I have two DSL lines from the same provider on two different static IPs
and two interfaces for my linux box. I am not particularly worried
about load-balancing here. I just want failover between the two lines,
with next-hop detection if possible. The idea is that I don't need
heavy-weight applications like OSPF or BGP (since it's the same
provider), nor any fancy routers; just something that determines if
line 1 is down, switch the default route to line 2 (automatically: I
know I can do it by hand, or even write a shell script).
For those who will ask, I did try a switch to bring everything to a
single interface and single IP on the linux box. But when line 1 is
down, the default route and IP for line 1 won't work over line 2.
Initially, I thought it was an arp issue, but it wouldn't resolve after
several minutes, nor after arp -d. The IPs are contiguous /29 networks
(which I have successfully combined into a /28), but it does not
failover properly. In the "single interface" scenario, I would have to
assign a new default route *and* IP (and even source routing,
I understand that iproute2 will/should allow multiple default routes,
but then it will round-robin based on destination (this is how I used
to setup Cisco behaviour and how I believe Solaris handles it). But
what is the failure detection? Link loss? Next-hop down? Anyone have
an easy solution to what should be relatively common?