Download Lecture-12(ADDRESS MAPPING)

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ADDRESSING MAPPING:
An internet consists of various types of network and the connecting devices like routers. At the
network level the hosts and router are recognized by their IP address (logical address)
Address Mapping:
Mapping is of two types
1. Static mapping
2. Dynamic mapping
Static mapping:
In static mapping, a table is created and stored in each machine. This table associates logical
address with physical address. If a machine knows the logical address of another machine then it
can search for corresponding physical address in its table.
To implement static mapping the static mapping table needs to be updated periodically.
Dynamic mapping:
In dynamic mapping some protocol is used to know the other address. The protocols are
1. ARP
2. RARP
ARP maps an IP address to MAC (physical) address and RARP maps MAC address to IP
address.
ARP:
When a router or host needs to find MAC address of another host or network the sequence of
event taking place. i.e
The router or host A who wants to find the MAC address of some other route, sends a ARP
request packet. These packets consist of IP and MAC address of the sender A and the IP address
of the receiver B. the request packet is broadcasted over the network
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Every host and router on the network receives and processes the ARP packet. But only the
intended receiver B recognizes its IP address in the request packet and sends back an ARP reply
packet. The ARP reply packet contains the IP and physical address of the receiver B. This packet
is delivered only to A using A‘s physical address in the ARP request packet.
RARP:
It is a part of TCP/IP protocol suite. It allows a diskless workstation to obtain a IP address from a
server.
When a diskless workstation is booted in a network it broadcast a RARP request packet on the
local network .this address packet is broadcast on the network for all to receive because the
workstation does not know the IP address of the server that can supply it with an address.
It includes its own physical network address in the request so the server will know where to
return a reply. The server that receives the request looks in a table and matches the MAC address
with an IP address and then return the IP address to the diskless workstation.
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ICMP (internet control message protocol):
The IP provides unreliable and connectionless datagram delivery. So IP is a best-effort delivery
service that delivers a datagram from its original source to its final destination.it has some
defiencies i.e lack of error control. So ICMP is designed to compensate this control.
ICMP message
1. Error reporting message.
2. Query message.
ERROR REPORTING MESSAGE:
Destination unreachable:
When a router cannot forward or deliver IP packet, it sends a destination unreachable ICMP
message back to original source.
Source quench:
A host or router uses source quench message to report congestion to the original source and to
request to it to reduce its current rate of packet transmission. There is no flow control or
congestion control mechanism in IP. So the source quench message is ICMP which is designed
to add a kind of flow control and congestion to IP.
Time exceeded:
If a router receives a datagram with a zero in the TTL field than it discards that datagram and
send a time exceeded message back to the original source.
Parameter problem:
There is no ambiguity in the header part of the message if a router finds any ambiguity in any
fields of the datagram then it discards that datagram and sends the parameter problem message
back to the source.
Redirection:
If a host wants to send a packet to another network then it should know the IP address of the next
router which maintains a routing table to find the IP address of the next router. So the routing
table updated constantly for such updating the ICMP sends a redirection message back to its
host.
MULTICASTING:
A process has to send a message to all other process in the group. In multicasting a router is used
called multicast routing. In multicast routing there is one source and group of destinations is
work.
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QUERY MESSAGE:
Due to some error reporting ICMP creates some network problem. This is controlled by some
query message.
 ECHO REQUEST AND REPLY:
This message determines whether two systems can communicate with each other or not
 TIME-STAMP REQUEST AND REPLY
This message is used to synchronize the clocks in two machines.
 ADDRESS MASK REQUEST AND REPLY
In this message the host can send an address mask request message to router then router sends a
mask in an address mask reply message.
 ROUTER SOLICITATION AND ADVERTISEMENT:
When a host sends data to a host or another network first it knows the address of router
connected to its own network. In such situation a host can broadcast or multicast a router
solicitation message. The router receiving this message and broadcast their routing
information using router advertisement.
DELIVERY:
Delivery refers to the way a packet is handled by the network under the control of the network
layer. The delivery of a packet to its final destination is performed using two different methods
of deliver i.e
1. Direct
2. Indirect
Direct delivery:
Direct delivery occurs when the source and destination are located on the same physical
networks.
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In Direct delivery:
In an indirect delivery, the destination host is not the same network, the packet is delivered
indirectly. The packet goes from router to router until it reaches the one connected to same
physical network as its final destination.
FORWARDING:
Forwarding refers to the way a packet is delivered to the next station.
There is different forwarding techniques are used to forward the message i.e
1. Next-hop routing method.
2. Network specific routing method.
3. Host specific routing method.
4. Default routing method.
Next –hop routing method:
In next-hop method the routing table holds only the address of the next hop.
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Network specific routing method:
Network specific routing method defines the address of the destination network.
Dstination
N2
Next hop
R1
Host specific routing method:
In host specific method it contains an entry for every destination host connected to same physical
network.
Default routing method:
The routing method uses the network address 0.0.0.0 is called default.