I have been successfully using monowall with my ISP for years - it has been great. Now I am transitioning to a new ISP. My network is NATed behind the monowall. My new connection has been installed, and I configured a second monowall box. It has the new ISP's IP address on the WAN, and an available local address on the LAN. I have configured individual workstations to use the new ISP simply by changing their default gateway (and DNS) to point at that local address. My problem is trying to switch my web and mail servers to the new ISP. Ideally, both monowalls would be active simultaneously so I can change the real world DNS entries for the web servers over time and any address caching issues would not come up.
The problem I have run into is that the web servers have the old ISP's monowall as their default gateway. I did an experiment with one domain by changing it's DNS A record to point to the new ISP. I created a Server NAT entry with the appropriate rule. If I try to access that site from the Internet, I see the log entry for the packet hitting the monowall and being forwarded to the correct internal address. But then it just dies - no connection is established, no data returned. My guess is that the web server sees the packet and replies, but it replies to the default gateway, which is the other monowall, which has no clue about that packet, and discards it.
SO - my questions:
(1) Is this analysis correct? is the "wrong" default gateway causing this to die?
(2) Is there a way to configure the "old" monowall to redirect the old real IP addresses to the "new" IP addresses?
(3) Is there a way to configure the web servers to reply to the correct monowall? If I added a supplementary local IP address (eth0:1), could it have it's own default gateway?
I'm not sure if it matters, but the web servers are running a bunch of domains as name virtual hosts.
Thanks in advance for your help.
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Topic: Problem Switching to New ISP