I have an ethernet network on which two subnets coexist:
(1) A 10.0.0.x DHCP/NAT subnet whose internet upstream is a cable modem connection.
(2) A 216.x.x.x static/public address block directly routed over a DSL connection.
A device plugged into the ethernet LAN at this location can:
(a) Pull a 10.0.0.x DHCP/NAT address and use the cable modem as its internet uplink.
or
(b) Be configured with a static 216.x.x.x address and use the DSL as its internet uplink. When this is the case, the device can be pinged from the outside world using its 216.x.x.x address.
Here is where I am seeking advice:
I have an iMac at this location (10.5.4 Leopard).
I would like the iMac to use the 10.0.0.x subnet (cable modem) as its default gateway, so that web browsing, email, etc uses the cable modem and other devices on the 10.0.0.x subnet are accessible to this iMac.
I would also like this iMac to be simultaneously configured with a static/public 216.x.x.x IP address so that certain services running on it can always be reached from the outside world using its 216.x.x.x address.
I have done this in the past (pre-Leopard) by duplicating the Built-In Ethernet interface in the Network Preference Pane, configuring each Built-In Ethernet for each subnet (10.0.0.x DHCP and 216.x.x.x static), and then making sure that the 10.0.0.x DHCP subnet is first in the list of interfaces by using “Set Service Order…” (or whatever that was called pre-Leopard).
However, I am running into a problem with this now with this 10.5.4 iMac.
Basically, if I set up this iMac as described above, it is not pingable on its 216.x.x.x address. Not the desired result.
If I switch the service order and place the 216.x.x.x subnet above the 10.0.0.x DHCP subnet, then the iMac is pingable on its 216.x.x.x address, but also outbound internet traffic (ie: web browsing, etc) always travels over the DSL instead of the 10.0.0.x cable modem subnet and devices on the 10.0.0.x LAN are not accessible to the iMac. Also not the desired result.
In essence, it seems like in this case, only the subnet config at the top of the service order list is available, whereas I need (and have done successfully in the past) to have both subnet configs available simultaneously.
Ideas as to what may be going on here?
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