Everyone,
I have been having a problem in setting up gateway/routers with Centos 7.4 machine and finally figured out the problem today. I am not sure if this bug occurred first in 7.3 but it is definitely in 7.4. I have other gateway routers that were created at the beginning of the Centos 7 that have been working perfectly even through the upgrades to 7.3 and 7.4, but the new gateways I have created would not work.
It seems simple now that I have the solution, but it took me an embarrassingly too long a time to debug and resolves the problem.
The problem appears to me to be a bug in the new gnome-command-center when using the network module to add or edit network interfaces. The problem that I identified is that the network module requires the user to enter a gateway ip address even on the internal networks. Normally the gateway ip address is left blank on the internal interfaces, and is only filled in on the external interface.
I was never able to get the gui using the network editor within the gnome-control-center to be able to remove the gateway ip address from the; internal interfaces; I was forced to enter something, and I entered the external gateway ip address. However, to bypass and fix this problem, the gateway ip address is easily removed by editing the appropriate file or files in :
/etc/sysconfig/network-scripts/ifcfg-emp3s0 /etc/sysconfig/network-scripts/ifcfg-emp4s0
The network editor in the gnome-control-center module required the entry of a gateway ip address. I had entered the gateway for the external ip address in this field, and all I did to solve the problem is to delete "GATEWAY=x.x.x.x" from both of the above files.
This allowed both of the new gateway machines I have recently created to work like they should.
Hope this saves someone else some time.
Greg