Chapter 17 Connecting Devices And Virtual LANs 17.# 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17.# 1

Chapter 17: Outline 17.1 CONNECTING DEVICES 17.2 VIRTUAL LANS 17.#

17-1 CONNECTING DEVICES Connecting devices are used to connect hosts together to make a network or to connect networks together to make an internet. 17.3 17.# 17.#

17-1 CONNECTING DEVICES Connecting devices can operate in different layers of the TCP/IP model. 17.4 17.# 17.#

three common connecting devices: repeater-hubs, link-layer switches, and routers. 17.5 17.# 17.#

Figure 17.1: Three categories of connecting devices 17.6 17.# 17.#

17.17.1 Repeater-Hubs A repeater-hub is a multiport device that operates only in the physical layer. Signals carrying information within a network can travel a fixed distance before attenuation endangers the integrity of the data. 17.7 17.# 17.#

17.17.1 Repeater-Hubs A repeater receives a signal then regenerates and retimes the original bit pattern. A repeater-hub (hub for short) is a multiport repeater. The incoming signal is regenerated, retimed and sent through all ports excluding the entry port. 17.8 17.# 17.#

Figure 17.2: Hub 17.9 17.# 17.#

17.17.2 Link-Layer Switches A link-layer switch operates in both the physical and the data-link layers. AKA, 2-layer switch 17.10 17.# 17.#

17.17.2 Link-Layer Switches As a physical-layer device, it regenerates the signal it receives. As a link-layer device, the link-layer switch can check the MAC addresses (source and destination) contained in the frame. Some switches operate using virtual circuit identifiers or virtual path identifiers (or both). 17.11 17.# 17.#

17.17.2 Link-Layer Switches Example (private Ethernet network with a 2-layer switch) The switch table needs entries for each connected device MAC addresses and the corresponding port number. MAC address: 48 bits, 12 nibbles, 6 octets. 17.12 17.# 17.#

Figure 17.3: Link-Layer Switch 17.13 17.# 17.#

17.17.2 Link-Layer Switches Example (private Ethernet network with a 2-layer switch) A 2-layer switch is much smarter than a repeater(hub). The switch forwards the message through the appropriate port or ports as determined by the frame header fields. 17.14 17.# 17.#

17.17.2 Learning Switch A learning switch can build a forwarding table by looking at the source address and corresponding port number. Frames can be broadcast to the unassigned ports (like a hub) until all the ports are assigned. This can be accomplished with Switch Port Mapping Software 17.15 17.# 17.#

17.17.2 Switch Software SNMP = Switch Network Mapping Protocol Managed Switch Port Mapping Tool NetDB = Network Tracking Database OpUtils Lan-sweeper 17.16 17.# 17.#

Figure 17.4: Learning switch 17.17 17.# 17.#

17.17.2 Switchs Unmanaged switches – plug-n-play, without a management interface. Managed switches – will include a command line interface. Smart switches Managed switches 17.18 17.# 17.#

Figure 17.5: Loop problem in a learning switch (Part a) 17.19 17.# 17.#

Figure 17.5: Loop problem in a learning switch (Part b) 17.20 17.# 17.#

Figure 17.5: Loop problem in a learning switch (Part c) 17.21 17.# 17.#

Figure 17.5: Loop problem in a learning switch (part d) 17.22 17.# 17.#

Figure 17.6: A system of connected LANs and its graph (Part a) 17.23 17.# 17.#

Switch link assignment Switch to Lan = 1 Lan to Switch = 0 17.#

Figure 17.6: A system of connected LANs and its graph (Part b) 17.25 17.# 17.#

Figure 17.7: Finding the shortest path and the spanning tree for a switch. 17.26 17.# 17.#

Figure 17. 8: Forwarding and blocking ports after using spanning Figure 17.8: Forwarding and blocking ports after using spanning tree algorithm 17.27 17.# 17.#

17.17.3 Routers We will discuss routers in Part IV of the book when we discuss the network layer. 17.28 17.# 17.#

17.17.3 Routers A router is a three-layer device; it operates in the physical, data-link, and network layers. 17.29 17.# 17.#

Figure 17.9: Routing example 17.30 17.# 17.#

17-2 VIRTUAL LANS A virtual local area network (VLAN) is a local area network configured by software, not by physical wiring. 17.31 17.# 17.#

Figure 17.10: A switch connecting three LANs by wire 17.32 17.# 17.#

Figure 17.11: A switch using VLAN software 17.33 17.# 17.#

Figure 17.12: Two switches in a backbone using VLAN software 17.34 17.# 17.#

17.2.1 Membership Characteristic used to group stations in a VLAN: interface numbers, port numbers, MAC addresses, IP addresses, or a combination of two or more of these. 17.35 17.# 17.#

17.2.1 VLAN VLANs … Save time and money because stations can be moved to any VLAN without re-wiring. Help manage network traffic Separate LANS for better security management 17.36 17.# 17.#