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As far as I know in order to use two subnets on one physical cable VLAN's are recommended.

However, is it possible to achieve this (i.e: two subnets on one physical network)

like and networks.

What kind of problems or hidden rocks this way contains?

With VLAN's it's possible to better isolate so users wouldn't easly sniff the other network. But in my environment it's okay if user on one subnet could listen to the traffic on another network. Is it the only problem?

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up vote 2 down vote accepted

It is perfectly possible -- and not terribly uncommon -- to run two separate layer 3 (i.e, "IP") networks over one layer 2 (i.e, "Ethernet") network. A common use case for this is in environments that allow self-registration of network clients. Unregistered clients get address on one subnet, and once registered they get an address on another, less restricted network (one that might allow outbound network access, for instance).

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thanks, how routing is configured then? should one pc have two ip addresses on both networks and set a route to it? – bakytn Apr 3 '12 at 9:32
Yes, a PC would need an address on both networks, and both networks would need a default gateway defined. – larsks Apr 3 '12 at 11:00

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