Should IP addresses on interfaces not UP respond to ping?

[Pekka Savola <pekkas@xxxxxxxxxx>]

Hi,

With 2.2.18 I noticed something that looked interesting:

# /sbin/ip a l dev eth4
7: eth4: <BROADCAST,MULTICAST,PROMISC> mtu 1500 qdisc pfifo_fast qlen 100
    link/ether 00:80:c8:c9:b8:14 brd ff:ff:ff:ff:ff:ff
    inet x.y.7.252/24 brd x.y.7.255 scope global eth4

Note that the interface is not UP.  Whether it's promisc or not does not
affect this.

However, the address is still pingable from outside, through eth0!

Also noticed the same behaviour in 2.4.10.

Is this the intended behaviour, probably?

One could argue that if interface isn't UP, it shouldn't be able to send
or receive packets at all.  I wonder what changing this would break..

-- 
Pekka Savola                 "Tell me of difficulties surmounted,
Netcore Oy                   not those you stumble over and fall"
Systems. Networks. Security.  -- Robert Jordan: A Crown of Swords