From: ccie2be (ccie2be@nyc.rr.com)
Date: Fri Aug 13 2004 - 19:40:17 GMT-3
OK, here's my understanding of this feature based on my reading of the
feature description at the link you posted.
This feature only has an affect on the router on which the command
random-detect ecn is configured. And, then it only affects a packet that
might have been dropped based on wred settings where the packet is in
between the minimum drop and max drop thresholds.
If the packet is below the min threshold, it is always transmited. If it's
above max threshold, it's always dropped.
So, the only situation where this command has any affect is when the packet
falls between the min and max thresholds.
First consider what happens when a packet falls between these thresholds
without this feature enabled. In this case, the packet faces a probability
of being dropped that based on the mark probability denominator which, by
default, is 10. This means that a packet faces a 1 in 10 chance of being
dropped.
Now, consider what happens when this feature is enabled. There are 3
possibilities:
a) the endpoints aren't ecn capable result: packet is treated by wred the
same as if ecn weren't enabled.
b) the endpoints are ecn capable result: if wred would have dropped
without ecn, it now marks both fields with 1 and transmits the packet.
c) the network is congested result: the packet is transmit
Now, as far as I'm concerned, this explanation isn't complete and I don't
understand why "C" is true, but that's what it says.
HTH a little, Tim
----- Original Message -----
From: <gladston@br.ibm.com>
To: <ccielab@groupstudy.com>
Sent: Friday, August 13, 2004 4:30 PM
Subject: ECN
> Any example of using ECN between 3 routes?
>
> I could not make a logical map of how it works reading Cisco Doc.
>
> If R1 sends a packet marked with ECT and CE, then would R2 learn that R1
is ECN capable and would consider this information when sending packets back
to R1?
>
> =====================================
> from Cisco
>
> If the number of packets in the queue is between the minimum threshold and
the maximum threshold, one of the following three scenarios can occur:
>
> If the ECN field on the packet indicates that the endpoints are
ECN-capable and the WRED algorithm determines that the packet should have
been dropped based on the drop probabilitythe ECT and CE bits for the
packet are changed to 1, and the packet is transmitted. This happens because
ECN is enabled and the packet gets marked instead of dropped.
> =======================================
>
> If R2 receives a packet from R1 with ECN field saying that it is a ECN
capable, which device R2 considers ECN capable, the routers that sends this
packet or the device to which this packet will be send?
>
> _______________________________________________________________________
> Please help support GroupStudy by purchasing your study materials from:
> http://shop.groupstudy.com
>
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
This archive was generated by hypermail 2.1.4 : Fri Sep 03 2004 - 07:02:43 GMT-3