ROUTER INTERFACES
GENERALLY IN CISCO ROUTER HAVE THREE KINDS OF INTERFACES :
1. LAN INTERFACES (ETHERNET AUI, BD-9): Allow The Router To Connect To The Lan Media Through Ethernet Or Some Other LAN Technology Such As TOKEN RING OR ATM.2. MANAGEMENT PORTS (CONSOLE, AUXILARY): Provide A Text-Based Connection For The Configuration And Troubleshooting Of The Router.
3. WAN INTERFACES (SERIAL, ISDN BRI): Are Made Through A Wan Interface On A Router To Service Provider To Distant Site Or To The Internet.
THE FOLLOWING PICTURE SHOWS A ROUTER WITH THE MOST COMMON ROUTER INTERFACES:
Ethernet AUI Port, SERIAL Port, CONSOLE Port And AUXILIARY Port.
Some Routers Have Additional Ports Such As BD-9 Port For Token Ring Network And Isdn Basic Rate Interface (BRI) Port For Low Cost Dial-On-Demand Wan Connection, As Illustrated In The Following Picture.
ROUTER - DTE / DCE CABLE
For Communication, Wans Use Serial Transmission. Serial Transmission Is A Method Of Data Transmission In Which Bits Of Data Are Transmitted Sequenctially Over A Single Channel. On The Contrary, Parallel Data Transmission Transmits Several Bits At A Time With Parallel Data Transmission.
Serial Ports On Cisco Routers Use 60-Pin DB-60 Connector Or The Smaller “Smart-Serial” Connector For The Purpose Of WAN Connections. Serial Ports On The Other End Of The WAN Connection Is Dependent On The Service Providers And The Type Of Their DCE Equipment. Some Of The Different Signaling Standards And Connectors That Might Be Found On DCE Equipment Include EIA/TIA-232, EIA/TIA-449, V.35, X.21, And EIA-530.
When You Order The WAN Connection Cable, You Receive A Serial Transition Cable With A DB-60 Connector (Also Called Five-In-One Serial Connector) At One End And The Connector Appropriate For The Standards You Specify At The Other End. Whereas The Five-In-One Connector Connects To The DB-60 Port On A Serial WAN Interface Card (WIC) On The DTE (Your Router), The Specified Connector Plugs Into The Specific WIC On The DCE (Provider’s Modem Or CSU/DSU). What Specific Connector To Use Depends On Whether We Need EIA/TIA-232, EIA/TIA-449, V.35, X.21, Or EIA-530.
In Some Cases Such As Back-To-Back Connection, Your Router Could Act As DCE, Instead Of DTE. Thererfor, In Addition To Determining The Cable Type, You Need To Determine Whether You Need DATA TERMINAL EQUIPMENT (DTE) Or DATA CIRCUIT-TERMINATING EQUIPMENT (DCE) Connectors For Your WAN Equipment.
When A Router Directly Connect To A Data Network Such As A Service Provider WAN Link, The Router Is Referred To As Data Terminal Equipment, Or DTE. We Need To Select DTE Serial Cable In This Case. The Router Connected To The DCE Cable Must Provide Clocking. Provides The Clock At 64 Kbps (Clock Rate 64000).
HOW ROUTER - DTE / DCE CABLE WORK
UNDERSTAND HOW CABLING WORKS ON ROUTERS :
The DCE-To-DTE Crossover Cable Will Have Two Different DB-60 Interfaces.
< li> And The Other Marked DCE, (Data Communication Equipment) Means That This Device Must Provide The Clocking On The Wire. DTE/DCE Cable To Directly Connect Two Cisco Router Serial Interfaces.
The Router Connected To The DCE End Of The Cable Will Need Its Serial Interface Configured As A DCE Device. In A Real-Life Network, Your Serial Interfaces Will Almost Certainly Be Configured As DTE Interfaces. Recall That A CSU/DSU Usually Handles The Clocking For A Synchronous Serial Interface.
When Connecting Two Routers Together With A Serial Cable, One Of The Routers Needs To Host The DCE (Data Communications Equipment) Side Of The Cable, And The Other Will Host The DTE (Date Terminal Equipment) Side. Most Serial Cables Are Marked On The Connector If It’s The DTE OR DCE.
Connecting The Serial Ports Of Two Routers Directly Using What Is Known As A DCE-To-DTE Crossover Cable. These Cables Allow You To Simulate A Serial Wan Connection Without Requiring A CSU/DSU Or Similar Device.
WHAT’S THE DIFFERENCE BETWEEN TWO SIDES?
The DCE Side Of The Cable Is The Side That Sets The Speed Of The Link (Also Known As Clocking). Based On This, It’s Safe To Assume That The Cable Coming Out Of Your Router And Going To Your Service Provider Is The DTE Side, Since You Service Provider Sets The Speed Of The Line Based On The Subscription You Have Purchased.
The DTE Side Of The Cable Is Where The Communications Terminate Ie: Your Router Terminates The Connection From The Service Provider.
The Main Issue With Connecting Your Serial Interfaces In This Manner Is The Fact That One Of The Devices Will Need To Be Configured As DCE In Order To Provide The Timing Mechanism Required. If Your Device Is The DCE, You Must Provide Clocking Using The Clock Rate Command.
CONFIGURATION ON ROUTER - DTE / DCE CABLE
CONFIGURATION POINT OF VIEW :
The DCE Side Of The Cable Is Able To Use The Clock Rate Command To Set The Speed Of The Line. If The Command Is Not Used The Interface Will Run At The Maximum Speed Supported By The Interface. If You Have Only Subscribed For A 64k Line, Then The Clock Rate Would Have Been Set On The DCE Side Of The Cable Using The Command ‘Clock Rate 64000’ Under The Interface.
Router(config)#int s0
Router3(config-if)#clock rate ?
Example - > Router A(Config-If)# Clock Rate 56000
Router A(Config-If)#^Z
Router A# Copy Running-Config Startup-Config
Router A#Show Run
REAL CONFIGURATION EXAMPLE :
Router A#Conf T
Router A(Config)#Int S1 (Switches To Configure The Serial1 Interface)
Router A(Config-If)#IP Address 20.0.0.1 255.0.0.0
Router A(Config-If)#No Shut (Enable An Interface)
Router A(Config-If)# Clock Rate 56000 (Set The Clock Rate 56000 For DCE Interface)
Router A(Config-If)# Bandwidth 64 (Set A Logical Bandwidth Assignment Of 64k To The Serial Interface)
To Enable The Back-To-Back Serial Connection Between Two Routers, You Need To Configure One Router As DCE Using The Following Command In Interface Configuration Mode For The Serial Connection On Two Different Routers.
Router A(Config-If)#Exit
Router A#Show IP Route
TO DISPLAY INFORMATION ABOUT ROUTER - DTE / DCE CABLE ON SERIAL INTERFACE
TO DISPLAY INFORMATION ABOUT DTE / DCE CABLE :
SHOW CONTROLLERS SERIAL :
To Display Information That Is Specific To The Interface Hardware, Use The Show Controllers Serial Privileged Exec Command.
Show Controllers Serial Command Also Displays Configuration Information Such As The Framing, Clock Source, Bandwidth Limit, Whether Scrambling Is Enabled, The National Bit, The International Bits, And DSU Mode Configured On The Interface. Also Displayed Is The Performance Statistics For The Current Interval And Last 15-Minute Interval And Whether Any Alarms Exist.
You Can Also Use A DTE/DCE Cable To Directly Connect Two Cisco Router Serial Interfaces. DTE/DCE Cable Is Connected To A Given Serial Interface, Just Use The Show Controller Serial Command To Get That Information. Most Of The Output Of That Command Isn't Comprehensible, But What We Need Is Right On Top:
EXAMPLES :
Router#Show Controller Serial 1
This Can Be Done By Using The "Clock Rate" Command, From The Interface Configuration Mode.
Router(Config)# Interface S0
Router(Config-If)# Clock Rate 64000
SHOW CONTROLLERS ETHERNET :
To Display Information On The Cisco 2500 Series, Cisco 3000, Or Cisco 4000 Series Routers, Use The Show Controllers Ethernet Exec Command.
Show Controllers Ethernet Number
BANDWIDTH ON SERIAL INTERFACE
BANDWIDTH :
You Can Find The Possible Values By Using Help.
Router(Config-If)# Clock Rate ?
All Interfaces Have A Bandwidth Value Assigned To Them. This Is Used By Certain Routing Protocols, Such As IGRP, OSPF, AND EIGRP, When Making Routing Decisions. For Lan-Based Interfaces, The Speed Of The Interface Becomes The Bandwidth Value (In Kilobits Per Second (KBPS)).
However, On Synchronous Serial Interfaces, The Bandwidth Defaults To 1,554kbps And This Is Not Related With The Clock Rate Set. To Change The Bandwidth Value For An Interface, Use The Bandwidth Interface Sub Configuration Mode Command.
The Bandwidth Command Is Issued Under The Interface, As Is Represented In Kilobits Per Second.
Router# Conf T
Router(Config)# Interface Serial 1/0
Router(Config-If)# Bandwidth 64 (Represented In Kilobits Per Second)
TRABLESHOOTING TIPS FOR SERIAL INTERFACE PROBLEMS
INTERFACE PROBLEMS CAN BE SEEN AND APPROPRIATE ACTION TAKEN :
#Interface Is Up, Line Protocol Is Up -> None Needed, Interface Working Properly.
# Interface Is Up, Line Protocol Is Down -> Clocking Or Framing Problem, Check Clock Rate And Encapsulation Type On Both Routers.
# Interface Is Down, Line Protocol Is Down -> Cable Or Interface Problem, Check Interfaces On Both Ends To Ensure They Aren't Shutdown.
# Interface Is Administratively Down, Line Protocol Is Down -> The Interface Has Been Shutdown, Use The No Shutdown Command In The Interface's Configuration Mode.
CONCLUSION:
The Goal Of This Article Is To Give An Easy Way To Understand The “DTE/DCE Cables On Cisco Router". Hope This Article Will Help Every Beginners Who Are Going To Start Cisco Lab Practice Without Any Doubts. Thank You And Best Of Luck.
This Article Written Author By: Premakumar Thevathasan. CCNA, CCNP, CCIP, MCSE, MCSA, MCSA - MSG, CIW Security Analyst, CompTIA Certified A+.
DISCLAIMER:
This Document Carries No Explicit Or Implied Warranty. Nor Is There Any Guarantee That The Information Contained In This Document Is Accurate. Every Effort Has Been Made To Make All Articles As Complete And As Accurate As Possible.
It Is Offered In The Hopes Of Helping Others, But You Use It At Your Own Risk. The Author Will Not Be Liable For Any Special, Incidental, Consequential Or Indirect Any Damages Due To Loss Of Data Or Any Other Reason That Occur As A Result Of Using This Document. But No Warranty Or Fitness Is Implied. The Information Provided Is On An "As Is" Basic. All Use Is Completely At Your Own Risk.
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