SMC Networks TigerStack II SMC8848M Programmierhandbuch

TigerStack II

10/100/1000

Gigabit Ethernet Switch

◆24/48 auto-MDI/MDI-X 10/100/1000BASE-T ports

◆4 RJ-45 ports shared with 4 SFP transceiver slots

◆2 10GBASE extender module slots

◆Non-blocking switching architecture

◆Support for a redundant power unit

◆Spanning Tree Protocol, RSTP, and MSTP

◆Up to 32 LACP or static 8-port trunks

◆Layer 2/3/4 CoS support through eight priority queues

◆Layer 3/4 traffic priority with IP Precedence and IP DSCP

◆Full support for VLANs with GVRP

◆IGMP multicast filtering and snooping

◆Manageable via console, Web, SNMP/RMON

◆Security features: ACL, RADIUS, 802.1x

◆Routing features: IP/RIP routing, CIDR

◆Supports IPv4/IPv6, dual protocol stack

Management Guide

SMC8824M

SMC8848M

38 Tesla

Irvine, CA 92618

Phone: (949) 679-8000

TigerStack II 10/100/1000

Management Guide

From SMC’s Tiger line of feature-rich workgroup LAN solutions

April 2006

Pub. # 150200054400A

Information furnished by SMC Networks, Inc. (SMC) is believed to be accurate and reliable. However, no

responsibility is assumed by SMC for its use, nor for any infringements of patents or other rights of third

parties which may result from its use. No license is granted by implication or otherwise under any patent or

patent rights of SMC. SMC reserves the right to change specifications at any time without notice.

SMC Networks, Inc.

38 Tesla

Irvine, CA 92618

Trademarks:

SMC is a registered trademark; and EZ Switch, TigerStack and TigerSwitch are trademarks of SMC

Networks, Inc. Other product and company names are trademarks or registered trademarks of their

respective holders.

IMITED

ARRANTY

Limited Warranty Statement: SMC Networks, Inc. (“SMC”) warrants its products to be

free from defects in workmanship and materials, under normal use and service, for the

applicable warranty term. All SMC products carry a standard 90-day limited warranty from

the date of purchase from SMC or its Authorized Reseller. SMC may, at its own discretion,

repair or replace any product not operating as warranted with a similar or functionally

equivalent product, during the applicable warranty term. SMC will endeavor to repair or

replace any product returned under warranty within 30 days of receipt of the product.

The standard limited warranty can be upgraded to a Limited Lifetime* warranty by registering

new products within 30 days of purchase from SMC or its Authorized Reseller. Registration

can be accomplished via the enclosed product registration card or online via the SMC Web

site. Failure to register will not affect the standard limited warranty. The Limited Lifetime

warranty covers a product during the Life of that Product, which is defined as the period of

time during which the product is an “Active” SMC product. A product is considered to be

“Active” while it is listed on the current SMC price list. As new technologies emerge, older

technologies become obsolete and SMC will, at its discretion, replace an older product in its

product line with one that incorporates these newer technologies. At that point, the obsolete

product is discontinued and is no longer an “Active” SMC product. A list of discontinued

products with their respective dates of discontinuance can be found at:

http://www.smc.com/index.cfm?action=customer_service_warranty.

All products that are replaced become the property of SMC. Replacement products may be

either new or reconditioned. Any replaced or repaired product carries either a 30-day limited

warranty or the remainder of the initial warranty, whichever is longer. SMC is not responsible

for any custom software or firmware, configuration information, or memory data of

Customer contained in, stored on, or integrated with any products returned to SMC pursuant

to any warranty. Products returned to SMC should have any customer-installed accessory or

add-on components, such as expansion modules, removed prior to returning the product for

replacement. SMC is not responsible for these items if they are returned with the product.

Customers must contact SMC for a Return Material Authorization number prior to returning

any product to SMC. Proof of purchase may be required. Any product returned to SMC

without a valid Return Material Authorization (RMA) number clearly marked on the outside

of the package will be returned to customer at customer’s expense. For warranty claims within

North America, please call our toll-free customer support number at (800) 762-4968.

Customers are responsible for all shipping charges from their facility to SMC. SMC is

responsible for return shipping charges from SMC to customer.

WARRANTIES EXCLUSIVE: IF AN SMC PRODUCT DOES NOT OPERATE AS

WARRANTED ABOVE, CUSTOMER’S SOLE REMEDY SHALL BE REPAIR OR

REPLACEMENT OF THE PRODUCT IN QUESTION, AT SMC’S OPTION. THE

FOREGOING WARRANTIES AND REMEDIES ARE EXCLUSIVE AND ARE IN

LIEU OF ALL OTHER WARRANTIES OR CONDITIONS, EXPRESS OR IMPLIED,

EITHER IN FACT OR BY OPERATION OF LAW, STATUTORY OR OTHERWISE,

INCLUDING WARRANTIES OR CONDITIONS OF MERCHANTABILITY AND

FITNESS FOR A PARTICULAR PURPOSE. SMC NEITHER ASSUMES NOR

AUTHORIZES ANY OTHER PERSON TO ASSUME FOR IT ANY OTHER

LIABILITY IN CONNECTION WITH THE SALE, INSTALLATION,

MAINTENANCE OR USE OF ITS PRODUCTS. SMC SHALL NOT BE LIABLE

UNDER THIS WARRANTY IF ITS TESTING AND EXAMINATION DISCLOSE THE

ALLEGED DEFECT IN THE PRODUCT DOES NOT EXIST OR WAS CAUSED BY

CUSTOMER’S OR ANY THIRD PERSON’S MISUSE, NEGLECT, IMPROPER

INSTALLATION OR TESTING, UNAUTHORIZED ATTEMPTS TO REPAIR, OR

ANY OTHER CAUSE BEYOND THE RANGE OF THE INTENDED USE, OR BY

ACCIDENT, FIRE, LIGHTNING, OR OTHER HAZARD.

LIMITATION OF LIABILITY: IN NO EVENT, WHETHER BASED IN CONTRACT

OR TORT (INCLUDING NEGLIGENCE), SHALL SMC BE LIABLE FOR

INCIDENTAL, CONSEQUENTIAL, INDIRECT, SPECIAL, OR PUNITIVE

DAMAGES OF ANY KIND, OR FOR LOSS OF REVENUE, LOSS OF BUSINESS, OR

OTHER FINANCIAL LOSS ARISING OUT OF OR IN CONNECTION WITH THE

SALE, INSTALLATION, MAINTENANCE, USE, PERFORMANCE, FAILURE, OR

INTERRUPTION OF ITS PRODUCTS, EVEN IF SMC OR ITS AUTHORIZED

RESELLER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

SOME STATES DO NOT ALLOW THE EXCLUSION OF IMPLIED WARRANTIES

OR THE LIMITATION OF INCIDENTAL OR CONSEQUENTIAL DAMAGES FOR

CONSUMER PRODUCTS, SO THE ABOVE LIMITATIONS AND EXCLUSIONS

MAY NOT APPLY TO YOU. THIS WARRANTY GIVES YOU SPECIFIC LEGAL

RIGHTS, WHICH MAY VARY FROM STATE TO STATE. NOTHING IN THIS

WARRANTY SHALL BE TAKEN TO AFFECT YOUR STATUTORY RIGHTS.

* SMC will provide warranty service for one year following discontinuance from the active

SMC price list. Under the limited lifetime warranty, internal and external power supplies, fans,

and cables are covered by a standard one-year warranty from date of purchase.

SMC Networks, Inc.

38 Tesla

Irvine, CA 92618

vii

ABLE

ONTENTS

Section I Getting Started

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-1

Key Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

Description of Software Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

System Defaults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9

2 Initial Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

Connecting to the Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

Configuration Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

Required Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3

Remote Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

Stack Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5

Selecting the Stack Master . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5

Selecting the Backup Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6

Recovering from Stack Failure or Topology Change . . . . . . . . . 2-7

Broken Link for Line and Wrap-around Topologies . . . . . 2-7

Resilient IP Interface for Management Access . . . . . . . . . . 2-8

Resilient Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8

Renumbering the Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8

Ensuring Consistent Code is Used Across the Stack . . . . . . . . . 2-8

Basic Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9

Console Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9

Setting Passwords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10

Setting an IP Address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11

Manual Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11

Dynamic Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-15

Enabling SNMP Management Access . . . . . . . . . . . . . . . . . . . . 2-18

Community Strings (for SNMP version 1 and 2c clients) . 2-19

Trap Receivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-20

Configuring Access for SNMP Version 3 Clients . . . . . . . 2-20

Managing System Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-21

Saving Configuration Settings . . . . . . . . . . . . . . . . . . . . . . . . . . 2-22

ABLE

ONTENTS

viii

Section II Switch Management

3 Configuring the Switch . . . . . . . . . . . . . . . . . . . . . . . . 3-1

Using the Web Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

Navigating the Web Browser Interface . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3

Home Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3

Configuration Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4

Panel Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5

Main Menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6

4 Basic Management Tasks . . . . . . . . . . . . . . . . . . . . . . 4-1

Displaying System Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

Displaying Switch Hardware/Software Versions . . . . . . . . . . . . . . . . . 4-4

Displaying Bridge Extension Capabilities . . . . . . . . . . . . . . . . . . . . . . . . 4-6

Setting the Switch’s IP Address (IP Version 4) . . . . . . . . . . . . . . . . . . . 4-8

Manual Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10

Using DHCP/BOOTP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-11

Setting the Switch’s IP Address (IP Version 6) . . . . . . . . . . . . . . . . . . 4-13

Configuring an IPv6 Address . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13

Configuring an IPv6 General Network Prefix . . . . . . . . . . . . . 4-22

Configuring Neighbor Detection Protocol and Static Entries . 4-24

Configuring Support for Jumbo Frames . . . . . . . . . . . . . . . . . . . . . . . . 4-28

Managing Firmware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-29

Downloading System Software from a Server . . . . . . . . . . . . . 4-30

Saving or Restoring Configuration Settings . . . . . . . . . . . . . . . . . . . . . 4-32

Downloading Configuration Settings from a Server . . . . . . . . . 4-34

Console Port Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-36

Telnet Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-38

Configuring Event Logging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-41

System Log Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-41

Remote Log Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-43

Displaying Log Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-45

Sending Simple Mail Transfer Protocol Alerts . . . . . . . . . . . . . 4-46

Renumbering the Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-48

Resetting the System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-49

Setting the System Clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-50

ABLE

ONTENTS

Configuring SNTP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-50

Setting the Time Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-51

5 Simple Network Management Protocol . . . . . . . . . . 5-1

Enabling the SNMP Agent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4

Setting Community Access Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4

Specifying Trap Managers and Trap Types . . . . . . . . . . . . . . . . . . . . . . . 5-6

Configuring SNMPv3 Management Access . . . . . . . . . . . . . . . . . . . . . 5-10

Setting a Local Engine ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10

Specifying a Remote Engine ID . . . . . . . . . . . . . . . . . . . . . . . . . 5-11

Configuring SNMPv3 Users . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12

Configuring Remote SNMPv3 Users . . . . . . . . . . . . . . . . . . . . . 5-15

Configuring SNMPv3 Groups . . . . . . . . . . . . . . . . . . . . . . . . . . 5-18

Setting SNMPv3 Views . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-24

6 User Authentication . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

Configuring User Accounts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

Configuring Local/Remote Logon Authentication . . . . . . . . . . . . . . . . 6-3

Configuring HTTPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7

Replacing the Default Secure-site Certificate . . . . . . . . . . . . . . . 6-9

Configuring the Secure Shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-10

Generating the Host Key Pair . . . . . . . . . . . . . . . . . . . . . . . . . . 6-13

Configuring the SSH Server . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-16

Configuring Port Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-18

Configuring 802.1X Port Authentication . . . . . . . . . . . . . . . . . . . . . . . 6-21

Displaying 802.1X Global Settings . . . . . . . . . . . . . . . . . . . . . . 6-22

Configuring 802.1X Global Settings . . . . . . . . . . . . . . . . . . . . . 6-23

Configuring Port Settings for 802.1X . . . . . . . . . . . . . . . . . . . . 6-24

Displaying 802.1X Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-27

Filtering IP Addresses for Management Access . . . . . . . . . . . . . . . . . . 6-29

7 Access Control Lists . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

Configuring Access Control Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

Setting the ACL Name and Type . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

Configuring a Standard IPv4 ACL . . . . . . . . . . . . . . . . . . . . . . . . 7-3

Configuring an Extended IPv4 ACL . . . . . . . . . . . . . . . . . . . . . . 7-4

Configuring a MAC ACL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7

ABLE

ONTENTS

Configuring a Standard IPv6 ACL . . . . . . . . . . . . . . . . . . . . . . . . 7-9

Configuring an Extended IPv6 ACL . . . . . . . . . . . . . . . . . . . . . 7-10

Binding a Port to an Access Control List . . . . . . . . . . . . . . . . . . . . . . . 7-13

8 Port Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

Displaying Connection Status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

Configuring Interface Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-4

Creating Trunk Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-8

Statically Configuring a Trunk . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-9

Enabling LACP on Selected Ports . . . . . . . . . . . . . . . . . . . . . . . 8-11

Configuring LACP Parameters . . . . . . . . . . . . . . . . . . . . . . . . . 8-13

Displaying LACP Port Counters . . . . . . . . . . . . . . . . . . . . . . . . 8-17

Displaying LACP Settings and Status for the Local Side . . . . . 8-18

Displaying LACP Settings and Status for the Remote Side . . . 8-21

Setting Broadcast Storm Thresholds . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-23

Configuring Port Mirroring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-25

Configuring Rate Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-26

Showing Port Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-28

9 Address Table Settings . . . . . . . . . . . . . . . . . . . . . . . . . 9-1

Setting Static Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1

Displaying the Address Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-3

Changing the Aging Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-5

10 Spanning Tree Algorithm . . . . . . . . . . . . . . . . . . . . . 10-1

Displaying Global Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-4

Configuring Global Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-8

Displaying Interface Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-13

Configuring Interface Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-17

Configuring Multiple Spanning Trees . . . . . . . . . . . . . . . . . . . . . . . . . 10-21

Displaying Interface Settings for MSTP . . . . . . . . . . . . . . . . . . . . . . . 10-24

Configuring Interface Settings for MSTP . . . . . . . . . . . . . . . . . . . . . . 10-26

11 VLAN Configuration . . . . . . . . . . . . . . . . . . . . . . . . . 11-1

IEEE 802.1Q VLANs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1

Enabling or Disabling GVRP (Global Setting) . . . . . . . . . . . . 11-5

Displaying Basic VLAN Information . . . . . . . . . . . . . . . . . . . . 11-6

Andere Handbücher für TigerStack II SMC8848M

Dieses Handbuch passt für folgende Modelle

Inhaltsverzeichnis

Andere SMC Networks Schalten Handbücher

SMC Networks

SMC Networks EZ6508TX Bedienungsanleitung

SMC Networks

SMC Networks PF2A7 Series Bedienungsanleitung

SMC Networks

SMC Networks ISE80 Bedienungsanleitung

SMC Networks

SMC Networks SMC EZ Connect SMCUSBH7 Bedienungsanleitung

SMC Networks

SMC Networks TigerStack III SMC6824MPE Bedienungsanleitung

SMC Networks

SMC Networks PFMC7-L Series Bedienungsanleitung

SMC Networks

SMC Networks ZSE40A Bedienungsanleitung

SMC Networks

SMC Networks TigerSwitch SMC6128L2 Bedienungsanleitung

SMC Networks

SMC Networks SMC6224M Bedienungsanleitung

SMC Networks

SMC Networks TigerSwitch SMC8724-10BT Bedienungsanleitung

SMC Networks

SMC Networks ZSE2 Series Bedienungsanleitung

SMC Networks

SMC Networks EZSwitch SMCGS24C-Smart Bedienungsanleitung

SMC Networks

SMC Networks SMCBGLLCX1 Bedienungsanleitung

SMC Networks

SMC Networks PF3W5 Series Bedienungsanleitung

SMC Networks

SMC Networks SMC8126L2 Programmierhandbuch

SMC Networks

SMC Networks SMC8024L2 Bedienungsanleitung

SMC Networks

SMC Networks EZ Switch SMC-EZ109DT Bedienungsanleitung

SMC Networks

SMC Networks SMC6752AL2 Bedienungsanleitung

SMC Networks

SMC Networks PF2A5 Series Bedienungsanleitung

SMC Networks

SMC Networks IS1000 Series Bedienungsanleitung

SMC Networks

SMC Networks PFA Series Bedienungsanleitung

SMC Networks

SMC Networks IS3000 Series Bedienungsanleitung

SMC Networks

SMC Networks TigerStack SMC6924MT Bedienungsanleitung

SMC Networks

SMC Networks SMCGS501 - FICHE TECHNIQUE Bedienungs- und Sicherheitshinweise

Beliebte Schalten Handbücher anderer Marken

URC

URC Total Control MFS-8 Bedienungsanleitung

Azbil

Azbil HPQ-D11 Bedienungsanleitung

Sony

Sony DFS-900M Bedienungsanleitung

SICK

SICK i17S Bedienungsanleitung

F&F

F&F SZR-277 Bedienungsanleitung

Shure

Shure UAMS/BK Bedienungsanleitung

Dräger

Dräger X-zone Switch Off Bedienungsanleitung

Asco

Asco Joucomatic 349 Series Bedienungsanleitung

BT Mini Hub Bedienungsanleitung

D-Link

D-Link DES-1226G Bedienungsanleitung

Johnson Controls

Johnson Controls FS80-C Bedienungsanleitung

Alcatel-Lucent

Alcatel-Lucent 7450 ESS-12 Bedienungsanleitung

MicroNet

MicroNet SP1200A Bedienungsanleitung

Ruijie

Ruijie RG-PF2920 Series Installations- und Betriebsanleitung

Altinex

Altinex DA1914SX Bedienungsanleitung

MiLAN

MiLAN MIL-SM2401M Bedienungsanleitung

RJM

RJM MASTERMIND PBC/6X Bedienungsanleitung

Atlas

Atlas MMK-KVM8 Bedienungsanleitung