I am a newbie in networking and is experimenting with CISCO Packet Tracer 5.0. I found that in Packet Tracer I cannot configure two legs of a router to be in the same subnet. In that software one simply can't configure a network card to be in the same subnet as an already configured card. However, I found that I can configure the two NICs in my PC to be in the same subnet, and can still get through to the Internet. I know that a router loses most of its role if both of its legs are configured to be in the same subnet, but theoretically are there an rules forbiding such practice?
Yes, the route table won't like the same subnet on two interfaces. I'm not sure if this would work if you didn't have "ip routing" configured... you could try turning off "ip cef" too... but i've never been able to do this on a real router.
Other option on a real router is to put both interfaces in "bridge" mode, or configure the second interface to clone the details from the first... although i've only ever done this with Dialer interfaces before.
So I guess the answer is yes... the router wants to put the route to the subnet in its route table (show ip route) and if you have two interfaces both with the same subnet, the route-path costs would be equal and identical... which is a huge issue in a networking environment.
Your PC doesn't care... it's not really routing. It's quite common to do this with a PC for the purposes of doubling bandwidth, load balancing, or having redundant links. (on the switch you would need to configure a "port-channel" to bond two ports together.)
Cheers!
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