The PNNI Network
PNNI is a network system for supporting ATM routing and path selection. It selects the best path that
interconnects two end systems or a group of end systems. It is structured as a hierarchy of successive
higher entities called
levels. The Control Point maps these levels into nodes. For example, when a switch
Control point is running three levels, the first level is executed in the PNNI's node_0 subsystem, the next
level is running in the node_1 subsystem, and so on.
The 8265 PNNI control point operates a single level only, the sole active subsystem being that of node_0.
Peer Groups
A peer group is a group of switches having a common identifier, called the
peer group id. This peer group
id is based on a specified length of a private ATM address, based either on the switch's own ATM address
or explicitly entered. All switches must share the same peer group id (both length and content, to be
included in the peer group.
Summary Addresses
In PNNI, reachability is the advertising of end system addresses throughout a peer group for the purpose
of setting up connections between end systems. Reachability in PNNI routing is simplified by the
capability of having groups of addresses with a common prefix to be represented by that prefix. Such a
prefix is called a
summary address. PNNI generates a default summary address to provide reachability to
all end systems attached to the switch whose addresses share the switch's 13 byte ATM address prefix,
that is, whose addresses are generated by the ILMI address notification protocol. Additional non-default
summary addresses can be configured to provide reachability for address groups that do not share their
switch's 13 byte ATM address prefix.
PNNI also supports path selection to end systems that lie outside a peer group, that is, end systems that
are connected to a peer group via non-PNNI links (typically IISP links).
Every switch Control Point feeds end system addresses (that do not share the switch's 13 byte address
prefix) to its PNNI subsystem which represents them by corresponding summary addresses if these are
already configured. The absence of a configured summary address does not impair the reachability of end
system addresses that would otherwise be represented by that summary address: it simply increases the
reachability overhead for these addresses. Consequently, the removal of a configured summary address
does not impair the reachability of end systems that were previously represented by the summary address:
it simply increases PNNI's reachability overhead.
Configuring a new summary address can affect the functioning of previously configured summary
addresses.
Chapter 1. Overview
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