Transcript dccn-ARP - WordPress.com

GROUP MEMBERS
LOPAMUDRA PANIGRAHI
SUNIL KUMAR PANDA
SWAGATIKA NAYAK
SOUMYA SUCHARITA BASTIA
SUBHASISH ROUT
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Address mapping
Mapping logical to physical address : ARP
Mapping physical to logical address:
RARP,BOOTP,DHCP
Proxy ARP& 4 cases
ICMP(error reporting,query)
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We need protocols to create a mapping between
physical & logical address.
IP packets use logical address &these packets
need to be encapsulated in a frame,which needs
physical address.
We sometimes need reverse mapping a physical
address to a logical address & vice-versa.
When sending packets from source to destination
it has passed by physical network. The host and
router are recognized at the network level by
their IP address.
Delivering a packet to a host requires 2 levels of
addressing i.e. discussed below.
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IP datagram send one host to another, it
contains IP(logical) address of receiver. This
IP address obtained from DNS.
The IP datagram encapsulated in a frame &
pass through physical network.
Host send a ARP query packet.(query
broadcast)
Every host receive it but only recipients
recognizes its IP address & sends back an
ARP response packet.(unicast)
BROADCAS
T
UNICAS
T
Type: 0x0806
Preamble
and SFD
Destination
address
Source
address
Type
8 bytes
6 bytes
6 bytes
2 bytes
Data
CRC
4 bytes
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The preamble of an Ethernet frame consists
of 8-bytes pattern of alternating 1 and 0 bits,
which allows devices on the network to easily
detect a new incoming frame. The SFD is
designed to break this pattern, and signal the
start of the actual frame.
the SFD is the 8-bit (1-byte) value marking
the end of the preamble of an Ethernet frame.
The SFD is immediately followed by the
destination MAC address.
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Sender knows the IP address of target.
IP ask ARP to create an ARP request message, fill with
senders physical address,IP address&target IP address.
Message is passed to DLL where it encapsulate in a
frame by using physical address of sender as the source
address & broadcast to destination address.
Every host receive that frame ,all station remove the
message &pass it to ARP.Only the target machine
recognize its IP address.
Target machine reply with an ARP reply message that
contains its physical address &unicast that message.
The sender receives the reply message &at last know the
physical address of target machine.
IP datagram, which carry data for target machine, is now
encapsulate in a frame &unicast to destination.
In some cases host knows its physical address
but needs to know its logical address.
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A diskless station is just booted
Assign IP address on demand
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RARP(Reverse Address Resolution Protocol)
BOOTP(Bootstrap Protocol)
DHCP(Dynamic Host Configuration Protocol)
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Request is created and broadcast on the local
network
Respond with a RARP reply
PROBLEM WITH RARP: Broadcasting is done at the data link layer
 Needs to assign a RARP server for each
network
 RARP is almost obsolete
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Client/server protocol
Encapsulated in a UDP packet
UDP packet is encapsulated in an IP packet
PROBLEM WITH BOOTP
 Static configuration protocol
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Provide static and dynamic address allocation
Static address allocation: Host running the BOOTP client can request a static
address from a DHCP server
Dynamic address allocation: Pool of available IP address
 Temporary IP address
 Issues a lease
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Static address created manually
Dynamic address created automatically
Case 1= The sender is a host and wants to send a
packet to another host on the same network.
HOST
SENDER
LAN
HOST
SERVICE OF ARP IS USED HERE
RECEIVER
Case 2= The sender is a host and wants to send a
packet to another host on another network.
HOST
SENDER
LAN
RECEIVER
ROUTE
R
Case 3= The sender is a router that has received a
datagram destined for a host on another network.
ROUTE
R
SENDER
LAN
RECEIVER
ROUTE
R
Case 4 = The sender is a router that has received a
datagram destined for a host on the same network.
ROUTE
R
SENDER
RECEIVER
LAN
HOST
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It is used to create a subnetting effect on ARP. If Proxy ARP
is enabled at the router level, any ARP requests that a router
may receive on behalf of the hosts connected to it, gets
handled appropriately at the router itself and is not passed
on to any of the hosts. That is,
Sender sends an ARP query broadcast.
The ARP query message reaches a router.
The router has a few hosts connected to it and has Proxy
ARP enabled.
If the IP address of the destination host in the ARP query is
infact one of the hosts connected to the router, then, the
router itself replies the sender with the physical address of
the router itself in a unicast ARP response message.
When a packet arrives with the destination host’s IP address
and the router’s physical address, the router checks with
it’s ARP information to find the destination host’s physical
address and routes the packet to it appropriately.
And of course, if the ARP query doesn’t match any of the IP
addresses of the hosts attached to the router, the router
ignores the ARP query message.
ICMP stands for internet control message
protocol.
 It is different from transport protocol i.e Tcp and
Udp.
 It is designed to compensate the deficiencies of
IP protocol i.e lack of error control and lack of
assistance mechanism.
 ICMP always reports error message to the original
source.
 IP protocol has no built-in mechanism to notify
the original host.
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ICMP messages are divided into 2 types.
Error reporting messages
Query messages
The error reporting messages report problems.
The query messages occur in pairs.
Query messages help a host or a network
manager to get specific information from a
router or another network.
Ex:-nodes can discover their neighbours,host
can discover and learn about routers on their
network etc.
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One of the main responsibility of icmp is to
report errors.
Icmp does not correct errors .it simply
detects the error.
Icmp always reports error messages to the
original sources.
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No ICMP error message will be generated in
response to a datagram carrying an ICMP
error message.
No ICMP error message will be generated for
a fragmented datagram that is not the first
fragment.
No ICMP error message will be generated for
a datagram having a multicast address.
No ICMP error message will be generated for
a datagram having a special address such as
127.0.0.0 or 0.0.0.0.
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It can be created either by a destination host
or by a router.
When a router can not route a datagram or a
host cannot deliver a datagram ,the
datagram is discarded and the router or the
host sends a destination-unreachable
message back to the source host that
initiated the datagram.
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IP protocol is a connectionless protocol.
Here the absence of communication is due to
lack of flow control.
Ip does not have flow control mechanism so it
creates congestion problem.
Source host never knows if the routers or the
destination host has been overwhelmed with
datagrams.
Source host never knows if it is producing
datagrams faster than can be forwarded by
routers or by destination host.
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A router or a host has a limited size buffer for
incoming datagrams waiting to be forwarded or
to be processed.
If the datagrams are received much faster then
they can be forwarded or processed,then queue
may overflow. Now the router or host discard the
datagram and sends a source quench message
to the sender of the datagram.
It has 2 purposes:It informs the source that the datagram has
been discarded.
It warns the source that there is congestion so
the source should slow down sending process.
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It is generated in two cases.
First one is by using routing tables router can
find another router that can receive the packet.
If there are errors in one or more routing tables,a
packet can travel in a loop or a cycle ,going from
one router to next router endlessly.
When it goes from one router to another the
value of this field is decremented by 1,when it
reaches 0,router discard the datagram and sends
a time-exceeded message to the original source.
It is also generated if the message i.e send by the
source not reach at the destination within a
certain time limit.
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Error in the header part of the datagram can
create problem .
If router or destination host discovers in the
datagram sends a parameter problem message
to the source.
In case of redirection if the host sending a
message and if that message goes to wrong
router insteed of correct router then the wrong
router that receives the datagram will forward the
datagram to the correct router.
To update the routing table of the host ,it sends
a redirection message to the host.
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In addition to error reporting , ICMP i.e.
(Internet control message protocol) can
diagonise some network problem.
This is accomplished through query
messages, a group of four different pairs of
messages.
In this type of ICMP message, a node sends a
message i.e. answered in a specific format by
the destination node.
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A query message is encapsulated in an IP
packet, which in turn is encapsulated in a
data link layer frame.
TYPES OF QUERY:
 ECHO REQUEST AND REPLY
 TIMESTAMP REQUEST AND REPLY
 ADDRESS-MASK REQUEST AND REPLY
 ROUTER SOLICITATION AND ADVERTISEMENT
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Echo request and echo reply are designed for
diagnostic purposes.
These are used for identification of network
problems.
The combination of both echo request and
reply messages determines whether two
systems can communicate with each other.
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Two machines can use the timestamp request
and timestamp reply messages to determine
the roundtrip time needed for ip datagram to
travel between them.
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A host may know it’s ip address, but it may
not
know it’s corresponding mask.
To obtain it’s mask , a host sends an address
mask request message to a router on the LAN
if the host knows the address of the router it
sends request directly to the router if it
doesn't know the address then it broadcast
messages. The router will immediately send a
address mask reply message providing mask
for the host
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A host that wants to send data to a host on
another network needs to know the address of
routers connected to its own network.
The router solicitation and router advertisement
can help in this situation.
A host can broadcast router solicitation message.
The router or routers that receive the solicitation
broadcast the routing information using router
advertisement message.
When a router sends out an advertisement , it
announces not only its own presence but also the
presence of all routers of network of which it is
aware.