Re: Changing ISP smoothly..

alexd wrote:
Gordon Henderson wrote:

In article <h6ulhj$181$1@xxxxxxxxxxxxxxxxx>,
The Natural Philosopher <tnp@xxxxxxxxxxxxxxx> wrote:

5/. Change all my public sites to point to the new static IP address. By
my reckoning the packets will all come in eventually by the new router,
but return traffic will go out of the old one?

Also - asymetric routing - it should work... And I don't know of any
ISP at present who block it if they see it, but you never know.

I reckon it won't work. NAT routers/firewalls [for one] seeing responses coming back from an IP address they didn't request them from will ignore the traffic, and the browser will just think your site is unresponsive.


OK, is that a fair point? MM. yes, it probably is. the responses will come from a different IP address. I'll ponder that one.
..

If you do manage to get a port forward working via a router that isn't the default route for the given server, I would be interested to know how you did it.


Its should not be beyond the wit of man.. actually there is one simple way to do it. I can add a second interface on a different subnet, to the (Linux) server, and bind a second default route to that. Nasty, but I've done it often enough to set up routers..

That will allow symmetrical routing via either virtual interface.

So in effect my server will have two IP addresses on two interfaces with a separate default route for either..if IP forwarding is off on it, it won't then magically route between the two
..

So
#ifconfig etho:1 192.168.2.100
to set up a second interface on eth0:1 and

#route add default gw 192.168.2.1 eth0:1

for example..

Actually, its a fair way to make a resilient-ish server using twin DSL if you have split DNS 'A' records.. or use DYNDNS for 'failover' DNS..

I cant remember what selects from a pair of equivalent default routes for outbound connections. I do remember that one an NT server that was giving precisely 50% packet loss, it simply picked alternately :-)

I do know that once a server is bound to a given interface, it will return packets via that interface, so the question would be as to how to bind apache to both...aha. It listens on all unless told not to. So no issues there.

Looks like you spotted the flaw, and there is a simple enough workaround.

I wonder what happens to desktops if you have TWO DHCP servers running.



.

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