What happens exactly after configuring a default gateway for a host ?

[chandra_rc16]

What happens exactly after configuring a default gateway for a host ?

Actually i was doing Router on-a-stick lab...

I forgot to configure DG for PC2 in VLAN2 but i configured DG for PC1 in VLAN1. So they were unable to communicate.

When i configured DG on PC2 they're fine....

The thing that i observed here is as soon as i configured DG they're fine.. so i think something happens behind the scene that will tell

to the router about the host that configured DG.

Can someone please explain this ?

Regards,

Chandu

[cadet alain]

Hi,

host in vlan 1(subnet 1) wants to talk to host in vlan 2(subnet 2):

-it first need to know if the host it wants to communicate with is in the same subnet as it is, for this it is going to do a bitwise logical AND between its IP and its mask and then compare to same operation between its mask and the destination IP.

-They aren't in the same subnet so it is going to need to send the packet to a L3 device(its default gateway) which will route the packet.

Regards

Alain

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[chandra_rc16]

Thanks Alain.

Thanks for the info.

Forgot about all the topology etc etc..

But my question is when we configure DG on a PC or SW or anything.... will that device send any information to the Gateway.. informing it that it has added you as the gateway ?

Regards,

Chandu

[Jon Marshall]

Chandu

will that device send any information to the Gateway.. informing it that it has added you as the gateway ?

No, it doesn't need work that way.When a device needs to send packets to another device on a different IP subnet it those packets need to be routed. So the device sends them to it's default gateway. It's that simple. There is no need to inform the gateway, you simply send packets to it and the gateway device is then responsible for routing the packets towards the destination.

Jon

[Joseph W. Doherty]

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Posting

But my question is when we configure DG on a PC or SW or anything.... will that device send any information to the Gateway.. informing it that it has added you as the gateway ?

No, it only sends off local network packets.