Public bug reported:
Release: Ubuntu Noble 24.04, systemd 255.4-1ubuntu8.17
Description: Static IPv4 routes configured with MTUBytes= can be
duplicated without their MTU after restarting systemd-networkd. A
subsequent networkctl reconfigure, netplan apply, or networkd restart
can then silently remove the routes that include MTU values. This can
cause fragmentation and connectivity failures.
Steps to reproduce:
Launch a VM running Noble 24.04: lxc launch ubuntu:noble noble-vm --vm -c
limits.cpu=1 -c limits.memory=4GiB
Shell into VM: lxc shell noble-vm
Create dummy netplan config: vim /etc/netplan/dummy.yaml
network:
version: 2
dummy-devices:
mgmt0:
addresses: [10.34.141.45/24]
dhcp4: false
mtu: 9000
routes:
- {to: 169.254.169.254/32, from: 10.34.141.45, scope: link}
- {to: 10.34.141.1, from: 10.34.141.45, scope: link, mtu: 1230, table:
252}
- {to: 10.34.141.0/24, from: 10.34.141.45, scope: link, mtu: 9000,
table: 252}
- {to: default, via: 10.34.141.1, from: 10.34.141.45, mtu: 1230, table:
252}
- {to: 10.34.134.128/25, type: unreachable, table: 252}
- {to: 10.34.128.0/22, type: unreachable, table: 252}
routing-policy:
- {from: 10.34.141.45, table: 252}
chmod 600 /etc/netplan/dummy.yaml
netplan generate && netplan apply
ip route list table 252
default via 10.34.141.1 dev mgmt0 proto static src 10.34.141.45 mtu 1230
unreachable 10.34.128.0/22 proto static
unreachable 10.34.134.128/25 proto static
10.34.141.0/24 dev mgmt0 proto static scope link src 10.34.141.45 mtu 9000
10.34.141.1 dev mgmt0 proto static scope link src 10.34.141.45 mtu 1230
Restart networkd: systemctl restart systemd-networkd
List duplicate routes in table:
ip route list table 252
default via 10.34.141.1 dev mgmt0 proto static src 10.34.141.45 mtu 1230
default via 10.34.141.1 dev mgmt0 proto static src 10.34.141.45
unreachable 10.34.128.0/22 proto static
unreachable 10.34.134.128/25 proto static
10.34.141.0/24 dev mgmt0 proto static scope link src 10.34.141.45 mtu 9000
10.34.141.0/24 dev mgmt0 proto static scope link src 10.34.141.45
10.34.141.1 dev mgmt0 proto static scope link src 10.34.141.45 mtu 1230
10.34.141.1 dev mgmt0 proto static scope link src 10.34.141.45
Reconfigure dummy mgmt0 interface: networkctl reconfigure mgmt0
List table to see missing mtu routes:
ip route list table 252
default via 10.34.141.1 dev mgmt0 proto static src 10.34.141.45
unreachable 10.34.128.0/22 proto static
unreachable 10.34.134.128/25 proto static
10.34.141.0/24 dev mgmt0 proto static scope link src 10.34.141.45
10.34.141.1 dev mgmt0 proto static scope link src 10.34.141.45
Relevant config excerpt: cat /run/systemd/network/10-netplan-
mgmt0.network
[Route]
Destination=10.34.141.1
PreferredSource=10.34.141.45
Scope=link
Table=252
MTUBytes=1230
[Route]
Destination=10.34.141.0/24
PreferredSource=10.34.141.45
Scope=link
Table=252
MTUBytes=9000
[Route]
Destination=0.0.0.0/0
Gateway=10.34.141.1
PreferredSource=10.34.141.45
Table=252
MTUBytes=1230
** Affects: systemd (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2167098
Title:
IPv4 route MTUs silently dropped after networkd restart / networkctl
reconfigure / netplan apply
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