Table of Contents
1. Introduction
2. Understanding Frame-Relay Point-to-Point Configuration with Sub-Interface
3. Configuration Steps
Step 1: Selecting the Main Interface
Step 2: Disabling IP Address on the Main Interface
Step 3: Setting Encapsulation
Step 4: Configuring LMI Type
Step 5: Creating the Sub-Interface
Step 6: Assigning IP Address to the Sub-Interface
Step 7: Configuring the DLCI
4. Sample Configuration
5. Additional Features
6. Best Practices
7. Conclusion
1. Introduction
Frame-Relay is a cost-effective and efficient WAN protocol used to connect LANs over a wide area network (WAN). This blog post provides a comprehensive guide to configuring Frame-Relay for a Point-to-Point connection using sub-interfaces.
2. Understanding Frame-Relay Point-to-Point Configuration with Sub-Interface
A Point-to-Point Frame-Relay configuration using sub-interfaces involves creating a logical sub-interface on a physical interface. Each sub-interface represents a unique point-to-point connection with its own IP subnet and DLCI.
3. Configuration Steps
Step 1: Selecting the Main Interface
Select the main serial interface on the router.
R1(config)# interface serial 0/0/0
Step 2: Disabling IP Address on the Main Interface
Remove any IP address configuration from the main interface to prepare it for sub-interface configuration.
R1(config-if)# no ip address
Step 3: Setting Encapsulation
Set the encapsulation type to Frame-Relay. The default is 'cisco', but 'ietf' can be used for interoperability with non-Cisco devices.
R1(config-if)# encapsulation frame-relay [ietf, cisco]
Step 4: Configuring LMI Type
Configure the Local Management Interface (LMI) type. The default is 'cisco', but 'ansi' or 'q933a' can also be specified.
R1(config-if)# frame-relay lmi-type [ansi, q933a, cisco]
Step 5: Creating the Sub-Interface
Create a sub-interface with a custom number, typically matching the DLCI number for clarity.
R1(config-if)# interface serial 0/0/0.752 point-to-point
Step 6: Assigning IP Address to the Sub-Interface
Assign an IP address to the sub-interface. A /30 subnet is typically used for point-to-point links.
R1(config-subif)# ip address 192.168.5.1 255.255.255.252
Step 7: Configuring the DLCI
Configure the Data Link Connection Identifier (DLCI) for the sub-interface.
R1(config-subif)# frame-relay interface-dlci 752
4. Sample Configuration
Below is the complete configuration example for Router R1 with a Point-to-Point Frame-Relay connection using sub-interfaces:
R1(config)# interface serial 0/0/0
R1(config-if)# no ip address
R1(config-if)# encapsulation frame-relay ietf
R1(config-if)# frame-relay lmi-type ansi
R1(config-if)# interface serial 0/0/0.752 point-to-point
R1(config-subif)# ip address 192.168.5.1 255.255.255.252
R1(config-subif)# frame-relay interface-dlci 752
In this example:
- interface serial 0/0/0: Specifies the main serial interface.
- no ip address: Removes any IP address from the main interface.
- encapsulation frame-relay ietf: Sets Frame-Relay encapsulation to IETF.
- frame-relay lmi-type ansi: Configures the LMI type to ANSI.
- interface serial 0/0/0.752 point-to-point: Creates a point-to-point sub-interface.
- ip address 192.168.5.1 255.255.255.252: Assigns an IP address to the sub-interface.
- frame-relay interface-dlci 752: Configures the DLCI for the sub-interface.
5. Additional Features
- Traffic Shaping: Implement traffic shaping to manage bandwidth and ensure Quality of Service (QoS).
- Inverse ARP: Utilize Inverse ARP to automatically map remote IP addresses to local DLCIs, simplifying the configuration.
6. Best Practices
- Consistent Configuration: Ensure consistency across all router configurations to avoid connectivity issues.
- Monitor LMI: Regularly monitor the LMI status to ensure the health of the Frame-Relay network.
- Secure Frame-Relay Links: Use access control lists (ACLs) and other security measures to protect Frame-Relay links from unauthorized access.
- Documentation: Maintain detailed documentation of Frame-Relay configurations for troubleshooting and maintenance.
