[Bug 1176046] Re: isc-dhcp dhclient listens on extra random ports

[Eric Desrochers]

After more investigation, it seems like the 2 extra port-bindings port assignation decision is made by "libdns" itself.
 
https://github.com/wklaebe/bind9/blob/ac1dcdd124a5abdec4969e2c33836d863bf73aa7/lib/dns/dispatch.c#L1921

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Title:
  isc-dhcp dhclient listens on extra random ports

Status in isc-dhcp package in Ubuntu:
  In Progress

Bug description:
  Ubuntu 13.04 Server 64-bit.  Fresh install.  Only one network adapter.

  dhclient process is listening on two randomly chosen udp ports in
  addition to the usual port 68.  This appears to be a bug in the
  discovery code for probing information on interfaces in the system.

  Initial research of the code also suggested omapi, but adding omapi
  port 9999 to /etc/dhcp/dhclient.conf only opened a forth port with the
  two random udp ports still enabled.

  Version of included distro dhclient was 4.2.4.  I also tested with the
  latest isc-dhclient-4.2.5-P1 and got the same results.

  Debian has the same bug:
  http://forums.debian.net/viewtopic.php?f=10&t=95273&p=495605#p495605

  One impact of these random ports is that security hardening becomes
  more difficult.  The purpose of these random ports and security
  implications are unknown.

  
  Example netstat -lnp  output:

  udp        0      0 0.0.0.0:21117           0.0.0.0:*                           2659/dhclient   
  udp        0      0 0.0.0.0:68              0.0.0.0:*                           2659/dhclient   
  udp6       0      0 :::45664                :::*                                2659/dhclient

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