Frank, Strictly speaking, whether or not a packet is marked DE has nothing to do with whether or not you will see FECN and BECN. Marking a packet DE simply means that you are exceeding the amount of bw that your are "guaranteed". It doesn't mean that a packet will be dropped, it only means that that packet is more likely to be dropped in the event of congestion. If the FR network is never congested, no packets will ever be dropped, regardless of whether they are marked DE. Some providers, Sprint for example, typically sell their circuits for 0k CIR, so _every_ packet is marked DE. (Sprint says "we don't oversubscribe our network, so we can mark everything DE")
FECN and BECN on the other hand, mean that somewhere in the FR cloud, a port on a switch reached a buffer threshold at which it needed to drop packets. Doesn't mean it was your packets, doesn't mean that the packets that got dropped were marked DE, it only means that some packets were dropped. If a buffer on a switch port fills up, it must drop packets, regardless of DE or non-DE markings. If the switch happens to have some packets marked DE and some not marked DE, the ones marked DE _should_ get dropped first. (I say _should_ because different switch vendors implement their discard algorithms differently, it may depend on where the DE packets are in the queue, how fast the switch is receiving packets, etc. etc) So, to answer your question, your seeing DE packets because your exceeding the CIR for that PVC. You aren't seeing FECN/BECN because no FR switches are seeing congestion on any ports. Essentially, your getting more than your paying for, congratulations. :-) Typically, you will only run into trouble when many customers are consistently bursting above their CIR. Generally, you won't see FECN/BECN if your not above CIR, but just because you are above CIR doesn't mean you _will_ see FECN/BECN. If you see FECN/BECN and you are below CIR, it probably means the carrier is experiencing an outage, they are oversubscribed on their backbone, or you are sending from a high bandwidth site to a low bandwidth site. (like T1 to 128kbps) I would say you only need to look at FR traffic shaping if you are seeing a lot of traffic from a high bandwidth site to a low bandwidth site and you are over-running the FR switch port at the low bandwidth site end. (you would see FECN's on the low bandwidth site router and BECN on the high bandwidth site router) Simply seeing DE packets is not a reason to implement traffic shaping. As I said, seeing DE packets is actually somewhat of a good thing since it means your getting more than your paying for. If you continually see lots of DE packets, you might think about whether your CIR is high enough, but if your not seeing FECN/BECN and your performance is fine, it's probably not worth worrying about. HTH, Kent -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of DAGENHARDT Frank Sent: Wednesday, December 19, 2001 11:43 AM To: [EMAIL PROTECTED] Subject: Fame Relay FECN BECN [7:29675] Group, I thought I had FECN and BECN down in regards to frame relay setup. Recently I have come across some router output that doesn't make sence to me. I don't understand why I have DE pkts when I don't have and FECN or BECN errors. Or for that matter how I can have so many DE pks and no of them were dropped. I was thinking of implementing traffic shaping, but I don't know if that will help if I am not receiving any BECN errors. On top of that I understand that when your CIR is reached packets get marked DE but at what point do they actually get dropped. Can someone try to make a little sence out of this for me? DLCI = 131, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0/1.131 input pkts 29103083 output pkts 23370364 in bytes 3538537810 out bytes 941866396 dropped pkts 13 in FECN pkts 0 in BECN pkts 0 out FECN pkts 0 out BECN pkts 0 in DE pkts 1154469 out DE pkts 0 out bcast pkts 1379364 out bcast bytes 110300947 pvc create time 10w2d, last time pvc status changed 3w2d Thank you, Frank Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=29693&t=29675 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
