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To be a successful CCNA, you must know the differences between IPX RIP and IP RIP, but also two other NetWare protocols used by the router, namely Service Advertisement Protocol (SAP) and Get Nearest Server (GNS). Because IPX RIP and IP RIP were originally based on the same protocol (XNS RIP), the two are very similar. SAP and GNS have no equivalent feature in TCP/IP. RIP for IPX works in a similar manner to IP RIP. The most obvious difference is that IPX RIP advertises IPX network numbers, not IP subnet numbers.
IPX RIP uses two metrics: ticks and hops. Ticks are 1/18 of one second; the metric is an integer counter of the number of ticks delay for this route. By default, a Cisco router treats a link as having a certain number of ticks delay. LAN interfaces default to one tick, and WAN interfaces default to six ticks. The number of hops is considered only when the number of ticks is a tie. By using ticks as the primary metric, better routes can be chosen, as opposed to using just hop count. For example, a three-hop, three-tick route that uses three Ethernets will be chosen over a two-hop, eight-tick route that uses two Ethernets and a serial link.
Service Advertisement Protocol
Service Advertisement Protocol (SAP) is one of the more important parts of the NetWare protocol specification, but it is also one of the biggest challenges when trying to scale an IPX network. SAP is used by servers to propagate information that describes their services. CCNAs are expected to be very familiar with SAP and the routers' roles in forwarding SAP information.
The SAP process is very much like the process used by a distance vector routing protocol. In fact, SAP uses a concept similar to split horizon to stop a node from advertising SAP information it learned on an interface with updates sent out that same interface. Each server sends SAP updates, by default every 60 seconds, that include its IPX address, server name, and service type. Every other server and router listens for these updates, but does not forward the SAP packet(s). Instead, the SAP information is added to a SAP table in the server or router; then the packets are discarded. When that router or server's SAP timer expires, then new SAP broadcasts are sent. As with IPX RIP for routing information, IPX SAP propagates service information until all servers and routers have learned about all servers.
Client initialization flows provide some insight into why routers need to learn SAP information. Consider Figure 6-14, which includes the use of the Get Nearest Server (GNS) request and shows a typical startup with a client configured with a preferred server of Server 2.
The overall goal of client1 is to log in to its preferred server, Server 2. The first step is to connect to some server that has a full SAP table, so the client can learn the IPX address of its preferred server. (The preferred server name is configured on the client, not the IPX address of the preferred server.) The router may know the preferred server's name and IPX address in its SAP table, but there is no IPX message defined that allows the client to query the router for "name resolution." However, an IPX broadcast message asking for any nearby server is defined by IPX-the GNS request. The router can supply the IPX address of some nearby server (Step 2 in Figure 6-14) because the router has a SAP table.
Next, the client needs to learn which router to use to forward packets to the server discovered by its GNS request. RIP requests and replies are used by the client to learn the route from any router (or server) on the same LAN, as seen in Steps 3 and 4 in Figure 6-14. As a result, client1 knows to use the LA router to deliver packets to network 1001.
After connecting to Server 1, the client learns the IPX address of Server 2, its preferred server (Steps 5 and 6 in Figure 6-14). The client needs to know the best route to the preferred server's network; therefore, a RIP request and reply to learn the best next-hop router to network 1002 is shown in Steps 7 and 8 in Figure 6-14. Finally, packets are sent between the client and Server 2 so that the client can log in; the intervening routers are simply routing the packets.
Note that IPX clients create their own IPX address using the network number in the source address field of the GNS reply. The GNS reply is always sent by a router or server on the same network as the client. The client examines the source IPX address of the GNS reply to learn its own IPX network number. The complete client IPX address is formed by putting that network number with the MAC address of the client's LAN interface...
|Ch. 1||All About the Cisco Certified Network Associate Certification||2|
|Ch. 2||Cisco Internetwork Operating System (IOS) Fundamentals||20|
|Ch. 3||OSI Reference Model & Layered Communication||68|
|Ch. 4||Bridges/Switches and LAN Design||128|
|Ch. 5||Network Protocols||210|
|Ch. 7||Understanding Access List Security||454|
|Ch. 8||WAN Protocols and Design||514|
|Ch. 9||Scenarios for Final Preparation||638|
|App. A||Answers to the "Do I Know This Already?" Quizzes and Q&A Sections||700|
|App. B||Decimal to Hexadecimal and Binary Conversion Table||776|
Posted April 19, 2001
Posted March 5, 2001
This book is definately a tough read and i don't recommend it at all especially if youare starting out with routers, this book just doesn't speak enhlish and gets you tired and frustrated.Was this review helpful? Yes NoThank you for your feedback. Report this reviewThank you, this review has been flagged.
Posted February 2, 2001
This book fails to communicate efficiently. The writing is all over the place with no focus. I absolutely do not recommend this book for a study guide.Was this review helpful? Yes NoThank you for your feedback. Report this reviewThank you, this review has been flagged.
Posted December 12, 2000
I purchased this book right after it was released to prepare for the CCNA 2.0. The book more than covered everything on the test. My only complaint is that the practice exams inculuded on the CD didn't cover the basics well enough (as the test does.)Was this review helpful? Yes NoThank you for your feedback. Report this reviewThank you, this review has been flagged.
Posted October 15, 2000
I actually teach a bootcamp to prepare students for the CCNA exam and this is the best book there is. It may be a tough read for people with no router background, but it is the best book available. The Sybex book is good too and a much easier read. The 216 question practice exam is simply the best set of practice questions available for this exam - BAR NONE; and is worth the price of this book by itself.Was this review helpful? Yes NoThank you for your feedback. Report this reviewThank you, this review has been flagged.
Posted September 7, 2000
While this book might be effective, it certainly is not efficiently prepare you for the exam. Mostly because this book is too technical for mere CCNA and the exam is not that hard at all. In that context, this book will present false idea of the exam. Beside, this book will drain your energy unnecesarily simply because book is terribly written. To become ccna certified efficiently and effectively, stay away from this book.Was this review helpful? Yes NoThank you for your feedback. Report this reviewThank you, this review has been flagged.
Posted September 3, 2000
What a terrible guide. This is a really waste of time to read. CCNA exam is not this hard. You don't need these tech talks and jargons at all. Unless you're really bored with absolutely nothing to do, this guide is not worth to read. Don't expect to make you prepared for the exam. I don't guarantee the failure with this guide but I guarantee this guide is a tough read (makes you tired).Was this review helpful? Yes NoThank you for your feedback. Report this reviewThank you, this review has been flagged.
Posted August 29, 2000
This is an excellent book for the exam. I used this book along with the companion book in the set, which is the equivalent of the ICND course. There is quite a bit of information in the book and you really need to know all of the little details to pass the test. I just passed the CCNA exam today with an 860. I would definitely recommend this book along with the wealth of free practice exams you can find on the Internet.Was this review helpful? Yes NoThank you for your feedback. Report this reviewThank you, this review has been flagged.