2/6/2015

1

Ethernet, ARP, RARP

Ethernet (LAN)Address Resolution Protocol (ARP)Reverse Address Resolution Protocol (RARP)

1 OPM

Eathernet LAN

Developed by Metcalfe's (Xerox company got patent)MAC address (48 bits) is used as address of a device. CSMA/CD is used for multiple access.Packet size is variable (payload varies from 46 to 1500 octet)

Pure Ethernet is no more in use, at present combination of Ethernet and Internet is used in LAN.

Ethernet can be setup using Coaxial cables or Twisted Wire cables (RJ 45 cat 5 and cat 6 cables)

2 OPM

Ethernet frame format

Preamble field consists of 64 bits alternating ‘0’ and ‘1’ to help receiving interface to synchronize.

48 bits MAC/Hardware/Physical/Ethernet address unique throughout the worldfor a devisefor a devise.

MAC address 0xFFFFFFFFFFFF is used to broadcast a packet in the network.Some software can generate duplicate MAC address also (generally used by hackers)

16 bits Frame Type Field is used to identify the type of data being carried in a frame. It determine which protocol software module should process the frame.

Packet size is variable (payload varies from 46 to 1500 octet in case of IPv4)32 bits CRC field helps to detect error in the frame.

3 OPM

Internet devicesHost devices- Computer, Laptop, PDA, IP telephone etc. Hub, Switch, Router, Repeaters, Bridge, Gateway, Server

IP allocation TechniquesStatic IP allocation

comparatively secure but not efficient in case of limited IP addresses

Dynamic IP allocation (DHCP)more efficient but less secure,can be secured by allocating user login & password to authenticate users

4 OPM

Internet devices (Cont.)

Hub:-connects PCs together,Works as multi-port repeater , simply passes on (repeats) all the information it receives broadcasts incoming packets from a port to other ports of the Hub.

5

Can not process packets.generates unnecessary traffic in network due to broadcasting of packets through undesired ports (not part of destination link) .

Hub can be used in a small network but for a larger, heavily used network a another network device (switch) may be used to reduce the amount of unnecessary traffic being generated.

OPM

Internet devices (Cont.)

Switch:-Switch has capability to process received packet and identify the destination port based on destination address in header of the packet.It forwards the received packets to respective destination ports

6

p p ponlyThus it doesn’t generate unnecessary traffic in networkThis allows simultaneous communication across the switch, improving bandwidth.

Switch is preferred over Hub to extend a network.

OPM

2/6/2015

2

ARP and RARPARP and RARP

Objectives

7

• Understand the need for ARP• Understand the cases in which ARP is used• Understand the components and interactions in an ARP package• Understand the need for RARP

OPM

ARP and RARP

ARPARP provides a dynamic mapping from an IP address to the corresponding hardware (MAC) address.We use the term dynamic since it happens or updates automatically after certain period of time and is normally not aautomatically after certain period of time and is normally not a concern of either the application user or the system administrator.

RARP (Reverse Address Resolution Protocol)RARP is used by systems without a disk drive but requires manual configuration (in ROM) by the system administrator to send bootstrap message.

8 OPM

9 OPM 10 OPM

ARP and RARP

11 OPM

Position of ARP and RARP in TCP/IP protocol suite

12

Notice that ARP and RARP are supplemental to IP.

OPM

2/6/2015

3

ARP operation

13 OPM

ARP packet (IP PDU)

Hardware Type - Ethernetis type 1, field length= 16 bits

Protocol Type- IPv4= x0800, field length= 16 bits

14

Hardware Length: Hardware Address length (6 byte), field length= 8 bits

Protocol Length: length ofIPv4 address (4 byte), field length= 8 bits

Operation: Request 1, Reply 2, field length= 16 bits

OPM

Encapsulation of ARP packet (IP PDU)

15

The ARP packet is encapsulated within an Ethernet packet.Note: Type field for ARP is x0806

OPM

Four cases using ARP

16 OPM

A host with IP address 130.23.43.20 and physical addressB2:34:55:10:22:10 has a packet to send to another host with IPaddress 130.23.43.25 and physical address A4:6E:F4:59:83:AB(which is unknown to the first host). The two hosts are on thesame Ethernet network. Show the ARP request and reply packets

l d i E h f

EXAMPLE 1

17

encapsulated in Ethernet frames.

See Next Slide

Network topology:- when two computers connected directly or through Hub in same networkOPM

Solutionthe ARP request and reply packets. Note that the ARP data fieldin this case is 28 bytes, and that the individual addresses do notfit in the 4-byte boundary. That is why we do not show theregular 4-byte boundaries for these addresses. Also note that theIP dd h i h d i l F i f i

EXAMPLE 1 (CONTINUED)

18

IP addresses are shown in hexadecimal. For information onbinary or hexadecimal notation see Appendix B.

See Next Slide

OPM

2/6/2015

4

Example 1

19 OPM

Proxy ARP

A proxy ARP, running in a router, can respond to an ARP request for any of its sub- ordinate device. The proxy ARP replies with its own MAC address. When the packet arrives, the router delivers it to the appropriate host.

20 OPM

ARP Software Package

AnAn exampleexample ofof aa simplifiedsimplified ARPARP softwaresoftware packagepackage

ARPARP softwaresoftware packagepackage consistsconsists ofof fivefive modulesmodules:: aa cachecache table,table, queues,queues, ananoutputoutput module,module, anan inputinput module,module, andand aa cachecache--controlcontrol modulemodule..

21

The topics discussed in this section include:The topics discussed in this section include:Cache TableCache TableQueuesQueuesOutput ModuleOutput ModuleInput ModuleInput ModuleCacheCache--Control ModuleControl Module

OPM

ARP components

22 OPM

The Cache Table

If ARP just resolved an IP address, chances are a few moments later someone is going to ask to resolve the same IP address.

When ARP returns a MAC address, it is placed in a cache table. When the next request comes in for the same IP address, look first in the cache table.

23

Essential for the efficient operation of ARP is the maintenance of an ARP cache on each host.

OPM

Original cache table used for examplesOriginal cache table used for examples

24 OPM

2/6/2015

5

The Cache Table Contents

State: FREE, PENDING, RESOLVEDHardware type: same as ARP fieldProtocol type: same as ARP fieldHardware length: same as ARP fieldProtocol length: same as ARP fieldInterface number: port number (m0 m1 m2)

25

Interface number: port number (m0,m1, m2)Queue number: which queue the ARP request is sitting inAttempts: how many times have you tried to resolve this address?Time-out: how long until this address is tossed out (need space in cache)Hardware address: destination hardware addressProtocol address: destination IP address

OPM

How Does the Cache Work?

Output ModuleThe output module waits for an IP packet with a requestChecks the cache for an existing entryIf entry found and state RESOLVED, we already have this MAC address

26

If entry found and state PENDING, packet waits until destination hardware address found

If no entry found, output module places this request in queue, and a new entry is placed in cache with state PENDING and ATTEMPTS set to 1. An ARP request is then broadcasted.

OPM

How Does the Cache Work?Input Module

The input module waits until an ARP request or reply arrives

Module checks the cache for this entry

If entry is found and state is PENDING, module updates entry’s

27

y p ytarget hardware address, changes state to RESOLVED, and sets the TIME-OUT value

OPM

How Does the Cache Work?

Input Module (cont.)

If entry is found and state RESOLVED, module still updates the entry (target hardware address could have changed) and the TIME-OUTvalue reset

28

If entry not found, module creates a new entry. State is set to RESOLVED and TIME-OUT is set

Now the module checks to see if arrived ARP packet is a Request. If it is, the module immediately creates an ARP Reply message and sends it back to sender.

OPM

How Does the Cache Work?Control Module

The cache-control module periodically checks each cache entry

If entry’s state is FREE, skips it

If t ’ t t i PENDING Att t fi ld i i t d b 1 Thi

29

If entry’s state is PENDING, Attempts field is incremented by 1. This value greater than max? Toss this entry (and mark entry as FREE). Less than max? Send another ARP request

If state of entry is RESOLVED, module decrements value of Time-out field accordingly

If Time-out field < 0, then remove entry and set state to FREEOPM

Original cache table used for examplesOriginal cache table used for examples

30 OPM

2/6/2015

6

The ARP output module receives an IP datagram (from theIP layer) with the destination address 114.5.7.89.

It checks the cache table and finds that an entry exists for thisdestination with the RESOLVED state (R in the table).

EXAMPLE 2

31

It extracts the hardware address, which is 457342ACAE32, and sendsthe packet and the address to the data link layer for transmission.

The cache table remains the same.

OPM

Twenty seconds later, the ARP output module receives an IPdatagram (from the IP layer) with the destination address116.1.7.22.

It checks the cache table and does not find this destination in the table.

The module adds an entry to the table with the state PENDING and the

EXAMPLE 3

32

The module adds an entry to the table with the state PENDING and theAttempt value 1.

It creates a new queue for this destination. It then sends an ARP requestto the data link layer for this destination.

See Next SlideOPM

Updated cache table for Example 3Updated cache table for Example 3

33 OPM

Fifteen seconds later, the ARP input module receives an ARP replypacket with target protocol (IP) address 188.11.8.71.

The module checks the table and finds this address.

It changes the state of the entry to RESOLVED and sets the time-out valueto 900.

EXAMPLE 4

34

The module then adds the target hardware address (E34573242ACA) to theentry.

Now it accesses queue 18 and sends all the packets in this queue, one by one,to the data link layer. The new cache table is shown in next slide.

See Next SlideOPM

Updated cache table for Example Updated cache table for Example 44

35 OPM

Twenty-five seconds later, the cache-control module updates everyentry.

The time-out values for the first three resolved entries are decremented by60.

The time-out value for the last resolved entry is decremented by 25.

EXAMPLE 5

36

y y

The state of the next-to-the last entry is changed to FREE because the time-out is zero.

For each of the three pending entries, the value of the attempts field isincremented by 1. One entry (IP address 201.1.56.7 is over max, so change toFREE.

See Next SlideOPM

2/6/2015

7

Updated cache table for Example 5Updated cache table for Example 5

37 OPM

ARP Probe message

ARP Probe is used in the IPv4 Address Conflict Detectionspecification (RFC 5227).

It is an ARP request constructed with an all-zero sender IP address.

38

Before beginning to use an IPv4 address (whether received from manual configuration, DHCP, or some other means), a host implementing this specification must test to see if the address is already in use, by broadcasting ARP probe packets

OPM

ARP announcement / gratuitous message

This is useful for updating other hosts' mapping of a hardware address when the sender's IP address or MAC address has changed.

ARP request is broadcasted containing the sender's protocol and Hardware address, with the target hardware address set to zero.

An alternative is to broadcast an ARP reply with the sender's hardware and protocol addresses .

39

An ARP announcement is not intended to solicit a reply.

Gratuitous ARP is also used by some interface drivers to provide load balancing for incoming traffic (sends information without requests).

In a team of network cards, it is used to announce a different MAC address within the team that should receive incoming packets.

OPM 40 OPM

RARPRARPRARP findsfinds thethe logicallogical addressaddress (IP)(IP) forfor aa machinemachine thatthat onlyonly knowsknows itsits

physicalphysical addressaddress..

ThisThis ifif oftenoften encounteredencountered onon thinthin--clientclient workstationsworkstations.. NoNo diskdisk (memory)(memory),, sosowhenwhen machinemachine isis booted,booted, itit needsneeds toto knowknow itsits IPIP addressaddress (don’t(don’t wantwant toto burnburnthethe IPIP addressaddress intointo thethe ROM)ROM)..

RARPRARP tt b d tb d t RARPRARP lili i ti t

41

RARPRARP requestsrequests areare broadcastbroadcast,, RARPRARP repliesreplies areare unicastunicast..

IfIf aa thinthin--clientclient workstationworkstation needsneeds toto knowknow itsits IPIP address,address, itit probablyprobablyalsoalso needsneeds toto knowknow itsits subnetsubnet mask,mask, routerrouter address,address, DNSDNS address,address, etcetc..

SoSo wewe needneed somethingsomething moremore thanthan RARPRARP.. BOOTP,BOOTP, andand nownow DHCPDHCP havehavereplacedreplaced RARPRARP..

OPM

RARP operation

42 OPM

2/6/2015

8

RARP packet (IP PDU)

43 OPM

Encapsulation of RARP packet

44 OPM

InARP (Inverse ARP)

Inverse Address Resolution Protocol (Inverse ARP or InARP) is used to obtain Network layer addresses (for example, IP addresses) of other nodes from data link layer (Layer 2) DLCI addresses.

It is primarily used in Frame relay networks based on TDMA,SDMA, FDMA, OFDMA based on Data Link Connection Identifier (DLCI)FDMA, OFDMA based on Data Link Connection Identifier (DLCI) and ATM networks, in which Layer 2 addresses of virtual circuits are sometimes obtained from Layer 2 signaling, and the corresponding Layer 3 addresses must be available before those virtual circuits can be used.

45 OPM

InARP (Cont.)

Since ARP translates Layer 3 addresses to Layer 2 addresses, InARP may be described as its inverse. In addition, InARP is implemented as a protocol extension to ARP: it uses the same packet format as ARP, but different operation codes as for request = 8, reply = 9.

46

The RARP, like InARP, translates Layer 2 addresses to Layer 3 addresses. However, in InARP the requesting station queries the Layer 3 address of another node, whereas RARP is used to obtain the Layer 3 address of the requesting station itself for address configuration purposes

OPM

Frame-relay inverse-ARP

Frame-relay is a layer 2 technique that uses a concept of Connection Identifier to distinguish user connections in TDMA, OFDM, OFDMA, SDMA based and ATM networks.

These days WiFi, WiMAX and LTE are OFDMA based wireless technique which uses Connection Identifiers (CID) at Layer 2.

47

q ( ) y

In WiMAX connection Identifiers (CID) are of 16 bit length (total 2^16 CIDs are classified as Initial, Management, Traffic and Relay sub-sets based on their utilization), All the CIDs can be reused in another network cell (under one Base Station) except replay sub-set of CIDs.

OPM

Connection techniques in Frame based networks

Two techniques are used to assign DLCI between adjacent devicesCommon DLCI (widely used)Distinct DLCI

Single virtual connection between two devicesCentral device assigns a DLCI and Protocol address (network address) to

48

Central device assigns a DLCI and Protocol address (network address) to a host device.The host device requests Protocol address of Central device/ other host device by sending InARP request.

Multiple virtual connection between two deviceCentral device assigns a DLCIs and Protocol addresses (network address) to a host device as per number of virtual connections for example based on type of services.

OPM

2/6/2015

9

Comparison of ARP, RARP & InARP

Parameter ARP RARP InARP

Protocol used in

TCP/IP based LAN TCP/IP based LAN Frame based Networks (WLAN, ATM, WiMAX, LTE etc.)

Mapping IP to Hardware Address(Static IP allocation)

Hardware to IP address(Dynamic IP allocation)

DLCI to IP address (Dynamic IP allocation)

Intermedi d i

Opportunistic as per k l

Opportunistic as per k l

Always necessary to access b d k

49

ate device required

network topology network topology Frame based networks

Eathernettype field

0x0806 0x8035 assigned by IANA based on different types of protocols and Technologies

Request & Reply fields

Request 1 , Reply 2 Request 3 , Reply 4 Request 8 , Reply 9

OPM

QoS scheduling in WiMAX

CID/SID= connection Identifier/Subscriber identifier50 OPM

The TDMA frame format

p1 p1 p0

Reserved

Random Access

p0 p1

Reserved

Random Access

Super-frame

0 1 0 1

Transmit Part Receive Part

51 OPM

Space Division Multiple Access

primitive applications are “Sectorizedantennas”

• in future adaptive antennas simultaneously steer energy in the direction of many users at once

52 OPM

SDMA in satellites

SDMA dual-beam receive antenna

simultaneously access from two diff t i f th th different regions of the earth

53 OPM

OFDM frame

54 OPM

2/6/2015

10

OFDMA/TDD frame (WiFi, WiMAX)

55 OPM