Cable modem won't connect to Mac with J45

[Ern-S]

I have a brand new C6300V2 cable modem/router that is connected to my Spectrum service and the wireless part (after some issues) works fine with my desktop Mac and with other devices. But, when I plug the cable from the yellow J45 output jack to the Mac's input, The Mac will not recognize the modern and the wired light flashes constantly. ???  Any ideas anyone?

[Ern-S · Accepted solution]

The end of this story is apparently my Mac was damaged by the lightning strike and the Ethernet (J45 connector on the back) will no longer make a wired connection to the modem/router. I blamed the modem/router at first because I couldn’t get my TV connected to wired Ethernet either, but that was a wiring error on my part. The modem/router device works fine. The lightning took out my old modem/router, either my TV or amplifier ARC function, and my Mac desktop Ethernet port. That much so far. 

Case closed.

[Ern-S]

ps Setup on Mac side it TCP/IP, IPv4 Address: 169.254.9.111, Configure IPv4: using DHCP

[plemans]

all other wired devices work fine? 

Just the one mac? 

Does that mac work over wireless?

[Ern-S]

One Mac but my LG TV won’t connect, either, via a wired connection. I thought this connection via a wired J45 connection was automatic. What settings need to be made beyond what I listed? Again, all wireless connections are up and running on multiple devices.

[plemans]

The tv you might need to re-run the network setup process. 

On your mac, see if you can go in and clear out the network settings on the mac. 

[Ern-S]

I don't know what you mean by "clear out the settings on the Mac". My settings are:

Location: set to Automatic as before

Configure iPv4: set to Using DHCP

IP Address: not setable but set by DHCP

Subnet Mask: same as above

Router: blank

DNS Server: blank

Search Domains: blank

Limit IP Address Tracking is checked (a security issue)

[michaelkenward]

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@Ern-S wrote:

I don't know what you mean by "clear out the settings on the Mac".

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Let's start with the subject of your first message. You say:

"Cable modem won't connect to Mac with J45"

It helps to look at it the right way round.

The cable modem does not connect to your Mac. The Mac connects to your modem/router.

So the first place to look for problems is the Mac, especially when everything else, apart from the TV, works as expected. (As @plemans says, the usual fix there is to check the setup process in the TV, because that also connects to the router.)

In Windows, the network security can get in the way and prevent a PC from connecting to the router.

It is always tempting to blame the router for anything that goes wrong on a network and to turn up here. A better source of help might be the people who understand how Macs connect to a network.

Cable modem won't connect to Mac - Google Search

The list at the top is a good place to start.

[Ern-S · Accepted solution]

The end of this story is apparently my Mac was damaged by the lightning strike and the Ethernet (J45 connector on the back) will no longer make a wired connection to the modem/router. I blamed the modem/router at first because I couldn’t get my TV connected to wired Ethernet either, but that was a wiring error on my part. The modem/router device works fine. The lightning took out my old modem/router, either my TV or amplifier ARC function, and my Mac desktop Ethernet port. That much so far. 

Case closed.

[plemans]

glad you got the issue figured out. Lightening is great at wrecking stuff. 

Sorry

[michaelkenward]

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@Ern-S wrote:

The end of this story is apparently my Mac was damaged by the lightning strike...

Ah. Had you mentioned the lightning we might have got their quicker.

As @plemans says, lightning is famously good at wrecking electronics. Whenever anyone mutters that dread L word, that's the first response.

At least it was, as predicted, down to the Mac rather than the router.

Good thing it didn't cause much more damage to the Mac. If you want to restore the LAN capability, a USB adapter  might work. Unless Macs don't accept those widgets.

[Ern-S]

Michael, good idea. Yes, This desktop Mac has USB ports. I just decided to be comfortable with a wireless connection. The Mac and the router are right beside each other, so no signal strength problem. I just liked having the wired Ethernet option, thinking it might be a tad faster. But, I'll stick with 5G wireless for the moment. Should be good to go. Too bad about the J45 Ethernet port on the Mac, tho.

Regarding the lightning strike it actually hit in my front driveway maybe 50 feet from the room where the Mac and router/modem reside. It did not directly hit anything electrical, just blew some paving stones on the side of my driveway out of the ground. But, apparently the level of static electricity was high enough that it somehow got to my entry coax cable. In checking afterwards, I found that the Spectrum installation people had NOT put a ground wire on the grounding block for the coax cable where is enters my property, so my coax shield did not have a local earth ground. The ground block was there, but no wire attached. I'm sure that did not help me at all. So, for anyone reading this, check out your TV antennas, gutters on the house, coax cables for TV/Internet, etc., and make sure they all have solid earth grounds. I also installed inline coax lightning arrestors on my TV and my router. That's about all you can do to protect yourself against lightning or static.

[FURRYe38]

Mac support USB to ethernet adapter. I have 3 variants for my Mac Book Pro with USB C ports. Works great and easy to setup. 

[michaelkenward]

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@Ern-S wrote:

I just liked having the wired Ethernet option, thinking it might be a tad faster.

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If 5 GHz does what you want great, but it might be more than "a tad" faster. And you can get a USB adapter that has extra USB ports.

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Regarding the lightning strike it actually hit in my front driveway maybe 50 feet from the room where the Mac and router/modem reside.

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A narrow escape. I once lost on office load of stuff when lightning hit the phone line. Took out a PC, fax machine (it was that long ago), printer and other stuff. The insurance assessor was impressed by the fried chips.