Keep all hosts connected even after a router breaks down


Junior Member
May 30, 2017
I'm still quite the beginner when it comes to networking and i faced a problem to which i wasn't able to figure out the right answer.

The hubs are of type Ethernet. The routers have ethernet interfaces. Router 3 has an additional interface of another type that allows it to connect to the internet.

So the problem is that in case Router 1 broke down, how to keep all machines on the intranet connected and capable of communicating with each other and with the outside. That been said, the solution requires the minimal changes possible of the topology and the configuration and there is no other router to replace the broken one with.

I just wasn't able to come up with any working solutions.


Elite Member
Super Moderator
Oct 25, 1999
I do not know what is the security consideration as far as Networks separation goes

The Network behind Router 1 can to be connected to Router 2 and its IPs range have to be change to fit Router 2.

The Network would function but the separation of the Network behind Router 1 would be gone.



Golden Member
Apr 13, 2010
"Faced a problem" as in "homework problem"?
The network in picture as it was before the start and the Router1 has just broken down?
Your "problem"/"task" is to salvage the situation with minimal steps?

I do now assume things that you did not tell and say: plug Hub1 into Router2.


Golden Member
Aug 28, 2010
You see how hub 2 and hub 3 are connected to multiple routers? Do that.
There is nothing wrong with that in itself. In fact, if you want redundancy in your network, your hosts need to be connected to 2 routers anyway.

Veoxer, the technology you want to look at is the VRRP protocol. Or, if you have all cisco equipment, the HSRP protocol. Those technologies exist specifically to solve the problem you are facing.

With VRRP you configure 2 (or more) routers that are connected to the same layer-2 domain (e.g. the same ethernet hub/switch) to create a "virtual router". This virtual router has its own IP address, and a made-up mac-address. One of the routers is the primary and will take the packets destined for the virtual router's mac address off the ethernet and forward them. If the primary vrrp router fails, the secondary router will take over. That's the basic idea. There are many extra things you can do, like configuring 2 virtual routers so you can do load-balancing, etc. But just start and try to get a basic VRRP set-up working. There must be lots of documentation on the web, because VRRP is a protocol widely used.

Even with VRRP your network design does not look good. E.g. if routeur2 fails, all devices connected to router1 will lose their Internet-connectivity. Not good. Also, in case you didn't do that yet, you need to make your DHCP-server redundant, so that if the primary DHCP-server (one of routeur1 or router2) fails, the other router can take over.

I don't have a drawing, but this is a description how I would design your network, with the equipment you have:
  Hub --- Serveur
   |   \
   |     \
Router1   Router2
   |   \  /   |
   |   /  \   |
  Hub       Hub
  / | \      / | \
 hosts     hosts
Add more hubs if you need to. Connect each hub to both routeur1 and router2.
Configure VRRP on the interfaces of router1 and router2 that connect to the hubs that connect to the hosts.
Run a routing protcol (OSPF or ISIS) on routeur3, router2 and router1.
That would be the proper way to set up this network, imho.
Last edited:
Feb 25, 2011
Sorry, I misread that for "Don't do that".
Still, I think the OP could use some more explicit help.
Sure, but he should get it from his prof. This forum is generally "aginnit" when it comes to doing peoples' homework for them, though.