Networking
==========

Netplan Reference
    https://netplan.io/reference/

    http://manpages.ubuntu.com/manpages/cosmic/man5/netplan.5.html

Dnsmasq Man Pages
    https://linux.die.net/man/8/dnsmasq




I/O and Resource Access Metrics::

    #execute typical instruction	               1 nanosec
    #fetch from L1 cache memory	                     0.5 nanosec
    #branch misprediction	                       5 nanosec
    #fetch from L2 cache memory	                       7 nanosec
    #Mutex lock/unlock	                              25 nanosec
    #fetch from main memory	                     100 nanosec
    #send 2K bytes over 1Gbps network	          20,000 nanosec
    #read 1MB sequentially from memory	         250,000 nanosec
    #fetch from new disk location (seek)       8,000,000 nanosec
    #read 1MB sequentially from disk	      20,000,000 nanosec
    #send packet US to Europe and back       150,000,000 nanosec







Linux Networking
-----------------

Here we are going to be dealing with ethernet, links, virtual network interfaces,
and virtual private networks, and tunnels.

https://en.wikipedia.org/wiki/Iproute2

The iproute2 collection includes the tools

#. arpd
#. bridge
#. ctstat
#. dcb
#. devlink
#. ``ip`` show / manipulate routing, network devices, interfaces and tunnels
#. lnstat
#. nstat
#. rdma
#. routef
#. rtacct
#. rtmon
#. rtstat
#. ss
#. tc
#. tipc

* ``ip addr`` and ``ip link`` and ``ip -s`` Address and Link Configuration
* ``ip route`` for routing tables
* ``ip neigh`` for Neighbors
* ``ip tunnel`` for Tunnels
* ``ip link set name`` rename network interface
* ``ip maddr`` multicast
* ``ip -s`` and ``ss`` for various network statustics
* ``bridge`` Handle bridge Addresses and devices
* ``lsmod`` show the status of modules in the linux kernel

* ``conntrack`` netfilter connection tracking tool


* ``ethtool`` settings and properties of an ethernet interface


.. code-block:: bash

    # bring up or down a network interface
    sudo ifconfig wlan0 down
    sudo ifconfig wlan0 up




Internet Protocol v4 and v6
---------------------------


.. code-block:: python

    # four octets
    ipv4 = 0xFF ** 4

    print(ipv4)

    # eight hextets
    ipv6 = 0xFFFF ** 8

    print(ipv6)





Reserved IP Addresses for IPv4 and IPv6
    https://en.wikipedia.org/wiki/Reserved_IP_addresses

Private Network Address Ranges/blocks for IPv4 and IPv6:
    https://en.wikipedia.org/wiki/Private_network



DNS
--------


.. code-block:: bash

    # flush dns caches
    sudo systemd-resolve --flush-caches

    # restart network d
    sudo systemctl restart systemd-networkd

    systemd-resolve --status | grep 'DNS Servers' -A2

    # make a dns request over dnsmasq over non standard DNS port
    dig @2601:181:c400:121b::feed -p 5399 uraspi.vpn

    # make a dns request over dnsmasq over the standard DNS port
    dig @2601:181:c400:121b::feed -p 53 uraspi.vpn


IPv4
----

Subnet Mask Cheatsheet:
    https://www.aelius.com/njh/subnet_sheet.html




None-Loopback open ports and interfaces
    This command greps everything that might need to be allowed
    through the firewall

    ``sudo netstat -plnt | grep -E '192.168*|2601*'``


IPv6
-----


General and Special Special Address Blocks and Ranges
*****************************************************


IPv6 Address Structure
    https://en.wikipedia.org/wiki/IPv6_address


Special Purpose Addresses:
    https://www.iana.org/assignments/iana-ipv6-special-registry/iana-ipv6-special-registry.xhtml#iana-ipv6-special-registry-1


Global Unicast Addresses:
    https://www.iana.org/assignments/ipv6-unicast-address-assignments/ipv6-unicast-address-assignments.xhtml

.. code-block:: bash

    # get IPv6 hosts
    ifconfig |grep inet6

    # another way
    ip -6 addr show

    # http requests via explicit IPv6 addresses
    wget http://[2601:181:c400:121b::999]/basic.html



Link Local IPv6 Addresses:
**************************

.. code-block:: bash

    # to reach link local address we need to include the interface name of the localhost
    # wlp61s0 is the interface name on thinkpad
    # 96c6:91ff:fe1b:8e15 is the link address of nuc

    ping fe80::96c6:91ff:fe1b:8e15%wlp61s0

    ssh fe80::96c6:91ff:fe1b:8e15%wlp61s0

    #assuming your the host interface name in variable MAIN_ETHERNET
    # to obtain your link address for a given ethernet interface
    ifconfig $MAIN_ETHERNET | grep link | awk '{print $2}'

    # manually assign link addresses

    ip -6 addr add fe80::feed/64 dev eno1 # nuc
    ip -6 addr add fe80::face/64 dev wlp61s0 # thinkpad



Listen to IPv6 Addresses in Nginx:
    For a specific Host

    ``listen [2601:181:c400:121b::999]:80;``

    Wildcard IPv6 host

    ``listen [::]:80;``


Configure Host IPv6 static addresses in home network or private network
************************************************************************

SLAAC+Stateless DHCP
    Each host to assign their own IPv6 addresses, and addresses don't get leased / released

Address Prefix
    The netmask in IPv4 language, which is usually 64, meaning 64 bit prefix.

Gateway LAN Address
    The gateway is the routers LAN IPv6 address, probably based on its MAC address,
    and looks something like this:

    ``2601:181:C400:121B:1E3B:F3FF:FED2:6309``

Static IPV6 address
    Each host to assign their own static IP, and NAT is not needed in IPv6.
    Either Automatically  (each host will ping others in the network to ensure IP
    is not already being used, or manually.

    Assuming network prefix is:

    ``2601:181:C400:121B``

    or 

    ``2601:181:C400:121B::/64``

    A host IP can range from

    ``2601:181:C400:121B::1``

    to

    ``2601:181:C400:121B:FFFF:FFFF:FFFF:FFFF``