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How are server IPs configured on the private end of GRE tunnels?
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How are server IPs configured on the private end of GRE tunnels?

rchurchrchurch Member
edited February 18 in Help

When you are using GRE tunnels how do you configure the IP address used in services in the private side?

Say I have a GRE tunnel that tunnels from 1.1.1.1 to 2.1.1.1 with 2.1.1.1 being the private side. The private IPs would be say 10.0.0.1 and 10.0.0.2 respectively

Prior to the tunnelling the hosts file at the private end would be configured with the real IP address, eg www.domain.com -> 2.1.1.1

After the tunnel is created the public IP changes - www.domain.com -> 1.1.1.1.

What would happen to the hosts file then?

Would the services need to be switched to the private IP address rather the public one, ie 10.0.0.2 rather than the original 2.1.1.1, or would the GRE tunnel forward the connection from 10.0.0.2 to 2.1.1.1 and leaving the local network configuration untouched?

GRE tunnel seems to be like NAT to me, but with forwarding from an internal private IP to a public IP, rather than the usual NAT which forwards from a public IP to a private IP behind the firewall.

I think I can sum up my question this way.

With GRE tunnels does the hosts file of the private server need to change?

Can other clients who have the real IP address in their own host files or have a private DNS which uses the real IP address connect directly without going through the tunnel?

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