Since IPX is a network-layer protocol, it doesn't know anything about other networks, apart from the fact that they exist. When IPX has a packet for a remote subnet, it passes it to the closest router and forgets about it. RIP and NLSP provide the routing services for IPX networks.
Networks that use RIP routing are very "chatty". When a device first comes onto the network, it issues a RIP request to find the network address of the segment it is attached to (this is how a NetWare client can determine the network address automatically). If a device is on multiple networks (by way of multiple adapters, or multiple links), and if it is configured to act as a router for those networks, then it will send a RIP update to all of the attached networks, advertising the networks that it is attached to. This concept is illustrated in Figure A.9 below.
Routers send out RIP updates every sixty seconds, so within a few minutes every router on the entire network will know about the router and the networks it is attached to. If a router doesn't send out an update within a few minutes, the other routers assume it is down and remove it from their routing maps.
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Just as SAP traffic can overwhelm a large or complicated network, RIP has the same effect. On small or mid-sized networks, these constant updates do not pose a significant threat, although on large networks, the constant exchanging of large routing maps becomes crippling.
To address this problem, Novell has developed a link-state routing protocol called NLSP (for NetWare Link State Protocol), which works much better in extremely complex networks. Rather than routers continuously broadcasting information about every other network and router they know of, they only send out information about the routes that they can provide (instead of all routes across the network), and only when the routes change. This link-state update design greatly reduces the amount of bandwidth required for routing services and advertisement.
For more information on IPX, refer to section A.3.1 Internetwork Packet Exchange (IPX). For more information on SPX, refer to section A.3.2 Sequenced Packet Exchange (SPX). For more information on PEP and NCP, refer to section A.3.3 Packet Exchange Protocol (PEP) and the NetWare Core Protocol (NCP). For more information on SAP, refer to section A.3.4 Service Advertisement Protocol (SAP).
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