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Today's Topics:

   1. isc dhclient not appling alias to interface (Theodore Wynnychenko)
   2. Re: isc dhclient not appling alias to interface (Simon Hobson)
   3. Re: isc dhclient not appling alias to interface
      (sth...@nethelp.no)


----------------------------------------------------------------------

Message: 1
Date: Wed, 21 Sep 2016 16:30:17 -0500
From: "Theodore Wynnychenko" <t...@uchicago.edu>
To: <dhcp-users@lists.isc.org>
Subject: isc dhclient not appling alias to interface
Message-ID: <007b01d2144f$598b50c0$0ca1f240$@edu>
Content-Type: text/plain; charset="us-ascii"

Hello
I am looking at replacing the base dhclient in OpenBSD with the isc-dhcp-client
available in OpenBSD's packages.

The primary reason for this is to take advantage of having an alias ip address
assigned to the interface.

But, I can't seem to figure out how to get this done.

I don't know why, but I can't get the isc-dhcp-client to assign an alias to the
interface, despite the documentation that states it should.

This is being run on OpenBSD current.

The isc dhclient available is 4.3.4

# /usr/local/sbin/dhclient --version
isc-dhclient-4.3.4


I have created an /etc/isc-dhclient.conf file:
---
timeout 60;
retry 60;
reboot 10;
select-timeout 5;
initial-interval 2;
script "/usr/local/sbin/dhclient-script";

supersede domain-name "domain.com";
supersede domain-name-servers d.n.s.1,d.n.s.2;

request subnet-mask, broadcast-address, time-offset, routers;

alias {
  interface "em0";
  fixed-address fi.xed.ip.addr;
  option subnet-mask 255.255.255.0;
}
---

But, after killing the running dhclient process (included with OpenBSD's base
installation), removing the leases at /var/db/dhclient.leases* and starting
isc-dhcp-client with:

# /usr/local/sbin/dhclient -cf /etc/isc-dhclient.conf em0

The isc client is able to get an offer from the dhcp server:

Sep 21 16:18:05 xxx dhclient: DHCPDISCOVER on em0 to 255.255.255.255 port 67
interval 2
Sep 21 16:18:05 xxx dhclient: DHCPOFFER from xx.xxx.xx.x
Sep 21 16:18:10 xxx dhclient: DHCPREQUEST on em0 to 255.255.255.255 port 67
Sep 21 16:18:10 xxx dhclient: DHCPACK from xx.xxx.xx.x
Sep 21 16:18:10 xxx dhclient: bound to xx.xxx.xx.xxx -- renewal in 111100
seconds.

However, the alias does _not_ get assigned to the interface.  The only address
is the dynamically assigned one.

According to the dhclient.conf man page, "the dhcp client can be set up to
configure an IP alias using the alias declaration."

I understand this to mean that the alias declaration above should result in the
interface being configured with both the dynamically assigned ip address, and
the fi.xed.ip.addr given in the alias declaration of my isc-dhclient.conf file.

But this is not happening.  I can find no guidance on what I am doing wrong, and
why the isc-dhcp-client is not assigning the alias.

Thanks for any advice.

Ted

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------------------------------

Message: 2
Date: Thu, 22 Sep 2016 08:01:18 +0100
From: Simon Hobson <dh...@thehobsons.co.uk>
To: Users of ISC DHCP <dhcp-users@lists.isc.org>
Subject: Re: isc dhclient not appling alias to interface
Message-ID: <9519264c-33c0-4624-988f-42a0445e4...@thehobsons.co.uk>
Content-Type: text/plain; charset=us-ascii

Theodore Wynnychenko <t...@uchicago.edu> wrote:

> But this is not happening.  I can find no guidance on what I am doing wrong, 
> and
> why the isc-dhcp-client is not assigning the alias.

FWIW, I agree with your interpretation of the man page - but it's not a feature 
I've ever tried to use.



------------------------------

Message: 3
Date: Thu, 22 Sep 2016 09:25:49 +0200 (CEST)
From: sth...@nethelp.no
To: dhcp-users@lists.isc.org, dh...@thehobsons.co.uk
Subject: Re: isc dhclient not appling alias to interface
Message-ID: <20160922.092549.74727003.sth...@nethelp.no>
Content-Type: Text/Plain; charset=us-ascii

> > But this is not happening.  I can find no guidance on what I am doing 
> > wrong, and
> > why the isc-dhcp-client is not assigning the alias.
> 
> FWIW, I agree with your interpretation of the man page - but it's not a 
> feature I've ever tried to use.

Moderately related followup on this: In connection with lab testing of
"ignore-client-uids" on FreeBSD 10.3, I used the standard FreeBSD client
(based on the OpenBSD client) to manually generate DHCP requests with
many different client UIDs.

Without the "ignore-client-uids" option on the server, I get a different
IP address from the DHCP server for each client UID (as expected), *and*
each of these IP addresses are assigned as an alias on the interface.

The end result is an interface with as many IP addresses as I have sent
DHCP queries with different client UIDs.

Steinar Haug, Nethelp consulting, sth...@nethelp.no


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