网络的经济基础篇-之二-IPv4、IPv6

1      IPv4

Header Length

4-byte (32 bit), minimum = 5 (20 bytes),maximum = 15 (60 bytes)

TOS (Type of Service)

D：0 = NormalDelay                   1 = Minimize Delay

T：0 = NormalThroughput           1 = Maximize Throughput

R：0 = NormalReliability             1 = Maximize Reliability

C：0 = NormalCost                      1 = Minimize Cost

Total Length

byte(8 bit), including header and data,maximum = 65,535.

Identification

An identifying value generated by thesender to aid in assembling the fragments of a datagram.

DF

0 = Can Fragment            1 = Don’t Fragment

MF

0 = Last Fragment            1 = More Fragments

Fragment Offset

8-byte (64 bit), it indicates where thefragment belongs. The first fragment has offset zero.

Protocol

It indicates the next level protocol usedin the data portion of the datagram.

HeaderChecksum

checksum on the header only. For computingthe checksum, the checksum field is set to zero. Since some header fieldschange (e.g., TTL), the checksum field is recomputed and verified at each pointwhere the header is processed.

Padding

The padding is used to ensure that the headerends on a 32 bit boundary.

2   IPv4 Address

Host Address is divided into Subnet ID andHost ID. Subnet Mask is used todistinguish them.

 

A

10.0.0.0 ~ 10.255.255.255

B

172.16.0.0 ~ 172.31.255.255

C

192.168.0.0 ~ 192.168.255.255

Private IPv4 Address

 

Network Address

Host Addresss

Source

Destination

 

Subnet ID

Host ID

0

0

 

0

hostid

O

X

host on the network

specific host on the network

127

 

*

O

O

loop-back address

-1

netaddr

netaddr

netaddr

 

 

subnetid

-1

-1

-1

-1

-1

X

O

limited broadcast address

broadcast to network

broadcast to subnet

broadcast to all subnets

 0: all bits setto 0

-1: all bits set to 1

*: any value

Subnet ID = null: Subnet is not deployed.

Limited broadcast address: Router must notforward, limited to the original network.

3      IPv6

PayloadLength

byte(8 bit). Note that any extensionheaders present are considered as part of the payload.

NextHeader

Identify the type of header immediatelyfollowing the IPv6 header, is same as IPv4 Protocol field.

Payload

Note that IPv6 Extension Headers are alsocontained in Payload.

3.1     IPv6 Extension Header

It is recommended that headers appear inthe following order:

1.      IPv6 header

2.      Hop-by-Hop Options header

3.      Destination Options header: options to beprocessed by the first destination that appears in the IPv6 Destination Addressfield plus subsequent destinations listed in the Routing header.

4.      Routing header

5.      Fragment header

6.      Authentication header / Encapsulating SecurityPayload header: recommendation regarding the relative order is given in RFC 2406“IP Encapsulating Security Payload (ESP)”.

7.      Destination Options header: options to beprocessed only by the final destination of the packet.

8.      Upper-layer header

Each extension header should occur at mostonce, except for the Destination Options header which should occur at mosttwice.

IPv6 nodes must accept and attempt toprocess Extension Headers in any order and occurring any times, except forHop-by-Hop Options header which is restricted to appear immediately after IPv6header.

Alignment requirements for the ExtensionHeader MUST be aligned on an 8-octet boundary.

3.1.1       Option (used in Hop-by-HopOptions header and Destination Options header)

The sequence of options within Extension Headermust be processed strictly in the order they appear in the header; a IPv6 nodemust not, for example, scan through the header looking for a particular kind ofoption and process that option prior to processing all preceding ones.

OptionData Length

byte(8 bit)

OptionType (highest-order two bits)

00 - skip over this option and continueprocessing the header.

01 - discard the packet.

10 - discard the packet and send an ICMPParameter Problem, Code 2, message to the packet’s Source Address, pointing tothe unrecognized Option Type.

11 - discard the packet and, only if thepacket’s Destination Address was not a multicast address, send an ICMPParameter Problem, Code 2, message to the packet’s Source Address, pointing tothe unrecognized Option Type.

OptionType (the third-highest-order bit)

0 - Option Data does not change en-route

1 - Option Data may change en-route

When an Authentication header is present inthe packet, for any option whose data may change en-route, its entire OptionData field must be treated as zero when computing or verifying the packet’sauthenticating value.

Pad1 Option

Note that Pad1 option does not have lengthand data fields.

PadN Option

3.1.2       Hop-by-Hop Options Header (Next Header = 0 )

The Hop-by-Hop Options header is used tocarry optional information that must be examined by each node along thedelivery path.

HdrExt Len

8-byte (64 bit), not including the first 8bytes.

3.1.3       Routing Header ( Next Header = 43)

The Routing header is used by an IPv6source to list one or more intermediate nodes to be visited on the way to the destination.

HdrExt Len

8-byte (64 bit), not including the first 8bytes.

SegmentsLeft

Number of route segments remaining, i.e.,number of explicitly listed intermediate nodes still to be visited beforereaching the final destination.

If encountering Routing header with anunrecognized Routing Type, the behavior of node depends on the value of theSegments Left field, as follows:

If Segments Left is zero, the node mustignore the Routing header and proceed to process the next header in the packet.

If Segments Left is non-zero, the node mustdiscard the packet and send an ICMP Parameter Problem, Code 0, message to thepacket’s Source Address, pointing to the unrecognized Routing Type.

3.1.4       Fragment Header ( Next Header =44 )

The Fragment header is used by an IPv6source to send a packet larger than the path MTU to its destination. (Note:unlike IPv4, fragmentation in IPv6 is performed only by source nodes, not by routersalong a packet’s delivery path.)

HdrExt Len

8-byte (64 bit), not including the first 8bytes.

FragmentOffset

8-byte (64 bit), the offset relative to thestart of the Fragmentable Part of the original packet.

M

1 = more fragments;

0 = last fragment.

Identification

An identifying value generated by thesender to aid in assembling the fragments of a datagram.

3.1.5       Destination Options Header (Next Header = 60 )

The Destination Options header is used tocarry optional information that need be examined only by the destinationnode(s).

HdrExt Len

8-byte (64 bit), not including the first 8bytes.

3.1.6       No Next Header ( Next Header =59 )

The value 59 in the Next Header field of anIPv6 header or any Extension Header indicates that there is nothing followingthat header.

4      IPv6 Address

1. The preferred form is   x:x:x:x:x:x:x:x.

2. An alternative form is  x:x:x:x:x:x:d.d.d.d.

3. "::" indicates one or moregroups of 16 bits of zeros. "::" can only appear once in an address.The "::" can also be used to compress leading or trailing zeros in anaddress.

Unspecified Address              0:0:0:0:0:0:0:0 = ::/128

Loop-back Address          0:0:0:0:0:0:0:1 = ::1/128

Multicast Address            FF00::/8

Link-local Unicast            FE80::/10

Global Unicast                 everything else

4.1     Unspecified Address ( ::/128 )

The unspecified address must never beassigned to any node. One example of its use is in the Source Address field of anyIPv6 packets sent by an initializing host before it has learned its ownaddress.

The unspecified address must not be used asthe destination address of IPv6 packets or in IPv6 Routing headers. An IPv6packet with a source address of unspecified must never be forwarded by an IPv6 router.

4.2     Loop-back Address ( ::1/128 )

The loop-back address is used by a node tosend an IPv6 packet to itself. It must not be assigned to any physicalinterface. It is treated as having Link-Local scope, and may be thought of asthe Link-Local unicast address of a virtual interface (typically called the"loop-back interface").

The loop-back address must not be used asthe source address in IPv6 packets that are sent outside of node. An IPv6packet with a destination address of loop-back address must never be sentoutside of node and must never be forwarded by an IPv6 router. A packet receivedon an interface with a destination address of loop-back address must bedropped.

4.3     Link-local Unicast ( FE80::/10)

Link-Local addresses are designed to beused for addressing on a single link for purposes such as automatic addressconfiguration, neighbor discovery, or when no routers are present.

Routers must not forward any packets withLink-Local source or destination addresses to other links.

4.4     Global Unicast

Not start with binary 000        64-bit interface ID field (i.e., n + m =64).

4.5     Anycast Addresses

Anycast address is an address that isassigned to more than one interface (typically belong to different nodes), withthe property that a packet sent to an anycast address is routed to the "nearest"interface having that address, according to the routing protocol measure ofdistance.

Anycast address is syntactically same as unicastaddress. When a unicast address is assigned to more than one interface, thusturning it into an anycast address, the nodes to which the address is assignedmust be explicitly configured to know that it is an anycast address.

Anycast address must not be used as thesource address in IPv6 packets.

Anycast address must not be assigned toIPv6 host, only can be assigned to IPv6 router.

4.6     Multicast Addresses ( FF00::/8)

Multicast address is an identifier for agroup of interfaces (typically on different nodes). An interface may belong toany number of multicast groups.

T = 0    permanently-assigned("well-known") multicast address, assigned by IANA.

T = 1     non-permanently-assigned("transient" or "dynamically" assigned) multicast address

P definition and usage can be found in RFC3306 “Unicast-Prefix-based IPv6 Multicast Addresses”.

R definition and usage can be found in RFC3956 “Embedding the Rendezvous Point (RP) Address in an IPv6 Multicast Address”.

scop is used to limit the scope of themulticast group:

1    Interface-Localscope

2    Link-Localscope

4    Admin-Localscope

5    Site-Localscope

8    Organization-Localscope

E    Globalscope

Multicast address must not be used as the sourceaddress of IPv6 packets or in IPv6 Routing headers

4.7     Map IPv4 Address to IPv6Address

4.7.1       IPv4-Compatible IPv6 Address

The "IPv4-Compatible IPv6address" is deprecated; the IPv4 address used must be a globally-uniqueIPv4 unicast address.

4.7.2       IPv4-Mapped IPv6 Address

 

5      Interface ID with EUI-6 Format

For all unicast addresses, except startingwith the binary value 000, Interface IDs are required to be 64 bits long and tobe constructed in EUI-64 format.

First three bytes of EUI-64 format

c    companyid

u    universal/local bit

0    local scope

1    universalscope

g    individual/groupbit

0    individual

1    group

6      IPv4 vs IPv6

1.      IPv6 header is constant length, 40 bytes.

2.      IPv4 TTL defines the lifetime of the packetin seconds, while IPv6 Hop Limit is decremented by 1 by each node that forwardsthe packet.

3.      IPv6 replace Protocol field of IPv4 with NextHeader field.

4.      IPv6 discard the Checksum field because theupper-layer protocol can handle the checksum.

5.      IPv6 replace Optional field of IPv4 withExtension Header.