> 1) should each dns cache server be configured a static > default route (0.0.0.0/0.0.0.0)? If server-(1,3) is > configured statically to use > router-1 as default router, will Quagga make it use > router-2 when router-1 is not reachable? No, because both routers are reached through the same L1/L2 medium, so Quagga can't use link-state to determine reachability of the next-hop. You could fix that by getting rid of the switches, and just having a bunch of router interfaces facing two Ethernet interfaces on each server, which would remove some points of failure, and would be a good idea if you can spare the router interfaces... or you could use the OSPF which you're already going to be running, to advertise a default from both routers to each of the servers. > 2) If each server is configured two default router ( > router-1 & > router-2), or each server learn route 0.0.0.0/0.0.0.0 > by OSPF ( our border router inject default route into > OSPF ); there should be > two equal cost path to 0.0.0.0/0.0.0.0 on each DNS > server, the DNS server should disperse any outgoing > packets onto the two paths, will > that do harm to DNS service ? Nope, no problem, particularly so long as the two routers are iBGP peers, so they'll both (for the most part) have the same idea of what selected paths are. > 3) Is there any requirement on BIND to fit to such > multipath routing situation? Nope. BIND doesn't know what's going on that far below it. -Bill