Computer Networks II: Switching and Virtual LAN from UCLM

UCLM Computer Networks II Overview

Version 4/23/24 UCLM UNIVERSIDAD DE CASTILLA~LA MANCHA Computer Networks II application transport network link physical

Switching and Virtual LAN Introduction

Switching and Virtual LAN David.Villa@uclm.esUCLM UNIVERSIDAD DE CASTILLA~LA MANCHA

Remarks on Study Material

• These slides are just a script for the class.
• The books specified in the bibliography together with what is explained in class represent the study material for the subject matter.
• All study material must be used for the preparation of the examinations.

Packet Tracer Simulations

Tip Packet Tracer simulations may be found at: https : //github. com/uclm-esi/redes-2-files

Congestion Control

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Contents of Switching and Virtual LAN

• Bridges and switches
• Spanning Tree Protocol
• Virtual LAN

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Ethernet Evolution Phases

• Phase 1 (1988): A shared (10 Mbps) with coaxial cable bus topology
• Phase 2 (1992): A shared (10 Mbps) twisted pair (structured cabling) and hubs in star topology

Coaxial Hub Twisted pair Switch Twisted pair

• Phase 3 (1996): A dedicated (10 Mbps) with twisted pair and switches in star topology (micro- segmentation) Computer Networks II 4UCLM UNIVERSIDAD DE CASTILLA~LA MANCHA

Bridge Functionality

• Join/separate LANs at link layer.
• Why?
• Performance: less collisions -> more througput
• Security: isolate data flows
• Reliability: less frames -> less fails.
• Interoperability: same MAC sublayer, different LLC.
• Distance: repeters (bridge type) may extend signals.
• Scalability: more nodes in same LAN.

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Bridge Classification and Operation

Bridge Classification

Classification Operation

• Transparent (IEEE 802.1; Bridging)
• With routing from source (802.5;Token Ring) Interoperability
• Homogeneous (802.3-802.3)
• Heterogeneous (802.3-802.11) By its scope
• Local (LANs interconnetion)
• Remote (LANs interconnet through WANs)

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Bridge Interoperability Layers

Interoperability Sublayers

Interoperability 2 sublayers

• LLC (Logical Link Control)
• MAC (Media Access Control)

Network layer Link Layer LLC MAC Physical layer packet LLC packet MAC LLC packet MAC Congestion Control 7UCLM UNIVERSIDAD DE CASTILLA~LA MANCHA

Bridge Interoperability Standards

LLC and MAC Sublayer Standards

Interoperability 802.2: LLC (Logical Link Control) Sublayer LLC 802.10: Security 802.1: Architecture 802.1: Managemment 802.1: Transparent Bridge Sublayer MAC (Media Access Control) 802.3: CSMA/CD (Ethernet) 802.4: Token Bus 802.5: Token Ring 802.6: DQDB 802.9: Iso- Ethernet 802.11: CSMA/CA (WLAN) 802.12: Demand Priority 802.14: CATV Physical Layer Congestion Control 88UCLM UNIVERSIDAD DE CASTILLA~LA MANCHA

Bridge Interoperability Diagram

Bridge Protocol Stack

Interoperability application application transport transport network network LLC LLC MAC MAC MAC physical physical physical physical bridge Congestion Control 9UCLM UNIVERSIDAD DE CASTILLA~LA MANCHA

Bridge Transparent Operation

Frame Handling in Transparent Bridges

Transparent operation frame MAC table A dst:C src: A C address port 1 2 MAC table B D Forwarding: bridge looks for destination MAC address at table. . If dst port == src port: DISCARD . If dst port != src port: FORWARD . If dest not in table: FLOOD Learning: · Port is updated for each frame src address, timeout is reset. Aging: . Table entry is removed when timeout expires, to allow mobility Congestion Control 10UCLM UNIVERSIDAD DE CASTILLA~LA MANCHA

Bridge Transparent Operation Example

Traffic Actions and MAC Table Updates

Transparent operation A C 1 2 B D Traffic Action MAC table Address Port A - B Flooding A (t1) 1 A - C Flooding A (t2) 1 B - A Discard B (t3) 1 C - A Forward C (t4) 2 D - B Forward D (t5) 2 Aging (timeout t2) A (t2) Congestion Control 11UCLM UNIVERSIDAD DE CASTILLA~LA MANCHA

IEEE 802.1D Transparent Bridges

Features of Transparent Bridging

Transparent bridges IEEE 802.1D . Any type of IEEE LAN (any LLC sublayer) · Bridge find out at what port is each station . It learns from source MAC addresses. · Forward frames only to right port . This bevahior is called "switching". . If the MAC is not found (or it's mcast/bcast): · Frame is sent to all of them (flood). . This is a security issue. · Table kept at RAM (about 1000-8000 entries). . Typical timout is 5 minutes Congestion Control 12UCLM UNIVERSIDAD DE CASTILLA~LA MANCHA

Transparent Bridge Algorithm

Frame Processing Steps

Transparent bridge algorithm Frame received without error at port x No Destination address found in table? Forwarding Yes Yes Output Port = x? Forward frame by all ports except x I No Forward frameto output port No Source address found in table? Yes Learning Update address and timer Add to database source address (with number of port and counter time) Finish Congestion Control 13UCLM UNIVERSIDAD DE CASTILLA~LA MANCHA

LAN with Two Bridges Example

Bridge Learning and Forwarding

LAN with 2 bridges los bridges aprenden porque interfaz deben mandar cada cosa C E D A 1 2 1 2 F B 1 2 1 2 A C BD A E BF E F C D Congestion Control 14UCLM UNIVERSIDAD DE CASTILLA~LA MANCHA

Multiport Bridges and Switches

Switch Port Speed and LAN Representation

Multiport bridges -> switches Switch may use a different speed at different port. · The minimal of all connected stations at these port. Cada interfaz representa una LAN C D A 1 2 10 Mbps 100 Mbps 3 10 Mbps B 1 2 3 ACE BDF E F Congestion Control 15UCLM UNIVERSIDAD DE CASTILLA~LA MANCHA

Typical LAN Switch Example

Cisco SG220-26 Specifications

Typical LAN switch CISCO 13F 24 TATJA IST 4A NETIA 187 BA 207 1A 21Y 10A 22Y15A 23712A 347 5G220-26 26-Port Gigabit Smart Plus Switch Cisco SG220-26 26-Port Gigabit Smart Switch . 38.69 Mpps (64-byte frames) / 52 Gbps · 8,192 MAC addresses · 802.1d - STP/RSTP/MSTP . 802.3ad - Link Aggregation Control Protocol (8 groups) · Up to 256 VLAN and 802.1Q STP: Spanning Tree Protocol RSTP: Rapid STP MSTP: Multiple STP VLAN: Virtual LAN Mpps: Mega packet per second https://www.cisco.com/c/en/us/products/collateral/switches/small-business-220-series-smart-plus-switches/datasheet-c78-731284.html Congestion Control 16UCLM UNIVERSIDAD DE CASTILLA~LA MANCHA

Bridge MAC Addresses

Port and Canonical MAC Addresses

Bridge MACS · Each port (interface) has its own MAC. . The bridge is identified with a specific MAC, called canonical address. . That MAC never appears in forwarded frames. . But the bridge may generate its own frames: STP, DTP, LLDP. Cada puerto tiene su MAC, la MAC canónica es la que identifica el bridge Canonical Address: 0030.9432.0C00 CISCO 21Y 104 227 114 237 124 5G220-26 26-Port Gigabit Smart Plus Switch Ports 0/1 to 0/24: 0030.9432.0C01 to 0030.9432.0C18 STP: Spanning-Tree Protocol DTP: Dynamic Trunk Protocol LLDP: Link Layer Discovery Protocol Congestion Control 17UCLM UNIVERSIDAD DE CASTILLA~LA MANCHA

Loops in Network Topology

Benefits and Harms of Loops

Loops are bad (and good) · Connecting same LAN segments with more than one bridge create loops. · We want topology loops, that provide reliability and fault tolerance. . But avoiding traffic loops, that generate broadcast storms and other harmful effects. · Spanning-Tree Protocol allows to have topology loops without traffic loops. Congestion Control 18UCLM UNIVERSIDAD DE CASTILLA~LA MANCHA

Loop Among Two LAN Segments

Traffic Duplication and Forwarding Issues

Loop among two LAN segments 1 2 A SW1 B 1 2 LAN X LAN Y SW2 · A sends a frame · Both SW1 and SW2 forward the frame · B receives 2 copies !! . SW1 receives the SW2 copy. . SW2 receives the SW1 copy. · Both SW1 and SW2 forward the frame from LAN Y to LAN X !! ● Congestion Control 19UCLM UNIVERSIDAD DE CASTILLA~LA MANCHA

Spanning Tree Concept

Definition and Loop Removal

Spanning Tree A spanning tree is a pruned graph which there is only a possible path between two nodes. · So, it removes loops. La raiz que elegimos sera casi siempre la que elige el admin, - Root EN EL EXAMEN: EL DE LA MAC MAS PEQUEÑA 1 1 1 / / Congestion Control 20UCLM UNIVERSIDAD DE CASTILLA~LA MANCHA

Spanning Tree Protocol (STP)

Bridge Communication and Cost Calculation

Spanning Tree Protocol (STP) · Bridges interchange info about their connections (BPDUs). . These frames are mcast'd to 01:80:C2:00:00:00 · Each port has an associated cost: · 10 Mbps -> costs 100 · 100 Mbps -> costs 10 . Each bridge calculate the LAN graph and detect loops. 2900-24TT SW1 2960-24TT BW2 2960L SVF 2960-24TT SW4 2960 SW5 La primera regla en el examen es mirar si en la linea ponemos coste o velocidad porque mayor coste es peor pero mayor velocidad es mejor BPDU: Bridge Protocol Data Unit Congestion Control 21UCLM UNIVERSIDAD DE CASTILLA~LA MANCHA

STP Example 1

Blocked Ports and Root Bridge Paths

STP: Example 1 LAN 2 (100 Mb/s) Bridge with two paths to the root. Blocked P2 (higher cost) Cost 10 Cost 10 P1 P1 ID 45 ID 44 This is no longer blocking anything because there are no loops Cost 10 P2 Root Bridge ID 42 LAN 5 (10 Mb/s) Cost 100 P2 ID 83 Two paths to the root bridge Cost 10 P1 LAN 1 (100 Mb/s) Cost 10 P2 Cost 100 Cost 100 Bridge without loops, blocks nothing P1 ID 97 P3 LAN 3 (10 Mb/s) LAN 4 (10 Mb/s) P2 Cost 100 P2 Cost 100 En rojo está bloqueado P1 Cost 10 Congestion Control 22UCLM UNIVERSIDAD DE CASTILLA~LA MANCHA

STP Example 2

Root Bridge and Blocked Ports

STP: Example 2 ROOT 0060.5C78.5D22 00DO.9758.D526 Este es el root porque es la id mas pequeña D R los cables son lanes 2960-24TT SW2 100 Mbps 2960-24TT SW3 D D 100 Mbps 1 Gbps R R D Blocked 2960-24TT SWO 1 100 Mbps 2960-24TT SW1 aqui no se bloquea porque como los cables representan lanes, si la bloqueamos quedaria aislada 00E0.8FE9.22C1 00DO.FF6A.5B73 Congestion Control stp-exercise. pkt 23UCLM UNIVERSIDAD DE CASTILLA~LA MANCHA

STP Procedure Steps

Root Bridge, Root Ports, and Designated Ports

STP procedure · Identify the LAN root bridge: · The one with lowest ID. Each bridge: · Set root ports (one per bridge): · The one to reach the root bridge with minimum cost. · Set designated ports (one per LAN segment): . The one to reach the LAN (from root br) with min cost. · Disable all other ports: blocked ports. Congestion Control 24UCLM UNIVERSIDAD DE CASTILLA~LA MANCHA

STP Tie Breakers

Election Criteria for Ports

STP tie breakers EN LOS EXAMENES NO NOS DAN PRIORIDADES EMPATES COMO ELEGIR EL CAMINO SI HAY EMPATE Election criterion for root and designated ports is: · Lowest cost to/from root bridge · (if tie) Lowest neighbor bridge ID · (if tie) Lowest neighbor port priority · (if tie) Lowest neighbor port ID Administrator may alter root bridge and port election by means of priorities. · Bridge default priority: 32.768 · Port default priority: 128 Congestion Control 25UCLM UNIVERSIDAD DE CASTILLA~LA MANCHA

STP Tie Breaker for Designated Ports Example

Choosing the Designated Port with Lowest ID

STP: Tie breaker for designated ports If cost from root bridge is same, choose bridge with lowest ID. Example: Tie at L2 for designated port. ● Same cost to root bridge for the two path · Designated port belongs to connected SW with lowest ID: SW1 · 0060.5C56.8A51 (SW1) < 0090.2127.6946 (SW2) 0001.C91D.899B (ROOT) L2 designated port 2060-24TT SWO 2960-24TT SW1 L2 2960-24TT SW2 Se elige esta porque la mac es menor 0060.5C56.8A51 0090.2127.6946 stp-ties.pkt Computer Networks II 26