Slide title

In CAPITALS

50 pt

Slide subtitle

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Manoranjan Mohanty

IPv4, IPv6, and IPSec

COMPSCI 316 (Cyber Security)

Source of some slides: Princeton University

Also thanks to J.F Kurose and K.W. Ross

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THE PLAN

This week and next week

Internet layer

– IPv4, IPv6, IPSec, BGP

Wifi security

Software Defined Network (SDN) – If time permits

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INTERNET LAYER

Provides service to

Transport Layer. Takes

service from Link Layer

Host-to-host

communication

– Host: An end system

(computer) having unique

IP (network) address

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INTERNET LAYER CONT

Packet delivery, routing, error/information

reporting

https://www.tutorialspoint.com/data_communication_co

mputer_network/network_layer_routing.htm

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INTERNET PROTOCOL PACKET

DELIVERY

Addressing

Encapsulation

Forwarding

Connectionless

Best service

IPv4 and IPv6 https://en.wikipedia.org/wiki/Encapsulation_(networ

king)#/media/File:UDP_encapsulation.svg

Destination

IP address

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IPv4

IPv4 is IP version 4

IP address: A 32-bit address that uniquely and

universally identifies a host on the Internet

– 10000000 11000000 11100000 11110000

– Dotted decimal form: 128.192.224.240

The IP address allocation is done as follows

– The “wholesale” approach (ICANN -> ISP ->

Organization -> You)

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CLASSFUL ADDRESSING VS CLASSLESS

ADDRESSING

For easier addressing, a group of similar IP

addresses are assigned to an organization

The address is divided into two parts

– netid (every device in the organization has the

same netid) and hostid (the hostid changes)

In classful addressing, there are only five

possible ways of division

Source: Data Communications and

Networking by Behrouz A. Forouzan

netid . hostid

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IPv4 : CLASSLESS ADDRESSING

Classful addressing often leads to misuse of IP

addresses

Classless addressing: The size of “block size”

can vary

– x.y.z.t / n – first n bits for the block (prefix)

Classless addressing also not enough to solve

shortage of IPv4 address

– In the best case, more than four billion IP

addresses (232)

– Only in 2018, more than 2.3 billions of computing

devices shipped (Gartner April 2018)

Network Address Translation (NAT)

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NAT

Why NAT replaces port numbers ?

Source: Computer

Networking: A Top-

Down Approach Book

by Jim Kurose

In an organization, allows large set of

addresses internally (private) but small set

externally (public)

S = 10.0.0.3, 3345

D = 128.119.40.0, 90

138.76.29.7, 3345 10.0.0.1, 3345

138.76.29.7, 3345 10.0.0.3, 3345

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IPv4 PACKET FORMAT

4-bit

Version

4-bit

Header

Length

8-bit

Type of Service

(TOS)

16-bit Total Length (Bytes)

16-bit Identification3-bit

Flags 13-bit Fragment Offset

8-bit Time to

Live (TTL)8-bit Protocol 16-bit Header Checksum

32-bit Source IP Address

32-bit Destination IP Address

Options (if any)

Payload

20-byte

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IP HEADER FIELDS

Version number (4-bit)

– Indicates the version of the IP protocol

– Typically 4 (for IPv4) and sometimes 6 (for IPv6)

Header length (4-bit)

– Number of 32-bit words in the header

– Typically 5 (for a 20-byte IPv4 header)

Type of service (8-bit)

– Used to manage quality of service

– E.g., low delay for audio and high bandwidth for bulk

transfer

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IP HEADER FIELDS CONT

Total length (16-bit)

– Number of bytes in the packet (header+payload)

– Maximum size can be 64KB

Underlying links may impose harder limits

Fragmentation information (32-bit)

– Packet identification, flags, and fragmentation offset (see

later)

– Supports dividing a large IP packet into fragments when a

link cannot handle that (large) packet

Time-to-live (8-bit)

– Lifetime of a packet

– Used to prevent loops

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TTL

TTL in packet header (8-bit)

– TTL is decremented as a packet traverses a router

– A packet is discarded when TTL reaches 0

– A ‘time exceeded’ message is sent to the source

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IP HEADER FIELDS CONT

Protocol (8-bit)

– A value that specifies the type of payload

– E.g., TCP or UDP

Header checksum (32-bit)

– For IP header only

– Recalculated by each router since TTL changes

Source or destination address (32-bit)

– IP address

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IP FRAGMENTATION AND

REASSEMBLY

Max IP datagram:

64KB

Network links have

Maximum Transfer

Unit (MTU)

Large IP datagrams

can be fragmented

Reassembled at

destination (not router,

internet layer)

fragmentation:

in: one large datagram

out: 3 smaller datagrams

reassembly

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IP FRAGMENTATION AND

REASSEMBLY CONT

Example

– 4000 bytes

datagram

– MTU is 1500

bytes

length=header+payload

ID=7

offset=0

fragflag=0

length=4000

ID=7

offset=0

fragflag=1

length=1500

ID=7

offset=185

fragflag=1

length=1500

ID=7

offset=370

fragflag=0

length=1040

One large datagram becomesseveral smaller datagrams

1480 bytes in data field

offset =1480/8

ID identifies IP datagram

fragflag=1 means

more fragments availableoffset points fragment

offset (in octet)

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ISSUES WITH FRAGMENTATION

Complicates router and end system

Reassembly computation cost

Interferes with TCP control flow

DoS attack

– Final fragment never sent

– Overlapping “offset”

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IP SPOOFING

Source IP address should be the sending host

– But, who is checking that?

– One could send packets with any source IP

Why would someone want to do this?

– Launch a DoS attack

– Evade detection

– An attack against the spoofed host

Spoofed host is wrongly blamed

Spoofed host may receive return traffic from the receiver

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IPv4 SECURITY

Confidentiality

Integrity

Authenticity

Availability

Replay attack

IPSec

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IPv6

The recent version of Internet Protocol (IP)

Designed in 90s

It offers larger address space

– 128-bits (16-byte) address

– 18 million trillion addresses

IPv6 is intended to replace IPv4

– Likely to co-exist with IPv4 for many years

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IPv6 ADDRESS

Source: Data Communications and Networking

by Behrouz A. Forouzan

"colon hex" notation – A colon between two

sections (four hex values)

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ABBREVIATED IPv6 ADDRESSES

Source: Data Communications and Networking

by Behrouz A. Forouzan

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IPv6 SIMPLIFIED HEADER

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IPv6 HEADER: SIMPLIFICATION

Fixed length for the basic header

– IPv4 header of variable length: 20-byte (min)

– IPv6 has the main header: 40-byte (fixed)

Leads to fast header processing

No need of header length (hlen)

Fragmentation only by traffic source

– Source does path MTU discovery

– No burden on routers to do fragmentation

– No need of identification, flag, and fragment offset

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IPv6 HEADER: SIMPLIFICATION CONT

Header checksums are eliminated

– IP header checksum is recalculated by every

node due to change in TTL

– The idea is to improve performance by saving

some resources

– Error detection check can be enforced by upper

layers

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NEXT HEADER FIELD

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IPv6 EXTENSION HEADERS

Separate header(s) between the base header and data

to carry optional internet-layer information

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TRANSITION FROM IPv4 to IPv6

What’s wrong with dual-

stack approach?

Computer Networking: A Top-Down Approach Book by Jim Kurose

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MAC ADDRESS TO IPv6 CONVERSION

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SUMMARY

IPv4 alone is not sufficient for providing global

connectivity

– Combining IPv4 with NAT solves the problem

IPv4 header checksum is recalculated by each router

since TTL changes

TTL is decremented as a packet traverses a router

– A packet discarded when TTL is 0

Source IP address could be spoofed

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SUMMARY

IPv6 uses 16-byte addressing scheme

IPv6 made some simplifications

– Fixed length basic header

– Fragmentation only by traffic source

– No header checksum

Flow label is a new field in IPv6 header, which is quite

useful

IPv6 is being deployed

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Questions?

Thanks for your attention!

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ACKNOWLEDGEMENT

Some slides are provided by Muhammad Rizwan Asghar.

Thanks to him!