CCNA認證(CCNA-思科網絡安裝和支持認證助理)是整個Cisco認證體系中最初級的認證，同時它也是獲得CCNP認證、CCDP認證和CCSP認證的必要條件(CCIP認證、CCIE認證不強制要求)，而且許多Cisco專業認證(Cisco Qualified Specialist)也要求考生首先得CCNA認證。CCNA認證屬於Cisco售後工程師認證體系得入門認證，通過CCNA可以證明妳已掌握網絡得基本知識， 並能初步安裝、配置和操作Cisco路由器、交換機及簡單的LAN和WAN。CCNA認證表示經過認證的人員具有為小型辦公室/庭辦公室(SOHO)市場聯網的基本技術和相關知識。通過CCNA認證的專業人員可以在小型網絡(100或100以下個節點)中安裝、配置和運行LAN、WAN和撥號訪問業務。他們可以使用的協議包括(但不限於)IP、IGRP、 IPX、Serial、Apple、Talk、Frame、Relay、IP RIP、VLAN RIP、Ethernet、Access Lists。
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640-802科目屬於Cisco認證體系中CCNA的指定考試科目，640-802：Cisco Certified Network Associate(CCNA)，640-802最新更新版涵蓋了183道真題，2008年11月12日進行了最新更新。CCNA 640-802考試題庫由KillTest認證題庫網資深IT認證講師和CCNA產品專家結合PROMETRIC或VUE的真實640-802考試環境最新原題傾心打造。CCNA 640-802(Cisco Certified Network Associate(CCNA))考題由我們的資深IT認證講師和CCNA產品專家精心打造，包括了當前最新的真實640-802考題，全部附有正確答案。所有購買KillTest 640-802 題庫的客戶都將得到60天的免費升級服務，保證了客戶的壹次通過率。KillTest IT認證題庫網助您壹次通過CCNA 640-802考試。

CCNA認證在考試條件上沒有任何的要求，只需要考生持有2個有效證件，如身份證和信用卡、駕駛證、學生證、護照等。CCNA認證的考試編號為640-802，時間為90分鐘，題目：50-60題，總分為1000分，考生需達到849分就可以過關。考試類型為：模擬題；少數連線題；多項選擇題及單項選擇題。

When you started studying for your CCNA certification exam, one of the very first things you learned was the major difference between the enable password and the enable secret – the enable secret is encrypted by default, where the enable password is just sitting there in clear text, waiting to be read!

When you look at the enable secret in a Cisco router configuration, it looks like it would be impossible to guess. 640-802:Cisco Certified Network Associate(CCNA) After setting the enable secret on this router to the word security, here’s how it appears in the configuration:enable secret 5 $1$24me$gVFxUOI4gYp0IQbhtH8Rz0

That password has been encrypted by MD5, the Message Digest 5 algorithm. The result of the MD5 algorithm being applied to the password is a 32-character hexadecimal value.

That password is hard to guess, but not terribly hard to crack. Anyone looking over your shoulder would not be able to come up with that password, but there are readily-available password cracking software devices that can crack that encryption in a matter of minutes. That’s true of any MD5-encrypted password, not just those on Cisco routers.So what can we do about this? We can add SALT to our MD5.

The salt itself is simply a string of random characters that are added to the encryption process. Salting makes it much more difficult for a hacker to come up with the password; each bit added by the salt process literally makes it twice as difficult for the password to be compromised. A recent Wikipedia entry states that if a password was one of 200,000 words, a 32-bit salt would require 800 trillion hashes for a full-blown brute force attack.

The actual creation and application of a salt is beyond the scope of the CCNA Security exam, but once you’ve earned that valuable certification – or maybe while you’re preparing for it – do a Google search on “salt md5” and read up on this powerful security tool. In the meantime, look for more CCNA Security tutorials on the site you’re on now as well as my website!

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of over 100 free certification exam tutorials, including Cisco CCNA certification test prep articles. His exclusive Cisco CCNA study guide and Cisco CCNA training is also available! Visit his blog and sign up for Cisco Certification Central, a daily newsletter packed with CCNA, Network+, Security+, A+, and CCNP certification exam practice questions! A free 7-part course, “How To Pass The CCNA”, is also available, and you can attend an in-person or online CCNA boot camp with The Bryant Advantage!

#01 solara

As part of my study for CCNA Security I have been making a list of all the commands I need to be adept with. I thought I would share this list of commands with others who may be interested.

For simplicty the list doesn’t offer explanations and in most cases there are a variety of options that could be used with each command that are not shown. It is also not suitable for copy/paste into a router or switch. However, I think it is still a useful quick reference sheet.

#02 B Haines

You are running both RADIUS as well as TACACS+ servers in your example configuration. I was wondering what RAD/TACS you were running on those two servers? FreeRadius? And what Tac Plus? Just trying to determine what software you are using for your lab studies! Thanks!

By the way, thanks for sharing your config!

#03 solara

The previous example isn’t my config but rather just a list of commands to be familiar with and so I’m not actually running TACACS+ and RADIUS on the separate server addresses that I have shown.

I do my lab work using GNS3 with the C3745-ADVENTERPRISEK9_SNA-M IOS and currently I’m using the 90-day trial version of Cisco ACS 4.2 running on a Win2k3 VMWare box.

Just for interest I’ve attached a text file showing a basic config I’ve used for testing TACACS+. I have enabled debugs on aaa authentication and IP packets between the router and the ACS server and then attempted to logon to the router via SSH.