Hello
I'm after a sanity check on my understanding of traffic shaping. In
particular, traffic shaping on a Cisco 2500 running IOS 11.3.
On my providers Internet router, they have the following command on the
Serial0 (connection to ISP), Ethernet0 (connection to local LAN) and
Ethernet1 (unused) interfaces:
traffic-shape rate 2048000 256000 512000 1000
show traffic-shape produces (modified to fit the screen):
router#show traffic-shape
ACL Target Byte Sustain Excess Inter Incr Adapt
I/F Rate Limit bits/int bits/int (ms) (bytes) Active
Et0 2048000 96000 256000 512000 125 32000 -
Et1 2048000 96000 256000 512000 125 32000 -
Se0 2048000 96000 256000 512000 125 32000 -
My understanding of the "traffic-shape rate" command is the following:
- first parameter specifies the committed information rate (CIR) in bits
- second parameter specifies the how much traffic will be sent per interval
(Bc) in bits.
- third parameter specifies the how much traffic can exceed the Bc per
interval (Be) in bits, if Bc was not exceeded in the previous interval.
- fourth parameter specifies the number of buffers to use for this traffic
shaper.
My understanding is that this means that the traffic shaping command above
acknowledges that the serial line speed is 2Mbps (which is correct) and will
attempt to send 256000 bits per 125ms interval (which equates to 2048000
bits per second) and will potentially accept up to 756000 bits for peak
intervals and buffer additional traffic up to 1000 additional packets.
However, from MRTG monitoring it appears that the traffic shaping command is
restricting traffic to 756000 bits per second.
Can anyone shed any light on this?
Thanks in advance.
Ross
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