Re: DNS lookup failing for LAN hosts with fixed DHCP leases

Hi there,

On Fri, 2 Jun 2017, David Christensen wrote:

> I am setting up an IPCop 2.1.9 machine for my home LAN.  I have created
> fixed DHCP leases for two workstations.  When I try to ping from one
> workstation to the other workstation, and vice-versa, DNS is failing:

It isn't clear to me how you expect the name resolution to happen, and
what results you expect if it does.

The OpenDNS nameservers don't recognize p43200.holgerdanske.com.  Is
dpchrist.holgerdanske.com the other workstation you're trying to ping?
They don't recognize that either.  Do you have public IP addresses for
the workstations or are they private only?  A public nameserver won't
resolve anything to 192.168.5.0/24 because that's not a public IP, and
you'll need your own private nameserver (whatever it is) to do that.
IPCop can do it but you have to tell the workstation's resolver to ask
it, and your existing resolv.conf:

> $ cat /etc/resolv.conf
> # Generated by NetworkManager
> search holgerdanske.com
> nameserver 208.67.222.222
> nameserver 208.67.220.220

won't do that.  You could try adding a line to /etc/resolv.conf on
each workstation:

nameserver ipcop.ip.addr.ess

but be aware that if you just edit the file, NetworkManager will then
overwrite it at the drop of a hat.  (One of the first things I do on a
Debian box is uninstall NetworkManager but I'm not suggesting you need
do that.)  You'll need to put the nameserver addresses in an 'iface'
stanza in /etc/network/interfaces (see 'man interfaces' on the Debian
machine) or set the interface to get the nameserver IPs to be used via
DHCP (so IPCop can supply them - but you'll need to make sure IPCop is
configured to do that and I'm afraid I don't know enough about IPCop 2
to tell you where the configuration resides.  On a 1.4.x IPCop it's in
/var/ipcop/dhcp/dhcpd.conf).  When you've edited the configuration you
need to reload the config with something like

ifdown eth0
ifup eth0

but as I've implied I'm not a great fan of Debian's networking so there
may be a more generic/DebianApproved way.

> I could add hosts entries on the workstations, but I'd rather let IPCop
> handle this for me (e.g. DHCP and DNS cache integration?).

Whatever you want, you have to do some configuration.

> I tried creating hosts entries on IPCop for the workstations, but that
> didn't work either.

IPCop will only give the answers if it's asked the questions.  The
/etc/resolv.conf you show above tells the resolver to ask OpenDNS.
You can ask your IPCop to tell you what it thinks by using '@host'
in a 'dig' query, for example

dig @ipcop.ip.addr.ess p43200
dig @ipcop.ip.addr.ess p43200.holgerdanske.com
dig @ipcop.ip.addr.ess p43200.local.holgerdanske.com

Note that I've added 'local.' into that but it needs some explanation.
I'd arrange p43200.holgerdanske.com and p43200.local.holgerdanske.com
to resolve to different IP addresses, one being a private LAN address.
When I set up workstations with RFC1918 private IPs on a LAN for an
entity which has a public domain name such as 'example.com' I create a
nameserver zone file for 'local.example.com' which gives non-routeable
IP addresses to the local workstations.  It would contain a line like

p43200 A 192.168.5.32

for the workstation in question.  You probably should read a good DNS
book like "DNS and BIND", or, if things aren't going to get a lot more
complex than they are now, just add the IPs to /etc/hosts on the two
workstations as you originally suggested.  There isn't a lot to do but
for it to make any sense you need to know quite a bit about it before
you actually do it.

HTH

-- 

73,
Ged.

------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot
_______________________________________________
IPCop-user mailing list
[email protected]
Manage your subscription or unsubscribe
https://lists.sourceforge.net/lists/listinfo/ipcop-user