After a brief review of what an end system and an intermediate system are,
this section describes how routing information is obtained and provided, and
how OTS/9000 uses it.
A system can act as an end system or as an intermediate system. OTS can
function only as an ES.
An end system (ES) initiates or responds to a communication (it supports layers
1 through 7).
An intermediate system (IS) forwards communication traffic across subnetworks
(it supports layers 1 through 3).
Routing means establishing a path across the subnetwork(s) and intermediate
system(s) so that data is exchanged between end systems. Normally, an ES
communicates directly with another ES. That is, they are connected to the same
subnetwork. If the local ES cannot directly reach the remote ES, the local ES
makes the first "hop'' to an IS. The IS determines the best path to the remote ES.
OTS/9000 can function as:
An ES connected to a single subnetwork.
An ES connected to multiple subnetworks. OTS/9000 is capable of choosing
different routes for sending a PDU, but it does not forward PDUs.
OTS/9000 does not function as an IS.
Routing information can be provided dynamically through the ES-IS
protocol, or it can be provided statically through the osiadmin configuration
screens. Remote LAN systems that support the ES-IS protocol periodically
multicast their NSAP and MAC addresses. By default, OTS/9000 records
these addresses in a routing table. These dynamic table entries are discarded
after a period of time specified by the remote system. Static table entries,
that do not time-out, can be configured using osiadmin. When the routing
table is full, any new dynamic routing information is ignored.
The maximum number of routing entries (by type of subnetwork) is as
follows:
* Total number of routing ES and IS entries across all CONS/X.25
subnetworks. This value is configurable. (ots_parms:
cons_max_route_entries)
The CLNS numbers are per subnetwork and are also configurable
(ots_subnets: snet_max_es_entries, snet_max_is_entries).
Static routes can be configured in osiadmin using the destination system's
configuration by specifying the NSAP to Physical Address mapping of
remote system(s) or a Network ID that identifies a whole class of remote
NSAPs (by prefix).
When OTS/9000 needs to communicate to a remote ES, it uses the following
algorithm to route PDUs:
 |
| |
|
 | NOTE: In all cases, if multiple Network IDs match, the longest match is chosen, but local
LAN Network IDs are always chosen over Network IDs configured as routes. |
|
| |
|
Printable version
