From: Marcus Jensen (marcus@pobox.com)
Date: Sat Aug 09 2003 - 20:00:46 GMT-3
Thank you Brian.
Marcus
-----Original Message-----
From: Brian McGahan [mailto:bmcgahan@internetworkexpert.com]
Sent: Sunday, August 10, 2003 4:21 AM
To: 'Marcus Jensen'; 'Ccielab (E-mail)'
Subject: RE: absolute vs relative BW reservation
Marcus,
Yes, I did misword that a bit. What I should have said is that
'bandwidth [kbps]' is an absolute reservation of what is available, while
'bandwidth percent' is a relative reservation of what is available.
When you say 'bandwidth [Kbps]', you are doing an absolute reservation,
however this reservation still cannot exceed what is available on the
interface. Take the following:
R1#sh run int e0/0
interface Ethernet0/0
max-reserved-bandwidth 100
fair-queue
!
R1#sh queue e0/0
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: weighted fair
Output queue: 0/1000/64/0 (size/max total/threshold/drops)
Conversations 0/0/256 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
Available Bandwidth 10000 kilobits/sec
R1 has an Ethernet interface of which 100% is reservable. As there
are no previous reservations, we see an available bandwidth value of
10000Kbps (10Mbps).
If we configure a bandwidth [Kbps] or priority [Kbps] reservation,
it will be subtracted from our available value of 10Mbps, and result in a
new available bandwidth value:
R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#class-map IP
R1(config-cmap)#match protocol IP
R1(config-cmap)#policy-map CBWFQ
R1(config-pmap)#class IP
R1(config-pmap-c)#priority 5000
R1(config-pmap-c)#int e0/0
R1(config-if)#no fair-queue
R1(config-if)#service-policy output CBWFQ
R1(config-if)#end
R1#sh queue e0/0
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: weighted fair
Output queue: 0/1000/64/0 (size/max total/threshold/drops)
Conversations 0/1/256 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
Available Bandwidth 5000 kilobits/sec
Now suppose we configure another reservation which will exceed what
is available:
R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#class-map NOT_IP
R1(config-cmap)#match not protocol IP
R1(config-cmap)#policy-map CBWFQ
R1(config-pmap)#class NOT_IP
R1(config-pmap-c)#bandwidth 5001
I/f Ethernet0/0 class NOT_IP requested bandwidth 5001 (kbps) Available
only 5000 (kbps)
As you can see the router will not allow us to do an absolute
reservation of more bandwidth than is available.
HTH,
Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
Toll Free: 877-334-8987
Direct: 708-362-1418 (Outside the US and Canada)
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Marcus Jensen
> Sent: Saturday, August 09, 2003 7:58 AM
> To: Ccielab (E-mail)
> Subject: absolute vs relative BW reservation
>
> Brian McGahan made an excellent post I was reviewing just now.
> http://www.groupstudy.com/archives/ccielab/200306/msg01688.html
>
> <snip>
>
> 1. The 'bandwidth percent' command does a relative bandwidth reservation
> based on the current available bandwidth of that interface.
>
> policy-map QOS
> class FTP
> bandwidth percent 50
> !
> interface FastEthernet0/0
> service-policy output QOS
> !
> R1#sh queue fa0/0 | in Available
> Available Bandwidth 75000 kilobits/sec
> We are reserving 50% of the bandwidth on this interface for FTP. Since
the
> available bandwidth on the interface is 75Mbps, and we are doing a
> percentage reservation, FTP is effectively guaranteed a minimum of
> 37.5Mbps
> (50% of 75% of 100Mbps).
>
> 2. 'bandwidth [kbps]' is an absolute reservation, and is NOT based on
the
> available bandwidth of the interface.
> policy-map QOS
> class FTP
> bandwidth 50000
> !
> interface FastEthernet0/0
> service-policy output QOS
> R1#sh queue fa0/0 | in Available
> Available Bandwidth 25000 kilobits/sec
> 'bandwidth [kbps]' is an absolute reservation, and is NOT based on the
> available bandwidth of the interface. You can see that after
configuring
> 'bandwidth 50000' under the FTP class, only 25Mbps is now available on
the
> interface.
>
> <end snip>
>
> The part that confuses me is where bandwidth in kbps is not based on
> available bandwidth. When using bandwidth percent, the available
bandwidth
> number does not decrease in the show queue output, but we know that is
> where
> the bandwidth is coming from. With bandwidth kbps, it does decrease. But
> when Brian said it is not based on available bandwidth, this caused me
to
> pause. I had always thought the 50000 is still coming from the available
> bandwidth of 75000. But maybe it means 50000 is taken from the whole
> interface? The results are the same in this case because of round
numbers,
> but which is it?
>
> Thanks,
>
> Marcus
>
>
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