For frame relay encapsulation type, use the hardware configuration interface command encapsulation frame-relay [cisco | ietf]. The default encapsulation type is cisco. Cisco Use this option if you connect to another Cisco router or, conversely, use the ietf when connected to a router from another manufacturer.
Once set up frame-relay, we can use the following commands to obtain status information and solve problems.
- Show interface. Displays information on the package and the status of layers 1 and 2. It also displays information about DLCI and LMI.
- Show frame-relay lmi. Displays the LMI traffic statistics.
- Show frame-relay pvc. Displays the status of each configured connection and traffic statistics. This command is also used to determine the number of BECN and FECN packets received by the router. An example would be sh frame pvc 100.
- Show frame-relay map. View static mapping entries learned by the router.
- Clear frame-relay-InARP. Deletes allocations created by Inverse ARP.
- Debug frame-relay lmi. It allows to verify and troubleshoot a frame relay connection. Use this command to determine if the router and switch are sending and receiving LMI packets properly.
Basic Configuration Interface Frame-Relay Point to Point
Config t
Int s0
Encapsulation frame-relay
Frame-relay interface-DLCI 100
Frame-relay lmi-type ansi
If you have the opportunity to connect two routers directly using V.35 DTE and DCE cables, you have to know the router that will serve as a DCE device. To this end, during the configuration of the serial interface, use the command frame-relay interface-type dce in interface configuration mode. You also need to configure the clock speed on the router you have specified as DCE. For the router to act as Frame-Relay switch, enter the frame-relay switching command in configuration mode.
It is seldom that we find a point to point topology only two locations on where to configure frame relay. In most cases, the topology is used is as follows.
- Star topology. Also known as hub-and-spoke. It is the most popular and least expensive because it requires the smallest number of PVC. The central router, provides a multipoint connection, using a single interface to connect multiple individual PVC.
- Full mesh topology. All routers have virtual circuits to other destinations. It is very expensive, but it supports redundancy.
- Partial mesh topology. In this, not all sites have direct access to other sites.
To operate an interface and multipoint frame-relay, we can configure the interface as multipoint subinterfaces or as several point to point. In all cases, Frame-Relay DLCI used to distinguish between different virtual circuits Frame-Relay network. Thus multiple virtual circuits terminating in a multipoint Frame-Relay interface so that it also can be assigned DLCI number as well as network addresses assigned to the corresponding DLCI.
When a single interface must interconnect multiple sites, accessibility problems may arise from the nature of non-broadcast multiaccess (NBMA) frame relay. The frame relay interfaces using the split horizon algorithm (split horizon) to reduce the number of routing loops, whereby not allow a routing update received on an interface is sent to the same interface. As a result, if a remote router sends a routing update to the central router, the central router can not send that broadcast through the same interface to other remote routers, even if they use separate PVC (since they are in the same interface). Another problem would be to consider the bandwidth consumed by routing updates, the CDP protocol, etc. The solution to this problem is the use of subinterfaces, because routing updates received by a subinterface if they can be sent by another subinterface. Subinterfaces can be configured to withstand the Point to Point connections (a DLCI, a subnet) and multipoint (multiple DLCI, a subnet).
Configuration two point to point subinterfaces
Interface Serial0
No ipaddress
Encapsulation frame-relay
Interface serial0.2 point-to-point
Ip address 10.17.0.1 255.255.255.0
Bandwidth 64
Frame-relay interface-DLCI 110
Interface serial0.3 point-to-point
Ip address 10.18.0.1 255.255.255.0
Bandwidth 64
Frame-relay interface DLCI 120
Configure a subinterface multipoint
Serial2 Interface
No ip address
Encapsulation frame-relay
No inverse-arp
Multipoint serial2.2 Interface
Ip address 10.17.0.1 255.255.255.0
Bandwidth 64
Frame-relay map ip 10.17.0.2 120 broadcast
Frame-relay map ip 10.17.0.3 130 broadcast
Frame-relay map ip 10.17.0.4 140 broadcast
To find the IP addresses of a multipoint Frame-Relay interface, you can use the command show frame-relay map.