IP fragmentation attack: Difference between revisions

Revision as of 09:14, 5 December 2017

Revision as of 10:01, 21 February 2018

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Three fields in the [[IPv4#Header|IP header]] are used to implement fragmentation and reassembly. The "Identification", "Flags" and "Fragment Offset" fields.

{| class="wikitable" style="margin: 0 auto; text-align: center;"

|+ IPv4 Header Format

<code>

|-

0 1 2 3

! ''Offsets''

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

! [[Octet (computing)|Octet]]

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

! colspan="8" | 0

|Version| IHL |Type of Service| Total Length |

! colspan="8" | 1

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

! colspan="8" | 2

| Identification |Flags| Fragment Offset |

! colspan="8" | 3

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

|-

| Time to Live | Protocol | Header Checksum |

! | [[Octet (computing)|Octet]]

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

! [[Bit]]

| Source Address |

! style="width:2.6%;"| 0

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

! style="width:2.6%;"| 1

| Destination Address |

! style="width:2.6%;"| 2

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

! style="width:2.6%;"| 3

| Options | Padding |

! style="width:2.6%;"| 4

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

! style="width:2.6%;"| 5

</code>

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|-

! 0

! 0

| colspan="4"|[[#Version|Version]]

| colspan="4"|[[#IHL|IHL]]

| colspan="6"|[[#DSCP|DSCP]]

| colspan="2"|[[#ECN|ECN]]

| colspan="16"|[[#Total Length|Total Length]]

|-

! 4

! 32

| colspan="16"|[[#Identification|Identification]]

| colspan="3"|[[#Flags|Flags]]

| colspan="13"|[[#Fragment Offset|Fragment Offset]]

|-

! 8

! 64

| colspan="8"|[[#TTL|Time To Live]]

| colspan="8"|[[#Protocol|Protocol]]

| colspan="16"|[[#Header Checksum|Header Checksum]]

|-

! 12

! 96

| colspan="32"|[[#Source address|Source IP Address]]

|-

! 16

! 128

| colspan="32"|[[#Destination address|Destination IP Address]]

|-

! 20

! 160

| colspan="32" rowspan="4" |[[#Options|Options]] (if IHL > 5)

|-

! 24

! 192

|-

! 28

! 224

|-

! 32

! 256

|}

Flags:

Line 44 ⟶ 112:

: Bit 2: (AF) 0 = Last Fragment, 1 = More Fragments.

{| class="wikitable" style="text-align: center;"

<code>

|-

0 1 2 13 bits

! Bit

+---+---+---+ +-----------------------------+

! 0 !! 1 !! 2 !! 3 |!! 4 !! |5 D!! |6 M!! |7 !! 8 !! |9 !! 10 !! 11 Fragment!! Offset12 !! 13 !! 14 !! |15

|-

| 0 | F | F | +-----------------------------+

! Field

+---+---+---+

| 0 || DF || MF || colspan="13" | Fragment Offset

</code>

|}

Fragment Offset specifies the fragment's position within the original Datagram, measured in 8-byte units.