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I'm teaching an introductory computer engineering course in HS and had students in the lab network together the computers they built in the hardware unit - I appreciate the irony of somebody teaching, among other things, networking - and needing help on this. Router #1 is the 'class router'.

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  • I have one router per bench of computers - for a total of 4 routers. I planned on having them all pull DHCP addresses from the main router in the room (giving each router a 192.168.1.X addresses).
  • I had the kids set up their network routers as 192.168.X.1 (so 192.168.3.1, 192.168.15.1 etc...) and pull dhcp under those addresses.
  • I had originally set the router masks to 255.255.255.0, but when I first realized i couldn't communicate between the individual networks, I thought to fix it by having them change the subnet mask to 255.255.0.0 since I realized each network wouldn't be able to talk to each other with the third octet being different.
  • when that failed, I had them set up routing tables on each computer so, for example, a student on computer 192.168.4.44 would be able to ping 192.168.5.2 by adding the entry on the router of: 192.168.5.2 with mask 255.255.0.0 and gateway 192.168.5.1

I am pretty sure the issue lies in the router delivering the ip addresses to each of the routers, but I don't have a login/pass for it since it's a school-board appliance. Any advice would be wonderful pls and ty. Tomorrow's plan is to use a different router as the 'main DHCP router' and I'll give up having them get internet access in that part of the lab (the only way to get internet in there without having the port shut down is through that board appliance).

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  • If you configure all your computers in the 192.168.0.0/16 subnet, they won't need routers to communicate (A computer will only send packets to its default gateway once it recognizes the destination IP address is from another subnet from its own). In your network diagram, please specify which interface you have the addresses configured on. What are the addresses between the routers? Please add full network diagram. Is this a routing exersice or a DHCP exersice? If you want to teach them routing concepts, first make the thing work without using a DHCP server.
    – manish ma
    Commented Apr 23 at 6:07
  • I had the addresses on the LAN ports on the router. I didn't create any vlans. Each router has their ethernet cable through WAN back to the main router (either directly or through a switch). It was originally intended on them extending a virtual exercise where I had them use linksys and asus virtual online interfaces. For grade 10, i should have just turned off DHCP and given each of the computers a static IP under the single router and saved a more advanced routing exercise for grade 11. Live and learn.
    – Jawsont
    Commented Apr 23 at 21:33

1 Answer 1

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You need to either

  • remove the routers, connect all clients to the switches directly, use a single, shared subnet (e.g. 192.168.1.0/24) or
  • use a distinct, non-overlapping subnet off of each router and a single, shared subnet between all routers

Since routers don't magically learn of all the connected subnets (in a way like switches = self-learning bridges learn of MAC addresses), the routers also need static routes to the remote subnets (those not directly connected). Alternatively, you could set up a routing protocol like OSPF to make them exchange routes automatically.

The end nodes just require their default gateway set to the router interface connecting them and, of course, share their subnet.

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  • Thanks for that! I wound up grabbing a different router as the 'main router' and setting routing tables in ddwrt to: wiki.dd-wrt.com/wiki/index.php/… - each of the routers has a 192.168.1.X address - each of the routers has a different subnet as per the instruction set (eg 192.168.5.1) - the routing tables on the main router for each router are: - 192.168.3.0 for the LAN / 192.168.1.1 for the gateway (and vary that way per router) - I have a script on the command page that: iptables -I FORWARD -j ACCEPT
    – Jawsont
    Commented Apr 23 at 20:53

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