From: mgreenlee@ipexpert.com
Date: Sat Feb 23 2008 - 00:38:36 ARST
Slight correction
1. Applying QoS to a circuit doesn't "take" 75% of the bandwidth.
The limitation of the max-reserved is to prevent someone from applying a
policy that is asking for a value higher than the max-reserved value. The
max-reserved value only affects whether or not your policy can be applied to
the interface, it doesn't affect the calculation.
So if you have a policy asking for 20%, and someone set your max reserved to
30%, the 30% is not used in the calculation, and only comes into play if
your policy was asking for more than 30%, in which case, the router gives
you a nice message, and doesn't take the command when you try to apply the
policy to the interface.
(Also, to be specific, bandwidth is reserved in policy-map statements, not
class-map statements)
The value could be from CIR, or it could be from line rate, I would expect
them to tell you in the question.
As mentioned before, make sure that your interface bandwidth matches the
bandwidth of the circuit. With a serial line default of 1544, if the actual
circuit is only 128k, then a reservation of 10% can overwhelm the circuit,
as the router "thinks" that 154k is 10%
However, the answer also is "it depends". There were some IOS versions
between 12.1t and 12.2 / 12.2T where they changed things around a bit, and
some versions actually did the calculations based on the 'max-reserved'
value, so asking for 20% with max-reserved set to 75% would really allocate
15%. So if you're on a device with an older IOS version, the results may
vary a bit from what the newer code will do. Make sure to take a close look
at your show commands - show policy-map int, etc. to see what the router is
telling you.
Marvin Greenlee, CCIE #12237 (R&S, SP, Sec)
Senior Technical Instructor - IPexpert, Inc.
A Cisco Learning Partner - We Accept Learning Credits!
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-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Todd, Douglas M.
Sent: Thursday, February 21, 2008 12:56 PM
To: Radioactive Frog; Cisco certification
Cc: ccie forum
Subject: RE: Frame-relay trafic shaping
Hmm -- some light heading your way I hope and not a dark spot...
Some correct me if I'm incorrect:
When you apply QoS to a circuit it takes 75% of the bandwidth, 25% is set
for
control and IGP (etc). If you need to reserve %20 percent, I would assume
that
it's 20% of the interface bandwidth, thus a max-bandwidth statement must be
applied. Then you are taking %20 of the interface bandwidth and not %20 of
%75
of the interface bandwidth.
Thus you are working with 75% of the interface bandwidth (sh int | i BW) (no
max-bandwidth statement).
Q2: If you are not using max-bandwidth then its %20 of the %75 interface BW.
CIR
is just the threshold of where you want the DE bit to be set. But obviously
it's
part of the Bc/Be formulas.
Douglas
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Radioactive Frog
Sent: Wednesday, February 20, 2008 7:13 PM
To: Cisco certification
Cc: ccie forum
Subject: Frame-relay trafic shaping
FRTS question folks,
Q1. in QoS class-map statement, if we have to reserve 20% bandwidth - will
that
be calculated from Frame-relay CIR???? (CIR=95% of BW). I am not sure....
Q2. Also if we have to allocate 20% bandwidth for signaling traffic - will
that
be calculated from CIR? or Total Bandwidth?
can someone shed some light on this please....
Frog
interface Serial6/0
description Parent FR Link for BRANCH#60 no ip address encapsulation
frame-relay
frame-relay traffic-shaping !
interface Serial6/0.60 point-to-point
description FR Sub-Interface for BRANCH#60 bandwidth 256
frame-relay interface-dlci 60 ppp Virtual-Template60 ! Enables MLPoFR class
FRTS-256kbps ! Binds the map-class to the FR DLCI
!
interface Virtual-Template60
bandwidth 256
ip address 10.200.60.2 255.255.255.252
service-policy output WAN-EDGE ! Attaches MQC policy to map-class ppp
multilink
ppp multilink fragment-delay 10 ! Enables MLP fragmentation ppp multilink
interleave ! Enables MLP interleaving !
!
map-class frame-relay FRTS-256kbps
frame-relay cir 243200 ! CIR is set to 95% of FR DLCI rate frame-relay bc
2432 !
Bc is set to CIR/100 frame-relay be 0 ! Be is set to 0 frame-relay mincir
243200
! MinCIR is set to CIR
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