IP and Routing in Linux

IP

# Assign static IP for Ubuntu 14, 16
$ sudo vim /etc/network/interfaces

iface eno1 inet static
        address 172.16.10.113
        netmask 255.255.255.0
        gateway 172.16.10.1
        dns-nameservers 8.8.8.8
        up ip route add 10.10.1.0/24 via 172.16.10.1
        up ip -6 addr add 2001::2/64 dev eno1

Commonly used IP addresses:

• The last octet of a network address is 0, gateway address is 255
• 127.0.0.1 loopback
• 0.0.0.0 IP address does not exist

Route trong Linux

• Routing table using Longest Prefix Match. For example
  • 192.168.0.0/16 next-hop 10.0.0.1 IF1
  • 192.168.1.0/24 next-hop 11.0.0.1 IF2
  • 192.168.1.128/25 next-hop 12.0.0.1 IF3
  • Thus, when you want to send a message to 192.168.1.129, you will send it via 192.168.1.128/28 IF3

route -n

or ip route show

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.1.254   0.0.0.0         UG    100    0        0 eno16777736
192.168.1.0     0.0.0.0         255.255.255.0   U     100    0        0 eno16777736
192.168.122.0   0.0.0.0         255.255.255.0   U     0      0        0 virbr0

Flags:

• G: using gateway, the difference between with and without this flag is shown below.
• U: up - active status

route add

How is the travel packet in the network?

Conclude

• IP address src. and IP des. unchanged when traversing the network (in the case of no NAT)
• MAC address src. and MAC des. is changed when passing through each Router