Routing table incorrect at startup

Question

Whenever I reboot my Ubuntu server, the routing table is incorrect for the default route. The routing table correctly specifies the LAN IP address 192.168.124.0/24. All other traffic should go through the router at 192.168.124.253, but the default route specifies 192.168.124.254 for the gateway:

jos@hallway:~$ ip route list
default via 192.168.124.254 dev eth1  proto static
192.168.124.0/24 dev eth1  proto kernel  scope link  src 192.168.124.101

and similarly:

jos@hallway:~$ sudo route -n
[sudo] password for jos: 
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.124.254 0.0.0.0         UG    0      0        0 eth1
192.168.124.0   0.0.0.0         255.255.255.0   U     0      0        0 eth1

I have to manually correct this to .253, using:

sudo ip route del default
sudo ip route add default via 192.168.124.253

Otherwise, the server won't be able to reach the Internet.
Where does this .254 come from? It is not in my /etc/network/interfaces, or anywhere in /etc/iproute2. The server has a single ethernet interface with a static address. My /etc/network/interfaces is simply this:

auto lo
iface lo inet loopback

auto eth1
iface eth1 inet static
  address 192.168.124.101
  netmask 255.255.255.0
  gateway 192.168.124.253
  dns-nameservers 192.168.124.253 8.8.8.8 8.8.4.4

My /etc/resolv.conf:

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 192.168.124.253
nameserver 192.168.124.253
nameserver 8.8.8.8
nameserver 8.8.4.4

So what is going on here?

Solution

NetworkManager is still configuring the interface because managed=true is set in /etc/NetworkManager/NetworkManager.conf

To disable NetworkManager and instead use /etc/network/interfaces, set managed=false in /etc/NetworkManager/NetworkManager.conf

Comments

[Lety]

please, can you post the output of sudo route -n after startup and /etc/resolv.conf content?

[Jos]

@Letizia I added the information to the question.

[Jos]

@bain Yes! Thanks. There was a file in /etc/NetworkManager/system-connections/ describing the network connection that contained the wrong router address. I must have created this years ago when I still ran X on it and used the network interface. I thought all network information was taken from /etc/network/interfaces, but it appears I was wrong.

[bain]

/etc/network/interfaces is ignored if managed=true is set in /etc/NetworkManager/NetworkManager.conf (NetworkManager docs)

[Jos]

@bain Thank you. I had indeed managed=true in NetworkManager.conf.