WebDNS Users' Guide
WebDNS is
a system developed at CSAIL to allow Lab members to manage entries in
the Lab's Domain Name System namespaces. Currently,
WebDNS serves the
ai.mit.edu,
csail.mit.edu,
dlp.mit.edu, and
lcs.mit.edu domains, as
well as a decreasing number of guest domains. Any authorized user may
make changes to any of these domains.
Understanding Domain Names
(It's OK to skip most of this section, but do pay attention to the
parts in
boldface.)
A Domain Name consists of a sequence of words, called "labels",
separated by dots ("
."). The labels identify branches on
a tree, with the root of the tree at right when the name is written
out. (The label of the root is the empty string. Normally, the root
and dot separating it from the first label below are represented
implicitly, like the leading one bit in a floating-point number. In
some contexts, however, a Domain Name must have an explicit root
label.)
Theoretically, a label may contain any characters other than ".".
However, there are practical limitations arising from the requirements
of the applications which use domain names. For example, spaces are
not allowed in domain names, because the standard written format for
DNS records uses whitespace to separate fields. For domain names
which are used as host names -- the only kind we'll be discussing from
here on out, the requirements are much stricter.
A host name may contain only the following characters: the Roman letters "A" through Z", digits "0" through "9", the hyphen "-", and the period (dot, full stop) ".". Neither dot nor hyphen may be the first character of a host name. Case is not significant, but custom in CSAIL is to use lower case.
(There is now a standardized mechanism to support "internationalized
domain names", whereby Unicode labels can be transformed into a
plain-text representation that fits the requirements for a host name.
CSAIL does not support this.)
A Fully-Qualified Domain Name is a Domain Name which includes a complete sequence of names all the way to the top level. For example, the FQDN of the
WebDNS server itself is
webdns.csail.mit.edu. All of the places where
WebDNS wants a host name
must be Fully-Qualified Domain Names. (As mentioned above, domain names may represent the root either explicitly, as a trailing "
.", or implicitly. When using the "Edit Raw Records" function, the root must always be explicit; in the main interface,
WebDNS will handle this for you as needed. This document will not describe the "Edit Raw Records" interface.)
Choosing a Host Name
WebDNS enforces no restrictions on the host names that you use, beyond
ensuring that the syntax is valid. You may choose any name you want,
provided that it consists only of letters, numbers, dots, and
hyphens. However, we offer the following guidelines to aid your
choice:
- Do check your group for a standard naming scheme. If most of the other machines in your group are named after French Impressionists, then you should probably do likewise.
- Do give similar names to machines which are part of a natural grouping such as a cluster.
- Don't use names which would be considered offensive.
- Don't use names which would cause undue confusion; if there's already a machine called "tobasco", you probably shouldn't call your machine "tabasco".
- Don't give workstations names which represent their current user or location. People move, and so do machines; the next user will thank you for your courtesy in naming.
Registering Your Host
Once you've selected a host name, you can create a DNS entry for your
machine. This will give you a static IP address for the computer. We
recommend that all machines belonging to CSAIL have a static IP
address registered on a network which is appropriate for the use to
which they are put; if you use our standard Linux or Windows
configurations, you will be required to do so. If your system has a
wired Ethernet network interface, then it should have an address on
the network which is used in your work space. If you have more than
one network interface (e.g., both wired and wireless), you will still
be able to use both, but you may only have a static assignment on one
network.
You will need CSAIL certificates to access
WebDNS. We
recommend that you access
WebDNS from a machine on the network your
new machine will be using—if the new system is already up and
running, it will make things easier if you run use a browser on that
machine. (This will allow
WebDNS to automatically figure out which
network you are on.) If you have certificates installed, you should
see a screen that looks like the following:
Enter the new host name you selected in the input box (I've used
example.csail.mit.edu here) and select
Add. If your name is
already taken, you'll get an error message along with a listing of the
records associated with that name. Otherwise, you'll need to choose a
network on the next screen, which looks like this:
The pull-down menu includes a list of all the networks
WebDNS knows
about. It's important to set this correctly; if you are running
WebDNS from the same network as the new machine will be on, it should
be correct by default. Otherwise, you'll have to figure out which
network you need from the menu. If you're having trouble, ask
help@csail for assistance. Ignore the
field that says
Or enter a netblock in CIDR notation. When you
click the
Submit button,
WebDNS will search the network you selected
for an available IP address and tentatively offer it to you. The next
screen is used both when adding a new host and also when editing an
existing entry:
Do not change the IP address assigned to you by WebDNS unless a
staff member explicitly directs you to do so. If you are currently
using a dynamic address, you
may not reserve that particular address
as a static IP; it belongs to the DHCP server. The address that
WebDNS gives you is guaranteed to be available for static assignment.
You may add as many aliases (
Nicknames or "CNAME records") as you
need. Aliases are considered host names, just like the official name,
and must conform to the same rules. If you need more fields for
aliases, you'll be able to add additional ones later. You should not
enter
Mail Exchangers. When you select
Commit Changes, if all
goes well, you'll see a display similar to the following:
The "change log" information is also mailed to system administrators.
If you do something that seems like a mistake, a sysadmin may contact
you to make sure that was what you really intended.
Propagation Time
All
WebDNS updates should be reflected in the DNS servers at half past
the hour after the change was made. That is to say, if you make a
change at 11:25, the servers will see the new information at 12:30.
However, DNS data may be cached up to four hours (depending on
lots of factors) at servers around the Internet. So, to use the same
example, if your update still hasn't shown up everywhere after 4:30,
you should ask for help.
Editing an Existing Registration
Editing data in
WebDNS uses the same display as adding a new host.
There will always be three more entry fields in each section of the
display than are currently needed; this allows you to add as many
aliases and mail exchangers as you need, incrementally.
Renaming a Host
Renaming a host in
WebDNS is nearly trivial. However, your machine
has its own idea of what its name is, and this needs to be updated at
the same time as you rename it. Contact
help@csail for assistance in renaming
Windows or CSAIL Debian machines.
You need to decide whether the old name should be kept around as an
alias. If there are likely to be people depending on the old name,
then you should keep it. If, on the other hand, the system is going
to be completely repurposed, then there's no point in keeping the old
name around; it will probably just confuse people.
The rename screen looks like this:
When you select
Confirm, if the new name you have requested is
available, you'll get a confirmation message like this:
Otherwise, you'll need to find another name.
Deleting a Registration
When a host is no longer being used, it should be deleted from the DNS
to allow someone else to use that name and IP address. You should
look over the DNS information shown in the confirmation screen:
If this looks like what you meant to delete, then select
Confirm and
your host name registration is history.
--
GarrettWollman - 15 Sep 2005
