Failed Activation of Network Connection-wrong subnet

Issues related to configuring your network
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FirebirdTN
Posts: 26
Joined: 2014/02/08 14:53:34

Failed Activation of Network Connection-wrong subnet

Post by FirebirdTN » 2019/04/09 21:48:00

Been battling this for half the day. I finally got it working but it makes NO SENSE to me. I guess it doesn't really matter "why", but I HAVE to know:

Tried plugging in my static IP info for my wired network connection. Whenever I do, I get "Failed Activation of Network Connection" (or something along those lines).

During the process of pulling my hair out, and trying both the GUI network settings and NMTUI in the terminal, I accidentally set my subnet WRONG, and low and behold, I got good network connection & internet access. WTH?

My subnet is SUPPOSED to be 255.255.255.248. I plug that in, I get the error above. I plug in 255.255.255.255 and I get good connectivity.

What gives here???

-Alan

FirebirdTN
Posts: 26
Joined: 2014/02/08 14:53:34

Re: Failed Activation of Network Connection-wrong subnet

Post by FirebirdTN » 2019/04/10 16:50:31

Thought I'd add some info in the event it helps someone else...

I have a second CentOS 7 box, configured exactly like the one mentioned above. Same updates, same packages, same hardware. Its an identical machine to the one above in almost every way. It exhibits the same behavior.

This second machine I have placed on another network whose mask is /28. On this network when I enter the correct mask, it works just fine. I didn't try 255.255.255.255 though.

The only conclusion I can come to is it doesn't like the first network where I am having issues for some reason. Now I don't pretend to be an IT guru, but I am pretty sure my first network is setup correctly. The only thing that raised an eyebrow with me on the first network is our ISP said it was a /29 and we had SIX usable IP addresses. I thought for some reason a /29 only gives you FIVE. But I guess it depends on the circumstances?

In any case, the problematic network has .160 as the router interface, I was trying to use .161, and I have DHCP set up on the router to serve addresses in the .162-.166 range, leaving .167 as the broadcast address. I am pretty sure I even tried to set the machine with .162 manually and it still didn't like the .248 mask.

I don't get it; it doesn't make sense, but for whatever reason the machine I originally posted about is happy with a 255.255.255.255 mask.

-Alan

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TrevorH
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Re: Failed Activation of Network Connection-wrong subnet

Post by TrevorH » 2019/04/10 17:00:14

Post the contents of /etc/sysconfig/network-scripts/ifcfg-*
The future appears to be RHEL or Debian. I think I'm going Debian.
Info for USB installs on http://wiki.centos.org/HowTos/InstallFromUSBkey
CentOS 5 and 6 are deadest, do not use them.
Use the FAQ Luke

FirebirdTN
Posts: 26
Joined: 2014/02/08 14:53:34

Re: Failed Activation of Network Connection-wrong subnet

Post by FirebirdTN » 2019/04/11 14:47:08

I'll post those contents if it becomes necessary, but the more I think about it, this is down to user error.....MINE.

Again to re-cap, two separate but identical machines tried on one specific network doesn't work unless I set the mask to /32.

One of those machines, placed on a different network works just fine.

I'm theorizing right now (damn thing is in production, so the best time to correct my mistake would be late Friday evening), but the problem isn't CentOS; the problem is the NETWORK.

Again, my isp gave me a /29 block. I think my mistake was using the FIRST address for the router interface (.160), when what I should have done was use the SECOND address for the router interface, since the first is reserved for the network.

I haven't made the corrections yet, but I am about 99% certain this is my issue.

Sorry for the time waste.

-Alan

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