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266 Understanding IPv6, Second Edition

Network Monitor Capture

Here is an example of an Internet Control Message Protocol version 6 (ICMPv6) Echo Request message encapsulated with an IPv4 header as displayed by Network Monitor 3.1 (capture 11_01 in the \NetworkMonitorCaptures folder on the companion CD-ROM):

Frame:

+ Ethernet: Etype = Internet IP (IPv4)

-Ipv4: Next Protocol = IPv6 over IPv4, Packet ID = 65372, Total IP Length = 100

+Versions: IPv4, Internet Protocol; Header Length = 20

+DifferentiatedServicesField: DSCP: 0, ECN: 0 TotalLength: 100 (0x64)

Identification: 65372 (0xFF5C)

+FragmentFlags: 0 (0x0) TimeToLive: 128 (0x80)

NextProtocol: IPv6 over IPv4, 41(0x29) Checksum: 60987 (0xEE3B) SourceAddress: 157.54.138.19 DestinationAddress: 157.60.136.82

-Ipv6: Next Protocol = ICMPv6, Payload Length = 40

+Versions: IPv6, Internet Protocol, DSCP 0 PayloadLength: 40 (0x28)

NextProtocol: ICMPv6, 58(0x3a) HopLimit: 128 (0x80)

SourceAddress: FE80:0:0:0:0:5EFE:9D36:8A13 DestinationAddress: FE80:0:0:0:0:5EFE:9D3C:8852

+ Icmpv6: Echo request, ID = 0x0, Seq = 0x11

Notice that the Protocol field in the IPv4 header indicates an IPv6 packet. In this example, the IPv6 packet is addressed to and from link-local ISATAP addresses to tunnel an ICMPv6 Echo Request message across an IPv4-only infrastructure.

DNS Infrastructure

You need a DNS infrastructure for successful coexistence because of the prevalent use of names rather than addresses to refer to network resources. For IPv6, resolving names to IPv6 addresses is highly desired because of the length and unfamiliar form of IPv6 addresses to most computer users. Upgrading the DNS infrastructure for IPv6 consists of populating the DNS servers with AAAA records for name-to-IPv6 address resolutions and with PTR records for IPv6 address-to- name resolutions. After a host obtains a set of addresses with a DNS name query, it must select which pairs of source and destination addresses to use for communication.

Address Records

The DNS infrastructure must contain the following resource records (populated either manually or dynamically) for the successful resolution of fully qualified domain names (FQDNs) to addresses:

A records for IPv4-only and IPv6/IPv4 nodes

AAAA records for IPv6-only and IPv6/IPv4 nodes

Соседние файлы в папке Lecture 2_10