From: Nick Davey (nicky.davey@gmail.com)
Date: Sun Nov 26 2006 - 19:46:15 ART
Brian,
Correct me if i am wrong but i thought that LLQ is only active if the link
is congested. What you describe below is congestion, ie a large packet being
serialised while a small packet waits. Once a large packet is on the tx-ring
any others must queue and thus this is congestion. If LLQ is active all the
time that would mean that this traffic is bound (policed) to the priority
percentage even if the link is not experiencing congestion. I thought the
documentation states that the LLQ traffic can exceed its percentage if the
link is not congested.
This is one of those area's that causes confusion. I dont think Cisco has
ever released the full details of the queueing algorithm for LLQ. Having
said that i have seen IOS's police even if the link is not congested as you
describe but i always assumed that was either buggy or with the older IOS's
(12.2 maybe).
Regards,
Nick.
On 11/25/06, Brian McGahan <bmcgahan@internetworkexpert.com> wrote:
>
> Hi Jay,
>
> The LLQ or "priority" statment in the MQC is in effect 100% of the
> time. This is due to the fact that even if the output queue is not full
> priority packets can experience delay while waiting for large packets to be
> admitted to the transmit ring. To prevent this the LLQ send all packets
> that "match" to the front of the queue, preempting any non-priority packets
> on their path to the transmit ring. Also congestion is a function of the
> size of the output queue of the interface and is not directly related to the
> provisioned rate or access rate of an interface.
>
>
> HTH,
>
> Brian McGahan, CCIE #8593 (R&S/SP)
> bmcgahan@internetworkexpert.com
>
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> ________________________________
>
> From: nobody@groupstudy.com on behalf of Jay Hanke
> Sent: Fri 11/24/2006 10:15 AM
> To: ccielab@groupstudy.com
> Subject: LLQ and bandwidth on ethernet interface
>
>
>
> [demime could not interpret encoding quoted-printable - treating as plain
> text]
> When defining bandwidth percentages in LLQ setting the bandwidth on a
> given Ethernet interface will adjust the calculated bandwidth
> proportionally. LLQ doesn't do anything until there is congestion. So
> when does congestion occur if the bandwidth is set below the interface
> rate? Does it occur when the interface utilization exceeds the
> provisioned bandwidth or does congestion occur at the interface line
> rate?
>
> This is the scenario that I have in mind:
>
> Router1 Ethernet port =3D=3D> 1 mb/s Ethernet bridge =3D=3D> Router 2
> Ethern=
> et
> port
>
> Jay
>
>
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