OK, I'm baffled. Well and truly baffled. Apparently something in TCP/IP
doesn't work quite like I thought it did. I thought a server would pass
packets back to the router that asked for them. Apparently my servers
prefer the default gateway instead since the original source is not on
the same subnet.



Here's what I'm trying to accomplish:



T1 from ISP1 with a Class C subnet

T1 from ISP2 with a Class C subnet



Gnatbox1 connected to ISP1's router.

Gnatbox2 connected to ISP2's router.



Group of servers on the PSN network of GB1 (10.0.0.0/24)



The servers are all set for IP addresses on ISP1's subnet through GB1.
What I'm trying to accomplish is having these servers respond to IPs on
both T1s and doing little to re-configure the machines themselves.



I've tried a couple of things:



GB1 only. I have a couple of aliases set on the EXT that corresponded to
IPs on ISP2's subnet. This worked as long as router1 was down. When
router1 came back up, the machines stopped responding on subnet2,
responding only on subnet1.



I stuck GB2 'in front' of GB1. Attached GB2's PSN interface to GB1's EXT
network. Tunnels created from Subnet2 aliases mapped to the Subnet1 IP's
on GB2'S PSN. Again, this worked as long as Router1 was down. When
Router1 came back up, the machines stopped responding on Subnet2, only
responding on Subnet1.



My next incarnation of my nightmare was to stick GB1 on Router1 and GB2
on Router2. I attached the PSN interfaces to the same LAN (GB1 PSN:
10.0.0.1, GB2 PSN: 10.0.0.2).... Wow...it was like putting a couple of
beta fish in the same fishbowl. Those firewalls started screaming red in
their logs. I decided that was a bad idea...which brought me to my
current setup. GB2'S PSN was put on its own switch with IP of 10.1.1.1
and a router (Cisco 1700) was dropped between the two PSN switches. No
screaming in the logs....all devices can see/ping each other. Traffic
flows into the servers...but then the servers dump them out through
their default gateway (GB1) and nothing goes anywhere. I've got static
routes in both the server I'm testing with and GB1 to point 10.1.1.0/24
traffic to the PSN router, but still...the server will not respond
directly to the router routing the request to it.



Is there actually a way to do this? My goal is that we're ditching ISP1,
but I want all of my servers responding to both IPs for a couple of
weeks to make sure there aren't any transition glitches. However, I
can't really spend a ton of time re-doing network settings on all of
these servers. If it comes to that, I'm just going to have to scrap the
transition plan and tell my customers to expect downtime one weekend and
just re-IP GB1 and re-propogate DNS.



Thanks for any/all help.

Chris

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