RE: Q. Terribly confused about interface bandwidth used for QoS

From: Brian McGahan (bmcgahan@internetworkexpert.com)
Date: Sat Sep 09 2006 - 20:59:44 ART

        Assuming the bandwidth of the link is 64Kbps then solution 1 would be correct. Technically you don't need to use the interface level command 'bandwidth' in that case because you're not doing a percentage based reservation as well.

Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com

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________________________________________
From: sabrina pittarel [mailto:sabri_esame@yahoo.com]
Sent: Saturday, September 09, 2006 5:57 PM
To: Brian McGahan; ccielab@groupstudy.com
Subject: Re: Q. Terribly confused about interface bandwidth used for QoS calculations - please help

Thank you Brian,
I understand now, but let me take an example of a possible lab scenario

Assuming I have a P2P link with the DCE side clocked at 64000 and I'm asked do guarantee 10% of the bandwitdh on both sides to a given flow X and *not* to use the percentage keyword What would be the configuration of R1 and R2?

   1/1 1/1
R1 -------------------------- R2
                          clockrate 64000

Solution1)
R1 

---
interface s1/1
  bandwith 64
  service-policy output s1/1-pm-out

policy-map s1/1-pm-out
  class X
    bandwith  6 

R2
---
interface s1/1
  clockrate 64000
  bandwith 64
  service-policy output s1/1-pm-out

policy-map s1/1-pm-out
  class X
    bandwith  6 

Solution2)
R1
---
interface s1/1
  service-policy output s1/1-pm-out

policy-map s1/1-pm-out
  class X
    bandwith 154    <<<<< 10% of 1544 

R2
---
interface s1/1
  clockrate 64000
  service-policy output s1/1-pm-out

policy-map s1/1-pm-out
  class X
    bandwith 154

Sabrina
----- Original Message ----
From: Brian McGahan <bmcgahan@internetworkexpert.com>
To: sabrina pittarel <sabri_esame@yahoo.com>; ccielab@groupstudy.com
Sent: Saturday, September 9, 2006 3:15:00 PM
Subject: RE: Q. Terribly confused about interface bandwidth used for QoS calculations - please help
    In a practical application any time that the link speed does not
match the maximum transmission speed you should set bandwidth value
accordingly.  For example suppose you have a FastEthernet interface
connected to your service provider but they are policing your traffic to
5Mbps.  If you issue the "bandwidth percent 75" command under the MQC
you would be configuring a bandwidth guarantee beyond your reservable
capacity.  The same case would hold true for serial interface, atm
interfaces, etc.  In the lab exam I wouldn't worry about setting
bandwidth values unless there was a specific reason to do so though.

HTH,

Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com 

Internetwork Expert, Inc.
http://www.InternetworkExpert.com
Toll Free: 877-224-8987 x 705
Outside US: 775-826-4344 x 705
24/7 Support: http://forum.internetworkexpert.com
Live Chat: http://www.internetworkexpert.com/chat/

> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> sabrina pittarel
> Sent: Saturday, September 09, 2006 4:06 PM
> To: ccielab@groupstudy.com
> Subject: Q. Terribly confused about interface bandwidth used for QoS
> calculations - please help
> 
> Hi all,
>  can somebody help me clarify what is the interface bandwith used for
QoS
> calculations in various interface types?
>  * Ethernet interface:
> 
>  R1 ------------- R2
>     fe          e
> 
>  R1 will auto negotiate a 10M speed with R2.
>  10Mbps will be used on R1 and R2 for QoS calculations. No need for
> explicit interface configuration.
> 
>  * Serial P2P interface Clocked at 64000
> 
>  R1 ------------- R2
>               clockrate 64000
> 
>  How the configured clockrate will affect reference bandwidth for QoS
> calculation?
> 
>  Should we configure "bandwidth 64" on R1 and R2 serial interfaces?
>  In my understanding the clockrate value determines how fast we can
really
> transmit on the media, but I don't see QoS calculations use that value
as
> reference number. Should we then configure the bandwidth command?
>  Similar question for routing protocols.
>  Should we alter default interface OSPF cost/eigrp interface bandwitdh
in
> respect to the media clocking?
> 
>  Sabrina
> 
>

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