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شبکه هاي کامپيوتريTCP/IPمبحث ششم: پروتکل

IP v 6.0بخش سوم: جهت مطالعه

وحید حقیقت دوستدانشکده فنی و مهندسی دانشگاه شاهد

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IPv6 Initial motivation: 32-bit address space

completely allocated by 2008. Additional motivation:

header format helps speed processing/forwarding

header changes to facilitate QoS new “anycast” address: route to “best” of

several replicated servers IPv6 datagram format:

fixed-length 40 byte header no fragmentation allowed

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IPv6 Header

Priority: identify priority among datagrams in flowFlow Label: identify datagrams in same “flow.” (concept of“flow” not well defined).Next header: identify upper layer protocol for data

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IPv4 & IPv6 Header Comparison

Version IHL Type of Service Total Length

Identification Flags Fragment Offset

Time to Live Protocol Header Checksum

Source Address

Destination Address

Options Padding

Version Traffic Class Flow Label

Payload Length Next Header Hop Limit

Source Address

Destination Address

IPv4 Header IPv6 Header

- field’s name kept from IPv4 to IPv6

- fields not kept in IPv6

- Name & position changed in IPv6

- New field in IPv6

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Other Changes from IPv4Checksum: removed entirely to reduce

processing time at each hopOptions: allowed, but outside of header,

indicated by “Next Header” fieldICMPv6: new version of ICMP

additional message types, e.g. “Packet Too Big”

multicast group management functions

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Transition From IPv4 To IPv6

Not all routers can be upgraded simultaneous

no “flag days”How will the network operate with mixed

IPv4 and IPv6 routers ?Two proposed approaches:

Dual Stack: some routers with dual stack (v6, v4) can “translate” between formats

Tunneling: IPv6 carried as payload in IPv4 datagram among IPv4 routers

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Dual Stack Approach

IPv6 IPv6 IPv6 IPv6IPv4 IPv4

Flow: XSrc: ADest: F

data

Flow: ??Src: ADest: F

data

Src:ADest: F

data

A-to-B:IPv6

Src:ADest: F

data

B-to-C:IPv4

B-to-C:IPv4

B-to-C:IPv6

A B C D E F

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Tunneling-Analogy

IPv6 IPv6 IPv6 IPv6

tunnelLogical view:A B E F

Analogy:

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Tunneling-Physical View

Physical view:

IPv6 IPv6 IPv6 IPv6IPv4 IPv4

Flow: XSrc: ADest: F

data

Flow: XSrc: ADest: F

data

Flow: XSrc: ADest: F

data

Src:BDest: E

Flow: XSrc: ADest: F

data

Src:BDest: E

A-to-B:IPv6

E-to-F:IPv6

B-to-C:IPv6 inside

IPv4

B-to-C:IPv6 inside

IPv4

A B C D E F

IPv6 IPv6 IPv6 IPv6

tunnelLogical view:A B E F