● Bridges● Routers● Gateways

submitted by

P.Mahalakshmi

sathyabama university

Bridges

operates in both the physical and the data link layer

physical layer-regenerates the signal it receives.

data link layer -physical (MAC) addresses

(source and destination)

Filtering

Example.

Types of bridges

● Transparent Bridges● Source Routing Bridges

Transparent Bridges

● stations are completely unaware of the bridge's existence.

● reconfiguration of the stations is unnecessary.

● IEEE 802.1 d specification, 3 criteria

I. Frames must be forwarded from one station to another.

2. The forwarding table is automatically made by learning

frame movements in the network.

3. Loops in the system must be prevented.

Learning

● The earliest bridges had forwarding tables that were static.

● A better solution -dynamic table

● example

Loop Problem

● Transparent bridges work fine as long as there are no redundant bridges in the system.

● redundant bridges (more than one bridge between a pair of LANs) to make the system more reliable.

● Redundancy can create loops in the system

spanning tree algorithm

● LAN can be reached from any other LAN through one path only (no loop)

● minimum hops(nodes),● the path with minimum delay, or● the path with maximum bandwidth● Each bridge is equipped with a software package● The bridges send special messages to oneanother, called

bridge protocol data units (BPDUs)

Source Routing Bridge

● to prevent loops in a system

● the frame must visit bridges

● exchange of special frame with the destination prior to sending data.

Routers

● three-layer device that routes packets based on their logical addresses

● connects LANs and WANs in the Internet● routing table(dynamic) ● Tables updated using routing protocols. Eg-RIP● The Routing Information Protocol (RIP) is one of the oldest

distance-vector routing protocols, which employs the hop count as a routing metric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from the source to a destination.

Gateway

● normally a computer that operates in all five layers of the Internet or seven layers of OSI model.

● application message, reads it, and interprets it● connecting device use different models● Eg OSI model can be connected to Internet

model

Thank you