Lecture 26
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Announcements:
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Final Exam is Wednesday, December 14, 8am10am. Review sheet is posted.
Reminders:
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No class on Thursday. Work on final project.
Homework 8 due next Tuesday at the beginning of
class for final exam review.
Final project due Friday, December 9.
Questions?
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Outline
Chapter 9 - Applications
9.1 Traditional Applications
9.2 Multimedia Applications
9.3 Infrastructure Services
9.4 Overlay Networks
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Infrastructure Services
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Some essential protocols do not fit into the
layered networking model. These protocols are
are necessary for the smooth running of the
Internet. Two such protocols are:
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Domain Name System (DNS) for mapping
host names to IP addresses
Simple Network Management Protocol
(SNMP) for managing network infrastructure
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Name Service (DNS)
All IP packets contain source and destination IP
addresses (32 bit binary numbers). Host names
however are much more user-friendly than IP
addresses.
Originally name-to-address bindings were
contained in a file called hosts.txt that was
maintained by the Network Information Center
(NIC). The Domain Name System (DNS) was
introduced in the 1980's.
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Name Service (DNS)
Typically a user gives
an application a host
name. The application
calls name resolution
routines to translate
the name to an IP
address.
The application then opens a connection to the
destination using the IP address.
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Name Service (DNS)
Domain Hierarchy
DNS uses a hierarchical namespace. Names are
processed from right to left and use a period as a
separator.
Domain Hierarchy
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Name Service (DNS)
Name Servers
The name hierarchy is partitioned into subtrees
called zones. The top-level zone is managed by
the Internet Corporation for Assigned Names and
Numbers (ICANN).
Zones Contain Name Servers
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Name Service (DNS)
Name Servers
Zones contain two or more (for redundancy) name
servers. Name servers contain all of the
information for the corresponding zone. Each
name server runs a program (BIND 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.
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Name Service (DNS)
Name Servers
DNS viewed (more accurately) as
a hierarchy of name servers
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Name Service (DNS)
Name Servers
DNS entries are a 5-tuple known as a resource
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.
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Name Service (DNS)
Name Servers
The Class field was intended to allow other than
Internet related entries. The only widely used
Class is IN.
The TTL is used by servers that cache resource
records. The server should purge the record from
the cache when the TTL expires.
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Name Service (DNS)
Name Servers
A root name server would contain NS and A
records for all top-level domains (TLDs):
<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.)
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Name Service (DNS)
Name Servers
A TLD server (for the EDU domain for example)
would contain entries of the form:
<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>
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Name Service (DNS)
Name Servers
The bigu.edu name server might contain entries
of the form:
<bigu.edu, email.bigu.edu, MX, IN>
<email.bigu.edu, 128.112.198.35, A, IN>
<www.bigu.edu, webserver.bigu.edu,CNAME,IN>
<webserver.bigu.edu, 128.112.198.40,A,IN>
<cs.bigu.edu,dns1.cs.bigu.ednu,NS,IN>
<dns1.cs.bigu.edu, 128.112.136.10, A, IN>
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Name Service (DNS)
Name Servers
Similarly a departmental level name server might
contain entries of the form:
<pluto.cs.bigu.edu, 128.112.136.20, A, IN>
<neptune.cs.bigu.edu, 128.112.136.21, A, IN>
<cs.bigu.edu, mail.cs.bigu.edu, MX, IN>
<mail.cs.bigu.edu, 128.112.136.72, 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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Name Service (DNS)
Name Resolution
If a client needs to resolve pluto.cs.bigu.edu, it
could send a query to the root server. The root
server would respond with the NS and A records
of the edu name server.
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.
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Name Service (DNS)
Name Resolution
In practice, a client queries a local name server
first. The IP address of a local name server is
configured manually or via DHCP.
Local servers cache responses. This allows them
to respond to future requests for information
without going out on the network.
(A client is usually configured with a default
domain. The default domain is appended to
simple names before the query goes out, e.g.
csserver becomes csserver.evansville.edu.)
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Name Service (DNS)
Name Resolution
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Network Management (SNMP)
Managing even a moderately sized network is no
easy task. The Simple Network Management
Protocol (SNMP) allows a network administrator
to read and write information to different network
nodes.
An SNMP server runs on each node and
responds to requests from an SNMP client.
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Network Management (SNMP)
SNMP can return information on the System
(uptime, name), Interfaces (MAC addresses,
packets transferred), ARP table, IP (routing table),
TCP (number of connections, timeouts), UDP
(number of datagrams).
There are several commercial and open source
network management clients that are available.
Nagios is popular among the open source crowd.
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In-class Exercise
Use the whois command to query the registration
database for contact and name server information
for the evansville.edu domain.
Use the dig command to query DNS for the IP
address of www.evansville.edu. Use dig to find
the name and IP address of the mail server for the
evansville.edu domain (query for the MX record).
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