How to keep the ethernet interface up when removing the cable?

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Level 2

305 points

How to keep the ethernet interface up when removing the cable?

On 10.6 I notice that if the ethernet cable is unplugged, it will not bring the interface up. As a result, I cannot test my server without the interface attached. For instance, if en0 is 192.168.2.10 and a web server is running, the local DNS translates the web servers domain to 192.168.2.10, I cannot reach my own web server as there is no route to host. This is probably energy conservation issue, but it makes life rather unpleasant, because if the interface goes down when there is a cable problem, I also get all sorts of internal problems because of the missing host (e.g. a virtual machine looking for a DNS server on 192.168.2.10 which is suddenly unreachable).

This was not the case with 10.5 Server and I think the last time I had this kind of behaviour was with my NeXT cube where the en0 interface would not come up without a cable attached to it and a switch.

So, is there a way I can force OS X 10.6 to bring up the en0 interface on 192.168.2.10 no matter what?

G4 Cube, MacBook Air, Mac mini C2D, Turbo NeXTdimension Cube

Posted on Sep 22, 2010 6:46 AM

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Answer 1

Camelot

Level 9

58,581 points

Sep 22, 2010 7:17 AM in response to Gerben Wierda

So, is there a way I can force OS X 10.6 to bring up the en0 interface on 192.168.2.10 no matter what?

No. At least not that I'm aware of. Test your sites against localhost instead. That will always be up.

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Answer 2

MrHoffman

Level 10

146,557 points

Sep 22, 2010 9:08 AM in response to Gerben Wierda

I have a box with networking drivers that allows that, and it blows chunks. Network Up. Network Down. Up. Down. Up. Down. Yo-Yo mode. Honks all over the network stack and fills the logs, too.

Post what you want to happen, and maybe we can help figure out how to address that. It might be an internal network via VM (or libpcap or...), or (ugh) maybe an external loopback RJ45 connector (which may well trigger its own problems), or something else.

Or how to cleanly shut down the network.

Given Mac OS X Server effectively requires functional DNS services, you'll need to figure out how to maintain that access, regardless.

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Answer 3

Gerben Wierda Author

Level 2

305 points

Sep 22, 2010 12:38 PM in response to MrHoffman

I have made my DNS reachable at all times by using 127.0.0.1 for the "DNS to use" in my ethernet settings in System Preferences.

Using localhost is no go, as I am running three separate IP-addresses (three en intrerfaces) on my single RJ-45. This way, I can let several web sites for different domains listen to different IP-addresses. Furthermore, I can make sure on the router's NAT that for instance only one of those gets the port 443 traffic and that one does not get port 80 and the other way around.

The solution I have now is a cable attached to a switch attached to nothing else. But it is inelegant, I'd rather know how to make the interfaces come up regardless what is attached to the RJ-45.

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