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Ruadh2 Author

Level 1

16 points

Network Issues

I have an odd network behaviour that started a couple of days after I started with my new iMac 27" running Catalina.

I network it using Ethernet. When I boot up I get network settings as follows:

Which looks fine, but I have no connectivity to the router or anything. So, checking on thethe Network Utility, I get:

So, simultaneously it has been allocated an IP address and it hasn't.

I can fix this, but in an inefficient and annoying way.

I physically remove the ethernet cable from the back of the iMac for 20s or so and then add it back.

Then I get the following sequence:

For about 35s nothing happens, then the following IP address comes up, which shows I'm not connected.

Then at a about 1m 25s without doing anything other than waiting I get this:

Which looks exactly the same as the settings at boot, but when I check in Network Utility:

So, now I really have an IP address and all works fine.

Any ideas how I can get it to do this first time without this wasteful manual handling?

iMac, 10.12

Posted on Aug 13, 2020 12:00 AM

Top-ranking reply

Ruadh2 Author

Level 1

16 points

Posted on Sep 11, 2020 2:30 PM

Well I got my answer from the Apple repairer, and it was very simple.

I changed the Location (see the first pull down in the first screen shot above) from Bigpond Broadband ADSL to Automatic, and then the computer found the IP address on boot properly on boot.

When I looked at the actual settings within the location, I could only find a different WINS name, which I can't see how that would have affected the finding of an IP address.

Anyway, thanks for all your assistance, but it was a very simple solution staring me in the face from the very first line from the beginning!

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24 replies

Aug 20, 2020 4:23 AM in response to Ruadh2

Remove Little Snitch.

Your network is segmented, and intermittent.

The image shows two hosts, .163 and .202, and .163 is slower to respond for whatever reason.

Your text indicates a different network, with .10, .105, and .130, and seemingly with packet loss.

Little Snitch can alter connectivity and has occasionally caused issues, so it’s a candidate cause.

And I can infer that there might be 9 Km between two sections of your network? If that’s the case, you will want two separate subnets, two DHCP servers, and routing.

Your job is to figure out why your network is segmented. Whatever network link or cable or port is physically between the .163 and .202 section, and the .10 and .105, and .130 section, is a good suspect, particularly if there’s some sort of hardware separation there. Bad cable, bad port, bad Wi-Fi, bad point-to-point link, etc. If there are multiple Wi-Fi routers here, subnet addressing will be required, or switching the Wi-Fi from routing mode to Access Point (bridged) mode, if the Wi-Fi boxes support that.

And Little Snitch is always on the removal list, whenever troubleshooting network issues. Same as VPN client, anti-malware, and cleaner add-on apps.

Ruadh2 Author

Level 1

16 points

Aug 24, 2020 6:08 PM in response to MrHoffman

Thanks again.

MrHoffman wrote:

Remove Little Snitch.

Your network is segmented, and intermittent.

The image shows two hosts, .163 and .202, and .163 is slower to respond for whatever reason.

Your text indicates a different network, with .10, .105, and .130, and seemingly with packet loss.

Little Snitch can alter connectivity and has occasionally caused issues, so it’s a candidate cause.

And I can infer that there might be 9 Km between two sections of your network? If that’s the case, you will want two separate subnets, two DHCP servers, and routing.

Your job is to figure out why your network is segmented. Whatever network link or cable or port is physically between the .163 and .202 section, and the .10 and .105, and .130 section, is a good suspect, particularly if there’s some sort of hardware separation there. Bad cable, bad port, bad Wi-Fi, bad point-to-point link, etc. If there are multiple Wi-Fi routers here, subnet addressing will be required, or switching the Wi-Fi from routing mode to Access Point (bridged) mode, if the Wi-Fi boxes support that.

Little Snitch turned off - no difference.

The wired network is no wore than two metres from router to any extremity.

I'm investigating the segmented network. I'll have to get some spare cables and do some testing on the weekend.

There are at three Wifi routers in the room, but one of them is turned off. I'm setting up a new modem-router as part of moving to the National Broadband Network (our VDSL2 broadband provider), and I've been testing this bug, which is why I have two going at the same time.

Sep 8, 2020 4:28 AM in response to Ruadh2

I see three hosts with the view from one computer (.2, .3, .5), and two hosts (.2, .3) from the other.

I’d expect to see a response from the modem, and from each other connected device.

Run an audit of your network.

Figure out what’s at each IP address, and how each is connected.

What’s using .5?

What’s the wiring or the Wi-Fi network layout?

Sep 10, 2020 1:41 PM in response to Ruadh2

How is the MacBook Pro connected? “Normally directly” via Wi-Fi, or “normally directly” via wired? There are other paths, too.

If by Wi-Fi, then there are seemingly two routers here, which means subnets or establishing an access point configuration.

Ruadh2 Author

Level 1

16 points

Sep 10, 2020 2:01 PM in response to MrHoffman

Normally directly by Ethernet. I don't use wireless unless I'm using the laptop away from it's office desk stand (eg. using it in the basement workshop, which has no wired connection).

I'm sure that there aren't two routers as, though I have four router-modems (! Technicolor from previous ISP, duplicate Technicolor from previous ISP, mobile broadband Netgear M1 for backup and Netcomm for current ISP) only one has the x.20.x IP address. So, I can be sure that I only had that one operating at the time of the above tests. I do have a Netgear Prosafe GS105 switch in the network though, as explained above.

I actually have a couple of switches in the network and I use lots of wired and wireless devices elsewhere (I have a second office which is entirely on wireless), but I had disconnected everything that I could to isolate the iMac and one other test device (the MBP) for the ping tests.