Transcript S6C8 – Frame-Relay Traffic

S6C8 – Frame-Relay Traffic
Controlling Frame-Relay Taffic
Packet Switched Networks
• Use Frame-Relay Switches
– Curriculum emulates with Router programmed to act
like a switch
• Switches can drop traffic
• Switches can prioritize traffic
• Can control, or "shape", traffic so that certain
protocols and VCs conform to specified
transmission rates.
• Switches can control flow of traffic
– Keeps high bandwidth switch from overpowering a slow router
• Can provide multiple levels of bandwidth and
service
Traffic Shaping Terminology
• Local Access Rate - clock speed (port speed) of
the connection (local loop) to the Frame-Relay
cloud.
• Committed Information Rate – bps rate which the
Frame Relay switch agrees to transfer data.
• Over-subscription - sum of the CIRs on all the
VCs exceeds the access line speed
• Committed Burst -- maximum number of bits that
the switch agrees to transfer during any Tc
=Bc/CIR
Traffic Shaping Terminology 2
• Excess Burst (Be) - maximum number of uncommitted bits that the
Frame Relay switch attempts to transfer beyond the CIR
• Excess Information Rate (EIR) - maximum bandwidth available to the
customer Be+CIR
• Forward Explicit Congestion Notification (FECN) - switch recognizes
congestion in the network and sends an FECN packet to destination
device to note congestion has occurred.
• Backward Explicit Congestion Notification (BECN) - switch
recognizes congestion in the network, sends BECN packet to the
source router to reduce the rate at which it is sending packets.
• Discard Eligibility (DE) bit – marks packet for possible drop if line is
congested
Rate Determination Factors
• Capacity of the local loop
– speed of the local loop is called the local access rate
• CIR – higher rates require more money
– if a customer's CIR is less than the local access rate, the
customer and provider agree on whether bursting above
the CIR is allowed
– CIR can be 0 – recommended you monitor closely
– Provider does not guarantee burst traffic will be
delivered
– DE bit identifies which frames will be discarded
Traffic Shaping
• Rate enforcement on a per-virtual-circuit basis configure a peak rate to limit outbound traffic to CIR, EIR
or some other defined value
• Generalized BECN support on a per-VC basis -The
router monitors BECNs and throttle traffic based on packet
feedback
• Priority/Custom/Weighted Fair Queuing (PQ/CQ/
WFQ) support at the VC level - allows for finer
granularity in the prioritization and queuing of traffic,
gives more control on an individual VC.
Use Traffic Shaping
• Topology consists of a high-speed (T1 line speed or
greater) connection at central site and low-speed (56 kbps
or less) at branch
– Rate enforcement can also be used in conjunction with
dlci
• Network constructed with many VCs to different locations
on a single physical line into the network
– can pre-allocate the bandwidth that each VC receives
on the physical line
• Different types of traffic (IP, Systems Network
Architecture [SNA], or Internetwork packet Exchange
[IPX]) to transmit on the same Frame Relay VC
– Prior to Cisco IOS Release 11.2, Custom Queuing was
defined only at the interface level. Now it can be
defined at the VC level
Configuring Traffic Shaping
• Specify a map class.
– map-class frame-relay map-class-name
• Configure the map class.
– Define the average and peak rates
– Specify that the router dynamically
rate at which it sends
packets
fluctuates the
• Enable Frame Relay on an interface
• Enable Frame Relay traffic shaping on
interface.
– frame-relay traffic-shaping
• Add the map class to VCs on the interface
– Router(config-if)#frame-relay class map-class-name
Rate Enforcement
• Define a map class
– Router(config)#map-class frame-relay map-class-name
• Define the rate enforcement parameters
– Router(config-map-class)#frame-relay
average [peak]
traffic-rate
• Enable both traffic shaping and per-VC queuing
for all VCs
– Router(config-if)#frame-relay Traffic-shaping
• Associate a map class with an interface
– Router(config-if)#frame-relay class name
Traffic Shaping - Dynamic
• Perform the following steps to configure
traffic
• Shaping-over-Frame Relay BECN support:
– define a map class and enter map class
configuration mode
– use the following command to enable BECN
support:
– Router(config-map-class)#frame-relay
adaptive-shaping becn
Dynamic Shaping - 2
• Enable both traffic shaping and per-VC
queuing for all VCs
– Router(config-if)#frame-relay traffic-shaping
• Associate a map class with an interface or
subinterface
– Router(config-if)#frame-relay class name
Queuing
• Queue lists prioritize traffic based on protocol type
• Queue lists can even prioritize traffic based on the
source and/or destination address
– Configure the router to prioritize certain traffic over
other traffic
• Packets cut in front of the line
– delay-sensitive application traffic, such as voice or Telnet, will
be as unaffected as possible by the shaping process
– Add Frame Relay map class to a VC, and you can specify
different peak and average rates on a per-VC basis
Traffic Mapping Show
Commands
• show frame-relay pvc dlci
• show traffic-shape
• show traffic-shape statistics
ODR
• Is not a true routing protocol
• Presents a more scalable solution than static routes
• Transport mechanism for ODR routes is the Cisco
Discovery Protocol (CDP)
– CDP runs on any media that supports the Subnetwork
Access Protocol (SNAP)
• Hub router can automatically discover stub
networks while the stub routers still use a default
route to the hub
– network portion does not have to be strictly classful.
• VLSM is supported
Configuring ODR
• ODR is enabled with a single command, router
odr
– Turn off any dynamic routing protocols in the spoke
routers.
– ODR and a dynamic routing protocol can be run on a
hub router
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RTA(config)#router odr
RTA(config)#router ospf 1
RTA(config-router)#redistribute
odr metric 100 subnets
RTA(config-router)#network
10.2.0.0 0.0.255.255 area 1