====== Networking tools in Linux ======

===== Basic =====

  * ''ip a'' to see interfaces + ip addresses.
  * ''ifw disable'' disables the ubuntu firewall.
===== iptables =====

===== netplan =====
To change the network configuration in new Ubuntu versions. 

There is an .yml software in ''/etc/netplan''. To apply changes use the next command:

<code>
netplan apply
</code>


===== Change IP =====
<code>
network:
  version: 2
  renderer: networkd
  ethernets:
    enp3s0:
      addresses:
        - 10.10.10.2/24
      gateway4: 10.10.10.1
      nameservers:
          search: [mydomain, otherdomain]
          addresses: [10.10.10.1, 1.1.1.1]
</code>
==== DHCP example ====
<code>
network:
  version: 2
  renderer: networkd
  ethernets:
    enp3s0:
      dhcp4: true
</code>


==== Using NetworkManager ====
<code>
network:
  version: 2
  renderer: NetworkManager
</code>
===== routes =====

==== Which ip has a domain? ====
<code>
alfred@Y50-70:~$ nslookup couch00.dev.getfinancing.us
Server:		127.0.0.53
Address:	127.0.0.53#53

Non-authoritative answer:
Name:	couch00.dev.getfinancing.us
Address: 10.1.50.195
Name:	couch00.dev.getfinancing.us
Address: 10.1.51.200
Name:	couch00.dev.getfinancing.us
Address: 10.1.52.100
</code>

==== What's your routing table? ====
<code>
alfred@Y50-70:~$ route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.1.1     0.0.0.0         UG    100    0        0 enp9s0
10.1.0.0        0.0.0.0         255.255.0.0     U     50     0        0 tun0
34.231.231.68   192.168.1.1     255.255.255.255 UGH   100    0        0 enp9s0
169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0        0 virbr0
192.168.1.0     0.0.0.0         255.255.255.0   U     100    0        0 enp9s0
192.168.1.1     0.0.0.0         255.255.255.255 UH    100    0        0 enp9s0
192.168.122.0   0.0.0.0         255.255.255.0   U     0      0        0 virbr0
192.168.255.1   192.168.255.21  255.255.255.255 UGH   50     0        0 tun0
192.168.255.21  0.0.0.0         255.255.255.255 UH    50     0        0 tun0
</code>
===== DNS =====

You can query dns records with the dig command. To do that, for example, for obtaining the CNAME record for url6816.alfredgg.dev:
<code>
dig cname url6816.alfredgg.dev
</code>
===== VPN with strongswan =====

==== ipsec command ====

  * ''ipsec status'' tells you who is connected.
  * ''ipsec reload'' reloads the config.
  * ''ipsec restart'' restarts the service.
==== Troubleshooting ====

===== Mapping the network =====

===== Which ports are open? =====

Locally and simply: 
<code>
nmap localhost
</code>

Remotely:
<code>
nmap -Pn -p 51414 95.169.230.182
</code>
Comprueba el puerto 51414 de 95.169.230.182.

Hay la posibilidad de lanzarlo via web desde: http://nmap.online-domain-tools.com/


==== Discover IP's ====

<code>
nmap -sP 192.168.1.*
</code>

<code>
nmap -sn 192.168.1.0/24
</code>

===== Emulate network problems =====
  * https://medium.com/@docler/network-issues-simulation-how-to-test-against-bad-network-conditions-b28f651d8a96
  * https://wiki.linuxfoundation.org/networking/netem

You will use "tc" command:
<code>
sudo tc qdisc add dev eth0 root netem delay 1s
sudo tc qdisc del dev eth0 root
</code>

For example, to simulate problems with dockers you will do the next:
  - ''docker inspect container'' -> And take the value for the IPAddress
  - ''route -n'' -> To see which device is used for that container
  - ''sudo tc qdisc add dev <device> root netem delay 1s''
  - Test it with a ping.
  - ''sudo tc qdisc del dev <device> root''


==== Other examples ====
<code>
tc qdisc add dev eth0 root netem loss 5%
tc qdisc change dev eth0 root netem corrupt 2%
tc qdisc change dev eth0 root netem duplicate 1%
</code>
===== How to... =====
==== Update DNS in Ubuntu 18.04 ====

Previously you only need to edit the ''/etc/resolv.conf''

In new versions Netplan manages the network. You can configure it on files places on ''/etc/netplan''; these have an yml format.

This is an example:
<code>
network:
  version: 2
  renderer: networkd
  ethernets:
    ens3:
      dhcp4: no
      addresses:
        - 192.168.121.199/24
      gateway4: 192.168.121.1
      nameservers:
          addresses: [8.8.8.8, 8.8.4.4]
</code>

To update from changes do:
<code>
netplan apply
</code>

To list dns entries:
<code>
systemd-resolve --status
</code>

==== ... know... ====

=== ... The default gateway? ===
<code>
$ route -n
0.0.0.0         91.126.134.177  0.0.0.0         UG    100    0        0 ens18
</code>