3 Replies Latest reply: Aug 11, 2019 4:15 AM by Juergen Ilse CCNA R&S RSS

    Packet Tracer: Set up DNS-server for forwarding a request

    Hans

      Hello,

       

      in Cisco Packet Tracer (7.0.0.0202) I would like to have a DNS-server that aks another DNS-server if he doesn't know a requested domain name. Just like in reality.

       

      All I found was a video on Youtube where somebody seems to have managed this: https://www.youtube.com/watch?v=ocPkHyuPo_0 Warning! Annoying sound in the beginning of the video!

       

      (The Video ist just about how DNS forwarding works in general, not about how he did this with Packet Tracer. However it seems to work: In 1:08 the second Server doesn't know the domain name, in 2:14 it seems to have learned the name through the request to the first Server)

       

      Does anyone know how to configure one DNS-server to forward a request?

       

      Thanks a lot!

        • 1. Re: Packet Tracer: Set up DNS-server for forwarding a request
          Les

          Hi there,

           

          I know this thread is getting a bit old but I was searching for the same solution and managed to make multiple DNS servers work in Packet Tracer as requested.   

           

          You need to add some records to the DNS servers that point them to the next server (up the tears).  Those being an “NS” record that then points to the “A Record” for the next server.  I created an NS record type buy the name of “com” that pointed to “root”.  “root” is an “A Record” that then points to the next DNS server IP address.  

           

          I would like to attach a packet tracer sample for you to see, but I am unable to attach the file to this message.  As such, pics will have to do. 


          The servers on the internet switch are all separate networks separated by different VLANS, so for each server communication it always has to go back though the router Router1 thus simulating many routers quickly and easily for this simple purpose.   


          Topology.JPG

           

          01 - DNS Local.JPG

          02 - DNS Web1.JPG

          03 - DNS Web2.JPG

          04 - DNS Web3.JPG


          I am by no means an expert but this solution seems to work.  If you open a web browser on PC0 and head to www.pt.com the page should open.  Not only that, when you then check the DNS servers, you will also notice that their cache also have the details.  

           

          There is also an example on packet tracer itself (in the PacketTracer\saves\server\DNS folder named: Multilevel_DNS.pkt) that goes into the setting in a bit more depth.  If anyone else has any suggestions, buy all means let me know. 

           

          Lastly, I did find a video…. Got about 5 mins in but for those who are willing to persevere… it may be worth a look.  https://www.youtube.com/watch?v=JmWu2jYQSXw

           

          Hope this is of help to someone. 

           

          Les

          • 2. Re: Packet Tracer: Set up DNS-server for forwarding a request
            Joshua

            worked for me, Les.  Thank you!

            • 3. Re: Packet Tracer: Set up DNS-server for forwarding a request
              Juergen Ilse CCNA R&S

              Les schrieb:

               

              Hi there,

               

              I know this thread is getting a bit old but I was searching for the same solution and managed to make multiple DNS servers work in Packet Tracer as requested.   

               

              You need to add some records to the DNS servers that point them to the next server (up the tears).  Those being an “NS” record that then points to the “A Record” for the next server.  I created an NS record type buy the name of “com” that pointed to “root”.  “root” is an “A Record” that then points to the next DNS server IP address.  

              Your NS record points to a name, for which you have an A record, that points to the IP address of the authoritative server for the other domain (in your case TLD .com). A NS record can only point to a hostname, not directly to an IP address. If you want to forward *all* requests for "non local names" to the same other DNS server, you may add a NS record for the domain "." (that is the root of the DNS system). In the internet, there are 13 root nameservers, which are authoritative for the domain ".". Those DNS Zone for domain "." includes the NS records for all TLDs (.com, .net, .org, .de, .us, ...) and the A records for the corresponding DNS servers for all that domains. The DNS servers for a TLD contain the NS records for the second level subdomains or maybe A records for hosts in a subdomain of that TLD, if there is no delegation for that subdomain in the TLD zone. Same for that subdomains. So every DNS server, that "knows" the DNS servers for the Domain "." can search the complete DNS tree, even if that complete tree is distributed over hundreds and thousands of DNS servers all over the world. On a real DNS server, there is a "cache zone" configured, that includes the delegation for the "." domain to the 13 root nameservers.

              Les schrieb:

               

              Hi there,

               

              I know this thread is getting a bit old but I was searching for the same solution and managed to make multiple DNS servers work in Packet Tracer as requested.   

               

              You need to add some records to the DNS servers that point them to the next server (up the tears).  Those being an “NS” record that then points to the “A Record” for the next server.  I created an NS record type buy the name of “com” that pointed to “root”.  “root” is an “A Record” that then points to the next DNS server IP address.  

               

              Topology.JPG

              It is not necessary, that all DNS servers are in different networks, but in the internet, this is usually the case. The routing is completely independent from DNS infrastructure, but it has to be setup, so that the DNS servers could reach each other to make the DNS system work.


              01 - DNS Local.JPG

              02 - DNS Web1.JPG

              03 - DNS Web2.JPG

              04 - DNS Web3.JPG

              thanks for this example in packet-tracer. But i would tend to change that example in a way, that the delegation is made for domain "." instead of "com" (if that is possible in packet-tracer, but i haven't tried it) to simulate a root nameserver ... Maybe it is possible to add a NS record for the empty domainname (which is in fact the domain ".").

              Hope, this helps to understand the DNS system a little bit better.