DNS
What is the model that DNS is based on?
DNS is based on the client server model. each DNS server can also be a DNS client. When a DNS server cannot find a client, it makes a request to the next highest level in the hierarchy
distributed?
could have on centralized DNS server but would not scale
what is the local DNS server?
each ISP has a local DNS server
How does DNS work?
gethostbyname() function call that an application calls in order to perform translation of hostname to IP
IP address
hosts identified by IP address consists of four bytes and has a rigid hierarchical structure (more detailed as we go from left to right) 0-255.0-255.0-255.0-255
how is the hierarchy organized
root -> top level domain (i.e. .edu)-> authoritative
How do you map between IP address and name and vide versa
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describe an example of a dns query
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how can I determine the local DNS server
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how does DNS caching reduce query traffic
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suppose the host cis.poly.edu desires teh IP address of gaia.cs.umass.edu
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What happens when you request the URL www.someschool.edu/index.html
2. browser extracts the hostname www.someshit.edu from the url and passes the hostname to the client side of the DNS application 3. DNS client sends query containing the hostname to a DNS server 4. DNS client eventually receives a reply includes the IP address for the hostname 5. once the browser receives the IP address from the DNS, it will initiate a TCP connection to the HTTP server located at port 80 at that IP address
Why is there a world wide collection of DNS servers
At the top level of the hierarchy, so-called root servers store the complete database of Internet domain names and their corresponding IP addresses. There are 13 servers.
how is the DNS a type of distributed system?
Busy sites such as cn.com are replicated over multiple servers, with each server running on a different end system and each having a different IP address.
recursive vs. iterative
If the query is recursive, the resolver expects the address back without performing any other work. If it is iterative, the DNS server returns an address where the address might be found, if it does not hold the address itself. It is up to the resolver whether to contact that address, or whether to work its way through its own list of DNS servers.
DNS is a distributed system. Why?
It's a hierarchy where each level only stores a subset of the total internet domain names. These lesser DNS are bought by ISP
How do you identify a website?
Through an IP address and a name
hostnames
names that are used by humans to id the Internet hosts. Not very useful because it doesn't provide location within the Internet of the host
distributed dns?
no single server has all of the mappings for all of the hosts in the Internet. Instead, the mappings are distributed across the DNS servers.
Hi My Name is 132-67-9875
please meet my husband 178-87-1146
DNS
runs over UDP
What is the different models of requesting DNS results
the recursive dns utilizes the root dns as a center of contact while the iterative dns utilizes the local dns as a center of contact
DNS
translate between router readable IP address and human readable hostnames.