 Hello and welcome to the lecture on networking devices to that is bridge Learning outcomes by the end of the session student will be able to describe the operation of internet working device bridge before starting this topic Try to answer this question The question is why the repeaters are called as level one relay You may pause here the video and try to find out the answer The answer to this question is a Repeater operates as a physical layer Data issued on one of its port is relayed or transmitted on the remaining all the ports bit by bit without looking into the content Hence the repeater is called as a rebel one really Bridges are used to interconnect two separate lines The bridge may connect to similar or dissimilar lines Here in figure number one as you can see a Bridge has two ports here and it connects land one and land two to each other The land one and land two may be similar or dissimilar Similar means land one and land two may be 10 bestie both or one could be 10 bestie and other could be 100 bestie So here the point to note is that bridge can connect Similar or dissimilar lines while hub connect only similar lines segment Bridge operates in the first two layer The data link layer of OSI model and is called as Sometimes is called as level to relay with the reference of OSI model you here in figure number two We can see that The first two layer that is physical layer and data link layer are the part of a bridge Bridges are designed to store filter and Forward the frames it is protocol independent and transparent to the end stations as well advantages of the bridges Bridges are highly reliable Bridges have a good performance as well as security and bridges cover larger geographic areas But the quality of service offered by the bridge should match to the quality of the service Pro supplied by the single line Quality of service comprises of availability of a network frame mishaps transit delays during transmission frame lifetime Undetected bit errors frame size and priority offered to the frame key features of the bridges are bridge operates in both physical and data link that is the first two layers of OSI model Addressing and routing capabilities are there Bridge uses a table for filtering or routing Bridge does not change the physical that is MAC address of a frame Types of the bridges. There are two types. The first type is transparent bridge. Second is source routing bridge Transparent bridge is an extension of IEEE 802.1 standard and transparent bridge Or this standard is applicable to all the 802 lines that is Ethernet lines The second type is source routing bridges IEEE 802.5 token ring standard is based on source routing approach this approach applies to LAN including token ring token bus and carrier sense multiple access can detect Bus we will deal with the first type that is transparent bridge in transparent bridge There are two processors involved in its operation. The first process is bridge forwarding the another is bridge learning in bridge forwarding process whenever a frame comes to the bridge before forwarding it The bridge looks into its database for the destination address if the destination address is present in its database then Bridge will forward that frame Particularly to a single port to which the destination host is attached If it is not present if the destination address Contained in the frame is not present in the bridge database then bridge will flood Or bridge will send the that frame on all the ports The second process is bridge learning in this process Whenever a frame arrives at the bridge bridge extract its destination address and It's tour the second process is bridge learning in this When a frame comes at the bridge bridge takes its source address and the incoming port number and Copy that in its database So it can be used later on to find out the particular address of her host and its Direction we will see the bridge forwarding process with the help of this flow Whenever a frame without error comes to a port then the bridge will Check its database before forwarding for the direction or the port number through which the frame should be sent out if The destination address is present in the database then to that through that particular port The frame is forwarded to the land if The bridge do not have the destination address in its database then The bridge will forward the frame to all the lands that is nothing but flooding of free This is a bridge forwarding process The second process is leisure bridge learning process whenever a Frames arrives at a bridge if the source address is already present in the database then The bridge will update its direction direction means through which port the frame has arrived and the timestamp If the source address of the frame is not present in the database Then that source address is added to the database with the direction means the port number Through which the frame has arrived and a new timestamp so that added source address From the database can be used While forwarding the frames later on let us see how the routing table or bridge learning is done with this diagram Here we have bridge and we have four ports and To each port number of machines or station are connected initially when The bridge is installed the database or the routing table or forwarding table is empty It does not have any information Basically the database or the forwarding table contains three fields. The first is address second is port number and Third is timestamp, but we have not shown that timestamp field initially The forwarding table is empty when Station a and station c sends a frame or forwards a frame that time the bridge will learn through bridge learning process that address a is connected to the bridge through port number one Address c is connected to the bridge through port number two After all the station send a frame the bridge will update its database or forwarding table with the particular address and The port number to which the address is connected all the addresses Dealed by bridge are Mac addresses or hardware addresses bridge. Do not deal in IP addresses The bridge forwarding and bridge learning process works fine until There is redundant bridge redundant bridge is nothing but an additional bridge the redundant bridge or redundancy is Desirable from the viewpoint of reliability if a bridge fails then its functions can be Carried out by a redundant bridge But redundancy leads to creation of loops how the loops are created we are going to See with this figure number six Here we have two lands land x land y two stations station B and station a two bridges bridges a and B Initially after the installation of bridges as we have seen The forwarding table are empty Supposed at that time station a sends a frame to station B That time both the bridges will receive the same frame and both bridges will forward that through all the ports because initially both bridges Do not have any information about the station B. So both bridges will send the frame on Land y so land y has two copies and both bridges do not know about the station B location so Bridge B will once again forward that received frame from bridge a on the land x so the same process of forwarding from land x to land y and Land y to land x will keep on repeating creating two loops as loops are undesirable to prevent the loops I Tripoli suggested one solution known as spanning tree These are the references. Thank you