Configuring the Serial Interface
This chapter describes configuring the serial interface for Cisco 800M Series ISRs in the following
sections:
• Configuring the Serial Interface, page 39
• Features Supported by Serial Module, page 39
• Information About Configuring Serial Interfaces, page 41
• How to Configure Serial Interfaces, page 45
• Configuration Examples, page 47
Configuring the Serial Interface
The Cisco 800M Series Integrated Services Router (ISR) provides serial WAN connectivity to remote
sites using Cisco High-Level Data Link Control (HDLC), Point-to-Point Protocol (PPP), or Frame Relay
encapsulation through the pluggable, serial WAN interface module. The Cisco 800M Series ISR supports
both synchronous and asynchronous modes of communication.
CHA PT ER
4
Features Supported by Serial Module
The Cisco 800M Series ISR has 2 WAN slots that can host single-port serial module or multi-mode 3G
module and supports the following combinations.
• Serial module in slot 0 and 3G module in slot 1
• 3G module in slot 0 and serial module in slot 1
• Serial module in slot 0 and serial module in slot 1
The features supported by the single-port serial module on Cisco 800M Series ISR is given as follows:
• Supports the following encapsulations :
–
HDLC
–
PPP
–
Frame Relay
–
Serial Line Internet Protocol (SLIP)
• Supports the following serial protocols
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Features Supported by Serial Module
–
EIA-232
–
EIA-449
–
EIA-530
–
EIA-530A
–
V. 3 5
–
X.21
• Supports synchronous speed of up to 8 Mbps
• Supports asynchronous speed of up to 115.2 kbps
• Supports network clock synchronization
Cisco 800M Series ISRs use Cisco smart serial connectors. Information about the cables supported by
Cisco 800M Series ISRs are provided in Tab le 4-1 .
Table 4-1 Smart Serial Cabling for Cisco 800M Series ISRs
Product Number Cable Type Length Connector Type
CAB-SS-V35MT V.35 DTE 10 ft (3m) Male
CAB-SS-V35FC V.35 DCE 10 ft (3m) Female
CAB-SS-232MT EIA/TIA-232 DTE 10 ft (3m) Male
CAB-SS-232FC EIA/TIA-232 DTE 10 ft (3m) Female
CAB-SS-449MT EIA/TIA-449 DTE 10 ft (3m) Male
CAB-SS-449FC EIA/TIA-449 DTE 10 ft (3m) Female
CAB-SS-X21MT X.21 DTE 10 ft (3m) Male
CAB-SS-X21FC X.21 DTE 10 ft (3m) Female
CAB-SS-530MT EIA/TIA-530 DTE 10 ft (3m) Male
CAB-SS-530AMT EIA/TIA-232 DTE 10 ft (3m) Male
Chapter 4 Configuring the Serial Interface
Table 4-2 describes the LEDs on the Cisco 800M series serial WAN module.
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Chapter 4 Configuring the Serial Interface
Information About Configuring Serial Interfaces
Table 4-2 LEDs on the Serial WAN Module
LED Name Color/ Status Description
CONN Green Indicates the interface status
OFF Shows that the line protocol is
LOOP BACK Green Indicates that the hardware
OFF Indicates that loopback is not
Information About Configuring Serial Interfaces
and shows that line protocol is
up.
down.
loopback status is configured
on the serial interface.
configured.
To configure serial interfaces, you should understand the following concept:
• Cisco HDLC Encapsulation, page 41
• PPP Encapsulation, page 41
• Keepalive Timer, page 43
• Frame Relay Encapsulation, page 44
Cisco HDLC Encapsulation
Cisco High-Level Data Link Controller (HDLC) is the Cisco proprietary protocol for sending data over
synchronous serial links. Cisco HDLC also provides a simple control protocol called Serial Line Address
Resolution Protocol (SLARP) to maintain serial link keepalives. Cisco HDLC is the default for data
encapsulation at Layer 2 (data link) of the Open System Interconnection (OSI) stack for efficient packet
delineation and error control.
Note Cisco HDLC is the default encapsulation type for the serial interfaces.
When the encapsulation on a serial interface is changed from HDLC to any other encapsulation type, the
configured serial subinterfaces on the main interface inherit the newly changed encapsulation and they
do not get deleted.
Cisco HDLC uses keepalives to monitor the link state, as described in the “Keepalive Timer” section on
page 4-43.
PPP Encapsulation
PPP is a standard protocol used to send data over synchronous serial links. PPP also provides a Link
Control Protocol (LCP) for negotiating properties of the link. LCP uses echo requests and responses to
monitor the continuing availability of the link.
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Information About Configuring Serial Interfaces
Note When an interface is configured with PPP encapsulation, a link is declared down and full LCP
negotiation is re-initiated after five echo request (ECHOREQ) packets are sent without receiving an echo
response (ECHOREP).
PPP provides the following Network Control Protocols (NCPs) for negotiating properties of data
protocols that will run on the link:
• IP Control Protocol (IPCP) to negotiate IP properties
• Multiprotocol Label Switching control processor (MPLSCP) to negotiate MPLS properties
• Cisco Discovery Protocol control processor (CDPCP) to negotiate CDP properties
• IPv6CP to negotiate IP Version 6 (IPv6) properties
• Open Systems Interconnection control processor (OSICP) to negotiate OSI properties
Chapter 4 Configuring the Serial Interface
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