npodonnell/linux_networking.md

## linux_networking.md

      
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              linux_networking.md
            
          
    Linux Networking

N. P. O'Donnell, 2021
Network Interfaces

Bring eth0 interface down:
WARNING: If you do this remotely (like through an SSH connection), it will disconnect you...
ip link set eth0 down

Bring eth0 interface up:
ip link set eth0 up

Set MTU

ip link set dev eth0 mtu 1420

IPIP Tunnel

Scenario involves 2 machines.
Machine 1's IP address is 172.31.95.154
Machine 2's IP address is 172.32.31.103
Step 1: Create tunnel interfaces

On machine 1:
ip tunnel add tun0 mode ipip remote 172.32.31.103 local 172.31.95.154

On machine 2:
ip tunnel add tun0 mode ipip remote 172.31.95.154 local 172.32.31.103

Step 2: Give them IP addresses

Make sure the IP addresses don't clash with existing ones!
On machine 1:
ip address add 192.168.0.1/24 dev tun0

On machine 2:
ip address add 192.168.0.2/24 dev tun0

Step 3: Bring them up

On both machines:
ip link set tun0 up

Then a ping test...
On machine 1:
ping 192.168.0.2

On machine 2:
ping 192.168.0.1

Routing

Display the routing table:
ip route show

Adding Routes

Route all traffic to a single IP address 135.125.202.171 through interface tun0:
ip route add 135.125.202.171 dev tun0

Route all traffic to IP address range 8.8.0.0/16 via 192.168.0.2:
ip route add 8.8.0.0/16 via 192.168.0.2

Getting Routes

Get the root for 8.8.8.8:
ip route get 8.8.8.8

Wireguard

Creating Keys

Create private key:
wg genkey
Create Public Key:
wg pubkey
Then paste in the private key followed by Ctrl-D.
Or use pipes.
One liner:
((wg genkey | tee privkey) | wg pubkey) > pubkey
Install Wireguard on Amazon Linux 2 (as root):
yum upgrade -y
amazon-linux-extras install -y epel
curl -Lo /etc/yum.repos.d/wireguard.repo   https://copr.fedorainfracloud.org/coprs/jdoss/wireguard/repo/epel-7/jdoss-wireguard-epel-7.repo
yum clean all
yum install -y wireguard-dkms wireguard-tools
Configuration File:
/etc/wireguard/wg0.conf

Check status:
wg

WG-Quick

WG Quick is used for quickly prototyping wireguard configurations.
Bring wg0 interface up:
wg-quick up wg0

Bring wg0 interface down:
wg-quick down wg0

Socat

Test sending of UDP datagrams

On receiving machine:
socat -u udp-recv:12345,reuseaddr -
On sending machine:
socat - udp-sendto:<ip>:12345
Then type some characters on the sending machine.
TCPDump

Show all traffic:
sudo tcpdump
Show UDP traffic:
sudo tcpdump udp