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I tried to change the network mask using Linux ip command and got confused. Google search doesn't clarify it either. If someone could explain? Say I have interface enp0s31f6 on my Linux machine

rtuser@rtuser:~$ ip addr show dev enp0s31f6 2: enp0s31f6: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN group default qlen 1000 link/ether 98:fa:9b:c7:37:a2 brd ff:ff:ff:ff:ff:ff

I want to assign ip address to the interface:

rtuser@rtuser:~$ sudo ip addr add 192.168.20.1/24 dev enp0s31f6 rtuser@rtuser:~$ ip addr show dev enp0s31f6 2: enp0s31f6: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN group default qlen 1000 link/ether 98:fa:9b:c7:37:a2 brd ff:ff:ff:ff:ff:ff inet 192.168.20.1/24 scope global enp0s31f6 valid_lft forever preferred_lft forever

Now I realized that my network mask is not correct, I want to change

rtuser@rtuser:~$ sudo ip addr change 192.168.20.1/25 dev enp0s31f6 rtuser@rtuser:~$ ip addr show dev enp0s31f6 2: enp0s31f6: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN group default qlen 1000 link/ether 98:fa:9b:c7:37:a2 brd ff:ff:ff:ff:ff:ff inet 192.168.20.1/24 scope global enp0s31f6 valid_lft forever preferred_lft forever inet 192.168.20.1/25 scope global enp0s31f6 valid_lft forever preferred_lft forever

I got couple same ip addresses on interface. Well, maybe change doesn't work lets try to replace it

rtuser@rtuser:~$ sudo ip addr replace 192.168.20.1/26 dev enp0s31f6 rtuser@rtuser:~$ ip addr show dev enp0s31f6 2: enp0s31f6: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN group default qlen 1000 link/ether 98:fa:9b:c7:37:a2 brd ff:ff:ff:ff:ff:ff inet 192.168.20.1/24 scope global enp0s31f6 valid_lft forever preferred_lft forever inet 192.168.20.1/25 scope global enp0s31f6 valid_lft forever preferred_lft forever inet 192.168.20.1/26 scope global enp0s31f6 valid_lft forever preferred_lft forever

I would expect change/replace ip command would change properties of ip address, but it seems they all add/change/replace keep adding the same ip over and over again. Why is that?

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  • Delete the ones you don't want by changing add to del. E.g. sudo ip addr del 192.168.20.1/24 dev enp0s31f6
    – Johan Myréen
    CommentedAug 21, 2020 at 16:08
  • Thanks for the comment. Using del command is quite obvious. It'll do what it's supposed to do - deleting ip address. I just want to understand the behavior and reasons for that behavior. Seems like add/change/replace commands do the same thing. I don't believe those smart people who developed ip command would put such duplication with no reason.
    – Yuriy
    CommentedAug 24, 2020 at 19:29
  • the object the command applies a change effect upon is not 192.168.20.1 but the whole 192.168.20.1/24. Using change (or replace) can't affect the object's value itself, only other properties of the object (such as valid_lft), though most can't be changed anyway.
    – A.B
    CommentedAug 29, 2020 at 14:57
  • This question is answered well here: serverfault.com/a/666521/90281
    – claymation
    CommentedDec 17, 2022 at 2:45

1 Answer 1

Reset to default
1

Just remove the original, erroneous entry with the del option.

ip address del 192.168.20.1/24 dev enp0s31f6

And then add the corrected IP/CIDR:

ip address add 192.168.20.1/25 dev enp0s31f6
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  • I needed to do this remotely, so BEFORE deleting the address, I created a temporary address, checked if it worked, when OK, I removed and fixed the previous address, then removed the temporary address. It worked just fine. Thanks for providing the answer with ip instead of ifconfig :)
    – Pedram
    CommentedApr 30, 2023 at 10:31
  • How do you make it permanent? Reboots reset the settings back to default. The machine has network-manager installed, but it doesn't change the network settings after a reboot.
    – Pedram
    CommentedMay 1, 2023 at 8:21
  • OK, so I added a new connection and brought it up with nmcli to make it survive a reboot. But please feel free to let us know if there is another way to make this change permanent with the ip command.
    – Pedram
    CommentedMay 1, 2023 at 9:25

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