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Multiple Subnets sharing a switch (no VLAN)

taraz0007
Beginner
Beginner

Is it possible to have multiple subnets sharing a single switch (without VLANs or routers)?

If so, what would happen?

Would the broadcast traffic be restricted to a single subnet, or would both subnets recieve the broadcast traffic (e.g., one broadcast domain or two)?

Would the subnets be completely isolated from each other?

Would the subnets be able to communicate?

Would the switch work, even though some of the devices would have a different network address?

 

16 Replies 16

InayathUlla Sharieff
Cisco Employee
Cisco Employee

Is it possible to have multiple subnets sharing a single switch (without VLANs or routers)?

Answer: NO.

 

2-Would the broadcast traffic be restricted to a single subnet, or would both subnets recieve the broadcast traffic (e.g., one broadcast domain or two)?

Answer: Broadcast traffic will be restricted to a single subnet. But here is the theory if users are been configured with the same subnet then without VLAN they will be able to communicate with each other.

Which means single broadcast domain.

Example:  --- Switch---

                  |              |

   PC1 192.168.0.1   PC2-192.168.0.2

These two machines will be able to communicate between each other but if you have PC is 192.x subnet and PC2 is other subnet like 10.x /172.x then the ping will fail which means there will not be any communication.

 

3-

Would the subnets be completely isolated from each other?

Answer":-- YES

 

4- Would the subnets be able to communicate?

Answer:- NO

 

5- 

Would the switch work, even though some of the devices would have a different network address?

Answer:- No it wont work untill you do the intervlan routing or proper communication on the switch.

 

HTH

Regards

Inayath.

 

 

 

Would the broadcast traffic be restricted to a single subnet, or would both subnets recieve the broadcast traffic (e.g., one broadcast domain or two)? 

 

Ans : Its the same broadcast domain since you have only one vlan (dafault vlan 1).

         The broadcast send by a pc will reach another pc eventhough it has different subnet.

 

Would the subnets be able to communicate?

Ans : Since you dont have multiple vlans or rouer that means you dont have a gateway ip address in you PC. So it cannot communicate to other subnets. A PC himself can understand whether the destination is on same subnet or different. If its different subnet, it looks for Gateway configured or not. In your case it will fail.

 

Hope this helps.

 

Thanks,

MAdhu

 

 

 

 

 

 

 

 

 

 

 

 

If I have some PCs with 192.168.2.xxx addresses and some with 192.168.10.xxx addresses, can they share a switch whose address is in the 192.168.2.xxx address space?  Can they communicate with each other?

For communication purposes, whether hosts can intercommunicate, between subnets, on the same L2 domain, again, depends on how the hosts are configured, and how the communication is being attempted.  The switch, as a host (i.e. its management IP), should behave like any other host.

There is not a clear or simple answer to the question of whether 192.168.2.0 devices can communicate with 192.168.10.0 devices. It depends on several tings. One factor is whether all of the devices are in the same layer 2 broadcast domain (in the same vlan)? If they are in the same broadcast domain then communication MIGHT be possible but if they are in different broadcast domains then communication is not possible without a layer 3 routing device.

Probably the most important factor is whether each device would arp for an IP address that was outside of its own subnet. For many versions of many OS this is not possible. The device needs a functioning default gateway to forward to a remote subnet. For some versions of some OS it is possible to arp for a destination in a remote subnet. For these devices communication might be possible. So it really depends on the OS and how the device is configured.

HTH

Rick