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IP command

  • All configuration made with this command are lost after reboot
  • Use a network manager for persistent configuration
  • You the parameter -c to add color
  • link/ether is the MAC address of the interface

show

ip link show # all interface (ip link)
ip link show "wlp3s0" # specific interface

set

ip link set "wlp3s0" up # activate
ip link set "wlp3s0" down # deactivate
ip link set "wlp3s0" address "00:11:22:33:44:55" # change MAC address (must be down first)

add

ip link add "wlp3s0" type "bridge"
ip link add "veth-red" type "veth" peer name "veth-blue" # veth cable

del

ip link del "wlp3s0"

Create a virtual Ethernet Pair (veth cable)

# Create virtual ethernet pair (a "cable" to connect 2 namespaces)
ip link add "veth-red" type "veth" peer name "veth-blue"

# Attach each veth to its corresponding namespaces
ip link set "veth-red" netns "red"
ip link set "veth-blue" netns "blue"

# Deleting one link, the other is deleted automatically (veth-blue)
ip link del "veth-red" -n "red"
ip link del "veth-blue" -n "blue" # not necessary

Create bridge interface

# Add new interface of type bridge
ip link add "v-net-0" type "bridge"
ip link set "v-net-0" up
ip link add "veth-red" type "veth" peer name "veth-red-br" # connects to the bridge

address

# List IP addresses assigned for each interface
ip address # addr or a

# Assign an IP to an interface (temporary)
ip address add "192.168.1.10/24" dev "interface-id"
ip address add "192.168.1.10/24" dev "veth-red" -n "red" # interface in a namespace

route

  • Routing tables are used to force traffic going to another network to pass through a gateway
  • The gateway joins every network. A gateway is assigned an IP for each network it is part of.
# show routing tables
ip route

# add entries into the routing table
ip route add "192.168.2.0/24" via "192.168.1.1"

netns

# list network namespaces
ip netns

# create namespace
ip netns add "red"
ip netns add "blue"

# execute a command in the namespace
ip netns exec "blue" "ip link"
ip link -n "blue" # same effect

Concepts

  • IP: Identifies each computer using Internet Protocol
  • Subnetmask: Masks the IP. Divide the IP into network address and host address
  • Gateway: Which route to take to send the traffic out or to receive traffic
  • Static IP: IP does not change for a machine
  • DHCP: Takes the address from a pool of IPs and assign to a machine upon connection
  • Interface: a NIC (Network Interface Controller) card. Ethernet, Wi-Fi, etc. Always have a MAC address that never changes (E.g, 3A-34-52-C4-69-B8)

Interface configuration files

  • /etc/nsswitch.conf
  • Tells the system where it should resolve some functionalities of the system (E.g, resolve the hostname to ip address -> hosts: files mdns4_minimal [NOTFOUND=return] dns)
  • /etc/hosts: resolve hostname to ip address
  • /etc/hostname: current hostname
  • /etc/network/interfaces: Interfaces
  • /etc/resolv.conf: IP to the DNS server! Resolve hostname-ip, ip-hostname, hostname-hostname
  • /etc/sysconfig/network-scripts/ifcfg-nic: Static IP configuration

Protocols or clients to access the system

  • Windows: Remote Desktop RDP (for Windows)
  • VMware ESC: vSphere client (for Windows)
  • Linux: Putty (for Windows), SecureCRT, SSH from Linux to Linux

NIC (Network Interface Card)

  • NICs in ip addr

  • lo: Loopback device. Interface for the computer to communicate with itself

  • virb0: Virtual bridge is used for NAT (Network Address Translation )
  • enp: Cabled network

  • wlp: Wireless network

  • enp2s0: Wired connection

  • wlp3s0: Wireless connection