DHCP server that itself gets an IP address by DHCP
Hello the list!
[I suppose this is a little bit OT -- but you guys are the best
concentration of experts I know, so here goes anyway...]
My local network consists of a bunch of Debian machines of various ages,
various iDevices, and the odd Windows machine connected either by wired
or wireless ethernet to a Buffalo AirStation, whose WAN port is
connected to a mini-ITX machine running LFS which acts as my firewall.
The firewall's other interface connects to my cable modem and thence to
the internet.
For co-operation with my ISP my firewall gets its external IP address
via DHCP from the ISP. I use systemd-networkd to achieve this, and this
also takes care of populating /etc/resolv.conf with the name servers
provided by the ISP.
So the firewall has 2 interfaces, the external facing one of which gets
an IP address from my ISP via DHCP, and the internal facing one has a
fixed private IP address.
The AirStation is also set up to get its WAN IP address via DHCP, since
A) that is how it comes out of the box, B) the AirStation was for years
the last line of defence between my network and the internet and the
addition of the dedicated firewall is a relatively recent thing, and C)
both the instructions and the web configuration tool are in Japanese
and, this being a Japan-market-facing device, the language can't be
changed. So I like to futz with the settings on the AirStation as little
as possible.
So I run dhcpd on the firewall machine, facing only the
local-network-facing interface, so that when the AirStation asks for an
IP address, it can be provided with one.
The Airstation is _itself_ running a DHCP server on its LAN ports /
WiFi, which is how the rest of my machines on my network get their local
IP addresses. So the DHCP server on my firewall in effect services
_only_ the AirStation.
My question is this -- I want to pass through the name servers my ISP is
providing, to the AirStation when it asks, so that the AirStation can
use the ISP's name servers. I did think about running a DNS on the
firewall also but this seems unnecessary, and would just create an extra
hop to answer DNS queries.
Right now I have the name server IP addresses hard coded in the
dhcp.conf config file, which is fine as long as the ISP doesn't change
them. But, if the ISP were to change its name servers, the firewall
would pick up the changes but as things stand it would continue to
provide the old name server addresses to the AirStation, which would
mean the rest of the network would no longer be able to resolve DNS
queries the AirStation didn't already have cached.
Is there any clever way to pass through the name server settings
the DHCP server provides, so that if the ISP should change its name
server IP addresses in the future, my local DHCP server would pass along
the new addresses when next asked?
In other words, instead of specifying the name server addresses
explicitly in the dhcp.conf file, is there a way to specify that they
should be taken from the host the DHCP server is running on?
Thanks
Mark
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