create & delete & list & exec network namespace
# ip netns add test1
# ip netns list test1
# ip netns delete test1
# ip netns exec test1 ip a
1: lo: <LOOPBACK> mtu 65536 qdisc noop state DOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
# ip netns exec test1 ip link
1: lo: <LOOPBACK> mtu 65536 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
# ip netns exec test1 ip link set dev lo up
# ip netns exec test1 ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
# mode由DOWN变为UNKNOWN
add interface to a network namespace
# ip link add veth-a type veth peer name veth-b
# ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
link/ether 52:54:00:25:66:c8 brd ff:ff:ff:ff:ff:ff
3: veth-b@veth-a: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/ether c2:32:fc:89:5c:61 brd ff:ff:ff:ff:ff:ff
4: veth-a@veth-b: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/ether da:8f:39:f7:09:1f brd ff:ff:ff:ff:ff:ff
assign ip address to veth interface
# ip addr add 192.168.8.155/24 dev veth-a
# ip link set veth-a up
# ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
link/ether 52:54:00:25:66:c8 brd ff:ff:ff:ff:ff:ff
3: veth-b@veth-a: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/ether c2:32:fc:89:5c:61 brd ff:ff:ff:ff:ff:ff
4: veth-a@veth-b: <NO-CARRIER,BROADCAST,MULTICAST,UP,M-DOWN> mtu 1500 qdisc noqueue state LOWERLAYERDOWN mode DEFAULT group default qlen 1000
link/ether da:8f:39:f7:09:1f brd ff:ff:ff:ff:ff:ff
# mode LOWERLAYERDOWN
# ip addr add 192.168.8.156/24 dev veth-b
# ip link set veth-b up
# ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
link/ether 52:54:00:25:66:c8 brd ff:ff:ff:ff:ff:ff
3: veth-b@veth-a: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000
link/ether c2:32:fc:89:5c:61 brd ff:ff:ff:ff:ff:ff
4: veth-a@veth-b: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000
link/ether da:8f:39:f7:09:1f brd ff:ff:ff:ff:ff:ff
# mode UP
