关于CCNP 642-813交换题库的问题

    最近几天准备CCNP考试，看题库时遇到了几道有争议的题目，根据自己搜索的资料做了如下总结解释：

 

    首先是一道与VTP有关的题目：

    对于选项B，相关资料表明domain names 是对大小写敏感的，有兴趣的人可以自己验证一下。

    对于选项D，官方文档中对VTP v.1和v.2的区别描述如下：

VTP version 2 offers the following support options not available with version 1:

Unrecognized type-length-value (TLV) support—A VTP server or client propagates configuration changes to its other trunks, even for TLVs it is not able to parse. The unrecognized TLV is saved in NVRAM.

Version-dependent transparent mode—In VTP version 1, a VTP transparent switch inspects VTP messages for the domain name and version and forwards a message only if the version and domain name match. Because only one domain is supported in the Supervisor engine software, VTP version 2 forwards VTP messages in transparent mode, without checking the version.

Consistency checks—In VTP version 2, VLAN consistency checks (such as VLAN names and values) are performed only when you enter new information through the command-line interface (CLI) or Simple Network Management Protocol (SNMP). Consistency checks are not performed when new information is obtained from a VTP message or when information is read from NVRAM. If the digest on a received VTP message is correct, its information is accepted without consistency checks.

    根据官方描述可以看出，对于VTP v.1中的VTP信息，transparent模式并不是不转发，而是不仅检测domain name而且还检测其中的version信息，要匹配了才会转发，要求较严格，所以D选项也不准确，只能说在默认情况下，transparent 的version 为 0，不会进行转发。

    再看E选项，乍看一下似乎是正确的，但查找了cisco官方文档解释说明如下：

By default all the VLANs that exist on a switch are active on a trunk link. As noted in section "6-3: Trunking", you can manually remove VLANs from a trunk link and then add them later. VTP pruning allows the switch to not forward user traffic for VLANs that are not active on a remote switch. This feature dynamically prunes unneeded traffic across trunk links. If the VLAN traffic is needed at a later date, VTP will dynamically add the VLAN back to the trunk

    注意到并不是修剪掉自己的无active端口的vlan， 而是vlans that are not active on a remote switch， 所以D选项不正确

    所以虽然答案给的是AD，但我只能确定A是正确的。

 

    接下来看一道关于packet cos priority的问题，题目如下

    题库给出的顺序是Voice、Call signaling、Video interactive、Video streaming、Network management、IP routing,然而查了官网的Qos（http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoSIntro.html）之后，可以看出真正从高到低的顺序应该是Ip routing、Voice、Interactive video、Streaming Video、Call-Signaling、Network management，有个疑问就是ip routing的优先级为什么这么高？难道是指的路由协议之类的控制数据流？在红头发的642-813的讲解视频中的参考顺序是:Voice、Interactive video、Streaming Video、Call-Signaling、Ip routing、network management。对于哪一种排序是正确的我也不太确信，只能暂时相信官方给出的优先级了。

 

还有一道拖图题是对于syslog priority的问题：是要求从高到低，看了看网上其它人的说法，对于答案给的emergency、alert、critical、error、warning、notice、informational、debug，关键的争议点在于是这个顺序还是debug在前。查了一些资料，基本的观点是，如果按照优先级的从高到低来排，似乎是应该把debug放在开始，也就是反过来，但是如果按照紧急程度来排的话，就应该是emergency在前，具体的问题还不是很清楚，确实有些模棱两可的地方，就看我过几天考交换会不会遇到这个题目了，求顺利PASS