RE: FRTS Default Bc value

Hi Tom,

This is a cosmetic bug in legacy FRTS. If you apply the same policy in MQC you'll see the correct Bc value reflected. Also the Bc isn't always the CIR/8. As the CIR goes up the router needs more intervals per second in order for the shaper to achieve the desired rate. For low speed CIR values you will see that Bc = CIR/8, but as CIR goes up this is not true. What would be more accurate would be to say that the CIR in Bits / Second = Bc in Bits / Tc milliseconds, or in other words that Bc = CIR/1000 * Tc, since Bc is expressed in milliseconds as opposed to seconds. This formula always stays true as the CIR goes up or down, or if you manually change the Bc.

HTH,

Brian McGahan, CCIE #8593 (R&S/SP/Security)
bmcgahan_at_INE.com

Internetwork Expert, Inc.
http://www.INE.com

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of Tom Kacprzynski
Sent: Sunday, April 01, 2012 9:51 PM
To: Cisco certification
Subject: FRTS Default Bc value

Hello,
I ran into an output of a FRTS show command that contradicts what I know so far and figure ask the experts to see where is the disconnect.

Based on what I know and the Enterprise QoS SRND, the Bc value by default should be set to Bc= CIR/8.
If I configure traffic shaping on an FR interface I see that bc on my DCLI
205 is set to 7000 bits (which is correct) :

Rack1R2#sh frame-relay pvc 205

PVC Statistics for interface Serial0/0/0 (Frame Relay DTE)

DLCI = 205, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0/0/0

  input pkts 275289 output pkts 125138 in bytes 20715768
  out bytes 12816805 dropped pkts 0 in pkts dropped 0
  out pkts dropped 0 out bytes dropped 0
  in 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 13544 out bcast bytes 1013448
  5 minute input rate 1000 bits/sec, 1 packets/sec
  5 minute output rate 1000 bits/sec, 1 packets/sec
  pvc create time 2d10h, last time pvc status changed 00:01:48
  cir 56000 * bc 7000 * be 0 byte limit 875 interval 125
<-------------------bc 7000
  mincir 28000 byte increment 875 Adaptive Shaping none
  pkts 135 bytes 15363 pkts delayed 0 bytes delayed 0
  shaping inactive
  traffic shaping drops 0
  Queueing strategy: fifo
  Output queue 0/40, 0 drop, 0 dequeued

Now if I apply a map-class with cir of 256,000 I don't see what I would expect, which is the Bc to be set to 32,000 but rather the Bc is set to 256,000. This does not make much sense to me especially that when I look at show traffic-shape the Tc is still set to .125sec.

map-class frame-relay FRTS
 frame-relay cir 256000

interface Serial0/0/0
 ip address 136.1.245.2 255.255.255.0
 encapsulation frame-relay
 no fair-queue
 frame-relay class FRTS
 frame-relay traffic-shaping
 frame-relay map ip 136.1.245.5 205 broadcast no frame-relay inverse-arp end

Rack1R2#sh frame-relay pvc 205

PVC Statistics for interface Serial0/0/0 (Frame Relay DTE)

DLCI = 205, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0/0/0

  input pkts 107 output pkts 0 in bytes 9918
  out bytes 0 dropped pkts 0 in pkts dropped 0
  out pkts dropped 0 out bytes dropped 0
  in 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 0 out bcast bytes 0
  5 minute input rate 1000 bits/sec, 1 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
  pvc create time 00:01:04, last time pvc status changed 00:01:04
  cir 256000 *bc 256000* be 0 byte limit 4000 interval 125
<<--------------bc 256,000
  mincir 128000 byte increment 4000 Adaptive Shaping none
  pkts 0 bytes 0 pkts delayed 0 bytes delayed 0
  shaping inactive
  traffic shaping drops 0
  Queueing strategy: fifo
  Output queue 0/40, 0 drop, 0 dequeued

Does anyone have any idea where the disconnect is?

Thank you,

Tom

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Received on Sun Apr 01 2012 - 22:07:39 ART