Difficulty with two ethernet interfaces

[jekillen]

I have two Macbook pros, One with OSX 10.5.8, which don't want to upgrade becuase of boatload of expensive software aboard. The other is running Yosemite. I also have a Mac mini running Yosemite.
The older OS Macbook pro has had no problems with built in en0 interface and usb-ethernet adapter
for the second interface. I have one interface set to connect to the internet with DCHP. The other is
set manually with static ip address. I know enough to keep the internet connected network separate
from the local network with different subnet mask: 255.255.255.0 for 192.68.1.1- 254.
The Yosemite systems are not letting me use this set up. The builtin ethernet port interface will set
itself to self assigned IP address for DCHP. And the second interface set with a local static (manual)
address will not route. If I use only one interface I can get on to the internet.
With a DSL modem, the DCHP will assign a local address, so I can network the machines through that.
But now I have a cable connection and DCHP assigns a remote address and sub net mask. So It means
that if the Yosemite systems will not do two interfaces, I cannot network the computes locally.
What is it with this situation? Anyone have a real clue?

EDIT: Route is probably the wrong term (".. address will not route"). It will not send and receive
packets on the network with other hosts on the same network.

 

[belvdr]

I'm not sure what you mean by it "will not route". Are you defining default gateways on both adapters? If so, you need to remove the default gateway on the second interface.

EDIT: From terminal, with both interfaces plugged in and configured, please execute the following and post the results:

ifconfig -a
netstat -rn

 

[Phil in ocala]

I'm not sure what you mean by it "will not route". Are you defining default gateways on both adapters? If so, you need to remove the default gateway on the second interface.

___________________________
Good alternative to ethernet port on Mac is using the Thunderbolt to Gigabit Ethernet Adapter....works great for me and not overly expensive

 

[jekillen]

re: response from
belvdr

I have recently switched from DSL provider to cable internet provider and need to install a router to handle
several internet connections. That will happen the middle of next week.

I have run ifconfig and even though the Mac OSX network preference shows one of the interfaces with a manual
local address configured correctly and connected, the output from ifconfig shows there are no interfaces configured
with that address. That is with two interfaces, one for internet connection, with DCHP configuration, and the other
with local static address. Often the interface that is supposed to connect to the internet shows "self assigned ip
address" and is unusable. One other oddity is that when a USB-ethernet adapter is plugged in, the system creates
a listing for it. But if the USB-ethernet adapter is disconnected and reconnected, the system creates a new listing
for the interface. So I have had several interfaces listed in ifconfig output. Then it is unclear which interface the
current USB-ethernet adapter is using, or is supposed to be using. I wish Apple wouldn't 'fix' things that aren't
broken and would fix things that are broken.

When I get the router connected to the cable modem and the various computers connected to the router, and every
thing is working; and if I am still having the same problem, I will post output from ifcong and screen shots of the
network preference panel on my web site for review.

Thank you for time and attention
JK