From: Eugene Ward (eward15@juno.com)
Date: Tue May 17 2005 - 19:50:11 GMT-3
Vijay,
Wendell Odom writes about this in the DQOS book. The value under the "Byte Limit" column using the "show traffic-shape" command actually reflects the Bc in bytes, rather than bits per interval. The IOS programmers for some reason or another wrote the code that way.
Eugene Ward
-------------------------------------------------------------------------
I have a question on the default Bc value assigned to a frame relay
interface when traffic shaping is enabled.
IEWB Vol1 Lab 8, Q9.1 - 9.3 task you with capping traffic at 128Kbps.
With the bare minimum configuration below, the router calculated the Bc
value shown below in the output of "sh frame pvc 104" as 128000bps.
From the output of "sh traff s0/0" I can see that the default Tc of
125ms has been applied to the frame relay interface.
The IEWB Bc value supplied in the solution was specified as "bc
16000".
This accurately reflects the burst value for a default Tc of 125ms.
My question,
Why does IOS calculate a burst value of 128000bps?
************************************
Router#sh run int s0/0
Building configuration...
Current configuration : 188 bytes
!
interface Serial0/0
no ip address
encapsulation frame-relay
no fair-queue
no arp frame-relay
frame-relay class FRCLASS
frame-relay traffic-shaping
no frame-relay inverse-arp
end
map-class frame-relay FRCLASS
frame-relay cir 128000
************************************
************************************
Router#sh frame pvc 104
PVC Statistics for interface Serial0/0 (Frame Relay DTE)
DLCI = 104, DLCI USAGE = UNUSED, PVC STATUS = INACTIVE, INTERFACE =
Serial0/0
input pkts 0 output pkts 0 in bytes 0
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 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
switched pkts 0
Detailed packet drop counters:
no out intf 0 out intf down 0 no out PVC 0
in PVC down 0 out PVC down 0 pkt too big 0
shaping Q full 0 pkt above DE 0 policing drop 0
pvc create time 00:02:54, last time pvc status changed 00:02:55
>>> cir 128000 bc 128000 be 0 byte limit 2000
interval
125 <<<
mincir 64000 byte increment 2000 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
Router#
************************************
************************************
Router#sh traff s0/0
Interface Se0/0
Access Target Byte Sustain Excess Interval Increment
Adapt
VC List Rate Limit bits/int bits/int (ms) (bytes)
Active
103 128000 2000 128000 0 125 2000 -
104 128000 2000 128000 0 125 2000 -
105 128000 2000 128000 0 125 2000 -
113 128000 2000 128000 0 125 2000 -
102 128000 2000 128000 0 125 2000 -
Router#
************************************
Vijay Ramcharan
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