Transcript Document

Overview
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» Internet Protocols (2)
» Source: chapter 15
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» Internet Protocols (3)
» Source: chapter 15
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» Internet Protocols (4)
» Source: chapter 15
TELE202 Lecture 11 Internet Protocols (3)
1
Lecturer Dr Z. Huang
CIDR
Classless Interdomain Routing
Address allocation problem
» Exhaustion of the class B network address
space
» A class C network is normally two small for
mid-size organizations
» Solution: allocate contiguous blocks of class C
networks
Routing table problem
» By default, a routing table contains an entry
for every network
» The entries for all class C networks are
beyond the ability of the current software and
hardware to manage
Solution
» Divide the world into 8 regions and allocate
the class C networks as below
Multi-regional 192.0.0.0 - 193.255.255.255
Europe: 194.0.0.0 - 195. 255.255.255
Others: 196.0.0.0 - 197. 255.255.255
North America 198.0.0.0 - 199. 255.255.255
C/S America 200.0.0.0 - 201. 255.255.255
Pacific rim 202.0.0.0 - 203. 255.255.255
Others: 204.0.0.0 - 205. 255.255.255
Others: 206.0.0.0 - 207. 255.255.255
TELE202 Lecture 11 Internet Protocols (3)
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Lecturer Dr Z. Huang
CIDR
Classless Interdomain routing
» Class C addresses become meaningless on the
routes between the above “domains”
» The technique CIDR is used to route between
domains without honoring class C addresses
» The key point is that multiple contiguous
class C addresses are aggregated to be one
entry in the routing table
CIDR is also called supernetting in
contrast to subnetting
Example
» An organization has four class C addresses
– 194.0.32.0, 194.0.33.0, 194.0.34.0,
194.0.35.0
» We can use the following supernet mask to
produce the network address of the group,
which is no longer observe the rules of IP
address classes
TELE202 Lecture 11 Internet Protocols (3)
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Lecturer Dr Z. Huang
IP routing
IP routes packets by using the IP
network number
» If the network number is the local network,
the destination is in the local network. Use a
link layer frame to send to the destination
» Otherwise the destination is outside the local
network. Use a link layer frame to send to a
local router (gateway) which can choose a
route and send the packet.
Every host and router contains a
routing table
» The table records which router to forward a
packet and which data link connection can be
used to reach the router
Routing tables can be modified by
» Hand - static routing
» Routing protocol - dynamic routing
» ICMP - redirect
Routing protocol
» Interior routing: the daemon is called routed,
which adopts Routing Information Protocol
(RIP) running distance-vector routing
algorithm for local networks
» Exterior routing: the daemon is called gated,
which adopts Open Shortest Path First
(OSPF) running link state routing algorithm
among gateways
TELE202 Lecture 11 Internet Protocols (3)
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Lecturer Dr Z. Huang
DNS
Domain Name System
Converts IP names (ASCII strings)
into IP addresses
Back in ARPANET, there was simply
a file, host.txt, that listed all the hosts
and their IP addresses. The file was
maintained by a server and fetched
by all other hosts and routers
» For a few hundred machines, this approach
worked reasonably well.
For hundreds of thousands of
workstations in Internet
» Using a single file will cause traffic overload,
name collision, and consistency problems
a hierarchical, domain-based naming
scheme and a distributed database
system are used to implement the
DNS
»
»
»
»
Map an IP name into an IP address
Map an IP address into an IP name
Provide email routing information
Handle aliases
TELE202 Lecture 11 Internet Protocols (3)
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Lecturer Dr Z. Huang
DNS
Internet domain name space
DNS name space is divided up into
non-overlapping zones.
» Each zone contains some part of the tree and
also contains name servers
» Each zone has at least one name server which
maintains file containing IP names and
addresses of all workstations in the zone
» DNS database is distributed among the name
servers
TELE202 Lecture 11 Internet Protocols (3)
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Lecturer Dr Z. Huang
DNS management
Network Information Center (NIC)
manages root and top level domain
Local administration manages lower
level domain
A name server must contact other
name servers for non-local IP
addresses
Root name server: root-servers.net
» Provides the IP addresses for the name server
authoritative for top level domain names
– e.g. domain edu has its name server eduserver.net
» 13 root name servers are currently available
» A name server has to know the IP address of
one of them
Domain name resolution
» If a host has a query about an IP name, it
passes the query to one of the local name
servers. If the IP name falls under the zone of
the name server, it returns the IP address of
the name to the host
» If, however, the IP name is remote and no
information about the name is available, the
name server sends a query message to the
top-level name server for the name requested
TELE202 Lecture 11 Internet Protocols (3)
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Lecturer Dr Z. Huang
DNS operation
Example of domain name resolution
» For example, a host flits.cs.vu.nl wants to
know the IP address of the host
linda.cs.yale.edu
» flits.cs.vu.nl sends a query to the local name
server cs.vu.nl
» Since linda.cs.yale.edu is a remote host and
the server cs.vu.nl knows nothing about it, the
server sends the query to the root name
server
» The root name server forwards the query to
the server of the edu domain, edu-server.net
» edu-server.net may not know
linda.cs.yale.edu, but it at least knows its
child yale.edu. So edu-server.net sends the
query to the name server for yale.edu
» In turn, the name server for yale.edu
forwards the query to the name server for
cs.yale.edu which has the requested
information and sends the answer hop by hop
back to the originator flits.cs.vu.nl
TELE202 Lecture 11 Internet Protocols (3)
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Lecturer Dr Z. Huang
BOOTP&DHCP
BOOTP & DHCP
» BOOTstrap Protocol
» Dynamic Host Configuration Protocol
» DHCP is a successor to BOOTP
Two bootstrap protocols that allow a
host to determine its IP address
without using RARP
» RARP operates at a low level and relies on
hardware address. These limit server
application and dynamic allocation of
hardware addresses
The protocols are based on high layer
protocol UDP/IP
BOOTP operation
» When a client machine bootstraps, it uses
BOOTP to broadcast an UDP datagram to
every machine in the local network,
requesting bootstrap information, such as its
IP address, file server IP address, router IP
address, boot file name, and etc.
» When a server machine receives the request,
its BOOTP sends a reply to the client using
broadcast
» The client takes all responsibility for reliable
communication by using timeout and
retransmission
TELE202 Lecture 11 Internet Protocols (3)
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Lecturer Dr Z. Huang
DHCP
BOOTP was designed for a relatively
static environment
» Each host has a permanent network
connection
» A manager creates a BOOTP configuration
file that specifies a set of BOOTP parameters
for each host. The file does not change
frequently
With the advert of Internet Service
Provider, wireless networks and
portable computers, automatic
allocation of IP addresses are needed
DHCP operation
» A manage must configure a DHCP server by
supplying a set of IP addresses
» DHCP allows manual allocation, permanent
automatic allocation, and temporary
automatic allocation of IP addresses
» Automatic allocation is subject to
administrative constraints
» Hardware address of a client is used as its ID
» A client needs to exchange messages with the
server to negotiate use of an IP address, such
as the lease time of the address
» A client can acquire all configuration info in a
single message
TELE202 Lecture 11 Internet Protocols (3)
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Lecturer Dr Z. Huang
Mobile IP
Problem
» How to route a packet to a mobile host
Two kinds of users
» Migratory users: stationary users who move
from one fixed site to another from time to
time but use the network only when they are
physically connected to it
» Roaming users: compute on the run and want
to maintain their connections as they move
around.
Mobile IP is for the migratory users
A mobile host has two addresses
» Primary address: permanent and fixed
» Second address: temporary and change from
location to location
How to find the mobile host?
» The world is divided into small areas
» Each area has a home agent, which keeps
track of users whose home is in the area
» Each area has one or more foreign agents,
which keep track of all mobile users visiting
the area
» When a new user enters an area, his
computer must register itself with the foreign
agent there, so that the foreign agent can
inform its home agent where it is
TELE202 Lecture 11 Internet Protocols (3)
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Lecturer Dr Z. Huang
Mobile IP
How to send a packet to a mobile
host?
» When a packet is sent to a mobile host, it is
routed to its home agent in the first place
» Because the home agent knows the address of
the host’s foreign agent, it forwards the
packet to the foreign agent which then passes
the packet to the mobile host
» Then the host’s home agent tells the sender to
henceforth send packets to the host’s foreign
agent, instead of sending to the home agent
» Then subsequent packets can now be routed
directly to the mobile host via the foreign
agent, by passing the home location entirely
TELE202 Lecture 11 Internet Protocols (3)
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Lecturer Dr Z. Huang
Voice and Video over IP
Additional protocol support is
required when sending real-time data
over IP
RTP
» Real-Time Transport Protocol
» Provides two key facilities
– A sequence number in each packet that
allows a receiver to detect out-of-order
delivery or loss
– A timestamp that allows a receiver to
control playback
IP telephony
» H.323 Standards proposed by ITU
» Session Initiation Protocol (SIP) proposed for
signaling by IETF
RSVP
» Resource ReserVation Protocol
» An endpoint uses RSVP to request a simplex
flow through an IP Internet with specified
QoS bounds.
» If routers along the path agree to honor the
request, they approve it; otherwise, they deny
it
» If an application needs QoS in two directions
(full duplex), each endpoint must use RSVP to
request a separate flow
TELE202 Lecture 11 Internet Protocols (3)
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Lecturer Dr Z. Huang
Summary
Classless Interdomain Routing
» Supernetting
IP routing
» Static routing
» Dynamic routing
– Bellman-Ford algorithm (RIP)
– Link state algorithm (OSPF)
» ICMP - redirect
Domain Name System
BOOTP & DHCP
Mobile IP
Multimedia applications over IP
» IP phone
TELE202 Lecture 11 Internet Protocols (3)
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Lecturer Dr Z. Huang