Question

2. The dig command can be used to obtain information from the DNS records for a giver domain name or IP address. What is the output for the following commands and what is the difference between them? a. dig www.cs.csub.edu b. dig soa www.cs.csub.edu 3. You are getting probes from some host in the 209.9.244.* (Class C) network. Which of the following commands will find the Start of Authority record for that network (the answer section will have an authority server that is NOT a root name server)? a. dig soa 224.9.209.in-addr.arpa b. dig soa 209.9.224 4. You are attempting to connect to ftp. foo.com and get the error message: -unknown host ftp.foo.com What is the likely problem and what commands would you use to investigate the problem?

Answer 1

Answer 2)

dig www.cs.csub.edu command will find the IP address for the given domain name and returns the IP address. Along with that it also provides listed nameservers and information about them in the authority and additional section respectively.

dig soa www.cs.csub.edu command will return the start of authority information for the domain name.DNS records details for the respective domain name will be given by authority section. It will not give IP address but list any alias names and omission will happen if there is no domain name.

Answer 3)

Option no.a will find the start of the authority record. As one cannot use IP address directly by default while using dig and option a specifies the address in proper notation.

Answer 4)

It regards issue with looking up the domain name ftp.foo.com. To investigate the problem, first we should use dig to see if IP address is listed or not. If the IP address for the domain name is missing then you should get a dig response with an authority section for the root domain which indicates whether foo.com existed. If dig does not have any of this information that means the nameservers are down. Namesevers can be checked by pinging.

If dig does respond with authority section for foo.com, then check foo.com nameservers. It can be done by using foo.com or whois foo.com. Now, ping the nameservers and if they are still down then retry it later. If all nameservers are up and problem still persists then it is an invalid domain name.

Answer 5)

In this case, DNS is working properly, we have successfully got the IP address for ftp.foo.com but we are timing out connecting to the IP address.

The cause of this issue is routing issues or any kind of interference connecting to FTP port. These interference can be because of no FTP service running in the machine, firewall blocking connection to the FTP port. Sometimes it also because of the traffic in the server.

Routing issues can be investigated by using ping and traceroute to check if server is up and to check the route from you to server respectively.