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.