Cabletron Systems MMAC-Plus SFCS-1000, Руководство по настройке

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2-12
Configuring a Classical IP ATM Network
2.3.4 Classical IP Operation
Once a host knows its own ATM address and the ATM address of its ARP
server it will attempt to establish a connection to the ARP server, which will
be used to send ARP requests and receive ARP replies. When the connection
to the ARP server has been established, the ARP server sends an inverse ARP
(InARP) request on the new VC to learn the host’s IP address. When an
InARP reply is received, the ARP server places that host’s IP address to ATM
address mapping in its ARP cache. Therefore, over time, the ARP server
dynamically learns the IP-to-ATM address mappings of all the hosts in its LIS.
It can then respond to ARP requests directed toward it for hosts in its LIS.
NOTE:
In order for a host to communicate with an
ARP server, it must have learned its own
ATM address and have been configured with
the ATM address of the ARP server.
A host can not resolve the ATM addresses of
hosts in its LIS unless it can communicate
with its ARP server.
Since there is no mechanism for ARP servers
to exchange mapping information with each
other, it is imperative that each LIS be
configured with only one ARP server.
When a host wants to communicate with another host in its LIS, it first sends
an ARP request to the ARP server containing the IP address to be resolved.
When an ARP reply is received from the ARP server, the host creates an entry
in its ARP cache for the given IP address and stores the IP-to-ATM address
mapping. This ARP cache entry will be marked as complete. To ensure that
all of the IP-to-ATM address mappings known by a certain host are
up-to-date, hosts are required to age their ARP entries. A host must validate
its ARP entries every 15 minutes (20 minutes on an ARP server).
A host validates its SVCs by sending an ARP request to the ARP server. A
host validates its PVCs, and an ARP server validates its SVCs, by sending an
InARP request on the VC. If a reply is not received, the ARP entry is marked
invalid. Once an ARP entry is marked invalid, an attempt is made to revali-
date it before transmitting. Transmission will proceed only when validation
succeeds. If a VC associated with an invalid ARP entry is closed, the entry is
removed.