From: Jason Guy \(jguy\) (jguy@cisco.com)
Date: Thu Jul 05 2007 - 16:57:33 ART
Correction, it is the 2 LSB of the DSCP byte...I mis-spoke.
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Jason Guy (jguy)
> Sent: Thursday, July 05, 2007 3:33 PM
> To: Mike Kraus (mikraus); darth router; ccielab@groupstudy.com
> Cc: Antonio Soares
> Subject: RE: ECN with congestion threshold
>
> Mike,
>
> I was confused by the term "TCP ECN" so I did a little digging to
figure
> out what this is. I was thinking the ECN was a bit in the DSCP byte
of
> the IP header. It turns out it is actually 2 most significant bits of
> the DSCP byte; called the ECT bit and the CE bit.
>
> I found this link that explains how IOS uses the ECN field:
>
http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_feature_
> guide09186a0080087c87.html
>
> According to this link it seems WRED just does some extra marking of
the
> packet depending on the thresholds and the queue length. I guess you
> would need to use some other mechanism on the receiving end to utilize
> the notification to cause the endpoints to scale back. Does TCP
> automatically respond to this? Maybe I need to read RFC 3168 and see
if
> it says anything about it. Can anyone clarify this?
>
> Thanks,
> Jason
>
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> > Mike Kraus (mikraus)
> > Sent: Thursday, July 05, 2007 2:40 PM
> > To: Mike Kraus (mikraus); darth router; ccielab@groupstudy.com
> > Cc: Antonio Soares
> > Subject: RE: ECN with congestion threshold
> >
> > As a correction/clarification, Antonio correctly pointed out to me
> that
> > the frame-relay congestion commands are intended to be used on the
> > Frame-Relay DCE side (switch).
> >
> > So, assuming you mean to use the TCP ECN capabilities, you need to
use
> > the WRED ECN feature. If you are just looking to control the
> FECN/BECN
> > behavior in Frame-Relay, then use the frame-relay congestion
> management
> > commands. It's probably inappropriate to compare them in the way
done
> > so below, since you are going to be doing them at different times
for
> > different reasons.
> >
> > I apologize for any confusion, and thank Antonio for pointing this
> out!
> >
> > Thanks,
> > Mike
> >
> >
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> > Mike Kraus (mikraus)
> > Sent: Thursday, July 05, 2007 11:38 AM
> > To: darth router; ccielab@groupstudy.com
> > Subject: RE: ECN with congestion threshold
> >
> > Note from the command reference:
> >
> > The frame-relay congestion threshold ecn command applies only to
> > default FIFO traffic-shaping queues.
> >
> > One ECN threshold applies to all traffic on a traffic-shaping
queue.
> > You cannot configure separate thresholds for committed and excess
> > traffic.
> >
> > However, if you do it at the interface level using frame-relay
> > congestion-management works differently:
> >
> > Frame Relay congestion management is supported only when the
> interface
> > is configured with class-based weighted fair queuing (WFQ).
> >
> > And, then you can have different threshold for committed and excess:
> > interface serial1
> > encapsulation frame-relay
> > frame-relay congestion-management
> > threshold ecn be 0
> > threshold ecn bc 20
> > threshold de 40
> >
> > This is important because:
> > "When the output interface queue reaches or exceeds the ECN excess
> > threshold, all Frame Relay DE bit packets on all PVCs crossing that
> > interface will be marked with FECN or BECN, depending on their
> direction
> > of travel. When the queue reaches or exceeds the ECN committed
> > threshold, all Frame Relay packets will be marked with FECN or
BECN."
> -
> > Frame Relay Configuration guide.
> >
> > Lastly, with random-detect ecn, you are also enabling WRED in the
> > process, and doesn't really directly relate to DE (unless matching
on
> > fr-de in your class). Not saying this is good/bad, just different.
> >
> > So, assuming it doesn't matter what queuing strategy is employed,
and
> > you don't care explicitly about how committed vs. excess/DE traffic
is
> > treated, then yes, I'd say it wouldn't matter.
> >
> >
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> > darth router
> > Sent: Thursday, July 05, 2007 6:53 AM
> > To: ccielab@groupstudy.com
> > Subject: ECN with congestion threshold
> >
> > Do these two commands (FRTS and MQC) behave the same way?
> >
> > frame-relay congestion threshold ecn 70
> >
> > OR
> >
> >
> > Router(config)# *policy-map pol1*
> > Router(config-pmap)# *class class-default* Router(config-pmap)#
> > *bandwidth per 70*
> > Router(config-pmap-c)# *random-detect*
> > Router(config-pmap-c)# *random-detect ecn*
> >
> >
> > or would I need to shape on the MQC version to get the desired
effect
> of
> > using ECN once the bandwidth threshold is hit? I am thinking they
are
> > the same, but just want to make sure.
> >
> >
> > DR
> >
> >
>
This archive was generated by hypermail 2.1.4 : Sat Aug 18 2007 - 08:17:39 ART