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(I posted this question earlier today on ServerFault. It was suggested that SuperUser is a better place for it.)

I'm trying to connect Ethernet from my Mac-Mini to devices on an unmanaged switch (Brainboxes SW-504). It's not working.

The Mac connects via wifi to a linksys router serving network addresses 192.168.2.0 255.255.255.0 with DHCP. This is working.

I've set the ethernet configuration to manual and assigned its address to be 192.168.1.120 with subnet mask 255.255.255.0 in order to create a separate class C subnet.

There is no router on the 192.168.1 subnet -- just 3 devices (2 raspberry pi's and a custom board). The three devices have hard addresses at 192.168.1.121, 192.168.1.122 and 192.168.123. All three are communicating with each other via ethernet cables plugged to the switch.

For development and debugging, I need to connect the Mac to these devices but have thus far been unsuccessful at finding a configuration that works. I can't even ping them.

Here's what ifconfig says about the ethernet (en0) and wifi (en1) interfaces:

en0: flags=8963<UP,BROADCAST,SMART,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
    options=10b<RXCSUM,TXCSUM,VLAN_HWTAGGING,AV>
    ether a8:20:66:4a:d5:5a
    nd6 options=201<PERFORMNUD,DAD>
    media: autoselect (100baseTX <full-duplex,flow-control>)
    status: active
en1: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
    ether 88:53:95:2c:9a:0d
    inet6 fe80::1085:342e:6382:e6b4%en1 prefixlen 64 secured scopeid 0x8
    inet 192.168.2.103 netmask 0xffffff00 broadcast 192.168.2.255
    nd6 options=201<PERFORMNUD,DAD>
    media: autoselect
    status: active

Note that the assigned ip for en0 is not appearing in the above. The GUI network setup is showing it as intended and indicates no error.

Running networksetup -getinfo Ethernet gives:

Manual Configuration
IP address: 192.168.1.120
Subnet mask: 255.255.255.0
Router: (null)
IPv6: Manual
IPv6 IP address:
IPv6 Router: none
IPv6 Prefix Length: 0
Ethernet Address: a8:20:66:4a:d5:5a

Running netstat -rn gives:

Destination        Gateway            Flags        Refs      Use   Netif Expire
default            192.168.2.1        UGSc           66       49     en1
default            link#13            UCSI            0        0 bridge0      !
default            link#15            UCSI            0        0 bridge1      !
127                127.0.0.1          UCS             0        0     lo0
127.0.0.1          127.0.0.1          UH              1     7877     lo0
169.254            link#8             UCS             1        0     en1      !
192.168.2          link#8             UCS             3        0     en1      !
192.168.2.1/32     link#8             UCS             1        0     en1      !
192.168.2.1        14:91:82:71:2f:e2  UHLWIir        28      199     en1   1153
192.168.2.81       74:40:bb:19:9d:a5  UHLWI           0      327     en1    996
192.168.2.103/32   link#8             UCS             0        0     en1      !
192.168.2.183      f4:f5:d8:ca:f5:18  UHLWIi          1      919     en1   1190
192.168.2.251      88:1f:a1:16:8e:a4  UHLWI           0        0     en1    285
192.168.3          link#15            UC              1        0 bridge1      !
192.168.4          link#13            UC              1        0 bridge0      !
224.0.0/4          link#8             UmCS            2        0     en1      !
224.0.0.251        1:0:5e:0:0:fb      UHmLWI          0        0     en1
239.255.255.250    1:0:5e:7f:ff:fa    UHmLWI          0      408     en1
255.255.255.255/32 link#8             UCS             1        0     en1      !
255.255.255.255    ff:ff:ff:ff:ff:ff  UHLWbI          0        6     en1      !
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6
  • Not sure why ifconfig wouldn't show it but the "standard" GUI method of Mac is showing everyhting the way you set it. Just for the sake of asking, I'll also ask if this is a known-good cable that you are using and that you don't have it plugged into a dedicated uplink port on the unmanaged switch. Also assume any blinking lights on the switch are doign their thing in respect to the port you are using? ... And of course, you did reboot right?
    – ivanivan
    Jul 3, 2019 at 21:20
  • @ivanivan Good things to check but changing cable and rebooting made no difference in this case. All the lights are blinking furiously. I suspect the problem is related to the lack of an explicit router or gateway in the switched subnet, i.e. I need somehow to tell the mac to send all traffic to 192.168.1.X addresses out via en0. Tried using network setup to add an additional route, but it made no difference.
    – Mike Ellis
    Jul 3, 2019 at 21:36
  • A router/gateway is not needed when everything is on the same switch. It sounds Like the mac has not activated the ethernet link, maybe it is disabled or not detecting the wire plugged in. Unfortunately I dont know MacOS well enough to say much more.
    – kicken
    Jul 3, 2019 at 22:03
  • @kicken That's what I thought. AFAICT the ethernet device is active (see ifconfig report in my question text). I also see a dramatic drop in network traffic reported in Activity monitor when I unplug the ethernet cable from the switch.
    – Mike Ellis
    Jul 3, 2019 at 22:11
  • Did you setup an ethernet bridge at some point? Your route output shows bridge0 and bridge1 interfaces with 192.168.3.x and 192.168.4.x networks. Seems odd to me, but again not a mac guy.
    – kicken
    Jul 3, 2019 at 22:39

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