CCNA有点郁闷的题

gavy · 发表于 2004-7-3 15:10:08

今天在chinaitlab上看到的两题 With regard to ISDN, which of the following are true? (Choose all that apply.) A. Legacy DDR can use port information to define interesting traffic. B. Legacy DDR can configure multiple dialer configurations on the same interface. C. Legacy DDR can use ACLs to define interesting traffic. D. HDLC or PPP can be used to encapsulate ISDN D channel information. E. The BRI interfaces on ISDN routers with dialer profiles configured cannot belong to multiple dialer pools. F. Dialer profiles cannot use ACLs to define interesting traffic. <img src="images/upfile/200473151618.jpg" border="0" alt="" style="max-width:400px"> ［此帖子已被 gavy 在 7/3/2004 3:16:47 PM 编辑过］

gavy · 发表于 2004-7-3 15:17:33

感觉第二题的内容好象很陌生啊

chinamoon · 发表于 2004-7-4 04:12:08

第一题要了解Dialer profiles ，我们做的题目注解里头有这道题，并且做了解释，等Boson85％后我会给你。 Network Layer Addressing OSI network layer addressing is implemented by using two types of hierarchical addresses: network service access point addresses and network entity titles. A network service access point (NSAP) is a conceptual point on the boundary between the network and the transport layers. The NSAP is the location at which OSI network services are provided to the transport layer. Each transport layer entity is assigned a single NSAP, which is individually addressed in an OSI internetwork using NSAP addresses. Figure 30-2 illustrates the format of the OSI NSAP address, which identifies individual NSAPs.

chinamoon · 发表于 2004-7-4 04:14:25

NSAP Address Fields Two NSAP Address fields exist: the initial domain part (IDP) and the domain-specific part (DSP). The IDP field is divided into two parts: the authority format identifier (AFI) and the initial domain identifier (IDI). The AFI provides information about the structure and content of the IDI and DSP fields, such as whether the IDI is of variable length and whether the DSP uses decimal or binary notation. The IDI specifies the entity that can assign values to the DSP portion of the NSAP address. The DSP is subdivided into four parts by the authority responsible for its administration. The Address Administration fields allow for the further administration of addressing by adding a second authority identifier and by delegating address administration to subauthorities. The Area field identifies the specific area within a domain and is used for routing purposes. The Station field identifies a specific station within an area and also is used for routing purposes. The Selector field provides the specific n-selector within a station and, much like the other fields, is used for routing purposes. The reserved n-selector 00 identifies the address as a network entity title (NET). End-System NSAPs An OSI end system (ES) often has multiple NSAP addresses, one for each transport entity that it contains. If this is the case, the NSAP address for each transport entity usually differs only in the last byte (called the n-selector). Figure 30-3 illustrates the relationship between a transport entity, the NSAP, and the network service.

chinamoon · 发表于 2004-7-4 04:18:47

看完这个图，应该会更清楚了。 Figure 30-3 The NSAP Provides a Link Between a Transport Entity and a Network Service

A network entity title (NET) is used to identify the network layer of a system without associating that system with a specific transport layer entity (as an NSAP address does). NETs are useful for addressing intermediate systems (ISs), such as routers, that do not interface with the transport layer. An IS can have a single NET or multiple NETs, if it participates in multiple areas or domains. 注意，这里提到的NET chinamoon： 这个NET和NSAP不是NA的课程内容和范围，但是Cisco现在有时也会弄点比较生僻的内容来考，要注意，比如线序等等。 一般遇到这样的问题，如果英文还可以的话，到Cisco网站上去查询一下，一般都可以有成果，注意看图理解。

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[讨论/求助] CCNA有点郁闷的题