From: Drew Whitaker (drew.whitaker@gmail.com)
Date: Sat Sep 25 2004 - 10:22:54 GMT-3
I've been reading through Vegesna's IP QoS book and had some questions
regarding its content that I thought I'd pass on to the group.
1) On page 40, listing 3-4, he lists the rate-limit syntax as:
rate-limit access-group 1 input 45000000 ...
Shouldn't this be: rate-limit input access-group 1 ... ?
2) On page 43, he states that CIR is measured in bits per second, but
on page 46 it says its in bytes. Which is it?
3) Page 48 example is designed to set all traffic except HTTP traffic
with an IPP of 4. Syntax given is:
access-list 101 permit tcp any any eq www
access-list 101 permit tcp any eq www any
int hssi1/0/0
rate-limit input 30000000 15000 15000 conform-action continue
exceed-action drop
rate-limit input access-group 101 150000 10000 10000 conform-action
set-prec-transmit 4 exceed-action set-prec-transmit 0
rate-limit input 30000000 15000 15000 conform-action set-prec-transmit
4 exceed-action set-prec-transmit 4
Because of the permit in the ACL, I would read this to be all HTTP
traffic gets an IPP of 4, not all traffic except HTTP. What am I
missing?
4) Syntax on page 51 gives:
rate-limit input access-group 2 rate-limit 5000000 ...
Yet, other examples give syntax of:
rate-limit input access-group rate-limit 2 ...
Which is it, or does it matter?
5) Page 58, listing 3-19 DTS example.
policy-map MYPOLICY
class MYCLASS
shape average 256000 16384 0
Why is Be set to 0? Wouldn't setting it to 0 be performing traffic
policing, and not traffic-shaping?
6) Page 60, listing 3-22.
policy-map FROMPOLICY
class FROMHOSTA
shape peak 128000 8192 1280
The Be is 1280. Yet the FAQ at the end of the chapter says Be should
be 2 X Bc, which would be 16384. What am I not understanding here?
7) Speaking of the FAQ on page 63, he writes that Bc = CIR x (1 byte /
8 bits) x 1.5 seconds
This is a little different than the way I have learned this. I
learned Bc = CIR x TI, with TI being set to .125. Given his example,
1 byte / 8 bits is .125, which is similar to the equation I learned
but then he adds multiplying by 1.5 seconds. However, when I do the
math, I do not come up with the same values as in his examples. For
instance, on page 62 he gives a DTS example where:
CIR = 256000
Bc = 16384
Be = 1280
However, 256000 x .125 x 1.5 = 48,000, not 16384. I'm confused.
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