Datasheet

Book VII
Chapter 1
Wide-Area
Networking Basics
817
Introducing Cable Connections
Before connecting a terminal to the console port, configure the terminal
to match the router console port settings, typically 9600 baud, 8 data bits,
no parity, and either 1 or 2 stop bits (depending on the router model).
DB-25 cabling and adapters
The types of cabling and adapters used for Cisco routers are categorized
into these main types:
✦ RS-232 straight-through cable: Standard serial cable known as CAB-R23.
This Cisco router cable uses a female DB-25 connector on one end and a
male DB-25 connector on the other end. Either end may be used by the
network or Cisco device, depending on DCE or DTE device designation
and assignment. If the Cisco router is designated as a DCE device, the
female DB-25 connector is the Cisco end of the cable. If the router is des-
ignated as a DTE device, the male DB-25 connector is the Cisco end.
✦ RJ-45–to–DB-9 adapter: Connects a router to a PC through a 9-pin COM port.
Connecting Cisco routers using a DCE-to-DTE
crossover cable
Although Cisco routers are considered DTE
devices (Cisco serial interfaces are DTE
by default), you can create a simulated lab
DCE-to-DTE WAN environment using two Cisco
routers and a DCE-to-DTE crossover cable.
Because channel service unit/data service unit
(CSU/DSU) devices (DCEs) control the timing
(clocking) for synchronous serial interfaces,
one Cisco router must be configured as a DCE
device. Each router’s serial interface should
be configured depending on which end of
the DB-60 cable is plugged in: One interface
configured as a DCE and the other end as
the DTE device. Make sure that both routers’
serial interfaces are configured with the no
shutdown command and the proper IP
addressing information, and then configure
clocking on the DCE device:
RouterDCE(config-if)#clock
rate 64000
This command sets the clock rate to 64,000
bits per second. Because no error message
was generated by the router, the command
executed successfully. What would happen if
the same clocking command was mistakenly
executed on the DTE device?
RouterDTE(config-if)#clock
rate 64000
%Error: This command applies
only to DCE interfaces
The show controllers command display
output allows an administrator to view which
interfaces are set up for DCE or DTE operation:
RouterDTE#show controllers
serial 0
HD unit 1, idb = 0x711CD0,
driver structure at
0x124140
buffer size 1524 HD unit 1,
V.35 DTE cable
48_489628-bk07ch01.indd 81748_489628-bk07ch01.indd 817 3/1/10 10:15 PM3/1/10 10:15 PM