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utl
New Member

why would you require a L3 device between two hosts of differenet subnets?

Why we require a Layer 3 Device between two hosts with different subnet addresses, so that they can transfer data. and why a Layer 2 device can't serve the purpose?

can anybody explain me or point me to a detailed explanation.

regards

kumar

1 REPLY
New Member

Re: why would you require a L3 device between two hosts of diffe

Do you mean that two hosts are in same physical network (let's say they are in same ethernet medium), and they are in different network address (let's say the first one's IP address is 192.168.1.1 and the second one's IP address is 192.168.2.1 with network mask of 255.255.255.0)?

In this case, they can communicate in L1 and L2, but not L3. In Layer 3, IP network layer, if 192.168.1.1 want to send a packet to 192.168.2.1, the first host knows that the destination's network address differs from itself and it send the packet to the gateway (L3 Router). It even does not try to send the packet to the destination directly. Therefore, we need L3 device.

However, they are physically connected, and they can communicate in L1 and L2. If you modified the IP network standard(L3), they can communicate, but it is really rare case, the standard does not support it.

If you really want to communicate each other without L3 device, you can use secondary network address. We can use two or more IP address in a single network port.

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