2) Give short answers to the following: a) State the functions of each of the fo

ID: 3754137 • Letter: 2

Question

2) Give short answers to the following: a) State the functions of each of the following LAN components and explain their key differences: hub, layer-2 switch. b) What are the benefits of using a bridge? State the main functions of a bridge. c) Answer the following questions with respect to the "address learning" mechanism in the IEEE 802.1 standard for routing in bridges: . What purpose does it serve? How does it work? . What is the potential problem caused by this mechanism in routing in interconnected LANs?

Explanation / Answer

Answer:

HUB: Hubs function as the central connection point for Local Area Network (LAN). Hubs are designed to work with Twisted pair cabling and normally use RJ45 jack to connect the devices. Network devices (Servers, Workstations, Printers, Scanners etc) are attached to the hub by individual network cables. Hubs usually come in different shapes and different numbers of ports. Hubs are considered to operate at Physical Layer (Layer 1) of OSI model.

Layer 2 Switches: Bridging technology has been around since the 1980s.Bridging involves segmentation of local-area networks (LANs) at the Layer 2 level. A multiport bridge typically learns about the Media Access Control (MAC) addresses on each of its ports and transparently passes MAC frames destined to those ports. These bridges also ensure that frames destined for MAC addresses that lie on the same port as the originating station are not forwarded to the other ports.

Layer 2 switches effectively provide the same functionality. They are similar to multiport bridges in that they learn and forward frames on each port. The major difference is the involvement of hardware that ensures that multiple switching paths inside the switch can be active at the same time.

HUB

2-LAYER SWITCHES

A hub doesn’t inspect the information being sent

A 2 layer switch inspect the information being sent over the network.

A hub broadcasts received packets to all other ports

A 2 layer switch does not broadcasts packets to all other ports

A hub’s bandwidth degrades with more clients.

A layer-2 switch does not bandwidth degrades with more clients.

A hub is a simpler device than layer 2 switch.

Layer 2 switch is complex device than Hub.

while hubs are already obsolete

Layer 2 switches are very common

Answer 2:

Benefits of bridges:

Prevents Bandwidth Waste: A bridge managed incoming traffic and reduces bandwidth waste by preventing all unnecessary flow of data between network segments.

Increases Network Length: network bridge increases the functional length of a network by connecting individual LAN segments

Links Dissimilar Network Transmission Segments: A bridge can connect both similar and dissimilar LAN segments

Major Functions of bridge:

Answer 3:

Purpose it serves:

When customer devices are routers, servers, or hosts, then the number of MAC addresses customer sites is very limited (most often one MAC address per CE). However, when CEs are bridges, then there can be many customer MAC addresses associated with each CE.[802.1ad] has devised a mechanism to alleviate MAC address learning within provider Ethernet networks that can equally be applied to VPLS networks. This mechanism calls for disabling MAC address learning for an S-VLAN (or a service instance) within a provider bridge (or PE) when there is only one ingress and one egress port associated with that service instance on that PE. In such cases, there is no need to learn customer MAC addresses on that PE since the path through that PE for that service instance is fixed.

How does it works

The Ethernet interface on each port of a bridge runs promiscuous Mode. In this mode, the interface reads all the frames it sees on the connected LAN, not just the frames that are being sent to the bridges own MAC address. As each frame is read in on each bridge port, the bridge software looks at the source of address of the frame and add the source address to a table of addresses that the bridge maintains. This is how the bridge figures out which stations are reachable on which port.as stations send traffic, the b ridge receives every frame sent and build a table that show the station can be reached on which port. After every station has transmitted at least one frame , the bridge will end u forwarding database. This database is used by bridges to make a packet forwarding .this type of bridge is called learning bridge as it has ability to dynamically add new addresses.

Potential problems:

Flooding: bridge may forward a frame out all ports other than the one it was received on. It there si no match int the bridge’s address database for frame’s destination address, then the bridge will forward frame to all ports causing flooding.