شبکه هاي کامپيوتري
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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