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I have four servers connected to our organization's network. I've obtained a layer 3 switch (Cisco SG300). I've separately connected each server's management interface NIC to this switch. (The management interfaces are Dell iDRAC, in case it matters.) Now I want to isolate the management network on this switch for security reasons, connect the switch to our organization's network, and only allow outside connections from specific hosts such as my laptop.

                                     ,- server 1 management interface
                           ,-------. +- server 2 management interface
external (open) network ---+ SG300 +-+- server 3 management interface
                           `-------' `- server 4 management interface

I think I can work out VLAN configuration for the management network on the right-hand side of the SG300, and if I understand ACLs on the Cisco switch correctly, I should be able to create an ACL that allows only a specific MAC address from the external network to connect through the SG300 to the VLAN on the right-hand side.

My problem is this: how can a connection from the outside network specify which destination (1-4) to connnect to? Suppose the management NICs have IP addresses 192.1.1.1 through 192.1.1.4, and say I'm on the external network, and I want to connect to machine 3's management interface. How do I do that? The servers' management interfaces will not have IP addresses on the external network, so I can't connect to a specific IP address. How do I indicate the desired destination?

This is probably a basic networking question, and obviously I lack clue, but after beating my head against Google for quite some time now, I can't figure this out. What is the basic approach to achieving this configuration, and are there resources that explain how to make it happen?

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You don't connect to a port though. You would connect to a socket (IP and port number) that corresponds with a service running in the server.

So for example you wouldn't connect to management port 1.

Let's say Server A has the IP address 192.1.1.1 and is running a web server on port 80. The Server A network adapter configured with 192.1.1.1 is connected to interface 1 on your switch.

So what you are asking is how do you remotely access the web server on Server A.

The answer is your firewall must have an ACL and NAT rule that allows your remote traffic into the network and it needs to perform either 1:1 network address translation (NAT) or port address translation (PAT).

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You need a router to route traffic between the VLAN's. You can then set your ACL's on the router rather than the switches, which would be the preferred method of using ACL's.

If you have available interfaces on your firewall you could use the firewall as a router as well as using it to secure the traffic between the VLAN's.

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