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--- ubuntu:network_-_netplan:anonymous_bridges_in_netplan [2019/11/30 19:25] – created peter
+++ ubuntu:network_-_netplan:anonymous_bridges_in_netplan [2021/01/07 10:59] (current) – removed peter
@@ Line 1: / Line 1: @@
-====== Ubuntu - Network - Netplan - Anonymous bridges in netplan ======
-**Netplan** is the default network configuration system for new installs of Ubuntu 18.04 (Bionic).  Introduced as the default in Artful, it replaces **/etc/network/interfaces**.
-An anonymous bridge is where the bridge doesn't have an IP address; it's more akin to a switch or hub.
-If you're trying to create a bridge without an IP address, the obvious first thing to try is this:
-<code bash>
-network:
-    version: 2
-    ethernets:
-        ens8:
-            match:
-                macaddress: 52:54:00:f9:e9:dd
-        ens9:
-            match:
-                macaddress: 52:54:00:56:0d:ce
-    bridges:
-        br0:
-           interfaces: [ens8, ens9]
-</code>
-This is neat, plausible, and wrong - the bridge will be created but will stay 'down'.
-Checking this:
-<code bash>
-ip a
-</code>
-displays:
-<code bash>
-: br0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
-    link/ether 0e:e3:1c:83:f8:e8 brd ff:ff:ff:ff:ff:ff
-</code>
-This is because systemd requires a 'network file' to bring up an interface, and netplan doesn't generate a systemd network file for the bridge.
- If you look at //src/generate.c//, in particular at //write_network_file//, you need at least one of a set of properties to trigger generation of a network file, and an anonymous bridge has none of them.  This is clearly a bug - [[https://bugs.launchpad.net/ubuntu/+source/nplan/+bug/1736975|LP: #1736975]].
-There's no fix yet, but in the mean time, you can work around it by just manually telling systemd-networkd to bring up the interface.  I created ///etc/systemd/network/br0.network//, containing the following:
-<file bash /etc/systemd/network/br0.network>
-[Match]
-Name=br0
-[Network]
-LinkLocalAddressing=no
-IPv6AcceptRA=no
-</file>
-Then upon restarting networking (netplan apply or just reboot), you will see that the bridge comes up, and - as desired - has no address:
-<code bash>
-: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000
-    link/ether 0e:e3:1c:83:f8:e8 brd ff:ff:ff:ff:ff:ff
-</code>
-Don't forget to include a comment in your netplan YAML to remind you that this extra file exists!
-----
-====== Comments ======
-An alternate way, just add an systemd service.
-<file bash /etc/systemd/system/up-bridge-100-interface.service>
-[Unit]
-Description=Bring br100 interface up after network settings are done (bug: anonymous bridges do not came up at boot-time)
-Wants=network-online.target
-After=network-online.target
-[Service]
-Type=simple
-ExecStart=/bin/ip link set br100 up
-[Install]
-WantedBy=multi-user.target
-</file>
-<code bash>
-sudo systemctl start up-bridge-100-interface
-sudo systemctl status up-bridge-100-interface
-sudo systemctl enable up-bridge-100-interface
-</code>
-You might find you get IPv6 link local addressing in that case though.
-----
-===== References =====
-  https://djanotes.blogspot.com/2018/04/anonymous-bridges-in-netplan.html