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New Member

Two VLANs, same Subnet, no IP Routing; Communication dilemma

Here is the scenario:

Part-A: Host 2) is able to ping host (vlan 3) WITHOUT layer-3 routing being enabled on 3560. The reason behind that is when the host generates an ARP request broadcast looking for host as target, the frame is received on VLAN 2 and is broadcasted out on all ports member of VLAN 2 but the receiving port. So, in our scenario, broadcast gets sent out fa0/24 of SW-1 and will be injected into VLAN 3 of Sw-2 via fa0/24 of SW-2. This broadcast will further be forwarded by SW-2 and will eventually reach the target. Target will send ARP req unicast and the return unicast mac of host is being known on SW-2 to be on fa0/24 member of VLAN 3. SW-2 will forward the arp reply unicast out fa0/24 an SW-1 will receive it on its fa0/24 member of VLAN 2 and SW-1 knows that the mac of host is actually on fa0/1 and this completes the switching.

Part-B: Host is not able to communicate with because SW-1 never even sends out the arp broadcast outside of VLAN 2, so fa0/2 a member of vlan 3 on SW-1 will not see ARP request as request is only being broadcasted out ALL vlan 2 ports.

Part-FINAL: Now, here is the confusing part:

Why is the host not able to communicate with int vlan 3 (  created on SW-2? How is it any different than Part-A? Frames will be broadcasted out fa0/24 of Sw-1 and will be received on fa0/24 of SW-2 a member of VLAN 3 and then SW-2 is forwarding the broadcast out all its physical ports that are member of VLAN 3. Why SVI 3, being like a host on VLAN 3, not ever receive it? I am lost? Why cant host communicate with SVI 3 (


Please help me finding the reason for Part-FINAL. I have also attached packet tracer topology here.

Everyone's tags (4)
New Member

Hi,Are you getting ping from


Are you getting ping from host to




 It is due to proxy-arp.


It is due to proxy-arp. Below discussion give you details.    or





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