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====== Linux IP/Network how-to ======

===== Setup a secondary IP on the same physical device =====

This how-to shows the procedure to setup an alias on a physical ethernet device. We are going to use 'ip' command line tool. We are going to setup following parameters:

^What           ^ ^Value         ^
|Physical device|:|ens33         |
|Default gateway|:|172.16.135.254|
|Netmask/Prefix |:|255.255.254.0 |
|Alias interface|:|ens33:1       |

**Attention:** The alias network IP only is routed, if you use the same Netmask/Prefix!

  * Get current IP configuration:

<code bash>
ip a list dev ens33
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 00:50:56:02:13:85 brd ff:ff:ff:ff:ff:ff
    inet 172.16.134.3/23 brd 172.16.135.255 scope global ens33
       valid_lft forever preferred_lft forever
    inet6 fe80::250:56ff:fe02:1385/64 scope link
       valid_lft forever preferred_lft forever
</code>
  * Add a secondary IP on the physical device:

<code bash>
ip addr add 172.16.134.5/23 dev ens33 label ens33:1
</code>
  * Check the configuration previously added:

<code bash>
ip a list dev ens33
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 00:50:56:02:13:85 brd ff:ff:ff:ff:ff:ff
    inet 172.16.134.3/23 brd 172.16.135.255 scope global ens33
       valid_lft forever preferred_lft forever
    inet 172.16.134.5/23 scope global secondary ens33:1
       valid_lft forever preferred_lft forever
    inet6 fe80::250:56ff:fe02:1385/64 scope link
       valid_lft forever preferred_lft forever
</code>

<WRAP center round important 60%>
The line containing the new alias name (''%%ens33:1%%'') must include ''%%secondary%%''!
</WRAP>

  * Delete alias from physical device:

<code bash>
ip addr del 172.16.134.5/23 dev ens33 label ens33:1
</code>

==== To make it permanent ====

To make it permanent, you do it using ''nmcli'' or just add the following lines into ''ifcfg-ens33'' file:

<code bash>
IPADDR1=172.16.134.5
PREFIX1=23
</code>

The ''nmcli'' command:

<code bash>
nmcli con mod ens192 +ipv4.addresses "172.16.134.5/23"
</code>

When done, just restart network: ''systemctl restart network''



===== Remove (delete) an IP address =====

<code bash>
ip addr del 172.16.134.5/23 dev ens33
</code>

===== Setup with VLAN tag =====
In some circumstances, a VLAN tagging is necessary. In this chapter, I show how-to setup such an interface.

^ What             ^    ^ Value               ^
| Physical device  | :  | ens2f0              |
| IP address       | :  | 192.168.1.54        |
| Netmask/Prefix   | :  | 255.255.255.0 / 24  |
| VLAN interface   | :  | ens2f0.90           |

==== Add a vlan tag to an interface ====
Here we add the VLAN tag ''90'' to the interface, ''ens2f0.90'':

<code bash>
ip link add link ens2f0 name ens2f0.90 type vlan id 90
</code>

==== Add the IP to the linked device ====

<code bash>
ip addr add 192.168.1.54/24 dev ens2f0.90
</code>

==== Add a default gateway ====

<code bash>
ip route add default via 192.168.1.1 dev ens2f0.90
</code>