| 1 | Building a DNS cache with BIND |
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| 2 | ------------------------------ |
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| 3 | |
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| 4 | 1. Check the version of BIND which is installed |
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| 5 | ----------------------------------------------- |
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| 6 | |
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| 7 | $ named -v |
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| 8 | BIND 9.x.x |
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| 9 | |
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| 10 | (you could also do: dig chaos txt version.bind @10.10.X.1) |
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| 11 | |
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| 12 | 2. Configure your AUTH1 host to accept queries from neighbors |
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| 13 | ------------------------------------------------------------- |
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| 14 | |
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| 15 | Log in to your AUTH1 host if you haven't already done so |
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| 16 | (auth1.grpX.dns.nsrc.org). |
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| 17 | |
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| 18 | ssh adm@10.10.X.1 |
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| 19 | |
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| 20 | Become root |
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| 21 | |
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| 22 | sudo bash |
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| 23 | |
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| 24 | Edit the file /etc/namedb/named.conf (using vi or ee) |
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| 25 | |
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| 26 | If it still exsist, find the line: |
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| 27 | |
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| 28 | listen-on { 127.0.0.1; }; |
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| 29 | |
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| 30 | ... and REMOVE. |
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| 31 | |
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| 32 | Remove or comment out the line |
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| 33 | |
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| 34 | recursion no; |
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| 35 | |
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| 36 | Add the following line: |
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| 37 | |
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| 38 | allow-recursion { 127.0.0.1; 10.10.0.0/16; }; |
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| 39 | |
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| 40 | Double check to see that there aren't any zones configured in your |
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| 41 | DNS. For instance, if you see a line like follows: |
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| 42 | |
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| 43 | zone "10.in-addr.arpa" { type master; file "/etc/namedb/master/empty.db"; }; |
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| 44 | |
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| 45 | ... remove them |
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| 46 | |
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| 47 | BUT leave |
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| 48 | |
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| 49 | zone "." { |
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| 50 | type hint; |
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| 51 | file "/etc/namedb/named.root"; |
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| 52 | }; |
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| 53 | |
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| 54 | and save the file. |
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| 55 | |
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| 56 | |
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| 57 | NOTE: Be careful about the semicolons ';' and braces { } - BIND |
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| 58 | will complain if they are not placed correctly |
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| 59 | |
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| 60 | By removing the line "listen-on ..." and adding the line |
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| 61 | "allow-recursion", we are telling BIND: |
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| 62 | |
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| 63 | - please listen to the network for queries, not only on |
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| 64 | the local interface "127.0.0.1"; |
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| 65 | |
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| 66 | - please allow clients in the 10.10.0.0/16 to send queries |
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| 67 | to me, as well as myself; |
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| 68 | |
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| 69 | 3. Restart the cache and check it is running |
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| 70 | -------------------------------------------- |
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| 71 | |
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| 72 | If you haven't done so earlier, edit `/etc/rc.conf` and add two lines saying: |
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| 73 | |
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| 74 | named_chrootdir="" |
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| 75 | named_enable="YES" |
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| 76 | |
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| 77 | NOTE: We would normally not turn off chroot, which is a security |
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| 78 | mechanism, but we need to do this here in the lab, because of |
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| 79 | restrictions from the virtualization environment. In a production |
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| 80 | environment, we wouldn't do this. |
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| 81 | |
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| 82 | Then run these commands: |
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| 83 | |
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| 84 | # service named stop |
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| 85 | # service named start |
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| 86 | # ps auxwww | grep named |
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| 87 | # tail /var/log/messages |
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| 88 | |
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| 89 | Check for successful startup with no error messages (you can ignore errors |
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| 90 | about missing `master/localhost.rev` and `master/localhost-v6.rev`, as well |
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| 91 | as messages regarding managed-keys-zone) |
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| 92 | |
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| 93 | 4. Test resolution |
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| 94 | ------------------ |
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| 95 | |
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| 96 | Issue a query, for instance: |
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| 97 | |
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| 98 | $ dig @127.0.0.1 google.com NS |
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| 99 | $ dig @127.0.0.1 noc.ws.nsrc.org A |
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| 100 | |
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| 101 | For each query: |
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| 102 | |
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| 103 | 1. Is the server responding ? |
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| 104 | 2. How do you know that you are talking to your OWN server ? |
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| 105 | 3. What do you notice ? |
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| 106 | |
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| 107 | If your neighbour has got their cache working, then try sending some queries |
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| 108 | to their cache: |
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| 109 | |
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| 110 | $ dig @10.10.Z.1 somedomain.name |
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| 111 | |
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| 112 | ... where ZZZ is the group number of your neighbour |
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| 113 | and "somedomain.name" is the query you would like to perform. |
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| 114 | |
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| 115 | Try and make some of the same queries you did before. |
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| 116 | Do the nameservers of the other machines answer you ? |
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| 117 | |
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| 118 | Are you getting answers ? What about for dns.nsrc.org ? |
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| 119 | |
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| 120 | Why ? |
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| 121 | |
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| 122 | Help your neighbours to get their cache working if required. |
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| 123 | |
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| 124 | 5. Watch the cache in operation |
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| 125 | ------------------------------- |
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| 126 | |
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| 127 | You can take a snapshot of the cache contents like this: |
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| 128 | |
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| 129 | # ln -s /var/named/var/dump /var/dump |
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| 130 | # rndc dumpdb |
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| 131 | # less /var/named/var/dump/named_dump.db |
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| 132 | |
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| 133 | (Don't do this on a busy cache - you will generate a huge dump file!) |
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| 134 | |
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| 135 | You can watch the cache making queries to the outside world using |
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| 136 | `tcpdump` in a different window (log in again via SSH): |
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| 137 | |
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| 138 | # tcpdump -n -s1500 -i eth0 udp port 53 |
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| 139 | |
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| 140 | If your ethernet interface isn't named `eth0`, then use the name of |
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| 141 | your ethernet interface - e.g. `em0` or `bge0` - run "ifconfig" to find out |
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| 142 | what your ethernet interface is named. CTRL-C to exit tcpdump. |
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| 143 | |
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| 144 | While tcpdump is running, in the first window flush your cache (so it forgets |
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| 145 | all existing data) and then issue some queries from another window. |
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| 146 | |
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| 147 | # rndc flush |
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| 148 | # dig @127.0.0.1 noc.ws.nsrc.org. -- and watch tcpdump output. What do you see? |
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| 149 | |
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| 150 | # dig @127.0.0.1 noc.ws.nsrc.org. -- watch tcpdump again. This time? |
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| 151 | |
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| 152 | NOTE: that we now have enabled BIND to be recursive! So we will want |
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| 153 | to remember this, and maybe turn off recursion later, since we have |
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| 154 | explained that running recursive and authoritative on the same server |
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| 155 | is not a good idea. |
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| 156 | |
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| 157 | From named.conf remove: |
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| 158 | |
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| 159 | # allow-recursion { 127.0.0.1; 10.10.0.0/16; }; |
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| 160 | |
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| 161 | and add: |
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| 162 | |
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| 163 | # recursion no; |
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| 164 | |
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| 165 | close the editor and restart the server: |
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| 166 | |
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| 167 | # service named restart |
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| 168 | |
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