Rate of Diffusion of Potassium permanganate, Potassium dichromate, and Methylene blue1

Rate of Diffusion of Potassium permanganate, Potassium dichromate, and Methylene blue1 1 The Effect of Molecular Weight and Time on the Rate of Diffusion of Potassium permanganate, Potassium dichromate, and Methylene blue1 scientific paper submitted in partial fulfillment of the requirements in General Biology I laboratory under Prof. Diana Rose Gonzales, 1st sem., 2013 2014 _ 2 ABSTRACT The effect of molecular weight and time on the rate of diffusion of potassium permanganate, potassium dichromate, and methylene blue was tested using a petri dish of agar water gel with three wells. The three substances were dropped simultaneously in the petri dish. Potassium permanganate (MW 158g/mole) increased rapidly (14.50 mm) while Methylene blue (MW 374 g/mole) gradually increased (9.50 mm) only. Thus, molecular weight and time affects the rate of diffusion. INTRODUCTION Diffusion is a movement of molecules from an area of higher concentration to an area of lower concentration. The particles will fuse when they are evenly distributed and have reached equilibrium. Potassium permanganate, potassium dichromate, and methylene blue are substances used as indicators and oxidizing agents. Potassium permanganate is used in organic compounds and used commercially to purify water and sanitizer. It is chemically used to regulate certain reducing compounds. Potassium dichromate is used to determine ethanol concentrations in solutions and determine the presence and purity of silver. Researches also suggest that potassium dichromate functions as an agent that cause genetic mutation against DNA repair deficient strains of Escherichia coli. Lastly, methylene blue is used as dye to identify bacteria and nucleic acids. The dye will have the deepest shade of blue when in contact with acids. As indicators and oxidizing agents, the substances stated above must prove that their diffusion must be fast in order to do their functions. Due to their difference in molecular weight, a test was conducted to prove what substance is more recommendable _ 3 to be used in getting the rate of diffusion. To further verify the experiment rate of diffusion was also tested with time. To test this, agar water gel is one of the materials was used. Agar water gel is a substance that functions as a thickener, stabilizer, and emulsifier since it do not melt at room temperature until it is heated to 85oC and more. Also, with a stopwatch the substances were measured (mm) at a regular three minute interval for thirty minutes. The study aims to determine the effect of molecular weight and time on the rate diffusion of potassium permanganate, potassium dichromate, and methylene blue. The specific objectives are 1. to prove that molecular weight affects the rate of diffusion; and 2. to explain why molecular weight must also be observed with time MATERIALS AND METHODS In testing the effect of molecular weight and time on the rate of diffusion of potassium permanganate, potassium dichromate, and methylene blue, agar water gel was used. Three bottles with dropper containing the substances and a petri dish with agar water gel were given to each group. As three members of the group dropped all substances together in the wells of the agar water gel, the stopwatch started simultaneously with it. One member measured each wells of the agar water gel with a ruler to get the initial measurement (mm) of the wells. The group then drew the initial appearance of the experiment (Figure 4.1.). One member was assigned to signal the group if three minutes have passed and the member of the group who is assigned to _ 4 measure the wells will immediately but carefully measure the area with the ruler. There was a regular three minute interval for thirty minutes. After thirty minutes, the group then drew the final appearance of the experiment Figure 4.2. Also, the group computed for the average of the substances by adding all the data that were gathered divided by number of time intervals. To test the effect of time on the rate of diffusion the data gathered were computed by partial rate. Partial rate is computed by subtracting the diameter of colored area immediately (di-1) before the diameter of colored area at a given time (d1) divided by the time when d1 was measured (t1) minus the time immediately before t1 (ti 1). Again, the average of each substances were computed by adding all the date divided by the number of time intervals. A graph comparing the average rate of diffusion of each substance was plotted against its molecular weight in Figure 4.3. Also, a graph comparing the partial rate of diffusion of each substance was plotted against the time elapsed in Figure 4.4 _ 5 Potassium dichromate Methylene blue Potassium permanganate Figure 4.1. Initial appearance of the substances in the agar water gel wells. Potassium dichromate Methylene blue Potassium permanganate Figure 4.2. Final appearance of the substances in the agar water gel wells. _ 6 RESULTS AND DISCUSSIONS As seen in Table 4.2, potassium permanganate (MW 158 g/mole) has the highest average rate of diffusion with 11.32 mm/min, followed by potassium dichromate (MW 294 g/mole) with 10.86 mm/min, and methylene blue (MW 374 g/mole) with 7.95 mm/min. In Table 4.3, potassium permanganate has the highest partial rates of diffusion with 0.35 mm/min, followed by potassium dichromate with 0.32 mm/min, and methylene blue with 0.19 mm/min. This results shows that molecular weight has an effect in the rate of diffusion. When the molecular weight is lower then the rate of diffusion will be higher meaning they have an indirect relationship. Also, with time the rate of diffusion of the substances decreased, meaning time and the rate of diffusion has an indirect relationship. _ 7 SUMMARY AND CONCLUSION The effect of molecular weight and time on the rate of diffusion of potassium permanganate, potassium dichromate, and methylene blue was determined. Each substance was dropped simultaneously with each other into the petri dish with agar water gel. With a stopwatch the time was observed with an interval of three minuets in thirty minutes. After thirty minutes, the average of the circumference and the partial rates of diffusion were computed. Results showed that potassium permanganate (MW 158 g/mole) which has the least molecular weight had the highest average rate of diffusion compared to methylene blue (MW 374 g/mole), which has the greatest molecular weight among the three. In time, the circumference (mm/min) of each substance increased since there was diffusion in the agar water gel wells. Hence, molecular weight and time has an effect in the increase, decrease, slowness, and fastness of the diffusion of substances. Nevertheless, further experimentation must be done to improve the results of the experiment. It is recommended to use other substances, a different medium other than the agar water gel, a longer time period to test the diffusion, a more stable environment, and have more trials to observe better results. _ 11 LITERATURE CITED Dean, John A. Lange's Handbook of Chemistry, 12th ed.; McGraw-Hill Book Company: New York, NY, 1979; p 9:4-9:94. Ebbing, Darrell D. General Chemistry 3rd ed.; Houghton Mifflin Company: Boston, MA, 1990; p 137. Andrew Mills, David Hazafy, John A. Parkinson, Tell Tuttle and Michael G. Hutchings The Journal of Physical Chemistry A 2009, 113 (34), 9575-9576 Chongmok Lee, Yoo Wha Sung, and Joon Woo ParkThe Journal of Physical Chemistry B1999, 103 (5), 893-898 _

Failure and Destruction of a Romantic Ideal in Fitzgerald’s The Great G

The Great Gatsby and the Destruction of a Romantic Ideal      Ã‚   In The Great Gatsby, F. Scott Fitzgerald tells the story of a romantic ideal and its ultimate destruction by the inexorable rot and decay of modern life. The story is related by Nick Carraway, who has taken a modest rental house next door to Jay Gatsby's mansion. Jay Gatsby is a young millionaire who achieves fabulous wealth for the sole purpose of recapturing the love of his former sweetheart, Daisy Fay Buchanan. Five years prior to the principal events of the story, Daisy broke off with Gatsby and married the vulgar and arrogant Tom Buchanan because he was rich and came from a respectable family. In the years since, Gatsby turns his memory of Daisy into a near-religious worship. He places her on a pedestal and transforms her into his own romantic ideal. In the process, he also transforms himself. He changes his name from Gatz to Gatsby; he invents a past, saying he was from a wealthy family and studied at Oxford; he affects the speech patterns of an English aristocrat ("ol d sport"), and stages parties that resemble theatrical productions.    The irony is that Gatsby's extreme pursuit of materialism is just an elaborate facade that allows him to pursue his enchanted spiritual vision. All of the trappings of his wealth have a sense of the unreal, as having no weight or substance. Our first sense of this occurs in Chapter 3, when Gatsby invites Nick to one of his parties. In Gatsby's library Nick encounters a drunken guest who announces that Gatsby's books are actually real:    "What do you think?" he demanded impetuously. "About what?" He waived his hand toward the book-shelves. "About that. As a matter of fact you needn't bother to... ..., boats against the current, borne back ceaselessly into the past."       Works Cited and Consulted: Bruccoli, Matthew J. Some Sort of Epic Grandeur: The Life of F. Scott Fitzgerald. New York: Carrol and Graf, 1993. Hobsbawm, Eric. The Age of Extremes. New York: Pantheon, 1994. Mizener, Arthur, ed. F. Scott Fitzgerald: A Collection of Critical Essays. Englewood Cliffs, NJ: Prentice-Hall, 1963. Posnock, Ross. "'A New World, Material Without Being Real': Fitzgerald's Critique of Capitalism in The Great Gatsby." Critical Essays on Scott Fitzgerald's "Great Gatsby." Ed. Scott Donaldson. Boston: Hall, 1984. 201-13. Raleigh, John Henry. "F. Scott Fitzgerald's The Great Gatsby." Mizener 99-103. Trilling, Lionel. "F. Scott Fitzgerald." Critical Essays on Scott Fitzgerald's "Great Gatsby." Ed. Scott Donaldson. Boston: Hall, 1984. 13-20.

The Internet Plagiarism Explosion Essay example -- Exploratory Essays

A great deal has been published in the media about the "explosion" of Internet plagiarism among high school and college students. Because the Internet is so young, there have been few studies conducted on the extent of Internet plagiarism. However, existing studies do show that the Internet is an extremely popular tool students use to cheat on written assignments. In any group of students, some will choose the path of academic dishonesty and copy the words or ideas of another person without giving credit to the author. The advent of the Internet has opened new ways for students to plagiarize written material. Not only can students copy material from individual Web sites, but they can use an online paper mill to pay for and receive an entire paper written by someone else. Educators are interested in the extent of Internet plagiarism, why some students plagiarize using the Internet, and what they can do to prevent students from cheating when they use online resources. I will attempt to address these concerns in this paper. The Center for Academic Integrity based at Duke University studies issues of academic integrity including trends in cheating and plagiarism across the United States. Its studies show that Internet plagiarism is a widespread problem among high school and college students. There are several types of Internet plagiarism. The most common way for a student to plagiarize material from the Internet involves copying material from a variety of independent Web sites and compiling them into an "original" document. A less common type involves a student obtaining a paper from a paper mill. There are now thousands of paper mills on the World Wide Web offering a variety of services. Some, such as www.realpapers.com, offer ... ...m. Los Angeles Times, 1. Retrieved October 28, 2001, from LEXIS-NEXIS Academic Universe database. Hricko, M. (1998). Internet plagiarism: Strategies to deter academic misconduct. Retrieved October 28, 2001 from the Mid-South Instructional Technology Conference Web site: http://www.mtsu.edu/~itconf/proceed98/mhricko.html Kleiner, C., Lord, M. & Faber, L. (1999, November 22). The great term-paper buying caper. U.S. News & World Report, 127 (20), 63. Retrieved October 28, 2001 from LEXIS-NEXIS Academic Universe database. Niels, G. J. (1996). Academic practices, school culture and cheating behavior. Retrieved October 28, 2001 from: http://james.hawken.edu/odris/cheating/cheating.html Walker, W. (2001, September 3). Teachers fight back against 'rampant' cyber-cheating. Toronto Star, A07. Retrieved October 28, 2001, from LEXIS-NEXIS Academic Universe database.

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Rudyard Kipling Required literature: Brodey K. , Malgaretti F. Focus on English and American Literature. M. , 2003. Pp. 191-197. Supplementary literature: ?. ?. . . ?. , , 2007. . 230-243. 1. English short-story writer, novelist and poet Kipling was the first Englishman to receive the Nobel Prize for Literature (1907). l His most popular works include â€Å"The Jungle Book† (1894) and the â€Å"Just So Stories† (1902), both children classics though they have attracted adult audiences also.He tried his hand at many sorts of genres: he was a dialect poet, folklorist, adventure novelist, writer of books for children. His books are valuable source of information not only about the 19th century, but about men in general. Born in India in 1865, Kipling was sent to England at the age of six, there to undergo eleven years of formal Victorian education. He returned to India in 1882, and for the next seven years worked as a reporter & soon turned to fiction writing. Speak about Kipling’s biography and its influence upon the creative works by the author. 2.Kipling never wrote by impulse – he had a doctrine and it sounds like â€Å"Art for Morality’s Sake†. He created the fantastic world of his own, very much rooted in reality. Speak about â€Å"Jungle Book† being a mixture of romanticism and realism. 3. Kipling became nationalist saying that English nation is the only that could bring the world to prosperity, to educate all people. But he does not speak about the English only but about the whole of mankind. And he shows some conditions under which a human being can become a man in his poem â€Å"If†. Prove that the author addresses the whole mankind in this poem. . One of his chief works – â€Å"Barrack-Room Ballad† – is a collection of poetry, about the experience of military service in India and other parts of the British Empire. It contains the most famous of Kipling’s dialect poems. There are two sections in this book. What do these two sections comprise? 5. â€Å"The Ballad of East and West† depicts the differences present between the east and west even though uniformity in human nature subsists around the world. In this ballad Kipling also displays his ability to create lifelike characters through â€Å"Kamal† and â€Å"The Colonel’s Son†.Through the use of imagery and witty verse he makes both of these fictional characters come alive. What is the most famous quotation from this ballad and why does it cause misinterpretation? 6. His novel â€Å"Kim† is generally regarded as his best novel. The story, set in India, depicts the adventures of an orphaned son of a sergeant in an Irish regiment. Kim is European, not an India, and he is not a Maugly because his system of values is a mixture of that of European and that of Indian, full of truth and superstitions. Judge the merits of the book. Speak about the philosophy of the book.

Positive Effects On Social Media Essay

I believe that their is a postitive affect in social media because it builds up confidence and allows people to stay organized and in the loop. It has been around since the 80’s. In an interesting DM article apparently 30 million of us who use the internet visit social networking websites such as Myspace, Facebook, and Bebo. Social media can also help find a missing person. The first reason social media has helped is because it lets you stay in touch with friends and family. You can get to know other students at your school or stay connected with other people who share a common interest. It also helps strengthen long distance relationships. For example, I have a friend whose parents got divorced and his dad lives far away from him. He said, â€Å"The only way we can communicate is through facebook†. I personally think facebook is a neat website that can help with communication. In the article â€Å"Teens in Survey Paint Positive Picture of Effect of Social Media on Their lives† I read that â€Å"Half of teens said social networks have helped their friendship† and I also agree with this. The second reason that it has helped is that it keeps us up to date with what’s going on. A reporter from a social media article stated that â€Å"Many teens express an almost-like wearness with the pressures of constant texting and posting involved in their lives†. People post and text online to express themselves. I talked to my sister this morning, and asked her how social media has helped her in life and she said â€Å"It provides me reminders for meets or practices for cross country†. I thought that was really intersting and I also believe it helps teachers with things like that too. Since theyre always busy and forget things I think they need some kind of reminder to remind them. see more:cause and effect of social media Finally, the third reason that social media has helped is that it makes you feel less lonely or if you’re not having a good day talking to your friends online can change your mood for the day. In the same social media article it said, â€Å"Many teenagers say that using social networking sites makes them feel more confident, popular, out going, and sympathetic to others†. So this is why social media is helpful for your life and others. Most parents I know and some teachers think social media has a negative perspective on it thinking it’s just a waste of time. But in cases like having communication with far away relatives, getting reminders or just by expressing yourself can bring a postive effort in your life style.

Aids Funding For Africa And Other Countries

The HIV/AIDS epidemic is a serious problem besetting the whole world. However, there is no other region in the world that could equal the sheer number and severity of the AIDS problem in Africa. The situation of AIDS victims in the region makes Africa deserving of help from the more fortunate nations in the world that are not hit as badly as the Africans, such as the United States.There are basically three reasons underlying Africa’s need for funding from other states. First, the number of AIDS victims in Africa is staggering. This reason alone is sufficient to arouse from people a compulsion to help. Basic notions of humanity and compassion dictate that those who are better situated and are able to help provide whatever assistance they can to those in need.Second, the situation in Africa is getting worse, not only for those who are actually afflicted by the disease, but also for their children. There is a growing number of orphans in Africa who desperately need help because t hey lost their parents to AIDS.Third, Africa is in no shape to solve this problem on its own. Almost all its countries are weighed down by the disease; and they have no resources to fund research on, and treatment of, the disease.Main BodyThe African SituationAfrica is the region most badly hit by the AIDS phenomenon. Compared to the number of victims in the United States, which only reached a little over 1 million in the year 2003 (A Glance, 2006), the number in Sub-Saharan Africa reached about 25 million at the end of 2005.Worse, it is approximated that about 2.7 million more infections occurred during that year. The number of deaths in the region is also devastating, reaching a total of about 2 million in the same year. (Kanabus & Fredriksson-Bass, 2006).The prevalence rates of HIV vary among the countries in Africa. Some are very much higher than others.   Among the countries that have the lowest prevalence rate are Somalia and Senegal, which is under 1% of the adult populatio n.Another country with relatively low prevalence rate is Nigeria, despite its being the country with the highest population in Sub-Saharan Africa, with only 3.9% in 2005. However, numbers are creeping up in the said country, as already â€Å"around 2.9 million Nigerians are estimated to be living with HIV.†On the other side of the spectrum, Botswana, Lesotho, Swaziland and Zimbabwe registered the highest adult HIV prevalence rates, reaching 24.1%, 23.2%, 33.4% and 20.1%, repectively. (Kanabus & Fredriksson-Bass, 2006).AIDS OrphansAnother grave problem facing Africa today is the number of children who are being orphaned because of AIDS. Although the whole world shares the weight of the 15 million children below 18 who have lost a parent to AIDS, Africa is again the region most badly hit by the situation.Africa is home to more than 12 million of these orphaned children, and it is predicted that this number will reach approximately 15.7 million by the year 2010 in Sub-Saharan Af rica alone.The gravity of the situation in Sub-Saharan Africa, where â€Å"children who have been orphaned by AIDS comprise half or more of all orphans nationally,† is manifested in the mere number of children who have been orphaned in 2005. (AIDS Orphans).South Africa has the most number of AIDS orphans, with 1,200,000 of them in 2005, while Malawi has the lowest population of orphans, with only 550,000. It would be noted that this smallest population of orphans of 550,000 is still a lot, and this in no way implies that the problem is less pressing in Malawi. (AIDS Orphans).The biggest crisis involving AIDS orphans consist in the emotional impact of deaths of their parents on the children. Negative changes are sure to be experienced, such as emotional neglect and trauma, occurring long before they are actually orphaned.For example, studies in Uganda show that high levels of psychological distress, manifested by feelings of anxiety, depression and anger, are common children w ho have been orphaned by AIDS. More fundamentally, the loss of a parent can lead to the subsequent loss of basic needs, such as food, shelter and education.Foreign FundingThe situation in Africa can be improved through the support of other countries and world organizations, particularly in funding. Africa has no sufficient resources to support anti-AIDS campaign on its own. Money, infrastructures and human resources are needed to form an effective HIV prevention and treatment program in the region.Unfortunately, these factors are not sufficiently developed in Africa. Therefore, foreign funding plays an important role in helping Africa combat its problem of AIDS. (Kanabus & Fredriksson-Bass, 2006).Funding to low-income countries, such as Africa, is sourced from only four streams: donations from national governments, major multilateral funding organizations, the private sector and domestic spending. With the other streams being unavailable, donations from foreign governments remain th e only viable source of resources for Africa.The United States is one of the biggest providers of funds in the fight against AIIDS. The American initiative consists mainly of the PEPFAR, or the President's Emergency Plan For AIDS Relief, which is a five-year commitment to donate $15 million to regions that are heavily beset by the AIDS epidemic. (Funding the Fight).ConclusionAfrica is the country that is most hit by the AIDS epidemic. The devastating effects of the said disease have led to other problems such as the psychological trauma caused on children who have been orphaned because of AIDS, who are growing in number through the years.With Africa lacking in much-needed resources, foreign funding from rich countries, such as the United States, remain its only hope in dealing with, and combating this deadly disease.ReferencesA Glance at the HIV/AIDS Epidemic. (2006). Retrieved December 1, 2006, from   Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   http://www.cdc.gov/hiv/resources/facts heets/At-A-Glance.htmAIDS Orphans. Retrieved December 1, 2006, from http://www.avert.org/aidsorphans.htmFunding the Fight Against AIDS. Retrieved December 1, 2006, from   Ã‚  Ã‚  Ã‚  Ã‚   http://www.avert.org/aidsmoney.htmKanabus, A. & Fredriksson-Bass, J. (2006). HIV & AIDS in Africa. Pembrey, G. Ed. Retrieved   Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   December 1, 2006, from http://www.avert.org/aafrica.htma

Address Resolution Protocol

————————————————- Address Resolution Protocol The  Address Resolution Protocol  (ARP) is a  computer networking  protocol for determining a network host's link layer or hardware address when only its  Internet Layer  (IP) or  Network Layer  address is known. This function is critical in local area networking as well as for routing internetworking traffic across gateways (routers) based on  IP addresses  when the next-hop router must be determined. ARP was defined by  RFC 826  in 1982. [1]  It is  Internet Standard  STD 37. ARP has been implemented in many types of networks, such as  Internet Protocol  (IP) network,  CHAOS,  DECNET, Xerox  PARC Universal Packet,  Token Ring,  FDDI,  IEEE 802. 11  and other  LAN  technologies, as well as the modern high capacity networks, such as  Asynchronous Transfer Mode  (ATM). Due to the overwhelming prevalence of  IPv4  and Ethernet in general networking, ARP is most frequently used to translate  IPv4 addresses  into Ethernet  MAC addresses. In the next generation Internet Protocol,  IPv6, ARP's functionality is provided by the  Neighbor Discovery Protocol  (NDP). ———————————————— Overview and IPv4-plus-Ethernet example Consider a LAN where machines using IPv4 over Ethernet wish to communicate. A sender wishes to send a message to some other machine on the LAN and knows a destination IPv4 address. The destination IPv4 address is hopefully associated with some appropriate network interface belonging to the recipient machine, and is present on the LAN. But in order for communication to succeed, the sending machine  first needs to discover the ethernet MAC address of the intended recipient network interface. This requirement comes about because Ethernet hardware does not (necessarily) understand IPv4 protocols or IPv4 addresses in the sense that Ethernet hardware ‘listens out for' relevant Ethernet MAC addresses but does not ‘listen out for' IPv4 addresses. (An impractical alternative would be to have all units listen to every Ethernet packet and inspect the contents for relevant IPv4 addresses, discarding the packets that are intended for other devices, but this would be very inefficient. ) So before sending an IPv4 packet, the sender sends a roadcast message onto the LAN using ARP in order to discover the Ethernet MAC address of some interface that is listening for that desired target IPv4 address. Some appropriate unit replies that it has a network interface with a certain MAC address that is associated with the IPv4 address in question. The original would-be sender now has the information needed and can go ahead and send its IPv4 packet to the destination inserting it int o an Ethernet frame with the correct destination MAC address for the appropriate recipient. The sender's operating system also stores the newly discovered MAC address in a table (‘caches' the result). This table of mappings from IPv4 addresses to MAC addresses is retained and consulted again and again, so the ARP discovery procedure only has to be performed one time, when a packet is sent to a ‘new' destination IPv4 address. ————————————————- Operating scope The Address Resolution Protocol is a low level request and answer protocol that is communicated on the media access level of the underlying network. For  Ethernet  systems, an ARP message is the payload of Ethernet packets. ARP therefore operates only across the local link that a host is connected to. Within the framework of the  Internet Protocol Suite, this characteristic makes ARP a  Link Layer  protocol. [2] ARP is also very often discussed in terms of the  Open Systems Interconnect  (OSI)  networking model, because that model addresses hardware-to-software interfaces more explicitly and is preferred by some equipment manufacturers. However, ARP was not developed based on the design principles and strict encapsulation hierarchy of this model and, therefore, such discussions create a number of conflicts as to the exact operating layer within this model. Most often ARP is placed into the  Data Link Layer  (Layer 2), but since it requires the definitions of network addresses of the  Network Layer, it is not unusual to find it referenced at that layer. An example of use in OSI networking, is ATMARP, used to resolve  Asynchronous Transfer Mode  (ATM)  NSAP  addresses in IP over ATM deployments. ————————————————- Packet structure The  Address Resolution Protocol  uses a simple message format that contains one address resolution request or response. The size of the ARP message depends on the upper layer and lower layer address sizes, which are given by the type of networking protocol (usually  IPv4) in use and the type of hardware or virtual link layer that the upper layer protocol is running on. The message header specifies these types, as well as the size of addresses of each. The message header is completed with the operation code for request (1) and reply (2). The payload of the packet consists of four addresses, the hardware and protocol address of the sender and receiver hosts. The principal packet structure of ARP packets is shown in the following table which illustrates the case of IPv4 networks running on Ethernet. In this scenario, the packet has 48-bit fields for the sender hardware address (SHA) and target hardware address (THA), and 32-bit fields for the corresponding sender and target protocol addresses (SPA and TPA). Thus, the ARP packet size in this case is 28 bytes. Hardware type (HTYPE) This field specifies the Link Layer protocol type. Example: Ethernet is 1. Protocol type (PTYPE) This field specifies the upper layer protocol for which the ARP request is intended. For example, Internet Protocol (IPv4) is encoded as 0x0800. Hardware length (HLEN) Length (in  octets) of a hardware address. Ethernet addresses size is 6. Protocol length (PLEN) Length (in octets) of a  logical address  of the specified protocol (cf. PTYPE). IPv4 address size is 4. Operation Specifies the operation that the sender is performing: 1 for request, 2 for reply. Sender hardware address (SHA) Hardware (MAC) address of the sender. Sender protocol address (SPA) Upper layer protocol address of the sender. Target hardware address (THA) Hardware address of the intended receiver. This field is ignored in requests. Target protocol address (TPA) Upper layer protocol address of the intended receiver. ARP protocol parameter values have been standardized and are maintained by  IANA Internet Protocol (IPv4) over Ethernet ARP packet| bit offset| 0 – 7| 8 – 15| 0| Hardware type (HTYPE)| 16| Protocol type (PTYPE)| 32| Hardware address length (HLEN)| Protocol address length (PLEN)| 48| Operation (OPER)| 64| Sender hardware address (SHA) (first 16 bits)| 80| (next 16 bits)| 96| (last 16 bits)| 112| Sender protocol address (SPA) (first 16 bits)| 128| (last 16 bits)| 144| Target hardware address (THA) (first 16 bits)| 160| (next 16 bits)| 76| (last 16 bits)| 192| Target protocol address (TPA) (first 16 bits)| 208| (last 16 bits)| ————————————————- ARP probe An  ARP probe  is an ARP request constructed with an all-zero  sender IP address. The term is used in the  IPv4 Addre ss Conflict Detection  specification (RFC 5227). 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. ————————————————- ARP announcements ARP may also be used as a simple announcement protocol. This is useful for updating other host's mapping of a hardware address when the sender's IP address or MAC address has changed. Such an announcement, also called a  gratuitous ARP  message, is usually broadcast as an ARP request containing the sender's protocol address (SPA) in the target field (TPA=SPA), with the target hardware address (THA) set to zero. An alternative is to broadcast an ARP reply with the sender's hardware and protocol addresses (SHA and SPA) duplicated in the target fields (TPA=SPA, THA=SHA). An ARP announcement is not intended to solicit a reply; instead it updates any cached entries in the ARP tables of other hosts that receive the packet. The operation code may indicate a request or a reply because the ARP standard specifies that the opcode is only processed after the ARP table has been updated from the address fields. [4][5][6] Many operating systems perform gratuitous ARP during startup. That helps to resolve problems which would otherwise occur if, for example, a network card was recently changed (changing the IP-address-to-MAC-address mapping) and other hosts still have the old mapping in their ARP caches. Gratuitous ARP is also used by some interface drivers to effect load balancing for incoming traffic. In a team of network cards, it is used to announce a different MAC address within the team that should receive incoming packets. ARP announcements can be used to defend  link-local  IP addresses in the  Zeroconf  protocol (RFC 3927), and for IP address takeover within  high-availability clusters. ————————————————- ARP mediation ARP mediation  refers to the process of resolving Layer 2 addresses when different resolution protocols are used on multiple connected circuits, e. . , ATM on one end and Ethernet on the others. ————————————————- Inverse ARP and Reverse ARP The  Inverse Address Resolution Protocol  (Inverse ARP or InARP), is a protocol used f or obtaining  Network Layer  addresses (e. g. ,  IP addresses) of other nodes from  Data Link Layer(Layer 2) addresses. It is primarily used in  Frame Relay  (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 these virtual circuits can be used. As ARP translates Layer 3 addresses to Layer 2 addresses, InARP may be described as its inverse. In addition, InARP is actually implemented as a protocol extension to ARP. It uses the same packet format from ARP; but has different operation codes. Reverse Address Resolution Protocol  (Reverse ARP or RARP), like InARP, also translates Layer 2 addresses to Layer 3 addresses. However, while in InARP the requesting station is querying the Layer 3 address of another node, RARP is used to obtain the Layer 3 address of the requesting station itself for address configuration purposes. RARP is now obsolete. It was replaced by  BOOTP, which was later superseded by the  Dynamic Host Configuration Protocol  (DHCP). ————————————————- Proxy ARP Proxy ARP  (Address Resolution Protocol) is a technique by which a device on a given network answers the  ARP  queries for a  network address  that is not on that network. The ARP Proxy is aware of the location of the traffic's destination, and offers its own MAC address in reply, effectively saying, â€Å"send it to me, and I'll get it to where it needs to go. Serving as an ARP Proxy for another host effectively directs LAN traffic to the Proxy. The â€Å"captured† traffic is then typically routed by the Proxy to the intended destination via another interface or via a  tunnel. The process which results in the node responding with its own MAC address to an ARP request for a different IP address for proxying purposes is sometimes referred to as ‘publishing'. ————————————————- Uses Below are some typical uses for proxy ARP: Joining a broadcast LAN with  serial  links (e. g. ,  dialup  or  VPN  connections). Assume an Ethernet broadcast domain (e. g. , a group of stations connected to the same hub) using a certain IPv4 address range (e. g. , 192. 168. 0. 0/24, where 192. 168. 0. 1 – 192. 168. 0. 127 are assigned to wired nodes). One or more of the nodes is an  access router  accepting dialup or VPN connections. The access router gives the dial-up nodes IP addressses in the range 192. 168. 0. 128 – 192. 168. 0. 254; for this example, assume a dial-up node gets IP address 192. 168. 0. 254. The access router uses Proxy ARP to make the dial-up node present in the subnet without being wired into the Ethernet: he access server ‘publishes' its own MAC address for 192. 168. 0. 254. Now, when another node wired into the Ethernet wants to talk to the dial-up node, it will ask on the network for the MAC address of 192. 168. 0. 254 and find the access server's MAC address. It will therefore send its IP packets to the access server, and the access server will know to pass them on to the particular dial-up node. All dial-up nodes therefore appear to the wired Ethernet nodes as if they are wired into the same Ethernet subnet. Taking multiple addresses from a LAN Assume a station (e. g. , a server) with an interface (10. 0. 0. 2) connected to a network (10. 0. 0. 0/24). Certain applications may require multiple IP addresses on the server. Provided the addresses have to be from the 10. 0. 0. 0/24 range, the way the problem is solved is through Proxy ARP. Additional addresses (say, 10. 0. 0. 230-10. 0. 0. 240) are  aliased  to the  loopbackinterface of the server (or assigned to special interfaces, the latter typically being the case with  VMware/UML/jails/vservers/other virtual server environments) and ‘published' on the 10. . 0. 2 interface (although many operating systems allow direct allocation of multiple addresses to one interface, thus eliminating the need for such tricks). On a firewall In this scenario a firewall can be configured with a single IP address. One simple example of a use for this would be placing a firewall in front of a single host or group of hosts on a subnet. Example- A network (10. 0. 0. 0/8) has a serve r which should be protected (10. 0. 0. 20) a proxy-arp firewall can be placed in front of the server. In this way the server is put behind a firewall without making any changes to the network at all. Mobile-IP In case of  Mobile-IP  the Home Agent uses Proxy ARP in order to receive messages on behalf of the Mobile Node, so that it can forward the appropriate message to the actual mobile node's address (Care Of Address). Transparent subnet gatewaying A setup that involves two physical segments sharing the same IP subnet and connected together via a  router. This use is documented in  RFC 1027 ————————————————- Advantages The advantage of Proxy ARP over other networking schemes is simplicity. A network can be extended using this technique without the knowledge of the upstream router. For example, suppose a host, say A, wants to contact another host B, where B is on a different subnet/broadcast domain than A. For this, host A will send an  ARP  request with a Destination IP address of B in its ARP packet. The multi-homed router which is connected to both the subnets, responds to host A's request with its MAC address instead of host B's actual  MAC  address, thus proxying for host B. In the due course of time, when host A sends a packet to the router which is actually destined to host B, the router just forwards the packet to host B. The communication between host A and B is totally unaware of the router proxying for each other. ————————————————- Disadvantages Disadvantage of Proxy ARP include scalability (ARP resolution is required for every device routed in this manner) and reliability (no fallback mechanism is present, and masquerading can be confusing in some environments). It should be noted that ARP manipulation techniques, however, are the basis for protocols providing  redundancy  on broadcast networks (e. g. ,Ethernet), most notably  CARP  and  Virtual Router Redundancy Protocol. Proxy ARP can create DoS attacks on networks if misconfigured. For example a misconfigured router with proxy ARP has the ability to receive packets destined for other hosts (as it gives its own MAC address in response to ARP requests for other hosts/routers), but may not have the ability to correctly forward these packets on to their final destination, thus blackholing the traffic.