Thanks for the heads-up for Netplan! IIUC this will be fixed by a
systemd SRU, so closing it as "Invalid" for Netplan. Please re-open if
you feel there is something to do on our side.
** Changed in: netplan.io (Ubuntu)
Status: New => Invalid
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https://bugs.launchpad.net/bugs/2055397
Title:
netplan/systemd-networkd: route metric not applied to routes to the
local subnet
Status in cloud-init package in Ubuntu:
Invalid
Status in netplan.io package in Ubuntu:
Invalid
Status in systemd package in Ubuntu:
Fix Released
Status in systemd source package in Focal:
New
Bug description:
Cloud-init introduced a feature to configure policy routing on AWS EC2
instances with multiple NICs in
https://github.com/canonical/cloud-init/commit/0ca5f31043e2d98eab31a43d9dde9bdaef1435cb
targeting v24.1.
Cloud-init generates the following netplan config:
```
$ cat /etc/netplan/50-cloud-init.yaml
network:
ethernets:
ens5:
dhcp4: true
dhcp4-overrides: &id001
route-metric: 100
dhcp6: true
dhcp6-overrides: *id001
match:
macaddress: 0a:c8:ab:90:c2:fb
set-name: ens5
ens6:
dhcp4: true
dhcp4-overrides:
route-metric: 200
use-routes: true
dhcp6: false
match:
macaddress: 0a:c6:55:a1:dc:3b
routes:
- table: 101
to: 0.0.0.0/0
via: 192.168.0.1
- table: 101
to: 192.168.0.0/20
routing-policy:
- from: 192.168.10.212
table: 101
set-name: ens6
version: 2
```
Which renders the following systemd-networkd config files:
```
$ cat 10-netplan-ens5.link
[Match]
MACAddress=0a:c8:ab:90:c2:fb
[Link]
Name=ens5
WakeOnLan=off
$ cat 10-netplan-ens5.network
[Match]
MACAddress=0a:c8:ab:90:c2:fb
Name=ens5
[Network]
DHCP=yes
LinkLocalAddressing=ipv6
[DHCP]
RouteMetric=100
UseMTU=true
$ cat 10-netplan-ens6.link
[Match]
MACAddress=0a:c6:55:a1:dc:3b
[Link]
Name=ens6
WakeOnLan=off
$ cat 10-netplan-ens6.network
[Match]
MACAddress=0a:c6:55:a1:dc:3b
Name=ens6
[Network]
DHCP=ipv4
LinkLocalAddressing=ipv6
[Route]
Destination=0.0.0.0/0
Gateway=192.168.0.1
Table=101
[Route]
Destination=192.168.0.0/20
Scope=link
Table=101
[RoutingPolicyRule]
From=192.168.10.212
Table=101
[DHCP]
RouteMetric=200
UseMTU=true
```
Which configures the instance with the following state in Ubuntu
Focal:
```
$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> 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
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: ens5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9001 qdisc mq state UP group
default qlen 1000
link/ether 0a:c8:ab:90:c2:fb brd ff:ff:ff:ff:ff:ff
inet 192.168.12.94/20 brd 192.168.15.255 scope global dynamic ens5
valid_lft 2087sec preferred_lft 2087sec
inet6 2a05:d012:ea0:c500:6d12:2b20:5fef:a502/128 scope global dynamic
noprefixroute
valid_lft 440sec preferred_lft 130sec
inet6 fe80::8c8:abff:fe90:c2fb/64 scope link
valid_lft forever preferred_lft forever
3: ens6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9001 qdisc mq state UP group
default qlen 1000
link/ether 0a:c6:55:a1:dc:3b brd ff:ff:ff:ff:ff:ff
inet 192.168.10.212/20 brd 192.168.15.255 scope global dynamic ens6
valid_lft 2083sec preferred_lft 2083sec
inet6 fe80::8c6:55ff:fea1:dc3b/64 scope link
valid_lft forever preferred_lft forever
$ ip route show
default via 192.168.0.1 dev ens5 proto dhcp src 192.168.12.94 metric 100
default via 192.168.0.1 dev ens6 proto dhcp src 192.168.10.212 metric 200
192.168.0.0/20 dev ens5 proto kernel scope link src 192.168.12.94
192.168.0.0/20 dev ens6 proto kernel scope link src 192.168.10.212
192.168.0.1 dev ens5 proto dhcp scope link src 192.168.12.94 metric 100
192.168.0.1 dev ens6 proto dhcp scope link src 192.168.10.212 metric 200
$ ip rule show
0: from all lookup local
0: from 192.168.10.212 lookup 101
32766: from all lookup main
32767: from all lookup default
$ ip route show table 101
default via 192.168.0.1 dev ens6 proto static onlink
192.168.0.0/20 dev ens6 proto static scope link
```
The issue here is that the instance is not reachable from the same subnet via
the private ipv4 of the primary NIC,
packets are routed to egress via ens6 and dropped.
The cause is that interface metrics are not applied to local subnet routes
with systemd 245 (245.4-4ubuntu3.23).
On newer systemd versions, as in Jammy, the metrics are correctly applied.
Correcting them manually fixes the issue in Focal.
Expected main route table:
default via 192.168.0.1 dev ens5 proto dhcp src 192.168.12.94 metric 100
default via 192.168.0.1 dev ens6 proto dhcp src 192.168.10.212 metric 200
192.168.0.0/20 dev ens5 proto kernel scope link src 192.168.12.94 metric 100
192.168.0.0/20 dev ens6 proto kernel scope link src 192.168.10.212 metric 200
192.168.0.1 dev ens5 proto dhcp scope link src 192.168.12.94 metric 100
192.168.0.1 dev ens6 proto dhcp scope link src 192.168.10.212 metric 200
It looks like the upstream systemd issue and PR fixing this problem
are:
https://github.com/systemd/systemd/issues/928
https://github.com/systemd/systemd/pull/19344
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