[pkg-dhcp-devel] Bug#852173: Starting dhclient without an interface does not work: No broadcast interfaces found - exiting.

[Alexander Kurtz]

Package: isc-dhcp-client
Version: 4.3.5-1

Hi!

dhclient(8) says:

	The names of the network interfaces that  dhclient  should  attempt  to
	configure  may be specified on the command line.  If no interface names
	are specified on the command line dhclient will normally  identify  all
	network  interfaces,  eliminating non-broadcast interfaces if possible,
	and attempt to configure each interface.

However, starting dhclient without an interface does not actually work:

	root at shepard:~# ip address show
	1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
	    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
	    inet 127.0.0.1/8 scope host lo
	       valid_lft forever preferred_lft forever
	    inet6 ::1/128 scope host 
	       valid_lft forever preferred_lft forever
	4: enp0s25: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
	    link/ether XX:XX:XX:XX:XX:XX brd ff:ff:ff:ff:ff:ff
	root at shepard:~# dhclient -v
	Internet Systems Consortium DHCP Client 4.3.5
	Copyright 2004-2016 Internet Systems Consortium.
	All rights reserved.
	For info, please visit https://www.isc.org/software/dhcp/

	No broadcast interfaces found - exiting.
	root at shepard:~# ip address show
	1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
	    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
	    inet 127.0.0.1/8 scope host lo
	       valid_lft forever preferred_lft forever
	    inet6 ::1/128 scope host 
	       valid_lft forever preferred_lft forever
	4: enp0s25: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
	    link/ether XX:XX:XX:XX:XX:XX brd ff:ff:ff:ff:ff:ff
	root at shepard:~# 

I also tried bringing the interface up first, but this didn't help:

	root at shepard:~# ip address show
	1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
	    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
	    inet 127.0.0.1/8 scope host lo
	       valid_lft forever preferred_lft forever
	    inet6 ::1/128 scope host 
	       valid_lft forever preferred_lft forever
	4: enp0s25: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
	    link/ether XX:XX:XX:XX:XX:XX brd ff:ff:ff:ff:ff:ff
	root at shepard:~# dhclient -v
	Internet Systems Consortium DHCP Client 4.3.5
	Copyright 2004-2016 Internet Systems Consortium.
	All rights reserved.
	For info, please visit https://www.isc.org/software/dhcp/

	No broadcast interfaces found - exiting.
	root at shepard:~# ip address show
	1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
	    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
	    inet 127.0.0.1/8 scope host lo
	       valid_lft forever preferred_lft forever
	    inet6 ::1/128 scope host 
	       valid_lft forever preferred_lft forever
	4: enp0s25: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
	    link/ether XX:XX:XX:XX:XX:XX brd ff:ff:ff:ff:ff:ff
	root at shepard:~# 

However, explicitly specifying an interface worked:

	root at shepard:~# ip address show
	1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
	    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
	    inet 127.0.0.1/8 scope host lo
	       valid_lft forever preferred_lft forever
	    inet6 ::1/128 scope host 
	       valid_lft forever preferred_lft forever
	4: enp0s25: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
	    link/ether XX:XX:XX:XX:XX:XX brd ff:ff:ff:ff:ff:ff
	root at shepard:~# dhclient enp0s25
	root at shepard:~# ip address show
	1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
	    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
	    inet 127.0.0.1/8 scope host lo
	       valid_lft forever preferred_lft forever
	    inet6 ::1/128 scope host 
	       valid_lft forever preferred_lft forever
	4: enp0s25: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
	    link/ether XX:XX:XX:XX:XX:XXff:ff
	    inet 192.168.178.29/24 brd 192.168.178.255 scope global enp0s25
	       valid_lft forever preferred_lft forever
	root at shepard:~# 

Please note that others have noticed this problem as well [0,1]. It was
apparently even submitted to upstream [2]. However, due to the lack of
a public bugtracker [3], I can't verify that.

Best regards

Alexander Kurtz

[0] https://serverfault.com/questions/714938/dhclient-no-broadcast-interfaces-found-but-eth0-is-up-and-broadcast
[1] https://lists.isc.org/pipermail/dhcp-users/2013-March/016563.html
[2] https://lists.isc.org/pipermail/dhcp-users/2013-March/016584.html
[3] https://www.isc.org/community/report-bug/
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