ethernet:  Switched Ethernet 10, 100, 1000 Mb/s Switch: Switches on MAC-addr Buffers frames, therefor no collision Competition only for switch capacity Gigabit Ethernet:  Gigabit Ethernet Gigabit switch Switch Switch Working group 1 Working group 2 100/1000 100/1000 1000 Mb/s 100 Mb/s Virtual LANs:  Virtual LANs A building with centralized wiring using hubs and a switch. Virtual LANs (2):  Virtual LANs (2) (a) Four physical LANs organized into two VLANs, gray and white, by two bridges. (b) The same 15 machines organized into two VLANs by switches. The IEEE 802.1Q Standard:  The IEEE 802.1Q Standard Transition from legacy Ethernet to VLAN-aware Ethernet. The shaded symbols are VLAN aware. The empty ones are not. The IEEE 802.1Q Standard (2):  The IEEE 802.1Q Standard (2) The 802.3 (legacy) and 802.1Q Ethernet frame formats. Conclusion:  Conclusion Bridges: efficient connection alternative Limits/isolates collision domains Can be used for traffic isolation Do not consume IP addresses Switches: High use degree, no danger of collisions Used for establishing virtual LANs Routing and Packet Switching:  Routing and Packet Switching Goal Overview of how routing fits into the Internet architecture Principles for typical routing protocols Strengths and weaknesses Structure Primary tasks of the network layer Datagram and virtual line Some performance considerations Routing and forwarding Network layer:  Network layer Disk Disk Server Client link Tasks of the Network Layer:  Tasks of the Network Layer Responsible for end-to-end transport Addressing of machines Forwarding Connectionless datagram; no fixed path through the network Connection-oriented (e.g. MPLS or ATM) Three phases: connection establishment, data transmission, teardown Fixed path through the network Relatively reliable and ordered transmission Flow control Forwarding:  Forwarding R B A R LAN-A LAN-B Routing and lookup:  Routing and lookup Mail: griff@ifi.uio.no Name to address conversion: ifi.uio.no til IP address: 129.240.64.2 Find MAC-address to router and send packet(s) Forward through the network w.r.t. the network address Based on lookup in routing tables At the destination router Convert machines IP address to a MAC address Send packet to the receiving machine Place of Routing in the architecture:  Place of Routing in the architecture Structured Network dimensioning Where should lines be established? Capacity of lines Traffic directioning Mapping of connections down to paths through the net Routing to choose paths Routing of individual packets Best effort Routers choose the next hops separately for each packet Routing:  Routing Routing tables can be computed based on state information about the network Data exchanged between nodes: Between neighbour nodes (distance vector routing; RIP) Between all nodes in the network (link state routing; OSPF, IS-IS) Routing types:  Routing types Static vs. dynamic Dynamic with error handling, new links, changes of the load Centralized vs. distributed Distributed when routes are computed at all nodes Global vs. local topology knowledge Source routing vs. routing Kilde ruting vs. ruting In source routing the source chooses the routing In routing each router choose the next hop Routing Parameters:  Routing Parameters Performance parameters Number of hops Price Delay capacity Routing decisions made In each node (distributed) In a central node (routing center) At the sender (source routing) Sources of routing information None Local to the node Neighbour nodes Nodes along the path All nodes in the network Update interval Continously Periodic In case of large load variations In case of topology changes Routing hierarchy:  Routing hierarchy In large networks Hierarchically structured Link state Open Shortest Path (OSPF) Intermediate System to Intermediate System (IS-IS) On campus or in companies Distance vector, RIP Static routing Ad-hoc networks, stationary or mobile wireless networks Many different protocols depending on scenarios Router model:  Router model Forwarding process Pre- process In 1 2 3 1 2 3 Out e Principle structure of a router with three incoming and three outgoing connections Routing table Topology database Routing prosess Route computation   Routing alternatives:  Routing alternatives Flooding Static routing Adaptive routing should handle Loss of a link (error, e.g. cable is broken) Loss of a node (error, e.g. power loss, OS crash) High traffic load (persistant of transient congestion, bottleneck) Disadvantages Complex, distributed, and not always correct Adaptivity must be balanced against additional overhead Can lead to oscillations (route flapping) if reactions are too fast Can be unattractive if reactions are too slow Demands on a routing strategy:  Demands on a routing strategy Shall give correct routes Shall demand minimal load on nodes Shall be stable and converge quickly Fair towards different data streams Provide optimal routes Scale with the size of the network Size with the number of destinations Plug-and-play capabilities:  Plug-and-play capabilities Find neighbour nodes and routers Detect when neighbours go up and down Detect capacity of own links Send and receive topology information Send after timer or major changes to the network Distance vector characteristics:  Distance vector characteristics Nodes exchange a vector with their shortest distance to all destinations Periodic exchange Convergence is ensured Advantage Simple Disadvantages Vulnerable to errors Slow dissemination in case of problems Distance Vector:  Distance Vector A B C D E F 1 2 5 2 2 9 1 Distance vector Next node vector Dest. delay Next node A 0 - B 2 B C 5 C D 1 D E 6 C F 8 C Node A before change 5 3 Distance vector (2):  Distance vector (2) 2 3 1 0 3 2 3 0 2 2 0 1 1 3 3 D2 D3 D4 Dest. delay next node 1 0 - 2 2 2 3 3 4 4 1 4 5 2 4 6 4 4 Routing table in node 1 after 1 2 3 4 5 6 1 2 5 2 9 2 9 1 5 3 Min dkj = i  A dij + lki A is the set of all neighbour nodes of k Distance vector Send to node 1 Router model:  Router model Forwarding process Pre- process In 1 2 3 1 2 3 Out e Principle structure of a router with three incoming and three outgoing connections Routing table Topology database Routing prosess Route computation   Link state:  Link state Routing database Routing table Periodical and in case of changes Nodes flood their state onto the link to all other nodes At start, new nodes downlink the database from a neighbour Different kinds of link Point-to-point Point-to-multipoint Broadcast Each node calculates the best route to all other nodes Checkpoints Voting av entire database for link state at a sequence number LS routing protocol architecture:  LS routing protocol architecture change change Protocol for handling of changes Link state database Routing algorithm Routing table route lookup Flooding of link state:  Flooding of link state Statistically reliable Each node forwards on all interfaces All incoming link state packets If sequence number of large than earlier sequence numbers Will most probably reach all node in the network Content Sequence number Avoid broadcast storms Node ID of the source Topology Identify bi-directional links List of all direct neighbour nodes with a cost function Time-to-live Link state, LSA:  Link state, LSA A B C D E F A 2 5 1 B 2 2 C 5 D 1 2 9 E F Routin database i D Link state problems/strengths:  Link state problems/strengths Problems Selection of a node that reports for a shared medium Flooding does not scale for large networks Division into hierarchical networks to limit flooding Strengths All nodes have full topology knowledge Error have only local relevance Link state problem:  Link state problem area 1 area 2 a b We have two problems with the link state method Static cost factor Can be the source of congestion, all traffic is routing through a single link Oscillation effects in forwarding traffic At one point in time a is the preferred router between areas Then routing information is exchange New tables are computed and b becomes the preferred router Router and Routecenter:  Router and Routecenter Network with router center Routers do not have to participate in a routing protocol Routing center receives status reports from routers Transfers forwarding table to routers Connection-oriented forwarding:  Connection-oriented forwarding Establish a channel = a path through the network Examples ATM, MPLS, X.25 Explicit signalling Data-driven signalling Signalling protocol Routing protocol to choose the nodes that should form the path In each node establishing a forwarding table Incoming interface, channel – to outgoing interface, channel Virtual lines:  node x node y C 1 1 2 V.C. tables 1 2 3 4 1 2 1 2 2 a b c b V.C. tables c D A B a 1 ; c ; 3 2 ; c ; 4 b 1 ; c ; 2 2 ; c ; 1 1 ; b ; 2 2 ; b ; 1 3 ; a ; 1 4 ; a ; 2 c 1 ; a; 3 2 ; a; 4 1 ; a; 1 2 ; a; 2 1 ; b ; 1 2 ; b ; 2 3 ; c ; 1 4 ; c ; 2 c b a a   Virtual lines Dynamic cost in route computation:  Dynamic cost in route computation Adaptation of routes to load Move traffic to lines with lower load Main problem Delay between measurement and computation Delay between route computation and traffic arrival Fast variation in load Bad predictability Route flapping (oscillations) Overhead of exchanging the routing information Performance of the network:  Performance of the network Performance of the networks means capacity, delay, delay variation (jitter), and reliable Has several elements Transmission delay Sending delay Signal propagiation time Node delay Processing time Queueing time Measuring the link state:  Measuring the link state Topology example:  Topology example Shortest path tree for nodes:  Shortest path tree for nodes   Routing tables for shortest path trees:  Routing tables for shortest path trees Packet size and delay:  Packet size and delay Modified load variation:  Modified load variation   Timing in line and packet switching:  Timing in line and packet switching

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