Arch Linux

abstrakct

Member

Registered: 2009-07-28

Posts: 35

My Arch install won't connect to/through a network switch

Hi,
I aquired a network switch today, and wanted to play around a little with that. One problem: My Arch install on my desktop refuses to connect to the network when it's plugged into the switch!

BUT when I booted the same computer from the Arch install iso (2015-08) it connected right away with no problems!! That is with the computer connected to the network switch (which is then connected to the router). LAN and internet worked perfectly without me having to do anything. Reboot back into my normal install: nope, no connection. Network is unreachable.

I used to use netcfg started by systemd. I tried to stop netcfg and use systemd.networkd + systemd.resolved but no luck. Disabled that, tried dhcpcd through systemd, still nothing. But if I unplug the computer from the switcher and plug it straight into the router, like before, network works as it should right away.

I'm not a networking expert, obviously, but the problem seems to be software/config related (since all the hardware works). Any idea where I should start? Let me know if you need any more info. The network card is built into the motherboard, here's some info from lspci:

05:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 06)
	Subsystem: Micro-Star International Co., Ltd. [MSI] Device 7693
	Flags: bus master, fast devsel, latency 0, IRQ 41
	I/O ports at d000 [size=256]
	Memory at fe104000 (64-bit, prefetchable) [size=4K]
	Memory at fe100000 (64-bit, prefetchable) [size=16K]
	Capabilities: [40] Power Management version 3
	Capabilities: [50] MSI: Enable+ Count=1/1 Maskable- 64bit+
	Capabilities: [70] Express Endpoint, MSI 01
	Capabilities: [b0] MSI-X: Enable- Count=4 Masked-
	Capabilities: [d0] Vital Product Data
	Capabilities: [100] Advanced Error Reporting
	Capabilities: [140] Virtual Channel
	Capabilities: [160] Device Serial Number 01-00-00-00-68-4c-e0-00
	Kernel driver in use: r8169
	Kernel modules: r8169

"ip addr" output when network works:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether d4:3d:7e:91:5c:43 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.2/24 brd 192.168.1.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::b2bb:a635:c4f1:888f/64 scope link 
       valid_lft forever preferred_lft forever

Thanks for any help or suggestions on how to solve this!

Head_on_a_Stick

Member

From: The Wirral

Registered: 2014-02-20

Posts: 8,779

Website

Re: My Arch install won't connect to/through a network switch

How about the `ip a` output when it's not working?

Does `dmesg` show anything when you plug your computer into the switch?

---

Jin, Jîyan, Azadî

msalerno

Member

Registered: 2014-08-15

Posts: 32

Re: My Arch install won't connect to/through a network switch

"ip route" when it's not working would also be useful.

abstrakct

Member

Registered: 2009-07-28

Posts: 35

Re: My Arch install won't connect to/through a network switch

Well. I just moved the cable that goes from the desktop to the router to the switch (in order to provide data from when things doesn't work), but now suddenly everything works flawlessly...! I have no idea why. I struggled for hours earlier today getting the exact same configuration to work.

the only change I did was connect an old netbook to one of the ports on the switcher and wait a few hours because I was watching tv...

dmesg just says link going up, then link going down.

I'll try a reboot to see if it persists.

Last edited by abstrakct (2015-08-24 22:53:15)

abstrakct

Member

Registered: 2009-07-28

Posts: 35

Re: My Arch install won't connect to/through a network switch

OK, so after a reboot, network is again unreachable.

"ip a" shows:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN group default qlen 1000
    link/ether d4:3d:7e:91:5c:43 brd ff:ff:ff:ff:ff:ff
    inet6 fe80::b2bb:a635:c4f1:888f/64 scope link tentative 
       valid_lft forever preferred_lft forever

"ip route" gives no output at all.

dhcpcd is running.
"sudo dhcpcd eth0" made no difference when the cable was plugged into the switcher (after reboot).

Moving the cable from the network switch to the router gives me instant access to the LAN and the internet.

EDIT: and then, moving the cable from the router to the switch, the connection is suddenly recognized and all is good!
I did "sudo ip link set dev eth0 up" before I went to move the physical cable, but I don't know if that has anything to do with anything.

Last edited by abstrakct (2015-08-24 22:55:05)

rsmarples

Member

Registered: 2009-05-12

Posts: 287

Re: My Arch install won't connect to/through a network switch

2: eth0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN group default qlen 1000

The clue is here.
NO-CARRIER means that the kernel thinks the cable is not plugged in at either end.
You can run dhcpcd, or other software, as much as you like, but they won't magically do anything until NO-CARRIER is not there.