Network
Note
We use systemd for network configuration here. To override the traditional Ubuntu network configuration you need to enable the systemd network service.
$ systemctl enable systemd-networkd.service
$ systemctl start systemd-networkd.service
We have dual-Stack IPv4 and IPv6 on our internal network (LAN).
The IPv6 addresses are globally routed official internet addresses assigned to us by our IPv6 internet provider.
The IPv4 addresses are private network addresses.
Note
The IP addresses shown here, are documentation examples. You need to use your own addresses. See Router for network and IP configuration.
The router supplies most of the relevant settings by auto-configuration, and we like to keep it that way. The only exception are additional fixed IP addresses for hosted services.
Device Configuration
Our server has two 1Gbit/s Ethernet devices. eth0 and eth1.
These days those names vary, depending on the manufacturer of the card and device driver they use.
You can list the interfaces on you system with the following command:
$ ifconfig
Link-Aggregation
By bonding them together two one virtual interface we can increase throughput and redundancy.
When bonded both interfaces can be used to send and receive traffic over what appears to the system as one link.
Should one of the bonded links fail for some reason (broken cable or socket, network card failure, accidental unplugging, etc.) the link will still be online and usable, as long as one of the bonded interfaces still work.
This is done using the Link Aggregation Control Protocol (LACP) also know as 802.3ad. The Ethernet switch or router that connects our server to the network needs to support LACP as well for this to work.
The bonded interface will be called bond0 and can be used as any other interface by the system.
We define the bond0 network device in the following configuration file
/etc/systemd/network/bond0.netdev:
[NetDev]
Name=bond0
Kind=bond
[Bond]
Mode=802.3ad
TransmitHashPolicy=layer2
LACPTransmitRate=fast
MIIMonitorSec=1s
UpDelaySec=100
DownDelaySec=0
AdSelect=bandwidth
The parameters in the [bond] section of the configuration may need to be adjusted for your switch or router. See the “[Bond] Section Options” of the systemd netdev manual page.
Adding the physical Ethernet devices themselves to our created device is very simple and self-explanatory:
Create and or edit the /etc/systemd/network/eth1.network.
[Match]
Name=eth0
[Network]
Bond=bond0
Create and or edit the /etc/systemd/network/eth1.network.
[Match]
Name=eth1
[Network]
Bond=bond0
Once this is done, we can move over to the configuration of bond0 device as our network interface.
Interface Configuration
Create and or edit the /etc/systemd/network/bond0.network.
The match section just specifies which device will be used for this network interface.
[Match]
Name=bond0
You can find additional configuration options in the [match] section of the systemd network man page
Configuration of the [network] section is described here
[Network]
BindCarrier=eth0 eth1
Address=192.0.2.0.10/24
Address=2001:db8:c0de::10/64
Gateway=192.0.2.0.1
DNS=192.0.2.0.14
DNS=2001:db8:c0de::14
DNS=192.0.2.0.1
DNS=2001:db8:c0de::1
Domains=lan
DNSSEC=allow-downgrade
DNSSECNegativeTrustAnchors=lan
IPv6PrivacyExtensions=true
IPv6AcceptRouterAdvertisements=true
IP Addresses
We add the static IP addresses of our hosted services directly to the [network] section.
Add as many addresses as needed, as long as they are not already defined on other devices or assigned trough auto-configuration. This gets easier if you reserve a range like 10 to 90 to this server and only assign addresses from that range.
For easier recognition and administration the last number of any IPv4 and IPv6 address is identical (e.g. 192.0.2.10 and 2001:db8::10).
[Network]
...
; Port-forwarded HTTP/HTTPS connections from firewall/router
Address=192.0.2.10/24
Address=2001:db8::10/64
; www.example.net
Address=192.0.2.11/24
Address=2001:db8::11/64
; cloud.example.net
Address=192.0.2.12/24
Address=2001:db8::12/64
; xmpp.example.net
Address=192.0.2.13/24
Address=2001:db8::13/64
; ns1.example.net
Address=192.0.2.14/24
Address=2001:db8::15/64
...
Legacy Network Leftovers
It is recommended to alter the traditional Ubuntu configuration
/etc/network/interfaces to the bare minimum, to not interfere with
systemd-networkd service:
# The loopback network interface
auto lo
iface lo inet loopback
In practice I left them as they where when I switched to systemd on my host and had no issues whatsoever.
Restart the Network Service
Restart the network services with:
$ systemctl restart systemd-networkd
Useful Commands
Add new IP address
Here is how to add a new IP addresses on the fly, without restarting the service.
Note
If the newly added address is not added in the
/etc/systemd/network/bond0.network it will be lost after system
reboot.
Add IPv4 address:
$ sudo ip addr add 192.0.2.99/24 dev eth0
Add IPv6 address:
$ sudo ip addr add 2001:db8:26:845::99/64 dev eth0
Show IP addresses
To show all currently active IP addresses:
$ ip addr show
Network Restart
Restart the network services with:
$ systemctl restart systemd-networkd
Although there is a networking service, it can not be restarted. The usual command sudo service networking restart fails with a message like the following:
stop: Job failed while stopping
start: Job is already running: networking
This is intentional on Ubuntu servers since 14.04
Instead of the service, the interfaces have to be restarted:
sudo ifdown eth0 && sudo ifup eth0
Removing a IPv6 Route
sudo ip -6 route del ::/0 via fe80::2cb0:5dff:fe7f:2dba