two interfaces one subnet

Patrick W. Gilmore patrick at
Mon May 11 16:47:43 CDT 2009

On May 11, 2009, at 5:19 PM, Alex H. Ryu wrote:

> Unless you configure Layer 2 for two interfaces, it's not going to  
> work.

It can work.  Of course it _may_ not, depending upon your  
implementation, but then some implementations can't get a single  
interface to work properly per subnet.

> It is invalid from networking principle.

You are confused, there is nothing invalid about the configuration.

> If you have to send the traffic for host in same subnet you  
> configured,
> which interface it should send out ?

Pick an interface and send the packet.  It's not rocket science.  I  
can come up with half a dozen algorithms off the top of my head while  
typing the last sentence.

> Basically it may create broadcast storm loop by putting two ip  
> addresses
> in same subnet in different interface.

That is an interesting statement.  Could you explain how this can  
happen without crafting an idiotic implementation spec (e.g. every  
packet goes out both interfaces)?

> It may be allowed from host-level, but from router equipment, I don't
> think it was allowed at all.

Ever used HSRP / VRRP?  Two interfaces in the same subnet.  Works  
fine.  In fact, most people think it works _better_ than one interface  
in the same subnet.


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