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Getting started with network configuration

Before starting with actually configuring the switch interfaces, you should first familiarise yourself with how interfaces are created and how they fit into the BISDN Linux architecture.

Interfaces

BISDN Linux maps the physical ports on the switch with an abstract representation via tuntap interfaces. These interfaces are special Linux software only devices, that are bound to a userspace program, specifically baseboxd in the case of BISDN Linux.

If you followed the instructions from Configure Baseboxd, you should now be able to display all ports.

$ ip link show
...
8: port1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether ea:db:2b:c1:f6:06 brd ff:ff:ff:ff:ff:ff
9: port2: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether 96:98:0a:8c:0d:a2 brd ff:ff:ff:ff:ff:ff
  ...

These interfaces can be managed via the iproute2 utilities, or any netlink supported Linux networking utility. The link state for these interfaces maps to the physical port state. Note that by default all data plane ports are disabled, so in order to see the physical port state a port needs to be enabled.

$ sudo ip link set port1 up
$ sudo ip link set port2 up
$ ip link show
...
8: port1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
    link/ether ea:db:2b:c1:f6:06 brd ff:ff:ff:ff:ff:ff
9: port2: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN mode DEFAULT group default qlen 1000
    link/ether 96:98:0a:8c:0d:a2 brd ff:ff:ff:ff:ff:ff
  ...

WARNING: Despite Linux providing multiple alternatives for network configuration, iproute2 is the preferred configuration tool for BISDN Linux. The usage of other network configuration tools (e.g. ifconfig) is not covered in our documentation and might lead to unintended results.

To prevent ssh access from dataplane ports, the switch has an iptables rule to block traffic destined to the default ssh port (TCP port 22) on all interfaces, except for the management interface. The management interface follows the Predictable Interface naming convention in Linux, and is usually enp*.

:INPUT ACCEPT [176:40142]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [150:38898]
-A INPUT ! -i enp+ -p tcp -m tcp --dport 22 -j DROP
COMMIT

The default path for iptables configuration is /etc/iptables/iptables.rules for IPv4 and /etc/iptables/ip6tables.rules for IPv6 traffic.

The physical link configuration (e.g. link speed) is reflected to the tap interface and can be checked using ethtool:

$ ethtool port1
Settings for port1:
        Supported ports: [ ]
        Supported link modes:   Not reported
        Supported pause frame use: No
        Supports auto-negotiation: No
        Supported FEC modes: Not reported
        Advertised link modes:  Not reported
        Advertised pause frame use: No
        Advertised auto-negotiation: No
        Advertised FEC modes: Not reported
        Speed: 25000Mb/s
        Duplex: Full
        Port: Twisted Pair
        PHYAD: 0
        Transceiver: internal
        Auto-negotiation: off
        MDI-X: Unknown

WARNING: All link configurations shown in ethtool are currently read-only and cannot be modified (meaning any changes done with ethtool will not be forwarded to the physical link, but just be shown on the tap interfaces without having any effect on the ASIC). Configuring the link speed as in Disable auto-negotiation however, will update the ethtool reported speed.

Loopback interface

The loopback interface lo is a special type of device destined to allow the switch to communicate with itself. It is not associated with any physical device and is used to provide connectivity inside the same switch.

There are two IP addresses associated by default with this interface: 127.0.0.1/8 for IPv4 and ::1/128 for IPv6 networks.

It is possible to configure the loopback interface with other IPv4 and IPv6 addresses, thus providing connectivity to the loopback interface itself. In order to reach this interface, a “via” route must be present.

Management interface

BISDN Linux uses systemd-networkd to configure the management network interface. To allow users to ssh to and configure the switch without any further configuration after installing an image, our yocto build chain adds a default configuration file to /lib/systemd/network/80-wired.network (shown below), which configures all interfaces named “eth” or “en” to use DHCP. By using this configuration, the management network interface of all switch platforms automatically uses DHCP for its own address configuration. All other switch ports are unaffected by this configuration, since they are all named like portX and therefore not matched. To override this configuration file, you can add a custom file in the /etc/systemd/network directory, with a prefix number lower than 80. The lower prefix will make sure this file is read first when starting systemd-networkd (only the first Match for each interface is applied). Please see the systemd-networkd docs for more information.

/lib/systemd/network/80-wired.network

[Match]
Name=en* eth*
KernelCommandLine=!nfsroot
KernelCommandLine=!ip

[Network]
DHCP=yes

[DHCP]
RouteMetric=10
ClientIdentifier=mac

Network configuration with iproute2

To configure an interface on the switch, you have to configure the corresponding port (tap interface) created by baseboxd. If, for example, you have connected “port1” of the switch to “eno2” of your server and want to test a simple ping between these two, you can assign IP addresses to both interfaces in a very similar way:

On the switch:

root@agema-ag7648: ip address add 192.168.0.1/24 dev port1

On the server:

root@myserver: ip address add 192.168.0.2/24 dev eno2

You should now be able to ping the IP address configured on “port1” on your switch from your server:

On the server:

root@myserver: ping 192.168.0.1

To configure more complex scenarios, please refer to the Network Configuration section.

Persisting network configuration with systemd-networkd

Multiple ways of storing network configuration exist on Linux systems. BISDN Linux supports systemd-networkd for single Basebox setups.

systemd-networkd uses .network files to store network configuration. For details please see the systemd-networkd manual The .network files (in directory /etc/systemd/network/) are processed in lexical order and only the first file that matches is applied.

In the example below, the file 20-port50.network is processed first, meaning that port50 will get a dedicated configuration while all other ports get the generic one. That also means port50 is not getting the configuration for LLDP, but all other ports do (as these are configured using file 30-port.network)

root@agema-ag7648:/etc/systemd/network# cat 20-port50.network
[Match]
Name=port50

[Network]
Address=10.20.30.20/24

root@agema-ag7648:/etc/systemd/network# cat 30-port.network
[Match]
Name=port*

[Network]
LLDP=yes
EmitLLDP=yes
LLMNR=no