isc dhclient not appling alias to interface

[Theodore Wynnychenko]

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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[Simon Hobson]

Theodore Wynnychenko <[hidden email]> 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.

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[sthaug]

> > 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, [hidden email]
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[paranoid.schizophrenic.2]

Not to ask stupid questions, but are you sure that you are actually
executing the right program? It actually takes a bit of work to get
the isc-dhcp-client package to work.

OpenBSD's network start up script (netstart) actually invokes
'dhclient' which is selected based on the PATH.. In my configuration
/sbin is listed before /usr/local/sbin. This means that Theo's version
is automatically selected and the the isc-dhcp-client package version.

If you have handled that little issue, is ir possible that you
actually have both versions running? You can get some very interesting
and unpredictable results by having two separate dhclients attempting
to manage a single interface.

Regards,
The Paranoid Schizophrenic

On 9/21/16, Theodore Wynnychenko <[hidden email]> wrote:

> 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
>
>

--


paranoid sysadmin
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[Mike-2]

On 9/22/2016 9:41 AM, paranoid.schizophrenic.2 wrote:

> Not to ask stupid questions, but are you sure that you are actually
> executing the right program? It actually takes a bit of work to get
> the isc-dhcp-client package to work.
>
> OpenBSD's network start up script (netstart) actually invokes
> 'dhclient' which is selected based on the PATH.. In my configuration
> /sbin is listed before /usr/local/sbin. This means that Theo's version
> is automatically selected and the the isc-dhcp-client package version.
>
> If you have handled that little issue, is ir possible that you
> actually have both versions running? You can get some very interesting
> and unpredictable results by having two separate dhclients attempting
> to manage a single interface.
>[snip]

fwiw, here is how I use the isc-dhclient in my OpenBSD install.

Here is the hostname.em0 file:

!/usr/local/sbin/dhclient -4 --no-pid -cf
/usr/local/etc/dhcp/dhclient4.conf -lf /var/db/dhcp/dhclient4.leases.wan
\$if


Note that it is one line that was folded by the email client.
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