(generic-linux-devices)= # Generic Linux Devices You can run Linux hosts or routers in virtual machines or containers. The default image used for a Linux virtual machine is Ubuntu 20.04, the default container image is Python 3.9 container running on Alpine Linux. To use any other Linux distribution or container, or to start a home-built Vagrant box or Docker container, add **image** attribute with the name of Vagrant box or Docker container to the node data[^GL]. The only requirements for a Linux virtual machine is working Python environment (to support Ansible playbooks used in **netlab initial** command) and the presence of **ip** command used in initial device configuration. Docker containers have no requirements ([see below](clab-linux)) ```eval_rst .. contents:: More Details :depth: 2 :local: :backlinks: none ``` [^GL]: You can also set the **defaults.devices.linux._provider_.image** attribute to change the Vagrant box or Docker container for all Linux hosts in your lab. (linux-hosts)= ## Hosts File As the typical lab topology does not include DNS, _netlab_ adds entries for all lab devices to the Linux `/etc/hosts` file. The initial configuration templates add entries mapping all non-VRF IPv4 and IPv6 addresses to node names and entries mapping VRF IPv4 and IPv6 addresses to the *vrf*.*node* name. *netlab* always creates entries for individual device interfaces in the `/etc/hosts` file; otherwise, the name resolution picks a random device IP address instead of the loopback IP address when doing **ping** or **traceroute**. For example, these entries would be generated for a router with two dual-stack interfaces: ``` 10.0.0.1 r 2001:db8:0:1::1 r 172.16.0.1 eth1.r 2001:db8:1::1 eth1.r 172.16.1.1 eth2.r 2001:db8:1:1::1 eth2.r ``` Similar entries are generated for hosts (devices without loopback interfaces): ``` 172.16.0.2 h1 eth1.h1 2001:db8:1::2 h1 eth1.h1 ``` On a VRF-enabled router, you might get the following entries (the router has only VRF interfaces; 10.0.0.42 and 10.0.0.43 are VRF loopback addresses): ``` 10.0.0.5 dut 172.16.0.5 eth1.red.dut 172.16.1.5 eth2.red.dut 172.16.2.5 eth3.blue.dut 172.16.3.5 eth4.blue.dut 10.0.0.42 red.dut 10.0.0.43 blue.dut ``` The netlab-generated entries are *appended* to the existing `/etc/hosts` file on virtual machines. The container `/etc/hosts` file is generated from scratch to remove the management IP addresses *containerlab* inserted into the `/etc/hosts` file. (linux-forwarding)= ## Static Routes and Packet Forwarding on Linux Linux devices are usually hosts using [static routes](node-router-host) toward the [default gateway](links-gateway). IPv4 and IPv6 packet forwarding on Linux devices also is controlled with the **role** node parameter: * **host** (default): a Linux device does not perform packet forwarding and cannot be the default gateway for other hosts. * **gateway**: a Linux device does not perform packet forwarding but acts as the default gateway for other hosts. You will have to install a proxy (or a similar solution) for inter-subnet packet forwarding. * **router**: A Linux device performs packet forwarding but does not run routing protocols. Use **frr** device if you want to run routing protocols on a Linux server. (linux-loopback)= ## Loopback Interface _netlab_ does not configure a global loopback IP address on Linux nodes with **role** set to **host** (the default _netlab_ setting). A loopback IP address is [allocated](../example/addressing-tutorial.md#loopback-addresses) to a Linux node if you set **role** to any other value, and the initial configuration script configures an additional IP address on the **lo** interface, for example: ``` vagrant@host:~$ ip addr 1: lo: mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever inet 10.0.0.1/32 scope global lo valid_lft forever preferred_lft forever 2: eth0: mtu 1500 qdisc fq_codel state UP group default qlen 1000 link/ether 08:4f:a9:00:00:01 brd ff:ff:ff:ff:ff:ff inet 192.168.121.101/24 brd 192.168.121.255 scope global dynamic eth0 valid_lft 3587sec preferred_lft 3587sec inet6 fe80::a4f:a9ff:fe00:1/64 scope link valid_lft forever preferred_lft forever 3: eth1: mtu 1500 qdisc fq_codel state UP group default qlen 1000 link/ether 52:54:00:50:03:5a brd ff:ff:ff:ff:ff:ff inet 10.1.0.1/30 brd 10.1.0.3 scope global eth1 valid_lft forever preferred_lft forever inet6 fe80::5054:ff:fe50:35a/64 scope link valid_lft forever preferred_lft forever ``` (linux-lldp)= ## LLDP LLDP is started on Ubuntu virtual machines if the **netlab_lldp_enable** group variable is set to **True** (default setting is **False**). LLDP is not started in Linux containers or in non-Ubuntu Linux virtual machines. To enable LLDP on Ubuntu virtual machines, set the **netlab_lldp_enable** node parameter or **defaults.devices.linux.group_vars.netlab_lldp_enable** variable to **True**. (linux-dhcp-relay)= ## DHCP Relaying on Linux DHCP relaying on Ubuntu and Cumulus Linux uses `isc-dhcp-relay`, and is implemented only for IPv4. The `isc-dhcp-relay` has a few limitations: * The list of DHCP servers is specified per daemon, not per interface. The configuration template combines DHCP servers specified on all interfaces into a single list of servers. * While it might be possible to run a DHCP relay within a single VRF (for intra-VRF, not inter-VRF relaying), _netlab_ does not implement that. DHCP relaying with `isc-dhcp-relay` does not work between VRF interfaces. (linux-initial-config)= ## Initial Configuration on Linux Virtual Machines _netlab_ supports two Linux networking configuration mechanisms: * Netplan-based configuration on Ubuntu -- used when the **netlab_linux_distro** group variable is set to **ubuntu** (default setting) * Traditional configuration with **ip** commands. You might have to change the initial configuration mechanism to *traditional configuration* if you're using Linux virtual machines that are not based on Ubuntu. To do that, set the node **netlab_linux_distro** parameter to **vanilla** or set **defaults.devices.linux._provider_.group_vars.netlab_linux_distro** variable to **vanilla**. (linux-ubuntu-package)= ## Ubuntu Package Installation During Initial Configuration If needed the _netlab_ initial configuration script installs **lldpd** and **net-tools** Ubuntu packages. * **net-tools** package is installed if the **netlab_net_tools** variable is set to **True** (default setting is **False**) and if the **arp** command cannot be found. * **lldpd** package is installed if the **netlab_lldp_enable** variable is set to **True** (default setting is **False**) and if the **lldpd.service** is not running. The package installation is performed only when the **netlab_linux_distro** variable is set to **ubuntu** (see [](linux-initial-config)) _netlab_ initial configuration script will skip Ubuntu package installation if it can find **arp** command or if the **lldpd.service** is already running, allowing you to build custom Vagrant boxes that require no Internet access during the initial configuration. (clab-linux)= ## Initial Configuration on Linux Containers The initial configuration process (**[netlab initial](../netlab/initial.md)**) does not rely on commands executed within Linux containers: * The `/etc/hosts` file is generated during the **[netlab create](../netlab/create.md)** process from the ```templates/provider/clab/frr/hosts.j2``` template (see [](clab-config-template)). * Interface IP addresses, static routes to the default gateway (see [](linux-forwarding)), and any lag bonding interfaces are configured with **ip** commands executed on the Linux host but within the container network namespace. * Static default route points to the management interface. You can, therefore, use any container image as a Linux node.