Agenda: dns-bind-caching-setup.txt

Building a DNS cache with BIND
------------------------------

1. Check the version of BIND which is installed
-----------------------------------------------

    $ named -v
    BIND 9.x.x



2. Configure your AUTH1 host to accept queries from neighbors
-------------------------------------------------------------

Log in to your AUTH1 host if you haven't already done so
(auth1.grpX.ws.nsrc.org).

Edit the file /etc/namedb/named.conf (using vi or ee)

If it still exsist, find the line:

        listen-on       { 127.0.0.1; };

... and REMOVE it.

Add the following line:

        allow-recursion { 127.0.0.1; 10.10.0.0/16; };

Double check to see that there aren't any zones configured in your
DNS. For instance, if you see a line like follows:

        zone "10.in-addr.arpa"     { type master; file "/etc/namedb/master/empty.db"; };

... remove it, and save the file.


NOTE: Be careful about the semicolons ';' and braces { } - BIND
will complain if they are not placed correctly

By removing the line "listen-on ..." and adding the line
"allow-recursion", we are telling BIND:

- please listen to the network for queries, not only on
  the local interface "127.0.0.1";

- please allow clients in the 10.10.0.0/16 to send queries
  to me, as well as myself;

3. Restart the cache and check it is running
--------------------------------------------

If you haven't done so earlier, edit `/etc/rc.conf` and add two lines saying:

        named_chrootdir=""
        named_enable="YES"

NOTE: We would normally not turn off chroot, which is a security
      mechanism, but we need to do this here in the lab, because of
      restrictions from the virtualization environment. In a production
      environment, we wouldn't do this.

Then run these commands:

    $ sudo service named stop
    $ sudo service named start
    # ps auxwww | grep named
    # tail /var/log/messages

Check for successful startup with no error messages (you can ignore errors
about missing `master/localhost.rev` and `master/localhost-v6.rev`, as well
as messages regarding managed-keys-zone)


4. Reconfigure your resolver to use your own cache only
-------------------------------------------------------

If you haven't done so earlier, edit `/etc/resolv.conf` as follows
(remember to use sudo !)

Remove any existing 'nameserver' lines, or comment them out by inserting '#'
at the front. 127.0.0.1 is the loopback address; that is, an IP address
which means 'send the packet to myself', and we'll use it as our nameserver:

    search ws.nsrc.org
    nameserver 127.0.0.1

Now save and exit.

5. Test resolution
------------------

Issue a query, for instance:

        $ dig google.com NS
        $ dig noc.ws.nsrc.org A

For each query:

1. Is the server responding ?
2. How do you know that you are talking to your OWN server ?
3. What do you notice ?

If your neighbour has got their cache working, then try sending some queries
to their cache:

    $ dig @10.10.X.1 somedomain.name

... where XXX is the IP of the machine in the class you want to send the
query to, and "somedomain.name" is the query you would like to perform.

Try and make some of the same queries you did before.  Do the nameservers
of the other machines answer you ?

Are you getting answers ? What about for ws.nsrc.org ?

Why ?

Help your neighbours to get their cache working if required.

6. Make sure you can resolve hostnames in the class
---------------------------------------------------

Ping other PCs in the room, where X is 1-32:

    $ ping auth1.grpX.ws.nsrc.org
    $ ping resolv.grpX.ws.nsrc.org
    $ ping auth2.grpX.ws.nsrc.org


7. Watch the cache in operation
-------------------------------

You can take a snapshot of the cache contents like this:

    $ sudo ln -s /var/named/var/dump /var/dump
    $ sudo /usr/sbin/rndc dumpdb
    $ sudo less /var/named/var/dump/named_dump.db

(Don't do this on a busy cache - you will generate a huge dump file!)

You can watch the cache making queries to the outside world using
`tcpdump` in a different window (log in again via SSH):

    # tcpdump -n -s1500 -i eth0 udp port 53

If your ethernet interface isn't named `eth0`, then use the name of
your ethernet interface - e.g. `em0` or `bge0` - run "ifconfig" to find out
what your ethernet interface is named.

While tcpdump is running, in the first window flush your cache (so it forgets
all existing data) and then issue some queries.

    # rndc flush
    # dig noc.ws.nsrc.org.   -- and watch tcpdump output. What do you see?

    # dig noc.ws.nsrc.org.   -- watch tcpdump again. This time?

NOTE: that we now have enabled BIND to be recursive! So we will want
to remember this, and maybe turn off recursion later, since we have
explained that running recursive and authoritative on the same server
is not a good idea.