On Fri Jan 30 10:57:53 2015, jpopelka@redhat.com wrote:
> Hi,
> 
> Yesterday, I got a bug report [1] that the patch [2] might be breaking
> dhcrelay (when used with vlan).
> I haven't had time to look at it so far, just wanted to let
> you know ASAP, as I see you've been preparing beta releases.
> 
> The only thing that changed between 4.1.1-43.P1.el6.centos.1 and
> 4.1.1-43.P1.el6.centos is this added patch.
> 
> --
> Jiri
> 
> [1] https://bugzilla.redhat.com/show_bug.cgi?id=1187107
> 
> [2]
> https://source.isc.org/cgi-
> bin/gitweb.cgi?p=dhcp.git;a=commitdiff;h=29170f9da9826bd7191f4ad644e61b76c49f6cc6

Hello Jiri:

Actually it isn't that the patch broke dhcrelay, rather it makes dhcrelay behave exactly as its man page states:

" The  -i flag can be used to specify the network interfaces on which the relay agent should listen.   In general, it must  listen  not  only  on those  network  interfaces  to  which clients are attached, but also on those network interfaces to  which  the  server  (or  the  router  that reaches  the  server)  is  attached.   However, in some cases it may be necessary to exclude some networks; in this case,  you  must  list  all those network interfaces that should not be excluded using the -i flag."

The user should have alwayws had to specify both interfaces on command line: " -i em2  -i em2.60".  They have simply gotten lucky with it until now because the vlan for their server is hosted on the interface that is also used for their clients.   Had they used two different interfaces, such as em1 for their server and em2 for their clients, they would have to either specified both: " -i em1 -i em2" or none.  The latter of which would cause dhcrelay to listen on all networks.