Verilink 9000 Series (34-00271) Product Manual - Manual (Page 338)

316 C HAPTER 19: IPX R OUTER
A gateway server, for instance, broadcasts a SAP packet every 60 seconds (the
period defined for all servers advertising with SAP) onto the network segment to
which it is connected. The SAP agent in each router on that segment copies the
information contained in the SAP packet into an internal table called the server
information table. Because the SAP agent in each router keeps up-to-date
information on available servers, a client wanting to locate the gateway server can
access a nearby router for the correct IPX address.
NLSP
Support
Details
NLSP is the Novell link-state routing protocol for IPX which has been developed to
address the limitations of the IPX Routing Information Protocol and Service
Advertisement Protocol (RIP/SAP). Because of their broadcast-oriented architecture,
RIP and SAP demand large amounts of bandwidth and do not scale well.
NLSP was introduced first as a NetWare Loadable Module (NLM) for NetWare
file servers for LAN support. And then, more recently, NLSP was introduced in
the Novell MPR 3.0 internetworking product for WAN support. Although NLSP is
designed as a scalable, hierarchical routing protocol, it is specified for only a
single area.
As a link-state routing protocol, NLSP fundamentally changes the way routing
information is handled in an IPX network. Each router in an NLSP area keeps a
complete topological map of the entire area network in its memory. As changes in
topology, such as link failures, are noticed, routers send multicast packets to the
other routers on the network advising them of the change. Routers receiving these
update packets execute the Dijkstra algorithm and recalculate their complete area's
topology. Because routing updates typically only occur after changes to the
network, (as opposed to the constant repetitive broadcasts used by distance-vector
routing protocols such as RIP), bandwidth is used more efficiently.
NLSP, as specified today, provides support only for single area, or Level 1,
routing.
RIP/SAP continues to be supported, not only to connect NLSP areas, but also
because some older devices only support these protocols.
IPX Type 20 Packet
for NetBIOS
The NetBIOS packet may be encapsulated inside an IPX packet. The
corresponding IPX packet type is 20.