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To be honest, I've never had experience with networks, so I thought someone here could help me out.

I have a switch connected to a router and then all devices are connected to the switch (it has five ports numbered 1-5) and the problem is that those devices are not listed on router's web interface. The LAN between the devices is working, but I need to forward server's (which is also connected to the switch) ports and I cannot see it on router's web interface. Though I do see all other devices which are connected directly to the router or via WiFi.

What are my options here?

Thank you!

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1 Answer 1

up vote 5 down vote accepted

You didn't say what make/model router you have, but that really shouldn't be relevant. The router doesn't need to "see" the hosts connected to the switch in order to set up port forwarding for hosts connected to the switch. At least not in the sense that these hosts show up as connected devices in the router's web interface. After you configure port forwarding the router will do the following for inbound traffic that matches your port forwarding rules:

  1. The router will check it's "service" rules to see if the inbound traffic is allowed.

  2. If the inbound traffic is allowed then the router will check it's port forwarding rules to see where to forward the inbound traffic.

Steps 1 and 2 might be (and probably are) combined in a single operation.

  1. The router will issue an ARP request to find the MAC address of the internal ip address of the host that is to recieve the inbound traffic. The router will broadcast this ARP request to all of it's ports.

  2. The switch will recieve this ARP broadcast on the port uplinked to the router and in turn broadcast this ARP request to all of it's ports.

  3. The host that is to recieve the traffic will answer the ARP request in the affirmative with it's MAC address.

  4. The router will forward the inbound traffic to the MAC address of the host.

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Thanks, very informative answer! So if I understood, there is a way to forward ports by MAC, not by local IP address (this is why I thought I need to "see" the devices connected), right? I cannot check it right now, but I sure will! –  Cinnamon May 12 '11 at 17:38
    
No, you need to configure your port forwarding based on the internal ip address of the server. The router will take care of finding the MAC address via ARP resolution on it's own. –  joeqwerty May 12 '11 at 17:42
    
So even if the router doesn't list the server as a connected device, I can still use server's local IP address in port forwarding? Just a reminder: the server is connected to the switch, not the router directly. –  Cinnamon May 12 '11 at 17:44
1  
Yes, that's correct. The router does not need to see the server as a connected host in order to port forward to the server. The router will find the server via ARP. –  joeqwerty May 12 '11 at 18:13

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