changing netmask of loopback interface

Question

I can change netmask of loopback inteface (usually lo interface has 127.0.0.1/8):

pi@raspberrypi:~ $ ifconfig
lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
    inet 127.0.0.1  netmask 255.0.0.0
    inet6 ::1  prefixlen 128  scopeid 0x10<host>
    loop  txqueuelen 1000  (Local Loopback)

pi@raspberrypi:~ $ sudo ifconfig lo 127.0.0.1 netmask 255.255.255.0 up

pi@raspberrypi:~ $ ifconfig
lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
    inet 127.0.0.1  netmask 255.255.255.0
    inet6 ::1  prefixlen 128  scopeid 0x10<host>
    loop  txqueuelen 1000  (Local Loopback)

What negative effects can this have? What pitfalls it hides?

score 2 · Answer 1 · answered Aug 28 '20 at 03:55

2

Then loopback only responds to 127.0.0.1/24. Do not do it, there is no purpose to this non-standard configuration.

Just one thing that might be broken: Debian systems that ensure their own hostname can be resolved via in /etc/hosts, possibly to 127.0.1.1.

Remember that on Linux ifconfig has been obsolete for many years.

The equivalent iproute is:

ip addr add 127.0.0.1/24 dev lo
ip addr del 127.0.0.1/8 dev lo

answered Aug 28 '20 at 03:55

John Mahowald

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and what about setting lo to 127.0.0.0/16? – mastupristi Aug 28 '20 at 06:40
It should be 127.0.0.0/8. Come up with a use case of why before making the effort to make something non-standard work. – John Mahowald Aug 28 '20 at 14:55
I tried to explain the use case in this post: https://superuser.com/questions/1581597/which-ip-address-to-assign-to-private-interfaces – mastupristi Aug 29 '20 at 17:08

score 0 · Answer 2 · answered Nov 17 '21 at 13:16

0

well, looks like it will be the future 127/16

according to this doc https://www.ietf.org/id/draft-schoen-intarea-unicast-127-00.html

answered Nov 17 '21 at 13:16

Peca

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changing netmask of loopback interface

2 Answers2