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I have a small RFC 1918 network at home; four PCs, four Sun SPARC, two
DEC Alphas and an HP printer with Jet Direct Card at the moment. It
connects to Comcast via a Linksys BEFSR81 router and switch.

The Linksys router/switch acts as both DHCP client to Comcast and DHCP
server to the internal network. The PCs configure everything by DHCP.
The Suns, DEC Alphas and the printer have static IP addresses in order
to be reachable from the PCs. I configure the DNS server addresses by
hand when needed.

Comcast has announced that it is upgrading to "Dynamic DNS" and has
instructed me to make sure my PCs are configured to use DHCP. I gather
that DNS server addresses may be changing more frequently (they already
change three or four times a year).

I've never needed to understand more of DHCP than how to configure the
PCs to use it. Is it possible to configure Solaris DHCP agent in such a
way that I can have static IP addresses but get the DNS server addresses
via DHCP?

I don't think that the DHCP server embedded in the Linksys router is
capable of assigning static IP addresses using the MAC address of the
machine to determine which machine gets which address; all I know how to
do is to tell it that addresses 192.168.1.100 and up are available to be
assigned by DHCP.

Richard B. Gilbert wrote:
> I have a small RFC 1918 network at home; four PCs, four Sun SPARC, two
> DEC Alphas and an HP printer with Jet Direct Card at the moment. It
> connects to Comcast via a Linksys BEFSR81 router and switch.
>
> The Linksys router/switch acts as both DHCP client to Comcast and DHCP
> server to the internal network. The PCs configure everything by DHCP.
> The Suns, DEC Alphas and the printer have static IP addresses in order
> to be reachable from the PCs. I configure the DNS server addresses by
> hand when needed.
>
> Comcast has announced that it is upgrading to "Dynamic DNS" and has
> instructed me to make sure my PCs are configured to use DHCP. I gather
> that DNS server addresses may be changing more frequently (they already
> change three or four times a year).
>
> I've never needed to understand more of DHCP than how to configure the
> PCs to use it. Is it possible to configure Solaris DHCP agent in such a
> way that I can have static IP addresses but get the DNS server addresses
> via DHCP?
>

If your network interface were hme0, you may be able to use:

ifconfig hme0 dhcp inform

to acquire information from the DHCP server, including the DNS
addresses, while still using a static address, assuming the Linksys
router supports DHCP inform messages. However, you then have to write a
script to pull the DNS server and domain out of dhcp (using the dhcpinfo
command) to place the settings into /etc/resolv.conf. If you're running
Solaris 10, the /etc/dhcp/eventhook script can be used to run that
update automatically, read the dhcpagent man page for more details.

Dave

Dave Miner wrote:

> Richard B. Gilbert wrote:
>
>> I have a small RFC 1918 network at home; four PCs, four Sun SPARC, two
>> DEC Alphas and an HP printer with Jet Direct Card at the moment. It
>> connects to Comcast via a Linksys BEFSR81 router and switch.
>>
<snip>
>> I've never needed to understand more of DHCP than how to configure the
>> PCs to use it. Is it possible to configure Solaris DHCP agent in such
>> a way that I can have static IP addresses but get the DNS server
>> addresses via DHCP?
>>
>
> If your network interface were hme0, you may be able to use:
>
> ifconfig hme0 dhcp inform
>
> to acquire information from the DHCP server, including the DNS
> addresses, while still using a static address, assuming the Linksys
> router supports DHCP inform messages. However, you then have to write a
> script to pull the DNS server and domain out of dhcp (using the dhcpinfo
> command) to place the settings into /etc/resolv.conf. If you're running
> Solaris 10, the /etc/dhcp/eventhook script can be used to run that
> update automatically, read the dhcpagent man page for more details.
>
> Dave

ifconfig hme0 dhcp inform
"timed out". This suggests to me that the BEFSR81 does not support DCHP
Inform messages.

Richard B. Gilbert wrote:
> Dave Miner wrote:
>
>> Richard B. Gilbert wrote:
>>
>>> I have a small RFC 1918 network at home; four PCs, four Sun SPARC,
>>> two DEC Alphas and an HP printer with Jet Direct Card at the moment.
>>> It connects to Comcast via a Linksys BEFSR81 router and switch.
>>>
> <snip>
>>> I've never needed to understand more of DHCP than how to configure
>>> the PCs to use it. Is it possible to configure Solaris DHCP agent in
>>> such a way that I can have static IP addresses but get the DNS server
>>> addresses via DHCP?
>>>
>>
>> If your network interface were hme0, you may be able to use:
>>
>> ifconfig hme0 dhcp inform
>>
>> to acquire information from the DHCP server, including the DNS
>> addresses, while still using a static address, assuming the Linksys
>> router supports DHCP inform messages. However, you then have to write
>> a script to pull the DNS server and domain out of dhcp (using the
>> dhcpinfo command) to place the settings into /etc/resolv.conf. If
>> you're running Solaris 10, the /etc/dhcp/eventhook script can be used
>> to run that update automatically, read the dhcpagent man page for more
>> details.
>>
>> Dave
>
> ifconfig hme0 dhcp inform
> "timed out". This suggests to me that the BEFSR81 does not support DCHP
> Inform messages.

Yeah, I was afraid that would be the case. Too bad they cut that
particular corner, supporting Inform messages is basically free once
you've got a fully working server such as they have.

Dave

Dave Miner wrote:

> Richard B. Gilbert wrote:
>
>> Dave Miner wrote:
>>
>>> Richard B. Gilbert wrote:
>>>
>>>> I have a small RFC 1918 network at home; four PCs, four Sun SPARC,
>>>> two DEC Alphas and an HP printer with Jet Direct Card at the
>>>> moment. It connects to Comcast via a Linksys BEFSR81 router and
>>>> switch.
>>>>
>> <snip>
>>
>>>> I've never needed to understand more of DHCP than how to configure
>>>> the PCs to use it. Is it possible to configure Solaris DHCP agent
>>>> in such a way that I can have static IP addresses but get the DNS
>>>> server addresses via DHCP?
>>>>
>>>
>>> If your network interface were hme0, you may be able to use:
>>>
>>> ifconfig hme0 dhcp inform
>>>
>>> to acquire information from the DHCP server, including the DNS
>>> addresses, while still using a static address, assuming the Linksys
>>> router supports DHCP inform messages. However, you then have to
>>> write a script to pull the DNS server and domain out of dhcp (using
>>> the dhcpinfo command) to place the settings into /etc/resolv.conf.
>>> If you're running Solaris 10, the /etc/dhcp/eventhook script can be
>>> used to run that update automatically, read the dhcpagent man page
>>> for more details.
>>>
>>> Dave
>>
>>
>> ifconfig hme0 dhcp inform
>> "timed out". This suggests to me that the BEFSR81 does not support
>> DCHP Inform messages.
>
>
> Yeah, I was afraid that would be the case. Too bad they cut that
> particular corner, supporting Inform messages is basically free once
> you've got a fully working server such as they have.
>
> Dave

I just had a quick look at RFC 2113. It does not appear that Inform
Message support is optional. I've opened a case with Linksys (citing
chapter and verse in RFC 2113) and we'll see what they have to say.