This blog was originally started to better help me understand the technologies in the CCIE R&S blueprint; after completing the R&S track I have decided to transition the blog into a technology blog.

CCIE #29033

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Sunday, April 25, 2010

Question 18

How is a FECN or BECN used?

1 comments:

Packets Analyzed said...

FECN's and BECN's are used in Frame Relay networks.

FECN - Forward Explicit Congestion Notification - Expect delays. Sent by the source asking the destination to slow down its request for data.

BECN - Backward Explicit Congestion Notification - back off transmission. Sent by the destination asking the source to send data more slowly.

Both FECN's and BECN's are used to minimize the number of DE (Discard Eligibility) packets from being dropped.

FECN can be configured in 3 ways
1. Map-class for FRTS (Frame Relay Traffic Shaping)
"frame-relay fecn-adapt"
2. Policy map in MQC
"shape fecn-adapt"
3. Interface
"traffic-shape fecn-adapt"

If any of the above situations receive a FECN by the sending device send a BECN back.

BECN can be configured in 3 ways
1. Map-class for FRTS (Frame Relay Traffic Shaping)
"frame-relay adaptive-shaping"
2. Policy map in MQC
"shape adaptive"
3. Interface
"traffic-shape adaptive"

If BECN is received slow down.

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