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BMW 5 Series V.S Citroen C6

L2與L3 Switch 的差異

一般常用的交換器 Switch 是屬於第二層交換器 Layer 2 Switch，這種交換器是利用 OSI 第二層 MAC 位址的資訊來進行資料交換，它可以記憶學習第一個 Port 連接的 MAC 位址，透過 MAC 位址及封包目的的位址的辨別，L2 Switch 會將該封包直接傳送至連接目的地的 Port，而不會將該封包傳送到其他的 Port。若並無此目的地 IP 的資訊時，則 L2 Switch 會廣播至所有的連接埠上，待目的 IP 回應時，將新的連接埠對應學習起來，那麼下次就不用廣播而直接傳送。
如果再把路由表的功能加入 L2 Switch，那麼它就會變成 L3 Switch，可以為 VLAN 建立適當的路由表，讓效能更加提昇。L3 的交換器又稱為 IP Switch 或 Switch Router，透過專屬的 ASIC 晶片來解析第三層表頭（如 IP Header）以達到傳送目的，因此通常可以提高到每秒百萬封包的效能以及數十個高速乙太網路連接埠之容量。L3 Switch 的路由表可以對 VLAN 做更有效的管制，讓廣播封包不會無限制的傳送。

啥是L3 Switch

Layer 3 Switch 又稱為IP Switch 或Switch Router, 意即其工作於第三層網路層的通信協定(如IP)，並藉由解析第三層表頭(Header)將封包傳至目的地，有別於傳統的路由器以軟體的方式來執行路由運算與傳送，Layer 3 Switch是以硬體的方式(通常由專屬ASIC構成)來加速路由運算與封包傳送率並結合Layer 2 的彈性設定，因此其效能通常可達每秒數百萬封包(Million packet per second)的傳送率，並具備數十個至上百個以上的高速乙太網路(Fast Ethernet)連接埠，或數個至數十個超高速乙太網路(Gigabit Ethernet)連接埠之容量。

傳統路由器通常可處理Multiprotocal 多重協定路由運算(如IP，IPX AppleTalk，DEC Net...etc)但Layer 3 Switch 通常只處理IP 及IPX，此乃為簡化設計，降低路由運算與軟體的複雜性以提昇效能，並配合網路協定發展的單純化(多重協定慢慢簡化至IP一種協定)趨勢所致。

由於Layer 2 的Switch 並無法有效的阻絕廣播域(Broadcast Domain)如ARP (Address Resolution Protocol)及Win95/98 中大量使用的NetBEUI協定均大量使用廣播封包，因此就算Layer 2 Switch 以VLAN (Virtual LAN)的方式(虛擬網路)將經常要通訊的群組構成一廣播域(Broadcast Domain)來試圖降低broadcast封包對網路層的影響，但仍無法完全避免廣播風暴問題(同一個VLAN間仍會產生廣播風暴)，再加上現今網路(尤其是Campus內部間流量及對外的Internet/Intranet流量)已不是80/20規則(80%流量在本地，20%是外地)，而是漸漸成為20/80規則，且加上Client/Server 及Distributor Server之運用，因此單靠Layer 2 Switch或傳統Router路由器便無法符合對效能(傳統路由器變成瓶頸)及Intranet上對安全顧忌(Layer 2 Broadcast Domain，對因廣播而使資訊傳送被盜取的安全疑慮)之要求，因此Layer 3 Switch便大量興起，初期只運用Core端(骨幹)，現在的趨勢已漸漸走向桌面(Layer 3 down to desktop)。

如同傳統路由器(Router)，Layer 3 Switch的每一個連接埠(port)都是一個子網路(Subnet)，而一個子網路就單獨是一個Broadcast Domain廣播域，因此每一個port的廣播封包並不會流竄到另一個port，其僅負責傳送要跨越子網路的封包(Routing Forward)，並以目的地的IP位址(目的地子網路的網路號碼)來決定封包要轉送至哪一個port，並以Routing Protocol(如RIP或OSPF)來交換Routing Table並學習網路拓蹼，其通常存放於Layer 3 Switch的Routing Forward Data-Base(FDB)，並以硬體及Route Cache的方式來加速IP table lookup並予以定址與更新(目前大多以ASICIC來執行)，因此才得以提昇運算效能達成Wiring Speed Forward之目的。

Layer 3 Switch通常提供較大頻寬的交換核心(Switch Fabric)以提供較大的容量(Port Capacity)與較高的交換效能，近來各廠家並不斷附以Layer 3 Switch更強大的支援能力，如Class of Service(服務等級優先權)，Quality of Service(服務品質保證)，Policy Management(策略分級品質與頻寬管制與管理)，Multicast Routing(群組廣播路由傳送)等功能，以符合網路環境的快速變化與應用。

Cisco Catalyst 2950 switch password recovery procedure

Cisco Catalyst 2950 Series Switches
Cisco Catalyst Fixed Configuration Layer 2 and Layer 3 Switches

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Cisco Catalyst Fixed Configuration Layer 2 and Layer 3 Switches



Document ID: 12040


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Contents
Introduction
Before You Begin
Conventions
Prerequisites
Step-by-Step Procedure
Related Information


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Introduction
This document describes the password recovery procedure for the Cisco Catalyst Layer 2 fixed configuration switches 2900XL/3500XL, 2940, 2950/2955, 2960, and 2970 Series, as well as the Cisco Catalyst Layer 3 fixed configuration switches 3550, 3560, and 3750 Series.

Before You Begin
Conventions
For more information on document conventions, see the Cisco Technical Tips Conventions.

Prerequisites
There are no specific prerequisites for this document.

Step-by-Step Procedure
Follow the password recovery procedure below.

Attach a terminal or PC with terminal emulation (for example, Hyper Terminal) to the console port of the switch.

Use the following terminal settings:

Bits per second (baud): 9600

Data bits: 8

Parity: None

Stop bits: 1

Flow Control: Xon/Xoff

Note: For additional information on cabling and connecting a terminal to the console port, refer to Connecting a Terminal to the Console Port on Catalyst Switches.

Unplug the power cable.

Power the switch and bring it to the switch: prompt:

For 2900XL, 3500XL, 2940, 2950, 2960, 2970, 3550, 3560, and 3750 series switches, do this:

Hold down the mode button located on the left side of the front panel, while you reconnect the power cable to the switch.

Catalyst Switch Series
LED Behavior and Mode Button Release Action

2900XL, 3500XL, 3550
Release the Mode button when the LED above Port1x goes out.

2940, 2950
Release the Mode button after approximately 5 seconds when the Status (STAT) LED goes out. When you release the Mode button, the SYST LED blinks amber.

2960, 2970
Release the Mode button when the SYST LED blinks amber and then turns solid green. When you release the Mode button, the SYST LED blinks green.

3560, 3750
Release the Mode button after approximately 15 seconds when the SYST LED turns solid green. When you release the Mode button, the SYST LED blinks green.



Note: LED position may vary slightly depending on the model.

Catalyst 3524XL



Catalyst 2950-24



For 2955 series switches only:

The Catalyst 2955 series switches do not use an external mode button for password recovery. Instead the switch boot loader uses the break-key detection to stop the automatic boot sequence for the password recovery purposes. The break sequence is determined by the terminal application and operating system used. Hyperterm running on Windows 2000 uses Ctrl + Break. On a workstation running UNIX, Ctrl-C is the break key. For more information, refer to Standard Break Key Sequence Combinations During Password Recovery.

The example below uses Hyperterm to break into switch: mode on a 2955.

C2955 Boot Loader (C2955-HBOOT-M) Version 12.1(0.0.514), CISCO DEVELOPMENT TEST
VERSION
Compiled Fri 13-Dec-02 17:38 by madison
WS-C2955T-12 starting...
Base ethernet MAC Address: 00:0b:be:b6:ee:00
Xmodem file system is available.
Initializing Flash...
flashfs[0]: 19 files, 2 directories
flashfs[0]: 0 orphaned files, 0 orphaned directories
flashfs[0]: Total bytes: 7741440
flashfs[0]: Bytes used: 4510720
flashfs[0]: Bytes available: 3230720
flashfs[0]: flashfs fsck took 7 seconds.
...done initializing flash.
Boot Sector Filesystem (bs:) installed, fsid: 3
Parameter Block Filesystem (pb:) installed, fsid: 4

*** The system will autoboot in 15 seconds ***
Send break character to prevent autobooting.


!--- Wait until you see this message before
!--- you issue the break sequence.
!--- Ctrl+Break is entered using Hyperterm.


The system has been interrupted prior to initializing the flash file system to finish
loading the operating system software:

flash_init
load_helper
boot
switch:Issue the flash_init command.

switch: flash_init
Initializing Flash...
flashfs[0]: 143 files, 4 directories
flashfs[0]: 0 orphaned files, 0 orphaned directories
flashfs[0]: Total bytes: 3612672
flashfs[0]: Bytes used: 2729472
flashfs[0]: Bytes available: 883200
flashfs[0]: flashfs fsck took 86 seconds
....done Initializing Flash.
Boot Sector Filesystem (bs:) installed, fsid: 3
Parameter Block Filesystem (pb:) installed, fsid: 4
switch:

!--- This output is from a 2900XL switch. Output from
!--- other switches will vary slightly.

Issue the load_helper command.

switch: load_helper
switch:Issue the dir flash: command.

Note: Make sure to type a colon ":" after the dir flash.

The switch file system is displayed:

switch: dir flash:
Directory of flash:/
2 -rwx 1803357 c3500xl-c3h2s-mz.120-5.WC7.bin

!--- This is the current version of software.

4 -rwx 1131 config.text

!--- This is the configuration file.

5 -rwx 109 info
6 -rwx 389 env_vars
7 drwx 640 html
18 -rwx 109 info.ver
403968 bytes available (3208704 bytes used)
switch:

!--- This output is from a 3500XL switch. Output from
!--- other switches will vary slightly.

Type rename flash:config.text flash:config.old to rename the configuration file.

switch: rename flash:config.text flash:config.old
switch:

!--- The config.text file contains the password
!--- definition.

Issue the boot command to boot the system.

switch: boot
Loading "flash:c3500xl-c3h2s-mz.120-5.WC7.bin"...###############################
################################################################################
######################################################################
File "flash:c3500xl-c3h2s-mz.120-5.WC7.bin" uncompressed and installed, entry po
int: 0x3000
executing...

!--- Output suppressed.
!--- This output is from a 3500XL switch. Output from other switches
!--- will vary slightly.

Enter "n" at the prompt to abort the initial configuration dialog.

--- System Configuration Dialog ---
At any point you may enter a question mark '?' for help.
Use ctrl-c to abort configuration dialog at any prompt.
Default settings are in square brackets '[]'.
Continue with configuration dialog? [yes/no]: n

!--- Type "n" for no.

Press RETURN to get started.

!--- Press Return or Enter.

Switch>

!--- The Switch> prompt is displayed.

At the switch prompt, type en to enter enable mode.

Switch>en
Switch#Type rename flash:config.old flash:config.text to rename the configuration file with its original name.

Switch#rename flash:config.old flash:config.text
Destination filename [config.text]

!--- Press Return or Enter.

Switch#Copy the configuration file into memory.

Switch#copy flash:config.text system:running-config
Destination filename [running-config]?

!--- Press Return or Enter.

1131 bytes copied in 0.760 secs
Sw1#The configuration file is now reloaded.

Overwrite the current passwords that you do not know. Choose a strong password with at least one capital letter, one number, and one special character.

Note: Overwrite the passwords which are necessary. You need not overwrite all of the mentioned passwords.

Sw1# conf t


!--- To overwrite existing secret password

Sw1(config)#enable secret



!--- To overwrite existing enable password

Sw1(config)#enable password



!--- To overwrite existing vty password

Sw1(config)#line vty 0 15
Sw1(config-line)#password

Sw1(config-line)#login


!--- To overwrite existing console password

Sw1(config-line)#line con 0
Sw1(config-line)#password

Write the running configuration to the configuration file with the write memory command.

Sw1#write memory
Building configuration...
[OK]
Sw1#
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Related Information
Password Recovery Procedures
Switches Product Support
LAN Switching Technology Support
Technical Support - Cisco Systems