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|
<!-- vim: set sw=2 et sts=2 ft=xml: -->
<!-- Last content review: 2024-01-21T07:35:56 UTC -->
<chapter id="_network_setup">
<title>Network setup</title>
<tip> <para>For modern Debian specific guide to the networking, read <ulink url="https://www.debian.org/doc/manuals/debian-handbook/sect.network-config">The Debian Administrator's Handbook — Configuring the Network</ulink>.</para> </tip>
<tip>
<para>Under <ulink url="https://en.wikipedia.org/wiki/Systemd">systemd</ulink>, <ulink url="https://en.wikipedia.org/wiki/Systemd#networkd">networkd</ulink> may be used to manage networks. See <literal>systemd-networkd</literal>(8).</para>
</tip>
<section id="_the_basic_network_infrastructure">
<title>The basic network infrastructure</title>
<para>Let's review the basic network infrastructure on the modern Debian system.</para>
<table pgwide="0" frame="topbot" rowsep="1" colsep="1">
<title>List of network configuration tools</title>
<tgroup cols="5">
<colspec colwidth="195pt" align="left"/>
<colspec colwidth="76pt" align="left"/>
<colspec colwidth="70pt" align="left"/>
<colspec colwidth="97pt" align="left"/>
<colspec colwidth="374pt" align="left"/>
<thead>
<row>
<entry> packages </entry>
<entry> popcon </entry>
<entry> size </entry>
<entry> type </entry>
<entry> description </entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>network-manager</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> config::NM </entry>
<entry><ulink url="https://en.wikipedia.org/wiki/NetworkManager">NetworkManager</ulink> (daemon): manage the network automatically </entry>
</row>
<row>
<entry> <literal>network-manager-gnome</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> config::NM </entry>
<entry><ulink url="https://en.wikipedia.org/wiki/NetworkManager">NetworkManager</ulink> (GNOME frontend) </entry>
</row>
<row>
<entry> <literal>netplan.io</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> config::NM+networkd</entry>
<entry><ulink url="https://netplan.io">Netplan</ulink> (generator): Unified, declarative interface to NetworkManager and systemd-networkd backends </entry>
</row>
<row>
<entry> <literal>ifupdown</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> config::ifupdown </entry>
<entry> standardized tool to bring up and down the network (Debian specific) </entry>
</row>
<row>
<entry> <literal>isc-dhcp-client</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> config::low-level </entry>
<entry> DHCP client </entry>
</row>
<row>
<entry> <literal>pppoeconf</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> config::helper </entry>
<entry> configuration helper for PPPoE connection </entry>
</row>
<row>
<entry> <literal>wpasupplicant</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> config::helper </entry>
<entry> client support for WPA and WPA2 (IEEE 802.11i) </entry>
</row>
<row>
<entry> <literal>wpagui</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> config::helper </entry>
<entry> Qt GUI client for wpa_supplicant </entry>
</row>
<row>
<entry> <literal>wireless-tools</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> config::helper </entry>
<entry> tools for manipulating Linux Wireless Extensions </entry>
</row>
<row>
<entry> <literal>iw</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> config::helper </entry>
<entry> tool for configuring Linux wireless devices </entry>
</row>
<row>
<entry> <literal>iproute2</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> config::iproute2 </entry>
<entry><ulink url="https://wiki.linuxfoundation.org/networking/iproute2">iproute2</ulink>, IPv6 and other advanced network configuration: <literal>ip</literal>(8), <literal>tc</literal>(8), etc </entry>
</row>
<row>
<entry> <literal>iptables</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> config::Netfilter </entry>
<entry> administration tools for packet filtering and NAT (<ulink url="https://en.wikipedia.org/wiki/Netfilter">Netfilter</ulink>) </entry>
</row>
<row>
<entry> <literal>nftables</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> config::Netfilter </entry>
<entry> administration tools for packet filtering and NAT (<ulink url="https://en.wikipedia.org/wiki/Netfilter">Netfilter</ulink>) (successor to {ip,ip6,arp,eb}tables) </entry>
</row>
<row>
<entry> <literal>iputils-ping</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> test </entry>
<entry> test network reachability of a remote host by <ulink url="https://en.wikipedia.org/wiki/Hostname">hostname</ulink> or <ulink url="https://en.wikipedia.org/wiki/IP_address">IP address</ulink> (<ulink url="https://wiki.linuxfoundation.org/networking/iproute2">iproute2</ulink>) </entry>
</row>
<row>
<entry> <literal>iputils-arping</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> test </entry>
<entry> test network reachability of a remote host specified by the <ulink url="https://en.wikipedia.org/wiki/Address_Resolution_Protocol">ARP</ulink> address </entry>
</row>
<row>
<entry> <literal>iputils-tracepath</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> test </entry>
<entry> trace the network path to a remote host </entry>
</row>
<row>
<entry> <literal>ethtool</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> test </entry>
<entry> display or change Ethernet device settings </entry>
</row>
<row>
<entry> <literal>mtr-tiny</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> test::low-level </entry>
<entry> trace the network path to a remote host (curses) </entry>
</row>
<row>
<entry> <literal>mtr</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> test::low-level </entry>
<entry> trace the network path to a remote host (curses and GTK) </entry>
</row>
<row>
<entry> <literal>gnome-nettool</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> test::low-level </entry>
<entry> tools for common network information operations (GNOME) </entry>
</row>
<row>
<entry> <literal>nmap</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> test::low-level </entry>
<entry> network mapper / port scanner (<ulink url="https://en.wikipedia.org/wiki/Nmap">Nmap</ulink>, console) </entry>
</row>
<row>
<entry> <literal>tcpdump</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> test::low-level </entry>
<entry> network traffic analyzer (<ulink url="https://en.wikipedia.org/wiki/Tcpdump">Tcpdump</ulink>, console) </entry>
</row>
<row>
<entry> <literal>wireshark</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> test::low-level </entry>
<entry> network traffic analyzer (<ulink url="https://en.wikipedia.org/wiki/Wireshark">Wireshark</ulink>, GTK) </entry>
</row>
<row>
<entry> <literal>tshark</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> test::low-level </entry>
<entry> network traffic analyzer (console) </entry>
</row>
<row>
<entry> <literal>tcptrace</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> test::low-level </entry>
<entry> produce a summarization of the connections from <literal>tcpdump</literal> output </entry>
</row>
<!--
<row>
<entry> <literal>snort</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> test::low-level </entry>
<entry> flexible network intrusion detection system (<ulink url="https://en.wikipedia.org/wiki/Snort_(software)">Snort</ulink>) </entry>
</row>
-->
<row>
<entry> <literal>ntopng</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> test::low-level </entry>
<entry> display network usage in web browser </entry>
</row>
<row>
<entry> <literal>dnsutils</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> test::low-level </entry>
<entry> network clients provided with <ulink url="https://en.wikipedia.org/wiki/BIND">BIND</ulink>: <literal>nslookup</literal>(8), <literal>nsupdate</literal>(8), <literal>dig</literal>(8) </entry>
</row>
<row>
<entry> <literal>dlint</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> test::low-level </entry>
<entry> check <ulink url="https://en.wikipedia.org/wiki/Domain_Name_System">DNS</ulink> zone information using nameserver lookups </entry>
</row>
<row>
<entry> <literal>dnstracer</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> test::low-level </entry>
<entry> trace a chain of <ulink url="https://en.wikipedia.org/wiki/Domain_Name_System">DNS</ulink> servers to the source </entry>
</row>
</tbody>
</tgroup>
</table>
<section id="_the_hostname_resolution">
<title>The hostname resolution</title>
<para>The hostname resolution is currently supported by the <ulink url="https://en.wikipedia.org/wiki/Name_Service_Switch">NSS (Name Service Switch)</ulink> mechanism too. The flow of this resolution is the following.</para>
<orderedlist>
<listitem> <para> The "<literal>/etc/nsswitch.conf</literal>" file with stanza like "<literal>hosts: files dns</literal>" dictates the hostname resolution order. (This replaces the old functionality of the "<literal>order</literal>" stanza in "<literal>/etc/host.conf</literal>".) </para> </listitem>
<listitem> <para> The <literal>files</literal> method is invoked first. If the hostname is found in the "<literal>/etc/hosts</literal>" file, it returns all valid addresses for it and exits. (The "<literal>/etc/host.conf</literal>" file contains "<literal>multi on</literal>".) </para> </listitem>
<listitem> <para> The <literal>dns</literal> method is invoked. If the hostname is found by the query to the <ulink url="https://en.wikipedia.org/wiki/Domain_Name_System">Internet Domain Name System (DNS)</ulink> identified by the "<literal>/etc/resolv.conf</literal>" file, it returns all valid addresses for it and exits. </para> </listitem>
</orderedlist>
<para>A typical workstation may be installed with its host name set to, e.g., "<emphasis>host_name</emphasis>" and its optional domain name set to an empty string. Then, "<literal>/etc/hosts</literal>" looks like the following.</para>
<screen>127.0.0.1 localhost
127.0.1.1 <emphasis>host_name</emphasis>
# The following lines are desirable for IPv6 capable hosts
::1 localhost ip6-localhost ip6-loopback
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
</screen>
<para>Each line starts with a <ulink url="https://en.wikipedia.org/wiki/IP_address">IP address</ulink> and it is followed by the associated <ulink url="https://en.wikipedia.org/wiki/Hostname">hostname</ulink>.</para>
<para>The IP address <literal>127.0.1.1</literal> in the second line of this example may not be found on some other Unix-like systems. The <ulink url="https://www.debian.org/devel/debian-installer/">Debian Installer</ulink> creates this entry for a system without a permanent IP address as a workaround for some software (e.g., GNOME) as documented in the <ulink url="https://bugs.debian.org/719621">bug #719621</ulink>.</para>
<para>The <emphasis>host_name</emphasis> matches the hostname defined in the "<literal>/etc/hostname</literal>" (see <xref linkend="_the_hostname"/>).</para>
<para>For a system with a permanent IP address, that permanent IP address should be used here instead of <literal>127.0.1.1</literal>.</para>
<para>For a system with a permanent IP address and a <ulink url="https://en.wikipedia.org/wiki/FQDN">fully qualified domain name (FQDN)</ulink> provided by the <ulink url="https://en.wikipedia.org/wiki/Domain_Name_System">Domain Name System (DNS)</ulink>, that canonical <emphasis>host_name</emphasis>.<emphasis>domain_name</emphasis> should be used instead of just <emphasis>host_name</emphasis>.</para>
<para>The "<literal>/etc/resolv.conf</literal>" is a static file if the <literal>resolvconf</literal> package is not installed. If installed, it is a symbolic link. Either way, it contains information that initialize the resolver routines. If the DNS is found at IP="<literal>192.168.11.1</literal>", it contains the following.</para>
<screen>nameserver 192.168.11.1</screen>
<para>The <literal>resolvconf</literal> package makes this "<literal>/etc/resolv.conf</literal>" into a symbolic link and manages its contents by the hook scripts automatically.</para>
<para>For the PC workstation on the typical adhoc LAN environment, the hostname can be resolved via <ulink url="https://en.wikipedia.org/wiki/Multicast_DNS">Multicast DNS</ulink> (mDNS) in addition to the basic <literal>files</literal> and <literal>dns</literal> methods.</para>
<itemizedlist>
<listitem> <para><ulink url="https://en.wikipedia.org/wiki/Avahi_(software)">Avahi</ulink> provides a framework for Multicast DNS Service Discovery on Debian. </para> </listitem>
<listitem> <para> It is equivalent of <ulink url="https://en.wikipedia.org/wiki/Bonjour_(software)">Apple Bonjour / Apple Rendezvous</ulink>. </para> </listitem>
<listitem> <para> The <literal>libnss-mdns</literal> plugin package provides host name resolution via mDNS for the GNU Name Service Switch (NSS) functionality of the GNU C Library (glibc). </para> </listitem>
<listitem> <para> The "<literal>/etc/nsswitch.conf</literal>" file should have stanza like "<literal>hosts: files mdns4_minimal [NOTFOUND=return] dns</literal>" (see <literal>/usr/share/doc/libnss-mdns/README.Debian</literal> for other configurations). </para> </listitem>
<listitem> <para> A host name suffixed with the <ulink url="https://en.wikipedia.org/wiki/.local">".local"</ulink> <ulink url="https://en.wikipedia.org/wiki/Pseudo-top-level_domain">pseudo-top-level domain</ulink> is resolved by sending a mDNS query message in a multicast UDP packet using IPv4 address "<literal>224.0.0.251</literal>" or IPv6 address "<literal>FF02::FB</literal>". </para> </listitem>
</itemizedlist>
<note> <para>The <ulink url="https://newgtlds.icann.org/en/program-status/delegated-strings">expansion of generic Top-Level Domains (gTLD)</ulink> in the <ulink url="https://en.wikipedia.org/wiki/Domain_Name_System">Domain Name System</ulink> is underway. Watch out for the <ulink url="https://icannwiki.com/Name_Collision">name collision</ulink> when chosing a domain name used only within LAN.</para> </note>
<note> <para>Use of packages such as <literal>libnss-resolve</literal> together with <literal>systemd-resolved</literal>, or <literal>libnss-myhostname</literal>, or <literal>libnss-mymachine</literal>, with coressponding listings on the "<literal>hosts</literal>" line in the "<literal>/etc/nsswitch.conf</literal>" file may override the traditional network configuration discussed in the above. See <literal>nss-resolve</literal>(8), <literal>systemd-resolved</literal>(8), <literal>nss-myhostname</literal>(8), and <literal>nss-mymachines</literal>(8) for more. </para> </note>
</section>
<section id="_the_network_interface_name">
<title>The network interface name</title>
<para>The <ulink url="https://en.wikipedia.org/wiki/Systemd">systemd</ulink> uses "<ulink url="https://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames/">Predictable Network Interface Names</ulink>" such as "<literal>enp0s25</literal>".</para>
</section>
<section id="_the_network_address_range_for_the_lan">
<title>The network address range for the LAN</title>
<para>Let us be reminded of the IPv4 32 bit address ranges in each class reserved for use on the <ulink url="https://en.wikipedia.org/wiki/Local_area_network">local area networks (LANs)</ulink> by <ulink url="https://datatracker.ietf.org/doc/rfc1918">rfc1918</ulink>. These addresses are guaranteed not to conflict with any addresses on the Internet proper.</para>
<note> <para>IP address written with colon are <ulink url="https://en.wikipedia.org/wiki/IPv6_address">IPv6 address</ulink>, e.g., "<literal>::1</literal>" for <literal>localhost</literal>. </para> </note>
<table pgwide="0" frame="topbot" rowsep="1" colsep="1">
<title>List of network address ranges</title>
<tgroup cols="5">
<colspec colwidth="32pt" align="left"/>
<colspec colwidth="157pt" align="left"/>
<colspec colwidth="76pt" align="left"/>
<colspec colwidth="81pt" align="left"/>
<colspec colwidth="70pt" align="left"/>
<thead>
<row>
<entry> Class </entry>
<entry> network addresses </entry>
<entry> net mask </entry>
<entry> net mask /bits </entry>
<entry> number of subnets </entry>
</row>
</thead>
<tbody>
<row>
<entry> A </entry>
<entry> 10.x.x.x </entry>
<entry> 255.0.0.0 </entry>
<entry> /8 </entry>
<entry> 1 </entry>
</row>
<row>
<entry> B </entry>
<entry> 172.16.x.x — 172.31.x.x </entry>
<entry> 255.255.0.0 </entry>
<entry> /16 </entry>
<entry> 16 </entry>
</row>
<row>
<entry> C </entry>
<entry> 192.168.0.x — 192.168.255.x </entry>
<entry> 255.255.255.0 </entry>
<entry> /24 </entry>
<entry> 256 </entry>
</row>
</tbody>
</tgroup>
</table>
<note> <para>If one of these addresses is assigned to a host, then that host must not access the Internet directly but must access it through a gateway that acts as a proxy for individual services or else does <ulink url="https://en.wikipedia.org/wiki/Network_address_translation">Network Address Translation (NAT)</ulink>. The broadband router usually performs NAT for the consumer LAN environment.</para> </note>
</section>
<section id="_the_network_device_support">
<title>The network device support</title>
<para>Although most hardware devices are supported by the Debian system, there are some network devices which require <ulink url="https://www.debian.org/social_contract#guidelines">DFSG</ulink> non-free firmware to support them. Please see <xref linkend="_hardware_drivers_and_firmware"/>.</para>
</section>
</section>
<section id="_the_modern_network_configuration_for_desktop">
<title>The modern network configuration for desktop</title>
<para>Network interfaces are typically initialized in "<literal>networking.service</literal>" for the <literal>lo</literal> interface and "<literal>NetworkManager.service</literal>" for other interfaces on modern Debian desktop system under <literal>systemd</literal>.</para>
<para>Debian can manage the network connection via management <ulink url="https://en.wikipedia.org/wiki/Daemon_(computer_software)">daemon</ulink> software such as <ulink url="https://en.wikipedia.org/wiki/NetworkManager">NetworkManager (NM)</ulink> (network-manager and associated packages).</para>
<itemizedlist>
<listitem> <para> They come with their own <ulink url="https://en.wikipedia.org/wiki/Graphical_user_interface">GUI</ulink> and command-line programs as their user interfaces. </para> </listitem>
<listitem> <para> They come with their own <ulink url="https://en.wikipedia.org/wiki/Daemon_(computer_software)">daemon</ulink> as their backend system. </para> </listitem>
<listitem> <para> They allow easy connection of your system to the Internet. </para> </listitem>
<listitem> <para> They allow easy management of wired and wireless network configuration. </para> </listitem>
<listitem> <para> They allow us to configure network independent of the legacy <literal>ifupdown</literal> package. </para> </listitem>
</itemizedlist>
<note> <para>Do not use these automatic network configuration tools for servers. These are aimed primarily for mobile desktop users on laptops.</para> </note>
<para>These modern network configuration tools need to be configured properly to avoid conflicting with the legacy <literal>ifupdown</literal> package and its configuration file "<literal>/etc/network/interfaces</literal>".</para>
<section id="_gui_network_configuration_tools">
<title>GUI network configuration tools</title>
<para>Official documentations for NM on Debian are provided in "<literal>/usr/share/doc/network-manager/README.Debian</literal>".</para>
<para>Essentially, the network configuration for desktop is done as follows.</para>
<orderedlist>
<listitem>
<para> Make desktop user, e.g. <literal>foo</literal>, belong to group "<literal>netdev</literal>" by the following (Alternatively, do it automatically via <ulink url="https://en.wikipedia.org/wiki/D-Bus">D-bus</ulink> under modern desktop environments such as GNOME and KDE). </para>
<screen>$ sudo usermod -a -G netdev foo</screen>
</listitem>
<listitem>
<para> Keep configuration of "<literal>/etc/network/interfaces</literal>" as simple as in the following. </para>
<screen>auto lo
iface lo inet loopback</screen>
</listitem>
<listitem>
<para> Restart NM by the following. </para>
<screen>$ sudo systemctl restart NetworkManager</screen>
</listitem>
<listitem>
<para> Configure your network via GUI. </para>
</listitem>
</orderedlist>
<note> <para>Only interfaces which are <emphasis role="strong">not</emphasis> listed in "<literal>/etc/network/interfaces</literal>" are managed by NM to avoid conflict with <literal>ifupdown</literal>.</para> </note>
<tip> <para>If you wish to extend network configuration capabilities of NM, please seek appropriate plug-in modules and supplemental packages such as <literal>network-manager-openconnect</literal>, <literal>network-manager-openvpn-gnome</literal>, <literal>network-manager-pptp-gnome</literal>, <literal>mobile-broadband-provider-info</literal>, <literal>gnome-bluetooth</literal>, etc.</para> </tip>
</section>
</section>
<section id="_the_modern_network_configuration_without_gui">
<title>The modern network configuration without GUI</title>
<para>Under <ulink url="https://en.wikipedia.org/wiki/Systemd">systemd</ulink>, the network may be configured in <literal>/etc/systemd/network/</literal> instead. See <literal>systemd-resolved</literal>(8), <literal>resolved.conf</literal>(5), and <literal>systemd-networkd</literal>(8).</para>
<para>This allows the modern network configuration without GUI.</para>
<para>A DHCP client configuration can be set up by creating "<literal>/etc/systemd/network/dhcp.network</literal>". E.g.:</para>
<screen>[Match]
Name=en*
[Network]
DHCP=yes</screen>
<para>A static network configuration can be set up by creating "<literal>/etc/systemd/network/static.network</literal>". E.g.:</para>
<screen>[Match]
Name=en*
[Network]
Address=192.168.0.15/24
Gateway=192.168.0.1</screen>
</section>
<section id="_the_modern_network_configuration_for_cloud">
<title>The modern network configuration for cloud</title>
<para>The modern network configuration for cloud may use <literal>cloud-init</literal> and <literal>netplan.io</literal> packages (see <xref linkend="_cloud_system_initialization"/>).</para>
<para>The <literal>netplan.io</literal> package supports <literal>systemd-networkd</literal> and <literal>NetworkManager</literal> as its network configuration backends, and enables the declarative network configuration using <ulink url="https://en.wikipedia.org/wiki/YAML">YAML</ulink> data. When you change YAML:</para>
<itemizedlist>
<listitem> <para>Run "<literal>netplan generate</literal>" command to generate all the necessary backend configuration from <ulink url="https://en.wikipedia.org/wiki/YAML">YAML</ulink>.</para> </listitem>
<listitem> <para>Run "<literal>netplan apply</literal>" command to apply the generated configuration to the backends.</para> </listitem>
</itemizedlist>
<para>See <ulink url="https://netplan.io/reference">"Netplan documentation"</ulink>, <literal>netplan</literal>(5), <literal>netplan-generate</literal>(8), and <literal>netplan-apply</literal>(8).</para>
<para>See also <ulink url="https://cloudinit.readthedocs.io/en/latest/index.html">"Cloud-init documentation"</ulink> (especially around <ulink url="https://cloudinit.readthedocs.io/en/latest/explanation/configuration.html">"Configuration sources"</ulink> and <ulink url="https://cloudinit.readthedocs.io/en/latest/reference/network-config-format-v2.html#netplan-passthrough">"Netplan Passthrough"</ulink>) for how <literal>cloud-init</literal> can integrate <literal>netplan.io</literal> configuration with alternative data sources.</para>
<section id="_the_modern_network_configuration_for_cloud_with_dhcp">
<title>The modern network configuration for cloud with DHCP</title>
<para>A DHCP client configuration can be set up by creating a data source file "<literal>/etc/netplan/50-dhcp.yaml</literal>":</para>
<screen>network:
version: 2
ethernets:
all-en:
match:
name: "en*"
dhcp4: true
dhcp6: true</screen>
</section>
<section id="_the_modern_network_configuration_for_cloud_with_static_ip">
<title>The modern network configuration for cloud with static IP</title>
<para>A static network configuration can be set up by creating a data source file "<literal>/etc/netplan/50-static.yaml</literal>":</para>
<screen>network:
version: 2
ethernets:
eth0:
addresses:
- 192.168.0.15/24
routes:
- to: default
via: 192.168.0.1</screen>
</section>
<section id="_the_modern_network_configuration_for_cloud_with_network_manager">
<title>The modern network configuration for cloud with Network Manager</title>
<para>The network client configuration using Network Manager infrastructure can be set up by creating a data source file "<literal>/etc/netplan/00-network-manager.yaml</literal>":</para>
<screen>network:
version: 2
renderer: NetworkManager</screen>
</section>
</section>
<section id="_the_low_level_network_configuration">
<title>The low level network configuration</title>
<para>For the low level network configuration on Linux, use the <ulink url="https://wiki.linuxfoundation.org/networking/iproute2">iproute2</ulink> programs (<literal>ip</literal>(8), …) .</para>
<section id="_iproute2_commands">
<title>Iproute2 commands</title>
<para><ulink url="https://wiki.linuxfoundation.org/networking/iproute2">Iproute2</ulink> commands offer complete low-level network configuration capabilities. Here is a translation table from obsolete <ulink url="https://wiki.linuxfoundation.org/networking/net-tools">net-tools</ulink> commands to new <ulink url="https://wiki.linuxfoundation.org/networking/iproute2">iproute2</ulink> etc. commands.</para>
<table pgwide="0" frame="topbot" rowsep="1" colsep="1">
<title>Translation table from obsolete <literal>net-tools</literal> commands to new <literal>iproute2</literal> commands</title>
<tgroup cols="3">
<colspec colwidth="103pt" align="left"/>
<colspec colwidth="97pt" align="left"/>
<colspec colwidth="260pt" align="left"/>
<thead>
<row>
<entry> obsolete net-tools </entry>
<entry> new iproute2 etc. </entry>
<entry> manipulation </entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>ifconfig</literal>(8) </entry>
<entry> <literal>ip addr</literal> </entry>
<entry> protocol (IP or IPv6) address on a device </entry>
</row>
<row>
<entry><literal>route</literal>(8) </entry>
<entry> <literal>ip route</literal> </entry>
<entry> routing table entry </entry>
</row>
<row>
<entry><literal>arp</literal>(8) </entry>
<entry> <literal>ip neigh</literal> </entry>
<entry> ARP or NDISC cache entry </entry>
</row>
<row>
<entry> <literal>ipmaddr</literal> </entry>
<entry> <literal>ip maddr</literal> </entry>
<entry> multicast address </entry>
</row>
<row>
<entry> <literal>iptunnel</literal> </entry>
<entry> <literal>ip tunnel</literal> </entry>
<entry> tunnel over IP </entry>
</row>
<row>
<entry><literal>nameif</literal>(8) </entry>
<entry><literal>ifrename</literal>(8) </entry>
<entry> name network interfaces based on MAC addresses </entry>
</row>
<row>
<entry><literal>mii-tool</literal>(8) </entry>
<entry><literal>ethtool</literal>(8) </entry>
<entry> Ethernet device settings </entry>
</row>
</tbody>
</tgroup>
</table>
<para>See <literal>ip</literal>(8) and <ulink url="https://lartc.org/">Linux Advanced Routing & Traffic Control</ulink>.</para>
</section>
<section id="_safe_low_level_network_operations">
<title>Safe low level network operations</title>
<para>You may use low level network commands as follows safely since they do not change network configuration.</para>
<table pgwide="0" frame="topbot" rowsep="1" colsep="1">
<title>List of low level network commands</title>
<tgroup cols="2">
<colspec colwidth="266pt" align="left"/>
<colspec colwidth="483pt" align="left"/>
<thead>
<row>
<entry> command </entry>
<entry> description </entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>ip addr show</literal> </entry>
<entry> display the link and address status of active interfaces </entry>
</row>
<row>
<entry> <literal>route -n</literal> </entry>
<entry> display all the routing table in numerical addresses </entry>
</row>
<row>
<entry> <literal>ip route show</literal> </entry>
<entry> display all the routing table in numerical addresses </entry>
</row>
<row>
<entry> <literal>arp</literal> </entry>
<entry> display the current content of the <ulink url="https://en.wikipedia.org/wiki/Address_Resolution_Protocol">ARP</ulink> cache tables </entry>
</row>
<row>
<entry> <literal>ip neigh</literal> </entry>
<entry> display the current content of the <ulink url="https://en.wikipedia.org/wiki/Address_Resolution_Protocol">ARP</ulink> cache tables </entry>
</row>
<row>
<entry> <literal>plog</literal> </entry>
<entry> display ppp daemon log </entry>
</row>
<row>
<entry> <literal>ping yahoo.com</literal> </entry>
<entry> check the Internet connection to "<literal>yahoo.com</literal>" </entry>
</row>
<row>
<entry> <literal>whois yahoo.com</literal> </entry>
<entry> check who registered "<literal>yahoo.com</literal>" in the domains database </entry>
</row>
<row>
<entry> <literal>traceroute yahoo.com</literal> </entry>
<entry> trace the Internet connection to "<literal>yahoo.com</literal>" </entry>
</row>
<row>
<entry> <literal>tracepath yahoo.com</literal> </entry>
<entry> trace the Internet connection to "<literal>yahoo.com</literal>" </entry>
</row>
<row>
<entry> <literal>mtr yahoo.com</literal> </entry>
<entry> trace the Internet connection to "<literal>yahoo.com</literal>" (repeatedly) </entry>
</row>
<row>
<entry> <literal>dig [@dns-server.com] example.com [{a|mx|any}]</literal> </entry>
<entry> check <ulink url="https://en.wikipedia.org/wiki/Domain_Name_System">DNS</ulink> records of "<literal>example.com</literal>" by "<literal>dns-server.com</literal>" for a "<literal>a</literal>", "<literal>mx</literal>", or "<literal>any</literal>" record </entry>
</row>
<row>
<entry> <literal>iptables -L -n</literal> </entry>
<entry> check packet filter </entry>
</row>
<row>
<entry> <literal>netstat -a</literal> </entry>
<entry> find all open ports </entry>
</row>
<row>
<entry> <literal>netstat -l --inet</literal> </entry>
<entry> find listening ports </entry>
</row>
<row>
<entry> <literal>netstat -ln --tcp</literal> </entry>
<entry> find listening TCP ports (numeric) </entry>
</row>
<row>
<entry> <literal>dlint example.com</literal> </entry>
<entry> check DNS zone information of "<literal>example.com</literal>" </entry>
</row>
</tbody>
</tgroup>
</table>
<tip> <para>Some of these low level network configuration tools reside in "<literal>/usr/sbin/</literal>". You may need to issue full command path such as "<literal>/usr/sbin/ifconfig</literal>" or add "<literal>/usr/sbin</literal>" to the "<literal>$PATH</literal>" list in your "<literal>~/.bashrc</literal>".</para> </tip>
</section>
</section>
<section id="_network_optimization">
<title>Network optimization</title>
<para>Generic network optimization is beyond the scope of this documentation. I touch only subjects pertinent to the consumer grade connection.</para>
<table pgwide="0" frame="topbot" rowsep="1" colsep="1">
<title>List of network optimization tools</title>
<tgroup cols="4">
<colspec colwidth="65pt" align="left"/>
<colspec colwidth="76pt" align="left"/>
<colspec colwidth="70pt" align="left"/>
<colspec colwidth="347pt" align="left"/>
<thead>
<row>
<entry> packages </entry>
<entry> popcon </entry>
<entry> size </entry>
<entry> description </entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>iftop</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> display bandwidth usage information on an network interface </entry>
</row>
<row>
<entry> <literal>iperf</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> Internet Protocol bandwidth measuring tool </entry>
</row>
<row>
<entry> <literal>ifstat</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> InterFace STATistics Monitoring </entry>
</row>
<row>
<entry> <literal>bmon</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> portable bandwidth monitor and rate estimator </entry>
</row>
<row>
<entry> <literal>ethstatus</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> script that quickly measures network device throughput </entry>
</row>
<row>
<entry> <literal>bing</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> empirical stochastic bandwidth tester </entry>
</row>
<row>
<entry> <literal>bwm-ng</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> small and simple console-based bandwidth monitor </entry>
</row>
<row>
<entry> <literal>ethstats</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> console-based Ethernet statistics monitor </entry>
</row>
<row>
<entry> <literal>ipfm</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> bandwidth analysis tool </entry>
</row>
</tbody>
</tgroup>
</table>
<section id="_finding_optimal_mtu">
<title>Finding optimal MTU</title>
<para>NM normally sets optimal <ulink url="https://en.wikipedia.org/wiki/Maximum_transmission_unit">Maximum Transmission Unit (MTU)</ulink> automatically.</para>
<para>In some occasion, you may wish to set MTU manually after experiments with <literal>ping</literal>(8) with "<literal>-M do</literal>" option to send a ICMP packet with various data packet size. MTU is the maximum succeeding data packet size without IP fragmentation plus 28 bytes for the IPv4 and plus 48 bytes for the IPv6. For example the following finds MTU for IPv4 connection to be 1460 and MTU for IPv6 connection to be 1500.</para>
<screen>$ ping -4 -c 1 -s $((1500-28)) -M do www.debian.org
PING (149.20.4.15) 1472(1500) bytes of data.
ping: local error: message too long, mtu=1460
--- ping statistics ---
1 packets transmitted, 0 received, +1 errors, 100% packet loss, time 0ms
$ ping -4 -c 1 -s $((1460-28)) -M do www.debian.org
PING (130.89.148.77) 1432(1460) bytes of data.
1440 bytes from klecker-misc.debian.org (130.89.148.77): icmp_seq=1 ttl=50 time=325 ms
--- ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 325.318/325.318/325.318/0.000 ms
$ ping -6 -c 1 -s $((1500-48)) -M do www.debian.org
PING www.debian.org(mirror-csail.debian.org (2603:400a:ffff:bb8::801f:3e)) 1452 data bytes
1460 bytes from mirror-csail.debian.org (2603:400a:ffff:bb8::801f:3e): icmp_seq=1 ttl=47 time=191 ms
--- www.debian.org ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 191.332/191.332/191.332/0.000 ms</screen>
<para>This process is <ulink url="https://en.wikipedia.org/wiki/Path_MTU_discovery">Path MTU (PMTU) discovery</ulink> (<ulink url="https://datatracker.ietf.org/doc/rfc1191/">RFC1191</ulink>) and the <literal>tracepath</literal>(8) command can automate this.</para>
<table pgwide="0" frame="topbot" rowsep="1" colsep="1">
<title>Basic guide lines of the optimal MTU value</title>
<tgroup cols="3">
<colspec colwidth="336pt" align="left"/>
<colspec colwidth="119pt" align="left"/>
<colspec colwidth="325pt" align="left"/>
<thead>
<row>
<entry> network environment </entry>
<entry> MTU </entry>
<entry> rationale </entry>
</row>
</thead>
<tbody>
<row>
<entry> Dial-up link (IP: PPP) </entry>
<entry> 576 </entry>
<entry> standard </entry>
</row>
<row>
<entry> Ethernet link (IP: DHCP or fixed) </entry>
<entry> 1500 </entry>
<entry> standard and default </entry>
</row>
</tbody>
</tgroup>
</table>
<para>In addition to these basic guide lines, you should know the following.</para>
<itemizedlist>
<listitem> <para> Any use of tunneling methods (<ulink url="https://en.wikipedia.org/wiki/Virtual_private_network">VPN</ulink> etc.) may reduce optimal MTU further by their overheads. </para> </listitem>
<listitem> <para> The MTU value should not exceed the experimentally determined PMTU value. </para> </listitem>
<listitem> <para> The bigger MTU value is generally better when other limitations are met. </para> </listitem>
</itemizedlist>
<para>The <ulink url="https://en.wikipedia.org/wiki/Maximum_segment_size">maximum segment size</ulink> (MSS) is used as an alternative measure of packet size. The relationship between MSS and MTU are the following.</para>
<itemizedlist>
<listitem> <para> MSS = MTU - 40 for IPv4 </para> </listitem>
<listitem> <para> MSS = MTU - 60 for IPv6 </para> </listitem>
</itemizedlist>
<note> <para>The <literal>iptables</literal>(8) (see <xref linkend="_netfilter_infrastructure"/>) based optimization can clamp packet size by the MSS and is useful for the router. See "TCPMSS" in <literal>iptables</literal>(8).</para> </note>
</section>
<section id="_wan_tcp_optimization">
<title>WAN TCP optimization</title>
<para>The TCP throughput can be maximized by adjusting TCP buffer size parameters as in "<ulink url="https://en.wikipedia.org/wiki/TCP_tuning">TCP tuning</ulink>" for the modern high-bandwidth and high-latency WAN. So far, the current Debian default settings serve well even for my LAN connected by the fast 1G bps FTTP service.</para>
</section>
</section>
<section id="_netfilter_infrastructure">
<title>Netfilter infrastructure</title>
<para><ulink url="https://en.wikipedia.org/wiki/Netfilter">Netfilter</ulink> provides infrastructure for <ulink url="https://en.wikipedia.org/wiki/Stateful_firewall">stateful firewall</ulink> and <ulink url="https://en.wikipedia.org/wiki/Network_address_translation">network address translation (NAT)</ulink> with <ulink url="https://en.wikipedia.org/wiki/Linux_kernel">Linux kernel</ulink> modules (see <xref linkend="_the_kernel_module_initialization"/>).</para>
<table pgwide="0" frame="topbot" rowsep="1" colsep="1">
<title>List of firewall tools</title>
<tgroup cols="4">
<colspec colwidth="97pt" align="left"/>
<colspec colwidth="76pt" align="left"/>
<colspec colwidth="70pt" align="left"/>
<colspec colwidth="504pt" align="left"/>
<thead>
<row>
<entry> packages </entry>
<entry> popcon </entry>
<entry> size </entry>
<entry> description </entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>nftables</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> administration tools for packet filtering and NAT (<ulink url="https://en.wikipedia.org/wiki/Netfilter">Netfilter</ulink>) (successor to {ip,ip6,arp,eb}tables) </entry>
</row>
<row>
<entry> <literal>iptables</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> administration tools for <ulink url="https://en.wikipedia.org/wiki/Netfilter">netfilter</ulink> (<literal>iptables</literal>(8) for IPv4, <literal>ip6tables</literal>(8) for IPv6) </entry>
</row>
<row>
<entry> <literal>arptables</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> administration tools for <ulink url="https://en.wikipedia.org/wiki/Netfilter">netfilter</ulink> (<literal>arptables</literal>(8) for ARP) </entry>
</row>
<row>
<entry> <literal>ebtables</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> administration tools for <ulink url="https://en.wikipedia.org/wiki/Netfilter">netfilter</ulink> (<literal>ebtables</literal>(8) for Ethernet bridging) </entry>
</row>
<row>
<entry> <literal>iptstate</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> continuously monitor <ulink url="https://en.wikipedia.org/wiki/Netfilter">netfilter</ulink> state (similar to <literal>top</literal>(1)) </entry>
</row>
<row>
<entry> <literal>ufw</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> <ulink url="https://en.wikipedia.org/wiki/Uncomplicated_Firewall">Uncomplicated Firewall (UFW)</ulink> is a program for managing a netfilter firewall </entry>
</row>
<row>
<entry> <literal>gufw</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> graphical user interface for <ulink url="https://en.wikipedia.org/wiki/Uncomplicated_Firewall">Uncomplicated Firewall (UFW)</ulink> </entry>
</row>
<row>
<entry> <literal>firewalld</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> <ulink url="https://en.wikipedia.org/wiki/Firewalld">firewalld</ulink> is a dynamically managed firewall program with support for network zones </entry>
</row>
<row>
<entry> <literal>firewall-config</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry> graphical user interface for <ulink url="https://en.wikipedia.org/wiki/Firewalld">firewalld</ulink> </entry>
</row>
<row>
<entry> <literal>shorewall-init</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry><ulink url="https://en.wikipedia.org/wiki/Shorewall">Shoreline Firewall</ulink> initialization </entry>
</row>
<row>
<entry> <literal>shorewall</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry><ulink url="https://en.wikipedia.org/wiki/Shorewall">Shoreline Firewall</ulink>, <ulink url="https://en.wikipedia.org/wiki/Netfilter">netfilter</ulink> configuration file generator </entry>
</row>
<row>
<entry> <literal>shorewall-lite</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry><ulink url="https://en.wikipedia.org/wiki/Shorewall">Shoreline Firewall</ulink>, <ulink url="https://en.wikipedia.org/wiki/Netfilter">netfilter</ulink> configuration file generator (light version) </entry>
</row>
<row>
<entry> <literal>shorewall6</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry><ulink url="https://en.wikipedia.org/wiki/Shorewall">Shoreline Firewall</ulink>, <ulink url="https://en.wikipedia.org/wiki/Netfilter">netfilter</ulink> configuration file generator (IPv6 version) </entry>
</row>
<row>
<entry> <literal>shorewall6-lite</literal> </entry>
<entry> @-@popcon1@-@ </entry>
<entry> @-@psize1@-@ </entry>
<entry><ulink url="https://en.wikipedia.org/wiki/Shorewall">Shoreline Firewall</ulink>, <ulink url="https://en.wikipedia.org/wiki/Netfilter">netfilter</ulink> configuration file generator (IPv6, light version) </entry>
</row>
</tbody>
</tgroup>
</table>
<para>Main user space program of <ulink url="https://en.wikipedia.org/wiki/Netfilter">netfilter</ulink> is <literal>iptables</literal>(8). You can manually configure <ulink url="https://en.wikipedia.org/wiki/Netfilter">netfilter</ulink> interactively from shell, save its state with <literal>iptables-save</literal>(8), and restore it via init script with <literal>iptables-restore</literal>(8) upon system reboot.</para>
<para>Configuration helper scripts such as <ulink url="https://en.wikipedia.org/wiki/Shorewall">shorewall</ulink> ease this process.</para>
<para>See documentations at <ulink url="https://www.netfilter.org/documentation/">Netfilter Documentation</ulink> (or in "<literal>/usr/share/doc/iptables/html/</literal>").</para>
<itemizedlist>
<listitem> <para> <ulink url="https://www.netfilter.org/documentation/HOWTO/networking-concepts-HOWTO.html">Linux Networking-concepts HOWTO</ulink> </para> </listitem>
<listitem> <para> <ulink url="https://www.netfilter.org/documentation/HOWTO/packet-filtering-HOWTO.html">Linux 2.4 Packet Filtering HOWTO</ulink> </para> </listitem>
<listitem> <para> <ulink url="https://www.netfilter.org/documentation/HOWTO/NAT-HOWTO.html">Linux 2.4 NAT HOWTO</ulink> </para> </listitem>
</itemizedlist>
<tip> <para>Although these were written for Linux <emphasis role="strong">2.4</emphasis>, both <literal>iptables</literal>(8) command and netfilter kernel function apply for Linux <emphasis role="strong">2.6</emphasis> and <emphasis role="strong">3.x</emphasis> kernel series.</para> </tip>
</section>
</chapter>
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