i have connected two buildings 80 meters apart wirelessly and connected two routers lan to lan. both buildings have their own internet connection which i was using before connection both buildings. lan to lan connection has brought all devices under same network which is fine by me but what will happen if i connect both internet to each router in their buildings. which internet connection will i be able to use? if i can use only 1 internet connection at a time how can i configure my network so that if internet in one building is down i can connect internet on other router's wan and connect all my devices to internet.

i also did a wan to lan connection creating two separate network in each buildings but i could no figure out how can i use either internet connection if one internet connection fails.


Assuming typical "soho" 4LAN + 1WAN type routers, you will have stability issues and confusion - the main stability issue will because you are running 2 DHCP servers - depending on the IP ranges this could mean 2 systems (or worse, 2 routers) get the same IP address, which will be problematic. Best case scenario, the link causes enough latency that each side prefers the closer DHCP server and thus uses it to route traffic - assuming the routers don't assign overlapping IP's.

Setting up automatic failure if 1 connection fails is HARD. There is no single simple solution. It would be quite hard, but (if I was on a budget), I'd make sure the routers spoke OpenWRT, and convert each router so it had 3 LAN ports and 2 WAN ports. The LAN ports for each router would feed the local building, with 1 WAN port feeding the WIFI bridge, and the second one feeding the Internet connection. You could then use some mechanism (depending on the connections) to balance / direct traffic either directly out the WAN to the Internet or out the WIFI bridge to the WAN of the other device. This is doable, but is quite advanced and requires a good understanding of routing I fear you do not have [ based on the question ].

You would probably be better off with a default configuration and some kind of manual fail over - eg everything goes through 1 router (with the second router off). If that connection fails turn off 1st router and turn on second router - being the simplest. In that case you want to make sure the routers have the same LAN gateway address, both run DHCP servers and that the IP addresses issued by DHCP don't overlap.

  • what if i always connect only one internet connection to wan port at a time and when its down i remove its cable from wan port, connect the other building's connection to its router wan and have internet on whole network again. both buildings have 15 fix devices and i already assign ip to them. will give different scopes to dhcp. – avy_9 Mar 29 '17 at 12:31
  • Yes, as per my answer, provided the routers LAN IP and netmask are the same, that will work. – davidgo Mar 29 '17 at 18:21

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