CS475 – Networks
Lecture 26
Chapter 9: Applications
Announcements and Reminders:
• No class on Thursday - work on final project, final exam review sheet posted
• Homework 8 due next Tuesday at the beginning of class for final exam review, final project due Friday, December 9
9.3 Infrastructure Services
Some essential protocols do not fit into the layered networking
addresses
model. These protocols are are necessary for the smooth running Simple Network Management Protocol (SNMP) for managing
of the Internet. Two such protocols are:
network infrastructure
Domain Name System (________) for mapping host names to IP
9.3.1 Name Service (DNS)
All IP packets contain source and destination IP addresses (32 bit Typically a user gives an
binary numbers). Host names however are much more user-
application a host name.
friendly than IP addresses.
The application calls name
Originally name-to-address bindings were contained in a file
resolution routines to
called ______________ that was maintained by the Network
translate the name to an IP
Information Center (NIC). The Domain Name System (DNS)
address.
was introduced in the 1980's.
The application then opens a connection to the destination using
the IP address.
9.3.1 Name Service (DNS) - Domain Hierarchy
DNS uses a ________________________ namespace. Names
are processed from right to left and use a period as a separator.
Domain Hierarchy
9.3.1 Name Service (DNS) - Name Servers
The name hierarchy is partitioned into subtrees called
Zones contain two or more (for redundancy) name servers.
______________. The top-level zone is managed by the Internet Name servers contain all of the information for the
Corporation for Assigned Names and Numbers (ICANN).
corresponding zone. Each name server runs a program
(__________________ or Microsoft DNS for example) that is
accessed over the Internet.
DNS clients send queries to name servers. The server can
respond with either the requested information or a pointer to
another DNS server.
Zones Contain Name Servers
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DNS entries are a 5-tuple known as a ____________________
record:
<Name, Value, Type, Class, TTL>
The Name is the host name. The Value depends on the Type. If
Type=A, Value is the IP address. If Type=NS, Value contains
the name of a name server that can answer the query. If
Type=CNAME, Value is an alias. If Type=MX, Value contains
the name of the mail server for the domain.
DNS viewed (more accurately) as
The Class field was intended to allow other than Internet related
a hierarchy of name servers
entries. The only widely used Class is ____________.
The TTL is used by servers that cache resource records. The
server should purge the record from the cache when the TTL
expires.
A ______________ name server would contain NS and A
A ______________ server (for the EDU domain for example)
records for all top-level domains (TLDs):
would contain entries of the form:
<edu, a3.nstld.com, NS, IN>
<a3.nstld.com, 192.5.6.32, A, IN>
<com, a.gtld-servers.net, NS, IN>
<a.gtld-servers.net, 192.5.6.30, A, IN>
(For simplicity the TTL field is omitted in the examples.)
<bigu.edu, dns.bigu.edu, NS, IN>
<dns.bigu.edu, 128.112.129.15, A, IN>
<evansville.edu, ns1.evansville.edu, NS, IN>
<ns1.evansville.edu, 208.94.148.4, A, IN>
The bigu.edu name server might contain entries of the form:
<bigu.edu, email.bigu.edu, MX, IN>
Similarly a departmental level name server might contain entries
of the form:
<email.bigu.edu, 128.112.198.35, A, IN>
<pluto.cs.bigu.edu, 128.112.136.20, A, IN>
<www.bigu.edu, webserver.bigu.edu,CNAME,IN>
<neptune.cs.bigu.edu, 128.112.136.21, A, IN>
<webserver.bigu.edu, 128.112.198.40,A,IN>
<cs.bigu.edu, mail.cs.bigu.edu, MX, IN>
<cs.bigu.edu,dns1.cs.bigu.ednu,NS,IN>
<mail.cs.bigu.edu, 128.112.136.72, A, IN>
<dns1.cs.bigu.edu, 128.112.136.10, A, IN>
<www.cs.bigu.edu,core.cs.bigu.edu,CNAME,IN>
<core.cs.bigu.edu, 128.112.136.35,A,IN>
<cs.bigu.edu,dns1.cs.bigu.edu,NS,IN>
<dns1.cs.bigu.edu, 128.112.136.10, A, IN>
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9.3.1 Name Service (DNS) - Name Resolution
If a client needs to resolve pluto.cs.bigu.edu, it could send a
(A client is usually configured with a default domain. The
_______________ to the root server. The root server would
default domain is appended to simple names before the query
respond with the NS and A records of the edu name server.
goes out, e.g., csserver becomes csserver.evansville.edu.)
The client could then query the edu server which would respond
with the NS and A records of the bigu server and so on, until the
cs.bigu.edu server responds with the desired IP address.
In practice, a client queries a local name server first. The IP
address of a local name server is configured manually or via
__________________.
Local servers cache responses. This allows them to respond to
future requests for information without going out on the
network.
9.3.2 Network Management (SNMP)
Managing even a moderately sized network is no easy task. The SNMP can return information on the System (uptime, name),
Simple Network Management Protocol (SNMP) allows a
Interfaces (MAC addresses, packets transferred), ARP table, IP
network administrator to read and write information to different (routing table), TCP (number of connections, timeouts), UDP
network nodes.
(number of datagrams).
An SNMP _______________ runs on each node and responds to There are several commercial and open source network
requests from an SNMP client.
management clients that are available. ________________ is
popular among the open source crowd.
In Class Exercise
Use the whois command to query the registration database for
Use the dig command to query DNS for the IP address of
contact and name server information for the evansville.edu
www.evansville.edu. Use dig to find the name and IP address of
domain.
the mail server for the evansville.edu domain (query for the MX
record).
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