"Local/Remote" Forwarding Decision in Switched Data Link Subnetworks
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Auteur(s) : Y. Rekhter
, D. Kandlur
Classé sous : Ip
RFC 1937 Forwarding in Switched Data Link Subnets May 1996
directly to that destination (using the Link layer services). If the
outcome is "remote", then the host uses one of its first-hop routers
(thus relying on the services provided by IP routing).
To summarize, two of the important attributes of the IP subnet model
hosts with a common subnet address prefix are assumed to be
attached to a common link (subnetwork), and thus communicate with
each other directly, without any routers - "local";
hosts with different subnet address prefixes are assumed to be
attached to different links (subnetworks), and thus communicate
with each other only through routers - "remote".
A typical example of applying the IP subnet architecture to an SVC-
based Data Link subnetwork is "Classical IP and ARP over ATM"
(RFC1577). RFC1577 provides support for ATM deployment that follows
the traditional IP subnet model and introduces the notion of a
Logical IP Subnetwork (LIS). The consequence of this model is that a
host is required to setup an ATM SVC to any host within its LIS; for
destinations outside its LIS the host must forward packets through a
router. It is important to stress that this "local/remote" decision
is based solely on the information carried by the destination address
and the address and prefix lengths associated with the local
The diversity of TCP/IP applications results in a wide range of
traffic characteristics. Some applications last for a very short
time and generate only a small number of packets between a pair of
communicating hosts (e.g. ping, DNS). Other applications have a short
lifetime, but generate a relatively large volume of packets (e.g.
FTP). There are also applications that have a relatively long
lifetime, but generate relatively few packets (e.g. Telnet).
Finally, we anticipate the emergence of applications that have a
relatively long lifetime and generate a large volume of packets (e.g.
SVC-based Data Link subnetworks offer certain unique capabilities
that are not present in other (non-SVC) subnetworks (e.g. Ethernet,
Token Ring). The ability to dynamically establish and tear-down SVCs
between communicating entities attached to an SVC-based Data Link
subnetwork enables the dynamic dedication and redistribution of
certain communication resources (e.g. bandwidth) among the entities.
This dedication and redistribution of resources could be accomplished
by relying solely on the mechanism(s) provided by the Data Link
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