GATE CSE 2004 | Question: 16

Question

Which of the following is NOT true with respect to a transparent bridge and a router?

• A. Both bridge and router selectively forward data packets

• B. A bridge uses IP addresses while a router uses MAC addresses

• C. A bridge builds up its routing table by inspecting incoming packets

• D. A router can connect between a LAN and a WAN

Comments

A bridge is LAN device and it's operation is based on MAC address whereas a router is a WAN device and it's operation is based on IP address.

So option b statement is false.

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what does “transparent” mean here in the question?

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@Cruzer bro 

 

Your statement is partially correct !!

A bridge is a LAN device that operates at the data link layer (Layer 2) of the OSI model. Its primary function is to connect two or more network segments together and forward traffic between them based on the destination MAC addresses of the devices connected to the network. Bridges are used to segment and extend LANs, and they can also be used to increase network capacity and improve network performance by reducing collisions and congestion.

A router, on the other hand, is a device that operates at the network layer (Layer 3) of the OSI model. Its primary function is to connect multiple networks together and forward traffic between them based on the destination IP addresses of the devices connected to the network. Routers are used to connect LANs and WANs (wide area networks), and they can also be used to provide security by filtering traffic based on various criteria, such as IP addresses, ports, and protocols.

So, while it's true that a bridge operates based on MAC addresses and a router operates based on IP addresses, it's not entirely accurate to say that a bridge is a LAN device and a router is a WAN device. Both bridges and routers can be used in LANs and WANs, depending on the network architecture and requirements.

Answer 1

• A. Both bridge and router selectively forward data packets $\Rightarrow$ True.
  Bridge can drop packets not meant for other side, so can router.

• B. A bridge uses IP addresses while a router uses $\text{MAC}$ addresses $\Rightarrow$ False .
  A bridge operate at layer $2$ (data link layer) so it uses $\text{MAC}$ address,
  while router at layer $3$ (network layer) so it using IP addresse

• C. A bridge builds up its routing table by inspecting incoming packets $\Rightarrow$ True.
  Self Learning Bridges

• D. A router can connect between a $\text{LAN}$ and a $\text{WAN} \Rightarrow$ True.
  Router connecting home $\text{LAN}$ To internet !

Correct Answer: $B$

Comments

Bridges don't really fit into a routing table ideology, because there is no routing involved with them. A computer on wlan0 will be able to see and talk directly to any computer on eth0. This is different from routing, where while computers on wlan0 can talk to computers on eth0 and vice-versa, they do not do so directly. Instead, the computers talk to the router, and trust the router will send it on to the appropriate destination.

https://superuser.com/questions/460082/network-bridge-and-routing-table

C) also should be a wrong option

 

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The main difference between router and bridge is router will do connection between two WAN packets, where as bridge do connection between 2 LAN packets

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@Sreshta

I think u r true...

Bridges works on physical layer as well as data link layer. So it can able to look at the MAC addresses of frames and we know that theoretically Bridges are used to connect two LAN segments, these LANs may be different(one is Ethernet, other is a token ring).

Routing word comes after the discoveries of Routers, it is used to connect two Networks(that became internet). Routers are more capable than these bridges, practically we don't use bridges to connect different LANs because they might have different MTU, so here fragmentation is needed but bridges can't do that.

Yes, bridges will have something known as Forwarding table or mapping table by which they are used to deciding to forward the packets but they can not have any routing table. 

Answer 2

ans b)

Comments

A bridge operate at layer 2 (data link layer) so it uses MAC address, while router at layer 3 (network layer) so it using IP addresses 

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for option (c), it has be mac table instead of routing table.??confused?

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@Hacker

Routng doesn't mean that it's always uses ip addresses.. .it may uses mac Addresses,or ip adressess....it defines only path to the destination