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
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.
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.
DTE – Data Termial Equipment
DCE – Data Circuit Terminal 
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
– 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
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:
Active
inactive
deleted
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
Keepalive
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
# encapsulation frame-relay
config-if # ip add
config-if # frame inverse-arp
OR
frame map ip DLCI
frame lmi-type cisco
keepalive
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 192.168.100.101
router 2 with dlci 18
int s0
encap frame
ip add 192.168.100.102
Another simple configuration is the following:
On the router use this config:
int s0
encap frame
frame-relay interface-dlci 101
ip add 192.168.100.101
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.
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