Ubuntu - Multiple Network CIDR Issue
The output of
sudo ip addr
...started as follows:
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: eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000 link/ether a0:36:bc:bd:09:c4 brd ff:ff:ff:ff:ff:ff altname enp7s0 inet 192.168.0.11/21 brd 192.168.7.255 scope global eno1 valid_lft forever preferred_lft forever inet 192.168.0.11/16 metric 100 brd 192.168.255.255 scope global dynamic eno1 valid_lft 86365sec preferred_lft 86365sec inet6 2a00:23c6:e380:e01:a236:bcff:febd:9c4/64 scope global dynamic mngtmpaddr noprefixroute valid_lft 298sec preferred_lft 118sec inet6 fe80::a236:bcff:febd:9c4/64 scope link valid_lft forever preferred_lft forever
As you can see from the output, my
eno1 interface had been assigned both of the following network CIDRs:
This was an issue for me because 192.168.0.11/16 is such a broad CIDR, that it covers the entire range of 192.168.0.0 to 192.168.255.155, which meant that even when I connected to my work VPN, which has a bunch of servers on the 192.168.10.0/24 CIDR, I could not connect to it, because my traffic was going to the home network gateway to be routed, instead of over the tun0 VPN interface.
Running this command to remove the IP address resolved my networking issues.
ip address del 192.168.0.11/16 dev eth0
Source Of The Problem - Bad Netplan Config
In the end, it turned out that my
/etc/netplan/current.yml file had
dhcp4: yes, instead of
dhcp4: no whilst also specifying the static IP address. E.g.
# This file describes the network interfaces available on your system # For more information, see netplan(5). network: version: 2 renderer: networkd ethernets: eno1: dhcp4: yes dhcp6: yes addresses: - 192.168.0.11/21 routes: - to: default via: 192.168.0.1 nameservers: addresses: - 192.168.0.222
... when it should have been:
# This file describes the network interfaces available on your system # For more information, see netplan(5). network: version: 2 renderer: networkd ethernets: eno1: dhcp4: no dhcp6: yes addresses: - 192.168.0.11/21 routes: - to: default via: 192.168.0.1 nameservers: addresses: - 192.168.0.222
- ServerFault - Ubuntu: netplan disable dhcp
- Ask Ubuntu - ip addr show is showing me two IP address on one interface
First published: 22nd March 2023