[CentOS] Configuring source-specific routing

[Les Mikesell]

On Wed, May 1, 2013 at 4:52 PM, Michael Mol <mikemol at gmail.com> wrote:
>
> Intent is to maintain the old, slow (but has an SLA) connection as a
> fallback, and migrate services to the new connection piecemeal.
> Meanwhile, the same DNS server on the new connection can be, e.g. "ns3".
> The same mailserver can have a new MX on the new connection...likely
> prioritized to it.

Note that there are more straightforward ways to do this.   One is to
pretend you are big enough to have a distributed server farm and
actually have independent servers at the other IPs, even if they are
VMs.  This is fairly easy for mostly-static or database-driven web
sites, fairly difficult for apllications that are more statefull but
perhaps possible with a common NFS backend.   Another is to have
application-level proxies or load balancers like haproxy, nginx,
apache configured as a reverse-proxy, or even port forwarding with an
xinetd 'redirect' configuration.  This loses the source ip from the
application logs, although the http proxys have an option to pass
them.   Similarly you could use iptables to source-nat on the
receiving side and forward to a backend server.    These all have some
disadvantages, but with separate hosts each having one default gateway
to the internet and static routes for your own local ranges you have a
lot less black magic involved.

--
   Les Mikesell
     lesmikesell at gmail.com