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Difference between L2 and L3 broadcasting?

Community Administrator
Community Administrator

Q - I like to know the difference between L2 broadcasting (MAC address FF:FF:FF:FF:FF:FF) and L3 broadcasting (IP address 255.255.255.255).

I know ARP uses L2 BC. In which protocol/situation where L3 broadcast is used?. Anyway as router is going to block all broadcast(both L2 and L3), what is the difference between them.

...I know ARP uses L2 BC. In which protocol/situation where L3 broadcast is used?...

 

A - The most common Network Layer protocol used today is IP but be aware there are others. So in computer networking, a broadcast address is an IP address that allows information to be sent to all machines on a given subnet rather than a specific machine.

So there's your situation. Where you want to send a message to multiple computers in a network you use a broadcast address. There are other types of routing schemes ie. multicast, unicast and anycast but they're outside the scope of your original question.

The second part of your question was what protocols use IP broadcasts. Below I've listed a few but there are many more.

Here are some protocols at the Network Layer that use IP.

  • IPv4/IPv6, Internet Protocol
    • DVMRP, Distance Vector Multicast Routing Protocol
    • ICMP, Internet Control Message Protocol
    • IGMP, Internet Group Multicast Protocol
    • PIM-SM, Protocol Independent Multicast Sparse Mode
    • PIM-DM, Protocol Independent Multicast Dense Mode


There are other protocols like Appletalk DDPand IPX but most of the net runs on IP.

At layer two you are limited to computers that are connected to your direct network. For example Computer A on network 192.168.25.0 could not talk to Computer B on network 192.168.100.0 without using a layer 3 protocol. Layer 2 uses MAC addresses which cannot be routed. For network A(192.168.25.0) and network B(192.168.100.0) to talk to each other you'll need to use Network Layer protocols. The computers in either network would be connected via a switch can talk to each other and have Layer 2 connectivity so no routing is required.

The question your asking is very broad so I hope I helped so how. To really get your head around it all you should understand the encapsulation process.

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