ICND2 – Chapter 16 – Frame Relay Configuration

Cisco IOS uses Inverse ARP by default which discovers the mapping between DLCIs and their next-hop address.

Configuring Frame Relay

1. Configure frame-relay encapsulation on the physical interface

Router(config-if)#encapsulation frame-relay (use frame-relay encapsulation instead of default HDLC)

2. Configure an IP Address on the interface or sub-interface(s)

3. Optional: Manually configure the LMI type on the physical interface

Router(config-if)#frame-relay lmi-type [ansi | cisco | q933a]

4. Optional: Change from Cisco frame-relay encapsulation to IETF on all or specific VCs:

Router(config-if)encapsulation frame-relay ietf (for all VCs on physical interface)

OR

Router(config-sub-if)frame-relay interface-dlci 99 ietf (for point-to-point sub-interfaces)

OR

Router(config-sub-if)frame-relay map ip 192.168.1.1 99 broadcast ietf (for multi-point interfaces or when not using Inverse ARP)

5. Optional: Define Static Mapping of DLCIs (no Inverse ARP)

Router(config-sub-if)frame-relay map ip 192.168.1.1 broadcast

When using static mapping the broadcast keyword is required to support routing

6. Sub-interfaces Only: Associate DLCIs to sub-interface using:

Router(config-sub-if)frame-relay interface-dlci 99

OR

Router(config-sub-if)frame-relay map ip 192.168.1.1 broadcast

You must use IETF encapsulation to communication with non-Cisco equipment.

The LMI setting is per physical interface.

Frame Relay mapping creates a correlation between layer 2 and layer 3 addresses.

Mapping is needed on multiaccess networks and is also needed if you disable Inverse ARP.

Inverse ARP (enabled by default) dynamically creates a mapping between the layer 3 address and the layer 2 address.

Inverse ARP goes in knowing the Layer 2 address but needs to find the Layer 3 address. (opposite of ARP on a ethernet LAN)

Inverse ARP is not needed on point-to-point interfaces but is still enabled by default.

Using the frame-relay map command on a sub-interface automatically disabled Inverse ARP on that sub-interface.

When using show commands on a router, only local DLCIs are shown.

Commands to verify frame-relay operation:

Router#show frame-relay pvc (lists details on each VC)

Router#show frame-relay map (lists VC mapping information)

Router#show frame-relay lmi (show counters for the various LMI messages)

Frame Relay PVC statuses:

Active – Operational
Inactive – Configured but down
Deleted – Frame switch and router configs do not match

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