What happen when we connect Two PC with IP from Same subnets

abhishekmohanty90 · ‎02-14-2015

Scenario 2nd : What happen when we connect Two PC with IP from Same subnets. PC1 -192.168.10.1/24 PC2 - 192.168.10.2 on a two different L2 Switch on different vlans which are connected via a LAN cable.
All ports are access ports
Interview Question : No More Info.
Pc1<SwA>------<SwB>PC2

Q.1 Will they communicate If yes what will be packet/frame flow.
Q.2 If not where will be the packet/frame drop. ? Why.

I need step by step if possible plz how the packet moves , vlan taggings n all internal works that happens behind .. plz

thnx in advnce ....

Cisco Freak · ‎02-16-2015

Hi Abhishesk,

The PCs should communicate each othet.

Since there is no trunk port involved, there is not tagging involved.

Since both the PCs are into the same subnet. PC1 will not need default gateway for the communication with PC2. So PC1 will start with sending ARP request for PC2 MAC address.

Since all the ports in SW1 are in same VLAN, the ARP should reach all ports including the switchport where SW2 is connected to.

Sw2 has got a complete different access port on ALL the switchports. Sw2 will receive the ARP from Sw1. Remember that there is no tagging for the frame. Hence Sw2 will again send the ARP packet to all the ports which belong to same VLAN wherein the packet is received. ie, Sw2 will send the ARP packet to all the ports in Sw2. PC2 will also get the the ARP.

The ARP reply will make it way back using the same logic.

Now both the PCs can start the actual packet exchange.

Jon Marshall · ‎02-16-2015

It may work or it may not work but without knowing how the switch interconnection is setup you can't tell.

If there is only one vlan on each switch then i agree with CF it will work.

But the question doesn't say that. It simply says all ports are access ports not how many vlans there are per switch and most importantly it does not tell you which vlan(s) the ports that are used to interconnect the switches are in.

So it's not possible to say without more information unless you missed that out of the question.

It is most likely as CF has described but if i was asked that question as you have stated it i would clarify how many vlans per switch and were the switch interconnect ports in the same vlan as the PC ports.

Jon