I am searching for an explanation what exactly the output of the commands ip link
and ip addr
means on a linux box.
# ip link
3: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT qlen 1000
link/ether 00:a1:ba:51:4c:11 brd ff:ff:ff:ff:ff:ff
4: eth1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN mode DEFAULT qlen 1000
link/ether 00:a1:ba:51:4c:12 brd ff:ff:ff:ff:ff:ff
What exactly are the LOWER_UP
, NO-CARRIER
and other flags? I have found a reference at http://download.vikis.lt/doc/iproute-doc-2.6.32/ip-cref.ps but it does not contain complete information and man pages are not detailed enough.
Best Answer
Those are interface's flags. They are documented in the
netdevice(7)
man-page. Below is the relevant part (reordered alphabetically):So,
LOWER_UP
means there is a signal at the physical level (i.e. something active is plugged in the network interface).NO-CARRIER
, is the exact opposite: no signal is detected at the physical level.