Symon,
Unfortunately, its not as simple as looking at the DE packets. Simply
looking at DE packets alone doesn't tell you anything really. The reason is
that if the FR cloud doesn't experience congestion, those DE packets will
get there just as well as the non-DE packets. Some carriers encourage their
customers to use 0K CIR because "we don't oversubscribe our network", so
_all_ packets are marked DE. (Sprint used to do this, don't know if they
still do or not)
In order to make any sense of the DE packets, you also need to look at the
ECN bits in the direction of the traffic flows. In your case, the Forward
direction (FECN's). Looking at your info, only .4% of the inbound packets
had the FECN bit set. This is very low obviously, but without knowing
_when_ those FECN's occured and the rate, you still don't know much.
You really need to do some qualatative analysis here during the periods when
users are complaining and look at total line utilization and packets marked
FECN and DE. If there is spike in the packets marked FECN and DE, chances
are good that significant amount of packets are getting dropped in the FR
cloud. You could run sniffers on each side of the link to verify this.
If you see the FECN's spike without a corresponding spike in the DE, that
means your provider is experiencing congestion, but its on a backbone link
and not your link. This means the provider's links are over-subscribed and
your packets are likely getting dropped without being marked DE.
If there are no FECN spikes when the users complain, you will need to start
looking at other things like TCP seq. and ack. numbers for site to site
traffic flows.
Bottom line, there's not really any number for DE, not even a rule of thumb.
If your provider is not over-subscribed, 100% DE is not bad, if they are
very over-subscribed, 10% DE could be bad if all 10% get dropped due to
switch congestion. All the DE tells you is that _you_ are over-subscribing
your CIR, to know what is happening in the FR cloud you need to look at the
FECN's and BECN's. (depending on the traffic flow direction)
HTH,
Kent
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
[EMAIL PROTECTED]
Sent: Monday, June 25, 2001 2:41 AM
To: [EMAIL PROTECTED]
Subject: Frame Relay acceptable DE packets [7:9746]
Hi All,
I have a PVC with a large amount of packets recieved with the DE bit
set, and in the mornings the users complain of slow access.
This is logical, as they are frequently over their CIR, and I guess
the Frame cloud must be congested in the mornings.
What I was looking for was some sort of guideline as to what is an
acceptable percentage of packets to recieve with the DE bit set. I
understand that this depends on the type of traffic that you are
sending over the PVC, my use is just typical NT based remote office,
being log in, email and and some file access.
Below is snipped from a sh frame pvc
input pkts 42007721 output pkts 33246300
in bytes 4262623522 out bytes 1153916597
dropped pkts 53
in FECN pkts 182632 in BECN pkts 0
out FECN pkts 0 out BECN pkts 0
in DE pkts 10348052 out DE pkts 0
out bcast pkts 1385303 out bcast bytes 110678462
As you can see, the percentage of input packets with DE set is about
25%. This seems high, but probably ok? PVC is 512k, CIR is 256.
Any words of wisdom/experience greatly appreciated.
Cheers,
Symon
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=9800&t=9746
--------------------------------------------------
FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
