Installing and Administering OSI Transport Services

Chapter 1 37

HP OTS/9000 Resources

How OTS/9000 Uses Network Identiﬁers

OTS/9000 will always check to see if it has a Destination system entry

(either dynamically or statically created) for a given NSAP ﬁrst. If no

such entry exists, it will try to determine which subnetwork the

destination may be reached on. This is accomplished using the Network

ID ﬁeld on the LAN (802.3 or FDDI) subnetwork conﬁguration screens. If

the destination can be reached on the LAN subnetwork, (the Network ID

is matched) OTS will either send the packet to an IS on the LAN, or, if no

IS is present, use the Query conﬁguration function to resolve the route.

If OTS cannot determine the outgoing subnetwork, it then looks at the

conﬁgured routes to see if the destination NSAP matches one of the

conﬁgured Network IDs (the front portion of the NSAP matches the

Network ID). If a Network ID matches, the conﬁgured IS is used to route

information to the destination NSAP. Since Network IDs vary in length,

OTS will check them using a longest-length-ﬁrst search order. For

instance, if two route entries have been created, 4901 and 490101, and

the NSAP OTS is trying to route to is 4901010001, the route associated

with the Network ID 490101 will be selected.

More precisely, Network IDs are checked using a most-1-bits-in-mask

search. The route entries with the greatest number of 1s in their

route_id_mask are considered ﬁrst. Since the default is to set the mask

to a string of Fs as long as the Network ID, this results in a

longest-length-ﬁrst search. However, if you edit the ots_routes ﬁle

directly and create custom masks, you must keep the actual search

algorithm in mind.