Keep all hosts connected even after a router breaks down

[mohamed.hadarch]

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.

[Joseph W. Doherty]

You would want hub 1 connected much like hubs 2 and 3, i.e. hub 1 having a connection with another router.

As another possible alternative, if the "hubs" are actually switches that support VLANs, you might also connect hub 1 to another hub and "trunk" the link to the another router.

[Julio E. Moisa]

Hi

This scheme has many point of failures, there is no high availability.

Working with this scheme and its components we have: If Router 1 is down everything goes down (at left side), Now you if Hub1 is a switch, you can use 2 interfaces  (trunk mode) and connect them to Hub2 (switch2) and to Hub3 (switch3) respectively and create the Host1's vlan on each switch and create finally the gateway for the Host1 on the Router 2, like it is created for Host 2 and 3. 

Basically Hub 1 will skip the Router 1, now router 2 will be the gateway for the host 1.

Other option is connect the Host 1 to the router 2 or router 3 directly to an ethernet port (using crossover cable) and create the gateway on one of these routers, if it will be connected to router 3 remember configure the interface with ip nat inside and include the subnet into the ACL to get internet access. 

*Remember verify the routing for the host 1.

Hope it is useful

:-)