2. cnp3-ebook
3. exercises/dns
4. English
5. Browse

1 / 2

/ 2

All strings

• Untranslated strings • state:empty
• Unfinished strings • state:<translated
• Translated strings • state:>=translated
• Strings marked for edit • state:needs-editing
• Strings with suggestions • has:suggestion
• Strings with variants • has:variant
• Strings with labels • has:label
• Strings with context • has:context
• Unfinished strings without suggestions • state:<translated AND NOT has:suggestion
• Strings with comments • has:comment
• Strings with any failing checks • has:check
• Approved strings • state:approved
• Strings waiting for review • state:translated

Target string

• Position and priority
• Position
• Priority
• Labels
• Source string
• Target string
• String age
• Number of words
• Number of comments
• Number of failing checks
• Key

	English
	You may obtain additional information about the root DNS servers from http://www.root-servers.org
	where
	When run without any parameter, `dig` queries one of the root DNS servers and retrieves the list of the names of all root DNS servers. For technical reasons, there are only 13 different root DNS servers. This information is also available as a text file from http://www.internic.net/zones/named.root. What are the IPv6 addresses of all these servers?
	When `dig` is run, the header section in its output indicates the `id` the DNS identifier used to send the query. Does your implementation of `dig` generates random identifiers ?
	When a client requests the mapping of a domain name into an IP address to its local resolver, the resolver may need to query a large number of nameservers starting from the root nameserver. The three exercises below show packet traces collected while the resolver was resolving the following names: `www.example.com`, `www.google.com` and `www.computer-networking.info`. If you understand how the DNS operates, you should be able to correctly reorder those packet traces.
	What is the lifetime associated to this IPv6 address ?
	What is the IPv6 address that corresponds to `www.computer-networking.info` ? Which type of DNS query does `dig` send to obtain this information ?
	What are the nameservers that are responsible for the `info` top-level domain ? Is it possible to use IPv6 to query them ?
	What are the IP addresses of the resolvers that the `dig` implementation you are using relies on [#fdig]_ ?
	Use `dig` to send a query to one of these root servers to find the IPv6 address of the DNS server(s) (NS record) responsible for the `org` top-level domain
	Use `dig` to send a query to one of these DNS servers to find the IP address of the DNS server(s) (NS record) responsible for `root-servers.org`
	Use `dig` to find the mail relays used by the `uclouvain.be` and `student.uclouvain.be` domains. What is the `TTL` of these records ? Can you explain the preferences used by the `MX` records. You can find more information about the MX records in :rfc:`5321`.
	`type` is the type of DNS record that is requested by the query such as `NS` for a nameserver, `A` for an IPv4 address, `AAAA` for an IPv6 address, `MX` for a mail relay, ...
	This is an unpolished draft of the third edition of this e-book. If you find any error or have suggestions to improve the text, please create an issue via https://github.com/CNP3/ebook/issues?milestone=5 or help us by providing pull requests to close the existing issues.
	The next three questions ask you to go one step further by predicting the values of specific fields in the DNS messages.
	The Domain Name System (DNS) plays a key role in the Internet today as it allows applications to use fully qualified domain names (FQDN) instead of IPv4 or IPv6 addresses. When using the DNS, it is important to remember the role of the different types of DNS records.
	The DNS protocol can run over UDP and over TCP. Most DNS servers prefer to use UDP because it consumes fewer resources on the server. However, TCP is useful when a large answer is expected. Compare `time dig +tcp` and `time dig` to query a root DNS server. Is it faster to receive an answer via TCP or via UDP ?
	The DNS
	Several software tools can be used to send queries to DNS servers. For this exercise, we use dig_ which is installed on most Unix/Linux systems.
	`server` is the IP address or the name of a DNS server or resolver