ip neigh show and NUD_NOARP state - is it possible ?

[Ian Brown]

Hello,
I know that there are devices which are not working with arp. For example,
the loopback device.
I was wondering whether it is possible to create neighbours in a
NUD_NOARP state; so that "ip neigh show"
will show such neighbours where their state is NUD_ARP.
I made some tests with the loopback device , but could not find such a
way to cause it
to appear as NUD_NOARP.
Also if I ping a (nonexisting) multicast address (like 224.0.0.0) I
don't see it in
"ip neigh show" (but I see it in the routing cache).

Could it be done ? (maybe with multicast/braodcast)?

BTW, I see an example in the documentation which demonstrates NUD_NOARP
on the loopback device, but this documentation is from quite a time ago.

See:
http://www.policyrouting.org/iproute2.doc.html#ss9.4.5

...
...
ip neigh ls

dev lo lladdr 000000000000 nud noarp

fe80200cfffe763f85 dev eth0 lladdr 00000c763f85 router nud stale

0.0.0.0 dev lo lladdr 000000000000 nud noarp

193.233.7.254 dev eth0 lladdr 00000c763f85 nud reachable

Regards,
Ian