What happen in my network architecture?

[MaskerTim]

Hi, I'm MaskerTim.
and I attach a diagram about my network architecture and what problem I have.

Under the premise on my network setting:

1. All firewall in host I close.
2. I set some route table. (That describes in picture)
3. Device A at the LAN side can succeed to ping to Server A at the WAN side, however, Server A didn't ping successfully to Device A. (Also in picture)

I don't know why fault it is?

[Banfa]

Can you ping the wif brouter from the server? I'd say the problem is in you WiFi router especially given its configuration.

[MaskerTim]

Oh, I forgot to mention. Indeed, I also can't ping to wifi router gateway. And static route setting in wifi router, I only can set WAN in interface column. Is wifi router only one NIC? I think Server A need to send WAN IP and transform into LAN IP and then send to Device A. Is my knowledge wrong?

[Banfa]

I am not at all sure what you are trying to do is possible, I am sure that with some hardware it would definitely be impossible. The problem is around how a router works.

A lot of the time a router works by using NAT forwarding, this only works in 1 direction, inside the network to outside because what the router does is replace the IP address in the packets it receives with it's own IP address before forwarding on a different port selected for the purpose of that communication. When it receives replies to that port it then knows which internal IP address the packet is destined for and re-writes the correct IP address into the packet.

What this means is that the router is just not expecting to see packets with IP addresses for its internal network on its external port so it ignores them (also why your routing table is limited to the WAN interface).

I think if you want that network topology to work you will need a Wireless AP rather than a Wireless router. An access point acts a bit more like a bridge, connecting 2 networks together seamlessly.

[MaskerTim]

If I want to build a internal network and two different sub-network. Like Device A and Server A in my diagram. They are two different internal network domain then I want to communicate each other. Can Wireless AP split two sub-network and connect between?

In my mind, two different network domain need to use router to transform IP into the other network domain (just NAT you mentioned) whatever they are internal or external. Do you have any opinion on my point of view?

[Banfa]

No with a Wireless AP you would effectively have a single sub-net with a single DHCP server somewhere (on the server??); unless of course your switch is a layer 3 switch supporting VLANs and routing between them.

With the Wireless Router the router is running a DHCP server for the Wireless sub-net while you must have another DHCP server running on the wired portion of the network. The problem is that the oruter you have doesn't appear to route traffic from the wired to the wireless side.

Keeping the wireless and wired devices in different sub-nets (or VLANs) is a good idea, for problem solving and security reasons but it requires the right hardware to do it; since you have not specified what your hardware is it is hard to know but I have been assuming consumer level kit (dumb switch, consumer Wireless router) which generally are not so easy to configure as the manufactures tend to lock down their functionality, presumable for cost reasons but I expect they'd say they were assisting the user in not displaying a dizzying array of configuration options which the user won't understand.

[MaskerTim]

My wifi router I use is DIR-859, Dlink manufacturer. I think that's a consumer kit. It can set QoS, route table, bind ip with Mac..., so I think that's not complex setting.

I'm still network beginner. Although I don't know what VLAN is, but I think it doesn't provide this function (I think that's for user not network manager).

I use static IP setting on server. So server A doesn't by dhcp. Wireless side use dhcp setting, so Devic A's IP is assigned from wireless router.

You point out a important view about router may not have router traffic from wired side to wireless side.

I want to connect with each other in different sub-net. If I want to solve this problem, do I need to use two router to connect? I use the switch (layer 2) with wifi router(WAN port) and server A. I just think I set static IP on server A to make different sub-net from device A below wireless router.

[MaskerTim]

Okay, I would try to search the case that is similar to mine on this forum and do more try-error in lab.

[MaskerTim]

Thanks. It's not assignment in college. I just learn to build network for the future of designing and constructing network architecture.

My problem is that I want to build two sub-net, and one side use wireless then another side use wired connected to wifi router's WAN port (just the diagram I draw). I can send from device below wifi router to WAN connected to Server, but reversely can't send successfully.

Just like Banfa says. Maybe I choose the fault hardware to do that. Maybe that architecture is not correct. I don't know If I want to split two sub-net and connect each other, Is wrong my network architecture and need to change it or How do I build to solve my problem?

[MaskerTim]

Thanks for Banfa. You give me lots of advices. I have some direction to try-error my network. If you have other opinion, I'm pleasure to communicate with you and tell what my point of view is.

[Banfa]

So the DIR-859 is a standard consumer router providing connections out to a WAN (broadband) as well as wired and wireless connections internally on the same network.

The routes you have set-up in the Wireless router are doing nothing because they concern the WAN port which is not in use. I can tell if you have a separate switch or if you are referring to the switch with-in the router providing the 4 gigabit Ethernet ports but the assumption in a router of this type is what everything is on the same subnet (because that is what is simplest for most consumers).

By giving your server a static IP in a different sub-net you are placing it on a different sub-net to everything else hence it can communicate with nothing.

By setting a static IP on the WAN in the router you have statically set the IP address of the WAN port, but note this is not the Ethernet ports that your wired network is using. Additionally if this was actually connected to a WAN you would almost certainly have broken the link as most networks expect equipment to request an IP address not set one statically.


To make this topology work with this equipment your best option is to switch on DHCP in your server, it will then obtain an IP address from the router putting it on the same subnet as the router and all the wireless devices.

If you want a topology with different sub-nets then there are a number of options but all of them involve buying new network gear.

[MaskerTim]

Don't worry about buying network gear, we have a lot Ethernet switches in our lab. So if I would like to one side using wireless and the other side using wired (Ethernet), I need to put Server under the Switch (Server wired to Switch), then Switch plug into wifi router's LAN and Device use the wifi router's DHCP assigned. Server set static IP to split its sub-net.

If I build what I talk above, is that concept correct?

[MaskerTim]

Just like what I draw.

That is my reconstruct I think.

[Banfa]

If you put the server on anything other than the subnet the router is on then it will not work; what you are battling is the router which is incapable of handling anything other than a single subnet.

If you are in a lab with bits a pieces lying around then what you could do is

Find some PC/Laptop/Box with 2 Ethernet ports (you can always add ports with a USB to Ethernet) Connect 1 port to the Wireless router using DHCP and the other port to your switch.

You now have 2 separate phsyical networks with a computer between them; I would install Linux on this computer (Windows may be able to do this I'm not sure, Linux can). This computer is going to bridge the 2 networks (i.e. connect them together).

On the computer

• Configure the port connected to the router to use DHCP so that it is part of the routers subnet (you can configure the router to always give it the same address (normally)).
• Give the port on the wired network a static IP in the same subnet as the router.
• Set up the routing table to route packets from 1 port to the other

On the server

• Configure it with a static IP address in the subnet of the wired network
• Configure the bridge computer as the gateway for the other network using its IP address on the wired network

On your wireless devices connected to the router

• Configure the bridge computer as the gateway for the wired network using its IP address from the router

Modified picture attached

[MaskerTim]

You give me a clear point, the Bridge. I forget that concept. I would try this architecture in lab when the work days start. The lab is closed during these days (because of the holidays in my country), so I can't entry my lab. That's why I can only image what it would run.

After Two days later, I would try it and then reply the result whether it is success or not.

Thanks Banfa. You give me a big advice. And the diagram you redraw makes me have a way to try.