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#1 2019-08-06 10:39:19

EdeWolf
Member
Registered: 2016-01-06
Posts: 32

[solved] Bring up interface with no link?

Hello,

In a multihomed host I have an unused ethernet interface, that I still would like to utilize internally instead of having to create an additional dummy interface.

In good old ifconig times this was no problem, one even could bind services onto it, it simply had no link, but was not "down". Now I am struggeling on how to archieve the same with systemd-networkd and/or the newfashioned iproute2 tools and I have been failing sofar.

ip set link dev eth2 up

does not do any magic, the interface stays down:

4: eth2: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN group default qlen 1000

Trying:

"ip link set dev eth2 carrier on"

fails as well:

RTNETLINK answers: Operation not supported

And my 10-eth2.network file looks like this:

[Match]
MACAddress=00:0d:b9:51:94:26

[Network]
ConfigureWithoutCarrier=true
IgnoreCarrierLoss=true
....

So, whatever I've tried so far, the interface stays down - neither can I ping it's ip internally nor, and that is the real problem, can I create any mac|ipvlan interfaces, as their respective links also complain about LOWERLAYERDOWN

Any way to get a sensible behaviour back as in the times of old?

I am aware, that netctl seems to offer SkipNoCarrier=yes, but I do not have netctl installed and if netctl is capable of offering this option, then at least the ip command lines tools should as well?

So hopefully I am just not capable of reading the ip man page properly. Any suggestions?

In case systemd-networkd should have limitations, well, ok, but at least on the shell I should be able to get the interface up and running without a cable attached?

Thanks for any clues

Last edited by EdeWolf (2019-08-06 12:33:35)

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#2 2019-08-06 10:46:00

loqs
Member
Registered: 2014-03-06
Posts: 8,792

Re: [solved] Bring up interface with no link?

The link is up

<NO-CARRIER,BROADCAST,MULTICAST,UP>

Edit:
Also

ip set link dev eth2 up

Should that not be

ip link set eth2 up

Last edited by loqs (2019-08-06 10:57:55)

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#3 2019-08-06 12:33:04

EdeWolf
Member
Registered: 2016-01-06
Posts: 32

Re: [solved] Bring up interface with no link?

loqs wrote:

The link is up

Gosh. This is so embarrasing. You are of course right. My nftables rules were blocking the IP address, that is why I got no ping reply, and I got distracted by the state DOWN

Thanks very much for doing my job. Now an ipvlan address still displays LOWERLAYERDOWN, but it replies to ping as well.


loqs wrote:

Should that not be

ip link set eth2 up

The way I've read ip link help, those two are identical. But I may well be wrong and happily stand corrected.

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