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The Internet Protocol (IP) is a protocol used for communicating data across a packet-

switchedinternetwork using the Internet Protocol Suite, also referred to as TCP/IP.

IP is the primary protocol in theInternet Layerof the Internet Protocol Suite and has the task of

delivering distinguished protocol datagrams(packets) from the source host to the destination hostsolely based on their addresses. For this purpose the Internet Protocol defines addressing

methods and structures for datagram encapsulation. The first major version of addressing

structure, now referred to as Internet Protocol Version 4 (IPv4) is still the dominant protocol of the

Internet, although the successor, Internet Protocol Version 6 (IPv6) is being deployed actively

worldwide.

An Internet Protocol address (IP address) is a numerical label that is assigned to devices

participating in acomputer network that uses the Internet Protocolfor communication between its

nodes.[1]An IP address serves two principal functions: host or network interface identification and

location addressing. Its role has been characterized as follows: "A nameindicates what we seek.

An address indicates where it is. A route indicates how to get there."[2]

The designers of TCP/IP defined an IP address as a 32-bit number[1] and this system, known

asInternet Protocol Version 4 orIPv4, is still in use today. However, due to the enormous growth

of the Internet and the predicted depletion of available addresses, a new addressing system

(IPv6), using 128 bits for the address, was developed in 1995 [3] and standardized byRFC 2460 in

1998.[4]Although IP addresses are stored as binary numbers, they are usually displayed

inhuman-readablenotations, such as 208.77.188.166 (forIPv4), and 2001:db8:0:1234:0:567:1:1

(forIPv6).

The Internet Protocol is used to routedatapackets between networks; IP addresses specify the

locations of the source and destination nodes in the topologyof the routing system. For this

purpose, some of the bits in an IP address are used to designate a subnetwork. The number of

these bits is indicated in CIDR notation, appended to the IP address; e.g.,208.77.188.166/24.

As the development ofprivate networks raised the threat ofIPv4 address exhaustion,RFC

1918set aside a group of private address spaces that may be used by anyone on private

networks. They are often used with network address translators to connect to the global public

Internet.

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The Internet Assigned Numbers Authority(IANA), which manages the IP address space

allocations globally, cooperates with five Regional Internet Registries (RIRs) to allocate IP

address blocks toLocal Internet Registries(Internet service providers) and other entities.

) A technique used to gain unauthorized access to computers, whereby the

intruder sends messages to a computerwith an IP address indicating that the

message is coming from a trusted host. To engage in IP spoofing, ahackermust

first use a variety of techniques to find an IP address of a trusted host and then

modify thepacket headers so that it appears that the packets are coming from

that host

Introduction: IP Spoofing

An article on "Security Problems in the TCP/IP Protocol Suite" by S.M.Bellovin in

1989 initially explored IP Spoofing attacks . He described how Robert Morris,

creator of the now infamous Internet Worm, figured out how TCP created

sequence numbers and forged a TCP packet sequence.

This TCP packet included thedestination address of his victim and using as IP

spoofing attack Morris was able to obtain root access to his targeted system

without a User ID or password.

Introduction:

IP spoofing is a technique used to gain unauthorized access to computers,

whereby the attacker sends messages to a computer with a forging IP address

indicating that the message is coming from a trusted host. There are a

few variations on the types of attacks that using IP spoofing.

Spoofing Attacks:

1.non-blind spoofing

This attack takes place when the attacker is on the same subnet as the target

that could see sequence and acknowledgement of packets. The threat of this type

of spoofing is session hijacking and an attacker could bypass

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any authenticationmeasures taken place to build the connection. This is

accomplished by corrupting the DataStream of an established connection, then re-

establishing it based on correct sequence and acknowledgement numbers with the

attack machine.

2.Blind spoofing

This attack may take place from outside where sequence

and acknowledgementnumbers are unreachable. Attackers usually send several

packets to the target machine in order to sample sequence numbers, which is

doable in older days. Today, most OSs implement random sequence number

generation, making it difficult to predict them accurately. If, however, the

sequence number was compromised, data could be sent to the target.

3.Man in the Middle Attack

This is also called connection hijacking. In this attacks, a malicious partyintercepts a legitimate communication between two hosts to controls the flow

ofcommunication and to eliminate or alter the information sent by one of the

original participants without their knowledge. In this way, an attacker can fool a

target into disclosing confidential information by spoofing the identity of the

original sender or receiver. Connection hijacking exploits a "desynchronized state"

in TCPcommunication. When the sequence number in a received packet is not the

same as the expected sequence number, the connection is called

"desynchronized." Depending on the actual value of the received sequence

number, the TCP layer may either discard or buffer the packet. When two hosts

are desynchronized enough, they will discard/ignore packets from each other. An

attacker can then inject forged packets with the correct sequence numbers and

potentially modify or add messages to the communication. This requires the

attacker to be located on thecommunication path between the two hosts in order

to replicate packets being sent. The key to this attack is creating the

desynchronized state.

4.Denial of Service Attack

IP spoofing is almost always used in denial of service attacks (DoS), in which

attackers are concerned with consuming bandwidth and resources by flooding the

target with as many packets as possible in a short amount of time. To effectivelyconducting the attack, attackers spoof source IP addresses to make tracing and

stopping the DoS as difficult as possible. When multiple compromised hosts are

participating in the attack, all sending spoofed traffic, it is very challenging to

quickly block the traffic.

Misconception of IP Spoofing:

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A common misconception is that "IP Spoofing" can be used to hide your IP

address while surfing the Internet, chatting on-line, sending e-mail, and so forth.

This is generally not true. Forging the source IP address causes the responses to

be misdirected, meaning you cannot create a normal network conncetion.

However, IP spoofing is an integral part of many networks that do not need to see

responses.

Detection of IP Spoofing:

We can monitor packets using network-monitoring software. A packet on an

external interface that has both its source and destination IP addresses in the

local domain is an indication of IP spoofing. Another way to detect IP spoofing is

to compare the process accounting logs between systems on your internal

network. If the IP spoofing attack has succeeded on one of your systems, you

may get a log entry on the victim machine showing a remote access; on the

apparent source machine, there will be no corresponding entry for initiating that

remote access.

Prevention of IP Spoofing:

To prevent IP spoofing happen in your network, the following are some common

practices:

Avoid using the source address authentication. Implement

cryptographicauthentication system-wide.

Configuring your network to reject packets from the Net that claim to

originate from a local address.

Implementing ingress and egress filtering on the border routers and

implement an ACL (access control list) that blocks private IP addresses on

your downstream interface.

If you allow outside connections from trusted hosts, enable encryption sessions at

the router.

IP Fragment Attacks:

When packets are too large to be sent in a single IP packet, due to interface

hardware limitations for example, an intermediate router can split them up unlessprohibited by the Don't Fragment flag. IP fragmentation occurs when a router

receives a packet larger than the MTU (Maximum Transmission Unit) of the next

network segment. All such fragments will have the same Identification field value,

and the fragment offset indicates the position of the current fragment in the

context of the pre-split up packet. Intermediate routers are not expected to re-

assemble the fragments. The final destination will reassemble all the fragments of

an IP packet and pass it to higher protocol layers like TCP or UDP.

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Attackers create artificially fragmented packets in order to

circumvent firewalls that do not perform packet reassembly. These only consider

the properties of each individual fragment, and let the fragments through to

final destination. One such attack involving fragments is known as the tiny

fragment attack.

Two TCP fragments are created. The first fragment is so small that it does not

even include the full TCP header, particularly the destination port number. The

second fragment contains the remainder of the TCP header, including the port

number. Another such type of malicious fragmentation involves fragments that

have illegal fragment offsets.

A fragment offset value gives the index position of this fragment's data in a

reassembled packet. The second fragment packet contains an offset value, which

is less than the length of the data in the first packet. E.g..

If the first fragment was 24 bytes long, the second fragment may claim to have

an offset of 20. Upon reassembly, the data in the second fragment overwrites the

last four bytes of the data from the first fragment. If the unfragmented packet

were TCP, then the first fragment would contain the TCP header overwriting

thedestination port number.

In the IP layer implementations of nearly all OS, there are bugs in the reassembly

code. An attacker can create and send a pair of carefully crafted but malformed IP

packets that in the process of reassembly cause a server to panic and crash. The

receiving host attempts to reassemble such a packet, it calculates a negative

length for the second fragment. This value is passed to a function (such as

memcpy ()), which should do a copy from/ to memory, which takes the negative

number to be an enormous unsigned (positive) number.

Another type of attack involves sending fragments that if reassembled will be an

abnormally large packet, larger than the maximum permissible length for an IP

packet. The attacker hopes that the receiving host will crash while attempting to

reassemble the packet. The Ping of Death used this attack. It creates an ICMP

echo request packet, which is larger than the maximum packet size of 65,535

bytes.

ICMP Smurfing

"Smurf" is the name of an automated program that attacks a network by

exploiting IP broadcast addressing. Smurf and similar programs can cause the

attacked part of a network to become "inoperable." Network nodes and their

administrators to exchange information about the state of the network use ICMP.

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A smurf program builds a network packet with a spoofed victim source address.

The packet contains an ICMP ping message addressed to an IP broadcast address,

meaning all IP addresses in a given network. If the routing device delivering

traffic to those broadcast addresses performs the IP broadcast to layer 2

broadcast function, most hosts on that IP network will reply to it with an ICMP

echo reply each. The echo responses to the ping message are sent back to thevictim address. Enough pings and resultant echoes can flood the network making

it unusable for real traffic.

A related attack is called "fraggle", simple re-write of smurf; uses UDP echo

packets in the same fashion as the ICMP echo packets. The intermediary

(broadcast) devices, and the spoofed victim are both hurt by this attack. The

attackers rely on the ability to source spoofed packets to the "amplifiers" in order

to generate the traffic which causes the denial of service.

In order to stop this, all networks should perform filtering either at the edge of

the network where customers connect (access layer) or at the edge of the

network with connections to the upstream providers, in order to defeat the

possibility of source address spoofed packets from entering from downstream

networks, or leaving for upstream networks.

One way to defeat smurfing is to disable IP broadcast addressing at each network

router since it is seldom used

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