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Description of problem:


DHClient creates an additional listening port in addition to UDP 68 which seems to be a random registered port value. 


How reproducible:
Install dhclient, start the service and perform a netstat -l -u -p and check each of the ports opened by dhclient.


Actual results:

In this example Opening 60964 port unnecessary :

# netstat -panl |grep dhcl
udp     0   0 0.0.0.0:60964   0.0.0.0:*           7594/dhclient       
udp     0   0 0.0.0.0:68      0.0.0.0:*           7594/dhclient       

Expected results:

It should open only 68 port :

udp     0   0 0.0.0.0:68      0.0.0.0:*           7594/dhclient       

Additional info:

Additional Info:
https://bugzilla.redhat.com/show_bug.cgi?id=962950
http://forums.debian.net/viewtopic.php?f=10&t=95273
http://forums.debian.net/viewtopic.php?f=10&t=95273&p=495605#p495605

As described in bug #962950, comment #5 it's libdns (bind package) what opens these ports and that the only workaround I'm aware of is building dhcpd/dhclient without DDNS support which is most likely not what we want. I can reassign this to bind to further investigate whether it'd be possible to not open these ports in libdns during initialization.

Created attachment 1269039 [details]
spawn dns ports on demand later

Simple fix delaying creation of those ports. I did not check for possible race conditions much, but it seems to fix the issue.

I think it would be useful for Red Hat to report this bug and the proposed fix to the upstream bug tracker:

https://bugs.isc.org/Public/Dist/Display.html?Name=dhcp-public

*** Bug 1486801 has been marked as a duplicate of this bug. ***

(In reply to Charlie Brady from comment #21)
> I think it would be useful for Red Hat to report this bug and the proposed
> fix to the upstream bug tracker:
> 
> https://bugs.isc.org/Public/Dist/Display.html?Name=dhcp-public

Since we follow the rule "upstream first", this was done months ago...

https://bugs.isc.org/Public/Bug/Display.html?id=45290
https://source.isc.org/cgi-bin/gitweb.cgi?p=dhcp.git;a=commit;h=ca22af89996483efd820de0084c964fc336ee7c1

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2018:0658