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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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The client h<strong>and</strong>les the table updates according to the following:<br />

► When an ATMARP table entry ages, the ATMARP client invalidates this table<br />

entry.<br />

► If there is no open VC associated with the invalidated entry, that entry is<br />

deleted.<br />

► In the case of an invalidated entry <strong>and</strong> an open VC, the ATMARP client<br />

revalidates the entry prior to transmitting any non-address resolution traffic on<br />

that VC. There are two possibilities:<br />

– In the case of a PVC, the client validates the entry by transmitting an<br />

InARP_REQUEST <strong>and</strong> updating the entry on receipt of an<br />

InARP_REPLY.<br />

– In the case of an SVC, the client validates the entry by transmitting an<br />

ARP_REQUEST to the ATMARP server <strong>and</strong> updating the entry on receipt<br />

of an ARP_REPLY.<br />

► If a VC with an associated invalidated ATMARP table entry is closed, that<br />

table entry is removed.<br />

As mentioned earlier, every ATM <strong>IP</strong> client that uses SVCs must know its<br />

ATMARP server's ATM address for the particular LIS. This address must be<br />

named at every client during customization. There is at present no well-known<br />

ATMARP server address defined.<br />

2.10.2 Classical <strong>IP</strong> over ATM<br />

The definitions for implementations of classical <strong>IP</strong> over asynchronous transfer<br />

mode (ATM) are described in RFC 2225, which is a proposed st<strong>and</strong>ard with a<br />

status of elective. This RFC considers only the application of ATM as a direct<br />

replacement for the “wires” <strong>and</strong> local LAN segments connecting <strong>IP</strong> endstations<br />

(members) <strong>and</strong> routers operating in the classical LAN-based paradigm. Issues<br />

raised by MAC level bridging <strong>and</strong> LAN emulation are not covered. Additionally, <strong>IP</strong><br />

over ATM was exp<strong>and</strong>ed by RFC 2492, which defines the transmission of <strong>IP</strong>v6<br />

over ATM.<br />

For ATM Forum's method of providing ATM migration, see 2.10.3, “ATM LAN<br />

emulation” on page 56.<br />

Initial deployment of ATM provides a LAN segment replacement for:<br />

► Ethernets, token rings, or FDDI networks<br />

► Local area backbones between existing (non-ATM) LANs<br />

► Dedicated circuits of frame relay PVCs between <strong>IP</strong> routers<br />

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

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