no DHCPRELEASE sent out by dhclient -r on Linux

[Marc Haber]

Hi,

I am seeing this behavior with dhclient 4.3.1 on grml, but I suspect
that other versions of dhclient do the same.

When I tell dhclient to explicitly release the current lease (dhclient
-r), I see the following behavior:

root at grml ~ # dhclient -v -r eth0
Killed old client process
Internet Systems Consortium DHCP Client 4.3.1
Copyright 2004-2014 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/eth0/52:54:00:4d:cc:3d
Sending on   LPF/eth0/52:54:00:4d:cc:3d
Sending on   Socket/fallback
DHCPRELEASE on eth0 to 192.168.181.13 port 67
send_packet: Network is unreachable
send_packet: please consult README file regarding broadcast address.
dhclient.c:2331: Failed to send 300 byte long packet over fallback interface.
root at grml ~ #

The README only documents some weirdness with Linux kernels older than
2.2, so I guess that it doesn't apply to my Linux 3.16.

But why does dhclient obviously take down the interface before it
tries to send out the DHCPRELEASE packet? What is that "failed to send
paket over fallback interface" message? I think that the vast majority
of systems running dhclient won't have a second interface.

How do I actually send out a DHCPRELEASE?

Greetings
Marc

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