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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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Site X is multihomed to two providers, PROV1 <strong>and</strong> PROV2. PROV1 gets its<br />

transit services from top-level provider TOP1. PROV2 gets its service from<br />

TOP2. TOP1 has the top-level aggregate (TLA ID + format prefix) of 2111. TOP2<br />

has the TLA of 2222.<br />

TOP1 has assigned the next-level aggregate (NLA) of 00AB to PROV1. PROV2<br />

has been assigned the NLA of 00BC by TOP2.<br />

PROV1 has assigned the subscriber identifier 00A1 to site X. PROV2 has<br />

assigned the subscriber identifier 00B1 to site X.<br />

Node ND1, at site X, which has the interface token of 10005A123456, is<br />

therefore configured with the following two <strong>IP</strong> addresses:<br />

2111:00AB:00A1::1000:5A12:3456<br />

2222:00BC:00B1::1000:5A12:3456<br />

Site X is represented by the domain name test.com. Each provider has their own<br />

domain, top1.com, top2.com, prov1.com, <strong>and</strong> prov2.com. In each of these<br />

domains, an <strong>IP</strong>6 subdomain is created that is used to hold prefixes. The node<br />

ND1 can now be represented by the following entries in the DNS:<br />

ND1.TEST.COM AAAA ::1000:5A12:3456 80<br />

<strong>IP</strong>6.TEST.COM<br />

<strong>IP</strong>6.TEST.COM AAAA 0:0:00A1:: 32 <strong>IP</strong>6.PROV1.COM<br />

<strong>IP</strong>6.TEST.COM AAAA 0:0:00B1:: 32 <strong>IP</strong>6.PROV2.COM<br />

<strong>IP</strong>6.PROV1.COM AAAA 0:00AB:: 16 <strong>IP</strong>6.TOP1.COM<br />

<strong>IP</strong>6.PROV2.COM AAAA 0:00BC:: 16 <strong>IP</strong>6.TOP2.COM<br />

<strong>IP</strong>6.TOP1.COM AAAA 2111::<br />

<strong>IP</strong>6.TOP2.COM AAAA 2222::<br />

This format simplifies the job of the DNS administrator considerably <strong>and</strong> makes<br />

renumbering changes much easier to implement. Say, for example, site X<br />

decides to stop using links from providers PROV1 <strong>and</strong> PROV2 <strong>and</strong> invests in a<br />

connection direct from the top-level service provider TOP1 (who allocates the<br />

next-level aggregate 00CD to site X). The only change necessary in the DNS is<br />

for the two <strong>IP</strong>6.TEST.COM entries to be replaced with a single entry, as follows:<br />

<strong>IP</strong>6.TEST.COM AAAA 0:00CD:: 16 <strong>IP</strong>6.TOP1.COM<br />

370 <strong>TCP</strong>/<strong>IP</strong> <strong>Tutorial</strong> <strong>and</strong> <strong>Technical</strong> <strong>Overview</strong>

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