On Thursday 19 December 2002 21:51, Brian Capouch wrote:
> I am new to shaping but not to routing; forgive me if this request is
> inappropriate for this list.
>
> I am a very small ISP and would like to use HTB to enforce contractual
> bandwidth limits on my customers. I am trying to think through one
> aspect of this that is vexing me. I'm sure it's no great secret that
> many ISPs oversell their bandwidth, and in our case we have a
> combination of accounts that total approximately 2.2Mbs on our feed,
> which is 1.2Mbs. (Concentrating right now on our download stream)
>
> How could something like this be accomodated? The documentation says
> that the total bandwidth allocations of a set of subclasses should total
> that assigned to the class.
>
> But my understanding is that if I bump up the bandwidth on the primary
> class to a value greater than my actual bandwidth, then I'm going to be
> filling up queues at the upstream ISP and negatively affecting my
> performance.
>
> I'm sure there is something I'm missing, but I've discussed this with a
> couple of fellow network engineers and neither was able to posit how
> such thing might work, although they both said they were sure that it is
> a common scenario.
You can create a root class with rate = ceil = 1.2 Mbps. Create a class for
each customer with ceil = selled bandwidth and the sum of the rates=1.2Mbps.
Example :
You selled 1.1 Mbps to customer1 and 0.37 (=2.2Mbps/6) to 3 other customers.
So you have a total bandwidth of 2.2Mbps. But you have only 1.2 Mbps
available.
class rate = ceil = 1.2 Mbps
class1 rate = 0.6, ceil = 1.1Mbps
class2 rate = 0.2, ceil = 0.37Mbps
class3 rate = 0.2, ceil = 0.37Mbps
class4 rate = 0.2, ceil = 0.37Mbps
The bandwidth you selled to the customers is the ceil. They never can use
more then the ceil. If one customer is using no bandwidth, the remaining
bandwidth is given to the other customers.
If all customers are using all bandwidth, each customer is "punished" in the
same way.
You can also give the customers a possibility to use as much bandwidth as
available. To do so, give each class ceil = 1.2Mbps, but that bandwidth is
not guaranteed. In this case, the rate is the minimum bandwidth they can
get. So for a SLA, you can say to the customer : "You have a minimum
bandwidth of 0.6Mbps and a maximum bandwidth of 1.2Mbps."
Stef
--
stef.coene@docum.org
"Using Linux as bandwidth manager"
http://www.docum.org/
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