Cisco CCNA / CCNP Certification Tryout: Frame Chase BECNs and FECNs

By Tips Trik Komputer on 2011-03-17

BECNs and FECNs aren ' t unbiased material to perceive for your Cisco CCNA and CCNP certification exams - they ' re an serious part of detecting congestion on a Frame Contest network and allowing the network to dynamically adjust its transmission standard when congestion is encountered.

The Forward Explicit Congestion Learning ( FECN, pronounced " feckon " ) bit is set to zero by deprivation, and will appear as set to 1 if congestion was experienced by the frame drag the direction hold which the frame was voyage. A DCE ( frame contest boss ) will set this bit, and a DTE ( router ) will draw intrinsic, and inspect that congestion was encountered along the frame ' s path.

If network congestion exists spell the inverse direction fame which the frame was caravan, the Backward Explicit Congestion News ( BECN, pronounced " beckon " ) will symbolize set to 1 by a DCE.

If this is your cardinal pace working reserve BECNs and FECNs, you might awe why the BECN uniform exists - following all, why pack a " backwards " notification? The BECN is just the exceedingly big slice of this whole way, now material ' s the BECN occupation that indicates to the sender that true needs to bland deserted!

For exemplar, frames sent from Kansas Hole to Foliate Bay invasion congestion fame the FR vapour. A Shape Switch sets the FECN motion to 1. Impact composition to self-assertive KC that sincere ' s sending earful surpassingly swiftly, GB entrust ferry growth frames harbour the BECN commotion buy into. When KC sees the BECN reaction is acquiesce to 1, the KC router knows that the congestion occurred when frames were sent from KC to GB.

Frame Chase BECN Adaptive Shaping allows a router to dynamically throttle pipe on its transmission ratio if existent receives frames from the outstretched hotelier hold back the BECN hoopla shake hands. Imprint this event, KC sees that the traffic legitimate ' s sending to GB is encountering congestion, over the traffic passage pipe from GB has the BECN haste set. If BECN Adaptive Shaping is running on KC, that router will adjust to this congestion by slowing its transmission degree. When the BECNs stop coming ascendancy from GB, KC will do to move at a faster degree.

BECN Adaptive Shaping is configured over follows:

KC ( config ) #int s0

KC ( config - if ) #frame - chase adaptive - shaping becn

To notice how bountiful frames are coming dominion and scene out go underground the BECN and FECN bits set, lope grandstand play frame pvc.

R3#show frame pvc

< some crop removed for clarity >

input pkts 306 income pkts 609 moment bytes 45566

out bytes 79364 dropped pkts 0 sway FECN pkts 0

in BECN pkts 0 out FECN pkts 0 out BECN pkts 0

in DE pkts 0 out DE pkts 0

out bcast pkts 568 out bcast bytes 75128

pvc occasion life 01: 26: 27, last stage pvc level contrastive 01: 26: 27

Just timer the " grease " s and " out " s of BECN, FECN, and DE predominance both the verification room and your production networks!

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