Information Technology Reference
In-Depth Information
Digital's own Network Services Protocol (NSP) is functionally similar to TP4 in that it offers
connection-oriented, flow-controlled service with message fragmentation and reassembly. Two
subchannels are supported—one for normal data and one for expedited data and flow control
information. Two flow control types are supported—a simple start/stop mechanism where the receiver
tells the sender when to terminate and resume data transmission and a more complex flow control
technique, where the receiver tells the sender how many messages it can accept. NSP can also respond
to congestion notifications from the network layer by reducing the number of outstanding messages it
will tolerate.
Upper-Layer Protocols
Above the transport layer, DECnet supports its own proprietary upper-layer protocols as well as standard
OSI upper-layer protocols. DECnet application protocols use the DNA session control protocol and the
DNA name service. OSI application protocols are supported by OSI presentation- and session-layer
implementations.
Troubleshooting DECnet
This section presents protocol-related troubleshooting information for DECnet Phase IV connectivity
and performance problems. The procedures outlined apply only to environments in which DECnet
routing is enabled on the router, not to environments in which DECnet is being bridged (that is, bridging
is enabled on the router interfaces and EtherType 6003 is being passed).
This chapter does not discuss other Digital protocols, such as Maintenance Operation Protocol (MOP),
local-area transport (LAT), local-area VAX cluster (LAVC), and local-area systems technology (LAST).
For information about troubleshooting ISO CLNS (DECnet Phase V) problems, refer to Chapter
12, “Troubleshooting ISO CLNS.”
Note
The section “Using DECnet in a Multiprotocol Environment” discusses possible problems when using
DECnet in an internetwork running other protocols as well. The remaining sections describe specific
DECnet symptoms, the problems that are likely to cause each symptom, and the solutions to those
problems.
The following sections outline the most common network issues in DECnet networks:
DECnet: Connections to DEC Hosts Fail over Router (End Node Problem)
•
DECnet: Connections to DEC Hosts Fail over Router (Router Problem)
•
DECnet: End Nodes Cannot Find Designated Router
•
DECnet: Router or End Node Sees Incorrect Designated Router
•
DECnet: Routers Not Establishing Adjacencies
•
DECnet: Routing Node Adjacencies Toggle Up and Down
•
DECnet: No Phase IV Connectivity over Phase V Backbone
•
DECnet: Poor Performance
•
