1. IPv6 address (abbreviated representation) 2. IPv6 address - - PowerPoint PPT Presentation

1. IPv6 address (abbreviated representation) 2. IPv6 address (abbreviation and expansion practice) 3. IPv6 advantages over IPv4 4. IPv4 address structure 5. IPv6 address structure

IPv4 Address

32 bit address (computer stores information in binary (binary notation) Use of dotted decimal notation for external data representation (values 0 to 255) 232 (about 4.3 billion) addresses Fields are separated by dots ("."). 8 bits in the first octet, 8 in the second etc. (01111011.00100010. etc.)

128 bit address (not easily handled by humans) 2128 (340 undecillion about 340 trillion, trillion, trillion addresses). Represented with the use of "coloned-hex" (hexadecimal) notation

Three hundred and forty undecillion, two hundred and eighty-two decillion, three hundred and sixty-six nonillion, nine hundred and twenty octillion, nine hundred and thirty-eight septillion, four hundred and sixty-three sextillion, four hundred and sixty-three quintillion, three hundred and seventy-four quadrillion, six hundred and seven trillion, four hundred and thirty-one billion, seven hundred and sixty-eight million, two hundred and eleven thousand, four hundred and fifty-six.

Addresses are written using 32 hexadecimal digits 8 fields with 16 bits in each field and with 4 hex characters inside 2340:1111:AAAA:0001:1234:5678:9ABCD:1234 Each hexadecimal character represents 4 bits i.e. (4 * 4) * 8 = 128 bits Fields or ‘hextet’ are separated by colons (:) Sixteen bits can hold binary values from 0000 0000 0000 0000 to 1111 1111 1111 1111 Each field with values from 0000 to ffff

Remember: Hexadecimal is a Base 16 numbering system uses the numbers 0 to 9 and the letters A to F.

Hexadecimal digits are NOT case sensitive i.e. case-independent

IPv6 accepts abbreviations in address notation 1090:0000:0000:0000:0009:0900:210D:325F Becomes 1090::9:900:210D:325F Even in hexadecimal format, an IPv6 address is long (hard to remember) and many digits are zero’s. Hosts/routers usually use the shortest abbreviation, even if you type in all 32 hex digits. You need to know abbreviated version

Here’s the thing

Leading zero’s in a 16-bit block can be dropped

NEVER remove trailing 0s in a quartet.

01AB can be represented as 1AB 0A00 → A00 00AB →AB 0000 → 0 FE80:0000:0000:0000:1232:E4BF:FE1A:8324 → FE80:0:0:0:1232:E4BF:FE1A:8324 3210 can not be abbreviated!

Omitting All 0 Segments (Zero Compression)

Pair of colons/double colon (::) Replace any single, contiguous string of two or more consecutive quartets of all hex 0s with :: Zero compression can only be used once in a given address,

• therwise the address will be ambiguous.

1090:0000:0000:0000:0009:0900:210D:325F → 1090::9:900:210D:325F

Show abbreviations for the following addresses

a. 0000:0000:FFFF:0000:0000:0000:0000:0000 0:0:FFFF::

• b. 1234:2346:0000:0000:0000:0000:0000:1111

1234:2346::1111

• c. 0000:0001:0000:0000:0000:0000:1200:1000

0:1::1200:1000

• d. 0000:0000:0000:0000:0000:FFFF:24.123.12.6

::FFFF:24.123.12.6

Structurally/superficially valid or invalid? If invalid, why? a. 2001:468:0d01:003c:0000:0000:80df:3c15 b. 2001:468:0d01:003c::80df:3c15 c. 2001:468:d01:3c::80df:3c15 d. 2001:760:2e01:1::dead:beef e. 2001:480:10:1048:a00:20ff:fe9a:58c1:80 f. 2001:500::4:13::80 g. 2001:13G7:7002:4000::10 h. 2607:f278:4101:11:209:5bff:fe8f:6609 i. fe80::209:3dff:fe13:fcf7

a. 2001:468:0d01:003c:0000:0000:80df:3c15 (Valid) b. 2001:468:0d01:003c::80df:3c15 (Valid) c. 2001:468:d01:3c::80df:3c15 (Valid) d. 2001:760:2e01:1::dead:beef (Valid) e. 2001:480:10:1048:a00:20ff:fe9a:58c1:80 Invalid (nine chunks instead of eight) f. 2001:500::4:13::80 Invalid (double colons appear more than once) g. 2001:13G7:7002:4000::10 Invalid (G is not a valid hexadecimal digit) h. 2607:f278:4101:11:209:5bff:fe8f:6609 (Valid) i. fe80::209:3dff:fe13:fcf7 (Valid)

2 Rules 1. In each quartet, add leading 0s as needed until the quartet has four hex digits 2. If a double colon (::) exists, count the quarters currently shown; total should be < 8. Replace the :: with multiple quarters so that 8 total quarters exist.

FULL Abbreviation

2340:0000:0010:0100:1000:ABCD:0101:1010 30A0:ABCD:EF12:3456:ABC:B0B0:9999:9009 2222:3333:4444:5555:0000:0000:6060:0707 3210:: 210F:0000:0000:0000:CCCC:0000:0000:000D 34BA:B:B::20 FE80:0000:0000:0000:DEAD:BEFF:FEEF:CAFE

FULL Abbreviation

2340:0000:0010:0100:1000:ABCD:0101:1010 2340:0:10:100:1000:ABCD:101:1010 30A0:ABCD:EF12:3456:0ABC:B0B0:9999:9009 30A0:ABCD:EF12:3456:ABC:B0B0:9999:9009 2222:3333:4444:5555:0000:0000:6060:0707 2222:3333:4444:5555:::6060:0707 3210:0000:0000:0000:0000:0000:0000:0000 3210:: 210F:0000:0000:0000:CCCC:0000:0000:000D 210F::CCCC:0:0:D 34BA:000B:000B:0000:0000:0000:0000:0020 34BA:B:B::20 FE80:0000:0000:0000:DEAD:BEFF:FEEF:CAFE FE80::DEAD:BEFF:FEEF:CAFE

Mixed representation of IPv6 address = colon hex + dotted decimal notation Appropriate during transition period in which IPv4 address is embedded in IPv6 (rightmost 32 bits) Happens when most/all of left most sections are zero’s ::192.168.0.2 (legitimate address & all 96 left most bits are zero) OR 0:0:0:0:0:0:0:192.168.0.2 OR ::C0a8:2 (hex representation of 192.168.0.2)

1. Leading zero’s must be suppressed 2. Single 0000 field must be represented as 0 and should not be replaced by double colon 3. Shorten as much as possible 4. Always shorten largest number of zero’s 5. If two blocks pf zeros are equally long, shorten the first one 6. Use lowercase of a - f

Larger Address Space

Shortage of IPv6 addresses would only happen in Year 2400 IPv4 – 4.3 Billion Addresses (short supply since early 1990’s) 4, 294, 967, 296 IPv6 – 340 undecillion Addresses 340, 282, 366, 920, 938, 463, 374, 607, 431, 768, 211, 456 Some say, address depletion in this version is impossible.

Non-Broadcast

Less expensive in terms of bandwidth and router resources Reduces collisions as less traffic No longer any broadcast i.e. only unicast, multicast, anycast In IPv6 all nodes must support multicast, otherwise services will not work

No more ARP

Replaced by Network Discovery Protocol (NDP)

No more NAT Brings back original end-to-end model of Internet

Security

IP Security Protocol (IPsec) is mandatory for IPv6 BUT only optional for IPv4 Secure IPv4 by updating all nodes to support IPsec support

Autoconfiguration

Hello “Stateless Address Autoconfiguration” (SLAAC) In IPv4 we assign IP addresses (static or DHCP) In IPv6, device can get prefix information (used for routing IPv6 packets) from the router on the link The device can then autoconfigure 1 or more global IP address by using its MAC identifier No more reconfiguring your DHCP server, reduce admin costs when you buy a new fridge! So many IP devices of all types.

During the connection phase between hosts (via TCP 3 way handshake) Maximum Segment Size (MSS) is exchanged (not negotiated) between hosts MSS: maximum (now minimum) largest amount of data the host will can handle in a single, unfragmented piece + We also have the MTU Maximum Transmission Unit (MTU): maximum packet size for a link Ethernet interfaces have a default MTU of 1500 byte

Maximum Segment Size (MSS) of data that the host would accept Lead to fragmentation at the endpoints as packets were larger than the interface MTU (endpoints – source and destination)

Minimum Segment Size of data that the host would accept Each host will first compare its outgoing interface MTU with its MSS Choose the lowest value as the MSS to send. Hosts then compare MSS sizes and choose the lowest Now avoiding fragmentation

TCP computes the MSS Using the MTU size of the network interface + Then subtracting the protocol headers to come up with the size of data in the TCP packet e.g. Ethernet with a MTU of 1500 would result MSS of 1460 after subtracting 20 bytes for IPv4 header and 20 bytes for TCP header.

TCP protocol includes a mechanism for both ends of a connection to advertise the MSS T

• be used over the connection when the connection is created.

Each end uses the OPTIONS field in the TCP header to advertise a proposed MSS. MSS that is chosen is the smaller of the values provided by the two ends. If one endpoint does not provide its MSS, then 536 bytes is assumed, which is bad for performance. The problem is that each TCP endpoint only knows the MTU of the network it is attached to. It does not know what the MTU size of other networks that might be between the two endpoints. So, TCP only knows the correct MSS if both endpoints are on the same network

ISP use much faster links e.g. gigabit & 10 gigabit and these allow bigger packets up to 9,000 bytes. Size of packet that can get from A → B without any difficulties depends on the smallest link in the chain Internet as a whole generally works with 1,500 byte packets with no problem But There are cases where smaller MTU links are used i.e. VPN (Virtual Private Network) Smallest link allowed is 576 bytes i.e. modems on dialup-internet

What happens if a packet is too big?

A. Don't send the packet and send an error message back saying it could not be sent B. Break the packet up in to smaller bits (fragments) which will fit, and send these on to the next router.

Choice depends on the packet

IPv6 packets have to take option (A) and send an error. IPv4 packets the packet has a flag called DF (Don't Fragment). If that is set you have to take option (A) and send an error. If not, then you take option (B) and fragment the packet

Fragments are

Create extra overhead as each packet has headers that have to be copied in to each fragment. Work badly when a link is congested as dropping any fragment in a packet means the whole packet is lost. Take up CPU time creating the fragments and putting them back together. All in all it is better if the sending end creates the smaller packets in the first place. Host decides to use Path MTU Discovery to avoid fragmentation

Path MTU Discovery with TCP works by setting the Don't Fragment (DF) flag bit in the IP headers of outgoing TCP packets. Any device along the path whose MTU is smaller than the packet will drop it & Send back an ICMP Fragmentation Needed message containing its MTU Allowing the source host to reduce its Path MTU appropriately. Process is repeated until the MTU is small enough to traverse the entire path without fragmentation

Fragmentation + Reassembly

Elimination of hop-by-hop packet fragmentation Packet can only be fragmented (if needed) by the source & NOT by the router Reassembly takes place at the destination Fragmentation at routers require a lot of processing Fields that handle fragmentation are put into fragmentation extension header

Individual packets to be sized according to the needs of the application as well as the needs of the network Designers of IP could not rely on a single packet size for all transmissions.

Any IP router that is unable to forward an IP packet into the next network As the packet is too large for this network May split the packet into a set of smaller IP fragments and forward each of these fragments. Fragments continue along the network path as autonomous packets Addressed destination host is responsible to re-assemble these fragments back into the original IP packet.

3 fields use to control whether routers are allowed to fragment a packet Identification Fragment Offset Flags When a packet needs to be fragmented, these fields need to be recalculated

IP header contains all the necessary information to deliver the packet at the other end. IPv4 header of variable length = min 20 bytes but can be extended up to 60 bytes Options field lead to IPv4 header of different sizes Options = security options, source routing, timestamping.

Version

Version of IP i.e. 4 for IPv4

Header Length

Length of IP header Included due to options field

Type of Service (ToS)

Rarely used (all bits set to zero) Specify specific handing of the packet. Two sub-fields: Precedence + TOS. Precedence: priority for packet e.g. routine, priority and used in QOS Applications TOS: selection of delivery service in terms of throughput, delay, reliability, monetary cost

Total Length

T

• tal length of a packet including the header

By subtracting the header length, one can determine the size of the packets data payload Maximum IP packet size is 65535

Indentifier + Flags + Fragment Offset = Fragmentation of a packet

Router marks each fragment with the same number in the identifier field, when they need to fragment the packet so the receiving device can identify the fragments that go together. Some protocols benefit from avoiding fragmentation i.e. used where entire message must be delivered intact as pieces will not make sense or when the receiver has limited IP implementation and can not reassemble fragments.

Flags

(3 bit field with 1st bit unused). 2nd bit is the “Don’t fragment me bit (DF) and when set to 1, routers can not fragment the

• packet. If the packet can not be forwarded without fragmenting, router drop the packets and sends an ICMP destination

unreachable error message back to source. 3rd bit is the ‘More Fragments (MF) bit. When the router fragments a packet, it sets the MF bit to 1 in all but the last fragment so the receiver knows to keep expecting fragments until it encounters a fragment with MF = 0

Fragment Offset

Solves the problem of sequencing fragments (as fragments may not arrive in order) by indicating to the receiver where in the overall message each particular fragment should be placed (0-8191) N.B: if a single fragment is lost during transmission, the entire packet must be resent, refragmented at same point in n/w.

TTL (Time to Live)

Measure of max router hops a packet can take on way to its destination. Set with a certain number when the packet is first generated. Decreased by each router until it reaches zero when the packet will be discarded & ICMP sent Default values are 15, 32 and 64. In a sense, TTL is ‘hop count’ and in IPv6 this field is called ‘Hop Limit’

Header Checksum

Error detection field for IPv4. A check sum is basically a value that is computed from data packet to check its integrity. Through integrity, we mean a check on whether the data received is error free or not. While traveling on network a data packet can become corrupt and there has to be a way at the receiving end to know that data is corrupted or not. At the source side, the checksum is calculated and set in header as a field. At the destination side, the checksum is again calculated and crosschecked with the existing checksum value in header to see if the data packet is OK or not. IP header checksum is calculated over IP header only as the data that generally follows the IP header (like ICMP, TCP etc) have their own checksums

Options

Loose Source Routing Series of IP addresses for router interfaces are listed so the packet must pass through each of these addresses (although multiple hops may be taken between addresses). Strict Source Routing Series of router addresses is listed but pack must follow the route exactly i.e. next hop must be the next address on the list (reasons for these routing styles in the notes section) Record Route

Router enters the address of its outgoing interface as the packet transmits so a record is kept of all routers that the packet encounters

Timestamp Same as record route but also adds a timestamp, when the packet was at the router as well as where it was. The 'options' field is variable length, and the padding field is used to bring packet header length to a multiple of 32 bits

Before sending IPv6 traffic, the source does Path MTU (PMTU) Discovery. (Maximum Transmission Unit) Idea behind it is to send packets that are as large as possible while still avoiding fragmentation. If source does not receive ‘packet too big’ error message from the router THEN It may keep sending packets that will not be dropped before they reach their destination

When a router receives a packet that’s too big Router must drop the packet & send an ICMPv6 error message ‘packet too big’ back to source node

Simplified Header

(faster processing)

Reduces the work done each time a router must route an IPv6 packet IPv6 have 1 fixed header and zero or more Optional (Extension) Headers Only important fields (necessary information for router) are in the header All non-essential fields and option fields are put into Extension Header (when needed) Fixed Sized (main header length fixed at 40 bytes, so makes the Header Length field obsolete)

Version

Version of IP i.e. 6 for IPv6

Traffic Class (Packet Priority)

Replaces T

• S in IPv4

Distinguish different payloads with different delivery requirements/handling (different classes/priorities of packets) by routers

Flow label

Sending host can label sequence of packets (flow of traffic) Routers keep track of flow + process packets belonging to the same flow (same source & destination address) more efficiently As the routes do not have to process the packet header. Packets also belong to same application of the source and destination Ensure load balancing as packets with belonging to same flow are forwarded over same path Flow label + addresses of source/destination nodes + source/destination ports = uniquely identify the flow

Payload Length

Length of data carried after IP header. Length field in IPv4 includes length of header whereas payload length in IPv6 contains only data following header. Extension headers are included in payload calculation.

Next Header

Protocol field in IPv4. If the next header is TCP or UDP, the this field will contain the same protocol numbers as in IPv4 (TCP -6 & UDP – 17) If extension headers are used, then will contain type of next extension header.

Hop limit

TTL field in IPv4 States the life duration of a packet in the network. Number of hops that a packet is permitted to travel before being discarded by a router. Value is decremented by 1 by a router when the packet is forwarded by the router. When the value becomes zero, the packet is discarded.

Extension Header

Inserted into packet ONLY if options are needed Located between header + payload Zero, one or more than one extension header Only processed by final destination (could be multicast) & not by intermediate devices

(except hop by hop options as processed by all nodes)

Give more functionality (special purpose) to the IP packet Strictly processed in the order (as below) 6 extension headers (many are options in IPv4) 1) Hop-by-Hop options header 2) Destination options header 3) Routing header 4) Fragment header 5) Authentication header 6) Encapsulating Security Payload

Hop-By-Hop Options Header

Optional information that must be examined by every node along the path of the packet Must immediately follow IPv6 header Indicated by “Next Header” field value of zero e.g. Jumbogram option

IPv6 payload length field supports max size of 65,535 bytes. Jumbo payload option allows for larger packets to be sent.

e.g. Router alert option T

ells the router that the packet contains important information to be processed when forwarding the packet

Routing Header

Loose source route option in IPv4 Used to give a list of one or more intermediate nodes that should be visited on the packets path to destination Indicated by “Next Header” field value of 43 in the proceeding header