MacDNS FAQ's & Troubleshooting
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Frequently-Asked Questions
What
can I do to speed up performance of
MacDNS?
Answer: "Detailed" and
"Microscopic" log messages can cause a
noticeable performance hit. For fastest
performance, choose "Important" or "Critical"
from the pop-up menu at the bottom of the
Message Log window, and keep the window closed
when you are not actively monitoring the
server.
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If I
need a "parent" server, why bother running MacDNS
at all? Why not just use my ISP’s name
server?
Answer: One clear advantage
of running MacDNS is that it reduces the amount
of outward-bound network traffic on your
local-area network (LAN). Lookups for a given
host name can be serviced very quickly from
MacDNS’s cache. Another advantage is that
you have control of your domains, instead of
your ISP having control. For example, you can
add or remove hosts instantly, instead of
waiting for a service provider to accomodate
your request.
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I work
for a large company/university with thousands of
computers on the Net. Can I use MacDNS as my
primary DNS server? Is MacDNS only for small and
medium-sized LANs? What are its limits?
Answer: The number of hosts
that MacDNS can support is limited only by the
amount of memory available to the application.
While it is possible to serve an organization of
any size with MacDNS, it is not currently
possible to delegate subdomains to another name
server. This means that you need to include all
hosts from all the subdomains of your domain in
the local database. For example, if you serve
"domain.com," you would need to include
"host1.subdomain.domain.com." and so forth. This
requirement might be a nuisance for large sites
that have many sub- domains in different
locations. In such a situation, you may want to
use a centralized, UNIX-based DNS server for the
top-level domain, and MacDNS servers for
individual subdomains.
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What is a recursive lookup, and does
MacDNS support them?
In a recursive lookup for a
host name, the DNS server contacts a parent
server to find the answer. If the parent server
does not have the host name address in it's
cache, the original DNS server follows a pointer
to the next DNS server until it finds the host
name.
MacDNS 1.04 does not
perform recursive lookups. However, to the end
user and client applications it appears that it
does. MacDNS acts as a forwarding nameserver.
When MacDNS is required to resolve a Domain Name
(Apple.Com) outside its domain(s) (i.e.,
acme.com) it forwards the request to a parent
DNS Server (such as an ISP's DNS server) which
then performs a recursive lookup and returns the
answer to MacDNS.
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How does MacDNS do zone
transfers?
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Is there
anything I should know about importing zone files
from Unix machines?
DNS running on Unix machines
is able to have information for several domain
name spaces within the same zone file; it does
so by having multiple SOA (start of authority)
records within the file. MacDNS requires
separate zone files for each domain name space,
each file starting with the SOA record. It's
uncommon to find a need to set up MacDNS in
place of an existing Unix machine running DNS,
but if one were to do this, you'd need to check
the file for multiple "SOA" records and some
manual editing of the file may be needed to
break it into separate zone files, each begining
with the SOA record.
In addition, the file
should not begin with ";" or "$ORIGIN."
See TIL article
19189 for more
information about importing existing BIND zones
into MacDNS.
Is
it possible to specify more than one secondary name
server for a given domain?
Answer: Only one secondary
name server can be entered in the Zone
Information dialog, but MacDNS does support
multiple secondary NS records. To specify more
than one secondary name server, you’ll need
to edit the zone file manually with a text
editor. Look for the line that says:
; Nameserver
entries
After this line,
you’ll notice the secondary name server
(NS) entry. If you need more secondary servers,
just add additional lines. For example:
mydomain.com. NS
secondary.provider.net. mydomain.com. NS
another.provider.net. mydomain.com. NS
third.provider.net. mydomain.com. NS
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How
do I serve multiple domains with MacDNS? I want to
map "www.intercloud.com" and "www.tyrell.org" to my
Web server.
Answer: For each unique
top-level domain name you want to serve, choose
"New Zone File..." from the File menu and enter
the domain name in the Zone Information dialog
box. You can have multiple zone files open at
once. Even if www.tyrell.org is just intended to
be an alias to your Web server at
www.intercloud.com, you still need to create a
zone file for tyrell.org, because you are
serving a host within that namespace. In the
Zone Information dialog for tyrell.org, enter
the same information that you specified for the
intercloud.com zone (with the exception of the
Domain Name field, of course.) Add a permanent
host entry for www.tyrell.org. You can then
assign the IP address of the "real" host machine
(www.intercloud.com) to this host.
When you map entries
across multiple domains to a single IP address
in this way, it’s important to be aware of
how reverse (PTR) queries for the IP address are
handled. Only the canonical domain name for a
given IP address is returned. Currently, MacDNS
defines the canonical name for an IP address as
the first permanent host entry it finds which
matches that address. To ensure that MacDNS
returns a particular name for a reverse lookup
when cross-domain host names are mapped to an IP
address, simply create or open the zone file
containing that entry first.
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How do
I set up multiple default home pages on my Web
server using MacDNS?
Answer: You don’t.
Serving up a different default HTML page based
on the domain name in a URL is an issue for HTTP
server software (or an add-on product which runs
on a Web server machine, such as HomeDoor from
Open Door Networks).
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How do I set
up a default MX record for my domain?
Answer: Enter the name of the
default mail exchanger in the dialog box for the
host whose name is the same as your domain name.
(If there isn’t one, then you need to
create an "MX-only" host.)
There’s no need to
enter explicit MX information for each host in
the domain.
For example, if you are
setting up MacDNS to serve "mydomain.net.",
there are two possibilities:
- You have a host
computer named "mydomain.net." Choose "Add
Permanent Host..." from the Hosts menu to
create a host named "mydomain.net."
- None of your host
machines is actually named
"mydomain.net."Choose "Add MX-Only Host..."
from the Hosts menu to create a host named
"mydomain.net."
Enter the MX information
in the dialog box that appears. A sample mail
exchanger record for "mydomain.net." might look
like this:
10
mail.mydomain.net., 20
altmail.mydomain.net.
In this example, a
computer named "mail.mydomain.net." is specified
as the preferred SMTP mail server for this
domain. The numbers 10 and 20 are preference
values which indicate the relative priority of
the mail exchangers: a lower number means a
higher priority. Because "altmail.mydomain.net."
has a higher preference value, mail will be
routed to it only when the preferred server
"mail" is unavailable.
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How do I
set up a wildcard PTR entry for a block of
addresses?
Answer: MacDNS does not
currently support wildcard entries. Generally,
this would be useful if you are running software
(such as the Apple IP Gateway) which assigns IP
addresses from a pool.
To provide reverse name
mapping for these IP addresses, you need to
create a permanent host entry with a name for
each, for example:
"IP-pool-1.mydomain.com",
"IP-pool-2.mydomain.com",
and so on.
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I’m
setting up MacDNS to serve an intranet at my
office. Our network isn’t connected to the
Internet. Should I just make up arbitrary IP
addresses for the hosts in my domain?
By convention, IP addresses
that you assign for a private network should
fall within the following three blocks of the IP
address space:
10.0.0.1 to
10.255.255.254, which provides up to 2^24
Class A addresses, which would use subnet
mask 255.0.0.0.
172.16.0.1 to
172.31.255.254, which provides up to 2^16
Class B addresses, which would use subnet
mask 255.255.0.0.
192.168.0.1 to
192.168.0.254, which provides up to 2^8 Class
C addresses, which would use subnet mask
255.255.255.0.
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Why do I
sometimes see incoming requests in the log file
with my local domain name tacked on the end? (i.e.
"www.apple.com.mydomain.com")
This situation usually occurs
due to the way your client application and
TCP/IP are configured on the client end. If you
try to look up a name that isn’t terminated
with a dot, the client assumes that the name
isn’t a fully-qualified domain name and
appends the default domain name to the end
before sending off the request. If your DNS
client is using MacTCP, try setting
‘.’ as the default domain name; on the
client machine, type a period in the box to the
left of where you entered the IP address of the
DNS server.
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How can I
add a new hardware/software type for a host? I have
a bunch of PCs, but that isn’t one of the
hardware options.
Answer: It’s possible to
add new hardware/software types to the popup
menus that appear in the Host Information dialog
box. However, you’ll need to be familiar
with ResEdit. Open the MacDNS server application
and edit ‘MENU’ resources ID=8 and
ID=9.
Each menu item is in the
form
[name]#[command-ID]. If
you add new items to the menu, be sure to
continue the command IDs in sequential order
(for example, 3002, 3003, 3004, 3005, and so
on.) (Disclaimer: This information is provided
for testing purposes only. Apple does not
recommend or support this modification. Use
ResEdit at your own risk.)
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My
secondary DNS provider wants the serial numbers for
my domain data to be in "YYMMDDnn" format. Does
MacDNS support this?
Answer: MacDNS starts the
serial number at 1 and increments it by 1 each
time the zone file is saved.
("DNS and BIND," published
by O’Reilly and Associates, describes this
method as one of the good ways to manage serial
numbers.) The YYMMDDnn format is not part of the
DNS specification.
However, you can satisfy
your provider’s requirements simply by
using a text editor to open and edit your zone
file. The serial number is stored as part of the
SOA (start of authority) record at the beginning
of the file; it’s the first number
following the administrator’s e-mail
address. For example, if today is February 5,
1996, and it’s the first change to this
file today, you would change the number to
96020501. After you make this change, just
re-open the zone file in MacDNS and you’re
set.
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