Archive for the ‘Frame-Relay’ Category

frame-relay configuration

Dienstag, Juli 11th, 2006

1. which interface?

– might be good to start with subinteraces from the beginning
– point-to-point or multipoint?

– Cisco recommends point-to-point with subinterfaces to allow scalability
2. which encapsulation?

– # encapsulation frame-relay

– add Layer 3 information: for example ip oder ipx address
3. protocol specific parameters

4. frame-relay characteristics

Split horizon with frame-relay with subinterfaces

Freitag, Juli 7th, 2006

An routing update will not go out the same interface it came through. So it will no go out to others. This Problem is solved with subinterfaces with frame-relay.

The update will go in on for example s0.1 and can go out s0.2. It will leave on a different subinterface.

Subinterfaces are also good for scalability reasons.


Freitag, Juli 7th, 2006

full mesh – very costly, large number of circuits
partial mesh


Freitag, Juli 7th, 2006

Frame Relay LMI – Local Management Interface

LMI Types:

Cisco (default)

ANSI – (Annex D)
Q933a – ITU-T standard (Annex A)

The LMI type is autodetected based on the messages recived from the frame-relay switch.

In differnence to the dlci type, the LMI type can only be configured on an interface level.

Frame-Relay Devices

Freitag, Juli 7th, 2006

DTE – Data Termial Equipment
DCE – Data Circuit Terminal Frame Relay
DTE and DCE Devices are connected with an CSU/DSU

DTE Devices are Cisco Routers.

DCE Devices build the Frame Relay Switch Cloud, they are the Frame-Relay Switches

cable types for frame-relay

Freitag, Juli 7th, 2006

– EIA / TIA-232 and EIA / TIA-449

Pinout for EIA / TIA 232 Pins:

2 TS Transmit Data DTE-to-DCE

3 RD Recive Data DCE-to-DTE

4 RTS Request to send DTE signal buffer available

5 CTS Clear to send DCE signal available

6 DSR Data set ready DCE is ready

7 GRD Signal ground

8 CD Carrier detect DCE senses carrier

20 DTR Data term. ready DTE is ready

– V.35 and X.21

Abbreviations and definitions to know about Frame-Relay

Donnerstag, Juli 6th, 2006

CIR – Committed Information Rate

a specified amount of guaranteed bandwidth (measured in bits per second) on a Frame Relay service

Local Access Rate

clock speed of theconnection CPE or last mile loop to the service providers frame switch, rate of speed that packets travel

VC Virtual Circuit

bi-directional path between network devices

PVC/SVW – Permanent Virtual Circuit / Switched Virtual Circuit

a permanently or switch circuit between a router and a frame-relay switch. when it is a switched path, it is established on-demand and torn down, when the transfer is complete. I it similar to an ISDN circuit.

A PVC is up all the time.

DLCI – Data Link Connection Identifier

assigned by the service provider. This number is used to identify the logical link between the router (DTE) and the frame relay switch (DCE). DLCI’s are only localy significant as they are only valid between the router and the frame-relay switch.

LMI – Logical Management Interface

Types: Ansi, Cisco, Q933a

it’s a signaling standard between the router and the service providers frame-relay switch. It manages the connection and maintains the status between devices. LMI messages will be send back and forth between the router and the switch. The status of the link can be:




it is a good idea to „debug frame-relay lmi“ to troubleshoot a connection.

Point-to-Point Connection

– talk only to one device

Multipoint Connection

– to more than one device

FECN – Forward Explicit Congestion Notification

sending FECN Packet if noticed congestion on the network

BECN – Backward Explicit Congestio Notification
if the frame-relay switch noticed congestion it send’s a BECN Packet


every 10 secound a keepalive is sent by the router. If no keepalive arrives, the link is assumed to be down.

usefull debug explanation for „debug frame-relay lm“

PVC information element, length, dlci, status, CIR in decimal, for PVC Status

Could be:

0x00 = added/inactive

the remote end is not able to receive traffic at this time

0x02 = added/active

both ends are up

0x04 = deleted

the end router is no longer receiving LMI from the CO

0x08 = new/inactive

0x0a = new/active

simple Frame-Relay config

Donnerstag, Juli 6th, 2006

# encapsulation frame-relay

config-if # ip add

config-if # frame inverse-arp


frame map ip DLCI

frame lmi-type cisco


One Frame-Relay Switch, i use a 2523 for switching. Configured with the following:

frame-relay switching

int s0

encap frame

no ip add

frame-relay route 17 int s1 18

int s1

no ip add

encap frame

frame-relay route 18 int s0 17

router1 with dlci 17

int s0

encap frame

ip add

router 2 with dlci 18

int s0

encap frame

ip add

Another simple configuration is the following:

On the router use this config:

int s0

encap frame

frame-relay interface-dlci 101

ip add

and on the frame-relay switch:

frame-relay switching

int s2

encap frame

frame-intf-type dce

frame-relay route 101 int ser3 102

the route command means, route everything with dlci 101 from int s2 to interface s3 with dlci 102.

so on the s3 interface you have to add:

frame-relay route s3 102 int s2 101

If your adding a third device to the frame-relay switch and want connectivity between them, you’er going to configure a full mesh. The number of connections is calculated with N(N-1)/2 where N is the number of routers. So for example 5 router (5*4/2=10) will need 10 connections (pvc’s) for a full mesh.