A PPT ONNETWORK LAYER:ADDRESS

MAPPING (ARP,RARP),ERROR REPORTING

GROUP MEMBERSLOPAMUDRA PANIGRAHI

SUNIL KUMAR PANDASWAGATIKA NAYAK

SOUMYA SUCHARITA BASTIASUBHASISH ROUT

Address mapping Mapping logical to physical address : ARP Mapping physical to logical address:

RARP,BOOTP,DHCP Proxy ARP& 4 cases ICMP(error reporting,query)

CONTENTS

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.

ADDRESS MAPPING

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)

ARP(ADDRESS RESOLUTION MAPPING)

BROADCAST

UNICAST

DataPreambleand SFD

Destinationaddress

Sourceaddress Type CRC

8 bytes 6 bytes 6 bytes 2 bytes 4 bytes

Type: 0x0806

ENCAPSULATION OF PACKETS IN ARP

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.

1. Sender knows the IP address of target.2. IP ask ARP to create an ARP request message, fill with senders

physical address,IP address&target IP address.3. 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.

4. Every host receive that frame ,all station remove the message &pass it to ARP.Only the target machine recognize its IP address.

5. Target machine reply with an ARP reply message that contains its physical address &unicast that message.

6. The sender receives the reply message &at last know the physical address of target machine.

7. IP datagram, which carry data for target machine, is now encapsulate in a frame &unicast to destination.

OPERATION OF ENCAPSULATION OF ARP PACKET

In some cases host knows its physical address but needs to know its logical address.

A diskless station is just booted Assign IP address on demand

MAPPING PHYSICAL TO LOGICAL ADDRESS

RARP(Reverse Address Resolution Protocol) BOOTP(Bootstrap Protocol) DHCP(Dynamic Host Configuration Protocol)

CONT….

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

RARP

Client/server protocol Encapsulated in a UDP packet UDP packet is encapsulated in an IP packet

PROBLEM WITH BOOTP Static configuration protocol

BOOTP

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

DHCP

Static address created manually Dynamic address created automatically

MANUAL AND AUTOMATIC CONFIGURATION

Four different case’s

Case 1= The sender is a host and wants to send a packet to another host on the same network.

SENDER

RECEIVER

HOST

HOSTLAN

SERVICE OF ARP IS USED HERE

Case 2= The sender is a host and wants to send a packet to another host on another network.

SENDER

RECEIVER

HOST

LAN ROUTER

Case 3= The sender is a router that has received a datagram destined for a host on another network.

SENDER

RECEIVER

ROUTER

ROUTER

LAN

Case 4 = The sender is a router that has received a datagram destined for a host on the same network.

SENDER

RECEIVER

ROUTER

LAN HOST

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.

PROXY ARP

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.

ICMP

ICMP messages are divided into 2 types.1. Error reporting messages2. 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.

TYPES OF MESSAGES

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.

ERROR REPORTING

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.

Imp. Points about error messages

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.

Destination Unreachable

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.

Source Quench

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:-1. It informs the source that the datagram has been

discarded.2. It warns the source that there is congestion so the

source should slow down sending process.

Contd..

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.

Time Exceeded

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.

Parameter Problem & Redirection

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.

QUERY:

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

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.

ECHO REQUEST AND REPLY:

Two machines can use the timestamp request and timestamp reply messages to determine the roundtrip time needed for ip datagram to travel between them.

TIMESTAMP REQUEST AND REPLY:

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

ADDRESS-MASK REQUEST AND REPLY:

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.

ROUTER SOLICITATION AND ADVERTISEMENT:

ANY QUERIES???

THANK YOU