Switch not connecting to all computers


I need help configuring a switch (Datacom DM4000).

It has 2 ports, one for management and one for console (obviously more 24 ports for normal use).

With a RJ-45 to serial cable I was able to configure the IP from the management port and with a normal RJ-45 cable I could ping, access it with telnet and so on.

The problem was that not all my computers could access the switch.

I have 4 computers:

1 - Desktop Dell Vostro with Ubuntu 15.04

2 - old PC with Ubuntu Server 16.04 and 2 network interface

3 - Notebook Dell Vostro with some ubuntu

4 - Notebook Lenovo Yoga 900 with Windows 10 and a USB ethernet

The computers 1 and 3 can connect with no problem, the computers 2 and 4 can't!

I tried with 3 different cables, when I connect 1 or 3 the LED "Link/act" become on and when I use the command "ethtool ethX" say it is on. But when I connect to 4 or both network interfaces on 2 the LED stays off and the ethtool says it has no link. I even tried to use wireshark to capture any packet but nothing arrived.

My computer 1 has a little bug (at least I think so) that when I connect the cable it get no IP, even though is configured with static IP (but the link/LED is on), so I have to reset the interface (the link/LED goes off and on) and then get the IP and I can connect. All other computers are setup with static IP too.

Any ideia why this is happening?

The only thing in common that I can see is that both computers that work are from Dell, so maybe they have any different configuration but besides that nothing in common.

Any test that I can execute to try to see what the problem is?

The computer that I need the most to connect is 2 because it has two interfaces and I pretend to run several tests with it.



Providing more information:

Computer 1 ethtool connected to mgmt-eth:

sudo ethtool eth0
Settings for eth0:
    Supported ports: [ TP MII ]
    Supported link modes:   10baseT/Half 10baseT/Full 
                            100baseT/Half 100baseT/Full 
                            1000baseT/Half 1000baseT/Full 
    Supported pause frame use: No
    Supports auto-negotiation: Yes
    Advertised link modes:  10baseT/Half 10baseT/Full 
                            100baseT/Half 100baseT/Full 
    Advertised pause frame use: Symmetric Receive-only
    Advertised auto-negotiation: Yes
    Link partner advertised link modes:  10baseT/Half 10baseT/Full 
                                         100baseT/Half 100baseT/Full 
    Link partner advertised pause frame use: No
    Link partner advertised auto-negotiation: Yes
    Speed: 100Mb/s
    Duplex: Full
    Port: MII
    PHYAD: 0
    Transceiver: internal
    Auto-negotiation: on
    Supports Wake-on: pumbg
    Wake-on: d
    Current message level: 0x00000033 (51)
                   drv probe ifdown ifup
    Link detected: yes

Computer 2 ethtool connected to mgmt-eth: http://imgur.com/a/bDj8k

Computer 2 ethtool connected to console: http://imgur.com/a/QfC8h

DM4000 configuration: (running on computer 1)

DM4000(config-if-mgmt-eth)#show ip interface 

DM4000(config-if-mgmt-eth)#show interfaces status mgmt-eth
Information of Mgmt-Eth
  Port admin:             Up
  Speed-duplex:           Auto
  Capabilities:           10M half, 10M full, 100M half, 100M full, TX/RX pause
 Current status:
  Link status:            Up
  Operation speed-duplex: 100M full
  Flow-control:           Disabled

DM4000(config-if-mgmt-eth)#show running-config
Building configuration...
! Board models in this configuration:
! Unit 1: ETH24GX H Series+L3
hostname DM4000
asked on Server Fault Oct 12, 2016 by tvortiz • edited Oct 13, 2016 by tvortiz

1 Answer


My bet is that the management port doesn't have auto-MDIX. If these computers also don't have auto-MDIX, you'll need a crossover cable to connect the two interfaces.

The port jacks are switch ports and are meant to connect to a device. The management jack is a device and is meant to connect to a switch port. Connecting a device to a device will only work if at least one device has auto-MDIX. Most devices do, but it seems you may have found some that don't.

answered on Server Fault Oct 13, 2016 by David Schwartz

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