Mozafar Bag-Mohammadi
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Transcript Mozafar Bag-Mohammadi
Frame Relay
Mozafar Bag-Mohammadi
Frame Relay Standards and Equipment
Frame Relay
A packet switching and encapsulation technology
A communications technique for sending data over high-
speed digital connections
Originally designed for use across ISDN
Provide connection between the data terminal
equipment (DTE) and the data communications
equipment (DCE) via virtual circuit
Switched virtual circuits (SVC)
Permanent virtual circuits (PVC)
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Before Frame Relay
After Frame Relay
Frame Relay Standards and Equipment
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Frame Relay Terminology
Frame Relay Standards and Equipment
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DLCI
Frame relay connections identify virtual circuits by
Data Link Connection Identifier (DLCI) numbers
A DLCI number associates an IP address with a specific virtual
circuit
DLCI numbers have only local significance
DLCI numbers are usually assigned by the Frame Relay
provider
Most likely not the same on either side of the Frame Relay switch
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Frame Relay Map
Frame Relay map
A table in RAM that defines the remote interface to which a
specific DLCI number is mapped
The definition will contain a DLCI number and an interface
identifier
Which is typically a remote IP address
The Frame Relay map can be built automatically or statically
depending on the Frame Relay topology
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Frame Relay Map
Subinterfaces
Virtual interfaces associated with a physical interface
Created by referencing the physical interface followed by a
period and a decimal number
For the purposes of routing, however, subinterfaces are
treated as physical interfaces
With subinterfaces, the cost of implementing multiple Frame
Relay virtual circuits is reduced
Because only one port is required on the router
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LMI
LMI basically extended the functionality of Frame Relay by:
Making the DLCIs globally significant rather than locally
significant
Creating a signaling mechanism between the router and
the Frame Relay switch, which could report on the status
of the link
Supporting multicasting
Providing DLCI numbers that are globally significant makes
automatic configuration of the Frame Relay map possible
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Inverse ARP
In multipoint configurations
Routers use the protocol Inverse ARP to send a query
using the DLCI number to find a remote IP address
As other routers respond to the Inverse ARP queries, the
local router can build its Frame Relay map automatically
To maintain the Frame Relay map, routers exchange
Inverse ARP messages every 60 seconds by default
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Encapsulation Types
Cisco routers support these types of LMI encapsulation:
cisco
ansi
q933a
Cisco routers (using IOS Release 11.2 or later) can
“autosense” the LMI type used by the Frame Relay switch
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Basic Multipoint Configuration with Two
Routers
• LMI will notify the router about the available DLCI numbers
– Inverse ARP will build the Frame Relay map dynamically
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Basic Multipoint Configuration with Two
Routers (continued)
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Multipoint Configuration Using a
Subinterface (continued)
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Point-to-Point Configuration Using
Subinterfaces
Point-to-point Frame Relay configurations do not support
Inverse ARP
You will have to configure each subnet separately
Use the frame-relay interface-dlci command to associate the
DLCI numbers with a specific subinterface
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Monitoring Frame Relay
You can check your Frame Relay configuration by using show
commands
These commands allow you to verify that the commands you
previously entered produced the desired effect on your router
The most common show commands for monitoring Frame
Relay operation are:
show
show
show
show
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interface
frame-relay pvc
frame-relay map
frame-relay lmi
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