two ISPs cONNECTIVITY
i have two sub-nets separated by 10km apart , the link is fibre but at times this link goes off and i have two ISPs one lands in one subnet and another lands in another subnet, i have 1 firewall and one proxy both at one subnet.
however, i need to connect these ISPs so that one is the standby link what i want is that if the link between the two sub-nets is down both sub-nets should still have internet connectivity.
what should i do? to effect this?
You need Two Firewalls. One at each site. If these are flat subnets (meaning that there is only 1 subnet at each site and they are joined by one router via the fiber link) then you can just have weighted Static Routes for 0.0.0.0/0 on each of the two Firewalls.
Point the PRIMARY to the LOCAL ISP and the SECONDARY to the REMOTE ISP. Use an ARP query to 'check' the LOCAL 0.0.0.0 route on each firewall to ensure that the other side is 'up'. Don't check the LOCAL route by IP you will get a false indication of 'UP' when the route fails over to the FAR ISP.
You do not need to check the REMOTE 0.0.0.0 becuase is it SECONDARY to the LOCAL one.
OR (better) Use BGP or OSPF to dynamically reroute if the fiber fails.
You can also Tunnel the PUBLIC interface of both Firewalls together over the INTERNET side so that you can still 'see' the other subnet even if the Fiber link is down. Be careful not to create a routing loop.
Consider Mikrotik as a vendor to do this economical ly.