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[Lukas Märdian <2119120@xxxxxxxxxxxxxxxxxx>]

I see you're already using "dhcp4-overrides.use-routes: false" for
ens192, which SHOULD avoid systemd-networkd from adding any routes
provided by DHCP. This also seems to be correctly reflected in the
.network file:

"""
[Match]
Name=ens192

[Network]
DHCP=ipv4
LinkLocalAddressing=ipv6

[DHCP]
RouteMetric=100
UseMTU=true
UseRoutes=false
"""


It's in a legacy "[DHCP]" section, though. Can you please try creating an override config in to translate it to a modern "[DHCPv4]" section to see if that makes any difference?

/etc/systemd/network/10-netplan-ens192.network.d/override.conf:
"""
[DHCPv4]
RouteMetric=100
UseMTU=true
UseRoutes=false
"""

I'm also adding a "systemd" bug task for further investigation.

** Also affects: systemd (Ubuntu)
   Importance: Undecided
       Status: New

** Summary changed:

- Netplan adds routes for DHCP-Server for multiple interfaces
+ Netplan/systemd-networkd adds routes for DHCP-Server for multiple interfaces

-- 
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https://bugs.launchpad.net/bugs/2119120

Title:
  Netplan/systemd-networkd adds routes for DHCP-Server for multiple
  interfaces

Status in netplan.io package in Ubuntu:
  Incomplete
Status in systemd package in Ubuntu:
  New

Bug description:
  Not sure how to word this one but I'll try:
  I've got a server with 2 Network-Interfaces, `ens160` and `ens192`.
  There's 3 files in `/etc/netplan/:

  /etc/netplan/00-installer-config.yaml.BeforeVMwareCustomization
  ```yaml
  # This is the network config written by 'subiquity'
  network:
    ethernets:
      ens160:
        dhcp4: true
    version: 2
  ```

  /etc/netplan/99-netcfg-vmware.yaml
  ```yaml
  # Generated by VMWare customization engine.
  network:
    version: 2
    renderer: networkd
    ethernets:
      ens160:
        dhcp4: yes
        dhcp4-overrides:
          use-dns: false
        dhcp6: yes
        dhcp6-overrides:
          use-dns: false
        nameservers:
          search:
            - mydomain
          addresses:
            - 10.251.0.18
            - 10.251.0.19
            - 10.251.0.20
  ```

  /etc/netplan/config.yaml
  ```yaml
  network:
      version: 2
      ethernets:
          ens192:
              dhcp4: true
              dhcp4-overrides:
                  use-dns: false
                  use-routes: false
  ```

  After booting, I have the following routes:
  ```bash
  > ip route show
  default via 10.4.0.1 dev ens160 proto dhcp src 10.4.1.47 metric 100
  10.4.0.0/16 dev ens160 proto kernel scope link src 10.4.1.47 metric 100
  10.4.0.1 dev ens160 proto dhcp scope link src 10.4.1.47 metric 100
  10.251.0.18 dev ens192 proto dhcp scope link src 10.255.0.31 metric 100
  10.251.0.18 via 10.4.0.1 dev ens160 proto dhcp src 10.4.1.47 metric 100
  10.255.0.0/16 dev ens192 proto kernel scope link src 10.255.0.31 metric 100
  ```

  This route-Configuration makes 10.251.0.18 unavailable.
  Once I delete the false route, connections to 10.251.0.18 work again:
  ```bash
  > ip route del 10.251.0.18 dev ens192
  > ping 10.251.0.18
  PING 10.251.0.18 (10.251.0.18) 56(84) bytes of data.
  64 bytes from 10.251.0.18: icmp_seq=1 ttl=63 time=0.320 m
  ```

  This wrong route configuration causes my DHCP-Lease to expire before it can be extended, creating a new lease every time and the network connection to be dropped for a few seconds each time it does expire.
  How can I prevent the false route?

  Tidbit: When I delete both routes to 10.251.0.18 and then do `netplan
  apply`, both routes are added again. But ordered the other way around.
  Meaning that the DHCP-Server is still reachable then.

  
  Versions:
  Ubuntu 22.04.5 LTS
  netplan 0.106.1-7ubuntu0.22.04.4

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