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two networks with one adapter

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Hyuk Kwon
Occasional Contributor

two networks with one adapter

While I googled network related articles, I encountered an article (http://asia.cnet.com/enterprise/netadmin/0,39035505,39148297,00.htm) which shows how to configure network interface card in various network environments.
However, it's hard for me to understand its second scenario -- two networks with one adapter -- in this article. How I can build two different subnets that I can connect with one adapter? I'd like to test it, but I had no idea how two physically build this environment.

Does someone give me an insight of how do I can build this?.

Thank you in advance.

PS. The diagram in question is attached.
4 REPLIES
HRE
Valued Contributor

Re: two networks with one adapter

Hi,

Some NICs schould be 802.1Q compliant. So they will support tagged VLANs. I have never done this, but it schould be possible to tag this to more then one VLAN. Please ask the manufacturer of your NIC or your onboard LAN interface. For example, i heard, that the NForce2 Chipset with the MCP-T LAN shall do that after manipulating the .inf File.

regards

HRE
Ron Kinner
Honored Contributor
Solution

Re: two networks with one adapter

It's not hard to do. Essentially you run two subnets in parallel. You don't have to do VLANs or do anything fancy with the switch. Any switch or hub will do. Just assign two different IP addresses/masks to an interface. Then plug the NIC into a switch. Then plug a device A on subnet A into the switch and a device B on subnet B into a different port on the switch.

Device A can not directly talk via IP to Device B or vice versa since they are in different subnets (if it receives packets belonging to a different subnet they will be discarded) but both can talk to your first device. They like to say in Cisco class that the packets from the different subnets pass each other in the switch like "ships in the night" and don't interact at all.

If you turn on IP forwarding on the first device you can then let A talk to B via the first device. This is a common scenario with a Cisco router. We program a secondary address on the interface and the router routes packets between the two subnets usually for purposes of filtering but also in some advanced switching scenarios. It's sometimes called "router on a stick" if that's all the router is doing.

Ron
Hyuk Kwon
Occasional Contributor

Re: two networks with one adapter

Ron,

Thank you for the instruction. I tried it with one switch (3Com PS 40) and two hubs, but it didn't work out.
I could access one subnet, but still not access the other subnet.
I may try again next week.
Hyuk Kwon
Occasional Contributor

Re: two networks with one adapter

Ron,

Thanks again for your solution.
It worked perfectly as you expalined. I picked a defected hub when I tried last week.

Thanks for HRE as well. I'll check out VLANs option.