Configuring Frame Relay

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Configuring Frame Relay

• Better example appropriate to the lab

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Frame Relay
Frame relay specifies the interface between the
DTE (FRAD) and the DCE (FRND) but does not
specify the connection within the Frame Relay
cloud.
FRAD
FRAD
Access Link
Access Link
FRND
FRND
Access link may be many types of access service
carriers provide including SW56, T1, FT1, etc.
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Frame Relay Frame
Frame Relay Address
Data
FCS
flag
flag
Address field (2 octets) First 10 bits Data
Link Connection Identifier Last 3 bits
Congestion Control Forward Explicit Congestion
Notification (FECN) Backward Explicit
Congestion Notification (BECN) Discard
Eligibility (DE) Data many types of data
including IP packet Flag mark beginning and
end of frame
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Frame-Relay Encapsulation

• Two types of Frame-Relay encapsulation
• Cisco
• Default used to connect two Cisco devices
• Proprietary
• IETF
• Encapsulation frame-relay ietf
• Used to connect to non-Cisco devices
• Standard

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Virtual Circuits
Permanent Virtual Circuits (PVC) established by
administrator and last until removed. Switched
Virtual Circuits (SVC) established by a
call setup frame and last until transmission ends.
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Frame-Relay DLCIs

• DLCI is a value between 16 and 1007
• Router can support multiple VCs on a single
  serial interface using subinterfaces
• You would obtain the DLCI values from the WAN
  provider

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(No Transcript)
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Local Management Interface (LMI)

• LMI are extensions to the Frame Relay standard
  that allow Frame Relay devices to communicate
  with one another
• Simplifies Frame Relay configuration since DTEs
  can automatically detect DLCI values
• Three types
• Cisco (default), ansi, q933a
• After IOS 11.2 LMI type is autosensed

RouterA(config-if)frame-relay lmi-type ansi
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LMI Extensions

• Common extensions
• Virtual circuit status messages allow router to
  determine what PVCs are available and to
  determine the operational status of PVCs the
  router knows about
• Router can transmit keepalive frames to ensure
  the PVC stays up

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LMI Extensions

• Optional extensions
• Multicasting
• Global addressing gives DLCIs global rather than
  local significance
• Simple flow control

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Inverse-ARP

• Inverse-ARP is used by routers to build frame
  relay maps by requesting the IP addresses
  associated with each DLCI
• Inverse ARP messages are exchanged every 60
  seconds between routers on a PVC

Route Table Frame
Relay Map Network Next Hop
Next Hop DLCI 10.0.0.0 172.16.1.2
172.16.1.2 100
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Frame Relay Map

• A routers frame relay map matches DLCIs with
  specific interfaces
• The map identifies DLCIs with network addresses

R3show frame-relay map  Serial0.1 (up) ip
129.130.32.1, dlci 301(0x12D,0x48D0),
broadcast status defined, active
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Configuring the Frame Relay Map Manually

• Without inverse-ARP the frame relay map must be
  built manually

RouterA(config-if)frame-relay map ip
172.16.30.17 16 ietf broadcast 16 DLCI Ietf
frame relay encapsulation type Broadcast send
broadcasts
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Point-to-Point Connections

• A subinterface on one router is connected to one
  interface or subinterface on another router
• Both are in the same subnet
• Broadcasts are not forwarded

10.0.0.2
10.0.0.1
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Multipoint Connections

• A subinterface on one router is connected to
  subinterfaces on multiple other routers
• All are in the same subnet
• Broadcasts are forwarded to all routers and split
  horizon is in effect

10.0.0.4
DLCI1
10.0.0.1
10.0.0.2
DLCI2
10.0.0.3
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Frame Relay Configurations

• Three possible Frame Relay networks
• Full Mesh VCs between every pair of routers
• Partial Mesh Some routers dont have VCs
  between them
• Hybrid Part of the network is full mesh and
  part is partial mesh

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Full Mesh Networks
A
199.1.1.1 199.0020.AAAA.AAAA
s0
s0
s0
199.1.1.3 199.0020.CCCC.CCCC
199.1.1.2 199.0020.BBBB.BBBB
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Configuration of Router A
RouterA(config)int serial 0 RouterA(config-if)en
capsulation frame-relay RouterA(config-if)ip
address 199.1.1.1 255.255.255.0 RouterA(config-if)
ipx network 199
Default settings used LMI type is automatically
sensed Encapsulation is cisco PVC DLCIs are
learned via LMI Inverse ARP is enabled and used
to build map
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Partial Mesh Network with Point-to-Point
Connections
A
DLCI 51
s0
140.1.3.0/24
140.1.1.0/24
192
191
140.1.2.0/24
190
s0
s0
s0
B
DLCI 52
DLCI 54
DLCI 53
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Configuration of Router A
RouterA(config)int serial 0 RouterA(config-if)en
capsulation frame-relay RouterA(config-if)int
serial 0.1 point-to-point RouterA(config-if)ip
address 140.1.1.1 255.255.255.0 RouterA(config-if)
ipx network 190 RouterA(config-if)frame-relay
interface-dlci 52 RouterA(config-if)int serial
0.2 point-to-point RouterA(config-if)ip address
140.1.2.1 255.255.255.0 RouterA(config-if)ipx
network 191 RouterA(config-if)frame-relay
interface-dlci 53
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Configuration of Router A
RouterA(config-if)int serial 0.2
point-to-point RouterA(config-if)ip address
140.1.3.1 255.255.255.0 RouterA(config-if)ipx
network 192 RouterA(config-if)frame-relay
interface-dlci 54
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Configuration of Router B
RouterB(config)int serial 0 RouterB(config-if)en
capsulation frame-relay RouterB(config-if)int
serial 0.1 point-to-point RouterB(config-if)ip
address 140.1.1.2 255.255.255.0 RouterB(config-if)
ipx network 190 RouterB(config-if)frame-relay
interface-dlci 51
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Partial Mesh Network with Multipoint Connections
DLCI 51
A
s0
140.1.1.0/24
140.1.1.0/24
190
190
140.1.1.0/24
190
s0
s0
s0
B
DLCI 52
DLCI 54
DLCI 53
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Configuration of Router A
RouterA(config)int serial 0 RouterA(config-if)en
capsulation frame-relay RouterA(config-if)int
serial 0.1 multipoint RouterA(config-if)ip
address 140.1.1.1 255.255.255.0 RouterA(config-if)
ipx network 190 RouterA(config-if)frame-relay
interface-dlci 52 RouterA(config-if)frame-relay
interface-dlci 53 RouterA(config-if)frame-relay
interface-dlci 54
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Configuration of Router B
RouterA(config)int serial 0 RouterA(config-if)en
capsulation frame-relay RouterA(config-if)int
serial 0.1 point-to-point RouterA(config-if)ip
address 140.1.1.2 255.255.255.0 RouterA(config-if)
frame-relay interface-dlci 51
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Hybrid Networks
DLCI 51
A
s0
140.1.2.0/24
140.1.1.0/24
192
190
140.1.1.0/24
190
s0
s0
s0
B
DLCI 54
DLCI 52
DLCI 53
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Router A Configuration
RouterA(config)int serial 0 RouterA(config-if)en
cap frame-relay RouterA(config-if)int serial 0.1
multipoint RouterA(config-if)ip address
140.1.1.1 255.255.255.0 RouterA(config-if)ipx
network 190 RouterA(config-if)frame-relay
interface-dlci 52 RouterA(config-if)frame-relay
interface-dlci 53 RouterA(config-if)int serial
0.2 point-to-point RouterA(config-if)ip address
140.1.2.1 255.255.255.0 RouterA(config-if)ipx
network 191 RouterA(config-if)frame-relay
interface-dlci 54
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Router B Configuration
RouterB(config)int serial 0 RouterB(config-if)en
cap frame-relay RouterB(config-if)int serial 0.1
multipoint RouterB(config-if)ip address
140.1.1.2 255.255.255.0 RouterB(config-if)ipx
network 190 RouterB(config-if) frame-relay map
ip 140.1.1.1 51 b RouterB(config-if) frame-relay
map ip 140.1.1.3 53 b
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Non-Broadcast MultiAccess (NBMA) Networks

• NBMA networks are those that allow multiple nodes
  to access the network but do not support
  broadcasts
• Broadcast (like routing updates) packets must be
  transmitted to each node individually in NBMA
  networks

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Broadcasts

• Since Frame Relay doesnt allow broadcasts,
  routers must transmit updates across every VC
  that you tell it to
• On a router with 100s of VCs this can cause
  problems
• Routers use different queues for broadcast
  packets and administrator can limit the amount of
  bandwidth devoted to broadcasts

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Split Horizon

• Since multiple VCs are connected to a single
  physical interface Split Horizon can cause
  problems
• Router doesnt advertise routes out an interface
  from which it learned them
• Split horizon is applied to subinterfaces as if
  they were separate physical interfaces
• Routes learned on one subinterface are advertised
  out other interfaces

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Split Horizon in Frame-Relay
DLCI 51
A
s0
140.1.1.0/24
140.1.1.0/24
190
190
140.1.1.0/24
190
s0
s0
s0
B
DLCI 52
DLCI 54
DLCI 53
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OSPF on NBMA Networks
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Hello and Dead Intervals

• Unlike on Ethernet interfaces, a router can
  detect when a serial interface goes down almost
  immediately
• Router doesnt need to rely on hello protocol to
  know whether a link is down
• Hello protocol is still necessary because of
  subinterfaces
• Intervals are increased on NBMA serial links
• Hello interval 60 seconds
• Dead interval 180 seconds

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OSPF Modes

• NBMA mode
• Similar to broadcast multiaccess networks
• Neighbors must be manually configured
• DR and BDR must be connected to all routers
• Usually seen on full-meshed networks
• Point-to-multipoint mode
• No DR or BDR are selected
• Usually seen on hub-and-spoke or partially-meshed
  networks

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IOS Commands to Know

• Encapsulation frame-relay
• Frame-relay map
• Frame-relay interface-dlci

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IOS Commands to Know

• Show interfaces serial
• Displays information about the multicast DLCI and
  DLCIs used on the Frame Relay configured serial
  interface, and the LMI DLCI used
• Show frame-relay PVC
• Displays the status of each configured connection
  as well as traffic statistics. This command is
  useful for viewing the number of BECN and FECN
  frames received by the router.

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IOS Commands to Know

• Show frame-relay map
• Displays the network-layer address and associated
  DLCI for each remote destination
• Show frame-relay lmi
• Displays LMI traffic statistics.

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Configuring DLCIs
Used with subinterfaces RouterA(config)interfa
ce serial 0.1 multipoint RouterA(config-if)frame-
relay interface-dlci 100 RouterA(config-if)interf
ace serial 0.2 multipoint RouterA(config-if)frame
-relay interface-dlci 200