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ip Command

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ip Command

ip is the modern replacement for ifconfig, route, arp, and netstat. It’s part of iproute2 and provides a consistent interface to all Linux networking configuration.

ip addr — Interface Addresses

ip addr show                     # show all interfaces
ip addr show eth0               # show specific interface
ip addr add 192.168.1.100/24 dev eth0    # add IP
ip addr del 192.168.1.100/24 dev eth0    # remove IP
ip addr flush dev eth0           # remove all IPs

Output Explained

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP qlen 1000
    link/ether 52:54:00:12:34:56 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.100/24 brd 192.168.1.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::5054:ff:fe12:3456/64 scope link
       valid_lft forever preferred_lft forever
  • <BROADCAST,MULTICAST,UP,LOWER_UP>: flags (UP means interface is admin-up)
  • mtu 1500: Maximum Transmission Unit (Ethernet default)
  • qdisc fq_codel: queueing discipline (traffic scheduler)
  • state UP: operational state (UP, DOWN, UNKNOWN)
  • inet 192.168.1.100/24: IPv4 address with CIDR prefix
  • brd 192.168.1.255: broadcast address
  • scope global: globally routable vs scope link (local-only)

ip link — Interface Configuration

ip link show                     # show all links
ip link set eth0 up             # bring interface up
ip link set eth0 down           # bring interface down
ip link set eth0 mtu 9000       # set MTU (jumbo frames)
ip link set eth0 promisc on     # enable promiscuous mode
ip link set eth0 name wan       # rename interface
ip link delete eth0             # delete a virtual interface

Create Virtual Interfaces

# Create a VLAN interface (802.1q)
ip link add link eth0 name eth0.100 type vlan id 100
ip addr add 10.0.100.1/24 dev eth0.100
ip link set eth0.100 up
 
# Create a dummy interface (for testing, loopback-like)
ip link add dummy0 type dummy
ip addr add 10.255.255.1/32 dev dummy0
ip link set dummy0 up
 
# Create a macvlan interface (shares host's MAC, separate IP)
ip link add link eth0 name macvlan0 type macvlan mode bridge
ip addr add 192.168.200.1/24 dev macvlan0
ip link set macvlan0 up

ip route — Routing Table

ip route show                    # show routing table
ip route add default via 192.168.1.1 dev eth0     # default route
ip route add 10.0.0.0/16 via 192.168.1.254 dev eth0  # static route
ip route add blackhole 10.0.0.0/8                 # drop traffic
ip route del 10.0.0.0/16                           # remove route
ip route get 8.8.8.8                    # which route for this IP?
 
# Change metrics (lower = preferred)
ip route add default via 192.168.1.1 dev eth0 metric 100

ip neigh — ARP/Neighbor Table

ip neigh show                    # show ARP cache
ip neigh add 192.168.1.1 lladdr aa:bb:cc:dd:ee:ff dev eth0 nud permanent  # static ARP entry
ip neigh del 192.168.1.1 dev eth0  # remove ARP entry
ip neigh flush all               # clear ARP cache

NUD states (Neighbour Unreachability Detection):

  • REACHABLE: confirmed working
  • STALE: valid but untested (will be verified lazily)
  • PERMANENT: static entry, never expires
  • FAILED: resolution failed

ip netns — Network Namespaces

# Create a network namespace
ip netns add myns
 
# List namespaces
ip netns list
 
# Run command in namespace
ip netns exec myns ip addr
ip netns exec myns ping 8.8.8.8
 
# Create veth pair and move one end to namespace
ip link add veth0 type veth peer name veth0ns
ip link set veth0ns netns myns
ip addr add 10.0.0.1/24 dev veth0
ip link set veth0 up
ip netns exec myns ip addr add 10.0.0.2/24 dev veth0ns
ip netns exec myns ip link set veth0ns up
 
# Delete namespace
ip netns del myns

ip maddr — Multicast Addresses

ip maddr show                    # show multicast memberships
ip maddr add 01:00:5e:00:00:01 dev eth0   # join IGMP group (for 224.0.0.1 all-hosts)

ip monitor — Watch for Changes

ip monitor all                   # watch all changes live
ip monitor route                # watch route changes
ip monitor neigh                 # watch ARP changes

Complete Workflow: Set Up a Static IP

# 1. Bring interface up
ip link set eth0 up
 
# 2. Set IP address
ip addr add 192.168.1.100/24 dev eth0
 
# 3. Set default gateway
ip route add default via 192.168.1.1
 
# 4. Verify
ip addr show eth0
ip route show
ping -c 1 192.168.1.1

Complete Workflow: Bridge with VETH for Containers

# 1. Create bridge
ip link add br0 type bridge
ip addr add 10.244.0.1/24 dev br0
ip link set br0 up
 
# 2. Create veth pair
ip link add veth0 type veth peer name veth1
 
# 3. Move one end to namespace (container)
ip link set veth1 netns container1
ip netns exec container1 ip addr add 10.244.0.10/24 dev veth1
ip netns exec container1 ip link set veth1 up
ip netns exec container1 ip link set lo up
ip netns exec container1 ip route add default via 10.244.0.1
 
# 4. Connect other end to bridge
ip link set veth0 master br0
ip link set veth0 up
 
# 5. Enable forwarding on bridge
iptables -A FORWARD -i br0 -o br0 -j ACCEPT

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