From: Arun Arumuganainar (aarumuga@hotmail.com)
Date: Mon Jun 19 2006 - 09:41:17 ART
mmmm ...Now I am terribly confused !!! I thought I had a fair idea of FRTS
based on FECN/BECN mechanism !!! I think I overestimated myself .
Can somebody summarize what we have been discussing. For getting maximum
clarity I would request experts to restrict the discussion in the context of
IP .
Thanks very much in advance.
Thanks and Regards
Arun
----- Original Message -----
From: "Scott Morris" <swm@emanon.com>
To: "'Faryar Zabihi (fzabihi)'" <fzabihi@cisco.com>; "'Brian Dennis'"
<bdennis@internetworkexpert.com>; "'Petr Lapukhov'"
<petr@internetworkexpert.com>; "'Ken'" <hpnkpn103@yahoo.co.jp>
Cc: "'Cisco certification'" <ccielab@groupstudy.com>
Sent: Monday, June 19, 2006 8:33 AM
Subject: RE: What does FECN do?
> Does that cover ALL words in Texas? ;)
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Faryar Zabihi (fzabihi)
> Sent: Sunday, June 18, 2006 12:56 PM
> To: Scott Morris; Brian Dennis; Petr Lapukhov; Ken
> Cc: Cisco certification
> Subject: RE: What does FECN do?
>
> Them's fightin words!!!
> At least it is in TX
>
> Faryar
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Scott Morris
> Sent: Sunday, June 18, 2006 9:26 AM
> To: 'Brian Dennis'; 'Petr Lapukhov'; 'Ken'
> Cc: 'Cisco certification'
> Subject: RE: What does FECN do?
>
> Wow... I'm sorry, I didn't know these were still current lab topics.
>
> I'll jump right up and test that out. And while I'm at it, I think I'll
> worry about Appletalk and IPX as well in case they come back. What about
> LLC2 or RSRB? I hear token ring is on the rebound.
>
> DecNet and CLNS have built in mechanisms for ECN and are much more closely
> related with Layer 2 framing. IP on the other hand has had minor
mechanisms
> in the past, but more enhancements lately than for "a very long time".
> Hence the terminology of passing to "upper layer protocols".
>
> So... For the record, if we look at EVERY possibility that you ever may
run
> across, then my statement may at times be incorrect. If we have some
> semblance of paying attention to our lab discussions around here, which
> revolve in the IP world, then I think you'll find the statement to make
> perfect sense.
>
> And the DocCD writers have had no comment either way on that part.
> Since you know more than they do, you may want to point that out so then
at
> least we can be sure everyone is as politically correct...
>
> Scott
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Brian Dennis
> Sent: Sunday, June 18, 2006 2:36 AM
> To: swm@emanon.com; Petr Lapukhov; Ken
> Cc: Cisco certification
> Subject: RE: What does FECN do?
>
> Scott,
> Can you post an example configuration of how to configure DECnet support
for
> FECN since you say it's not the default? The reason I ask is because the
> DocCD states that "no configuration is required" which normally means
> "default".
>
> <DocCD>
> Cisco's Implementation of Frame Relay
>
> The Frame Relay software provides the following capabilities:
>
> * Transmission of congestion information from Frame Relay to DECnet Phase
IV
> and CLNS. This mechanism promotes Forward Explicit Congestion Notification
> (FECN) bits from the Frame Relay layer to upper-layer protocols after
> checking for the FECN bit on the incoming DLCI. Use this Frame Relay
> congestion information to adjust the sending rates of end hosts.
> FECN-bit promotion is enabled by default on any interface using Frame
Relay
> encapsulation. No configuration is required.
> </DocCD>
>
> Also if this is against Cisco's long-standing idea as you say someone
better
> let the people who write the DocCD know ;-)
>
> Thanks!
>
> Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)
> bdennis@internetworkexpert.com
>
> Internetwork Expert, Inc.
> http://www.InternetworkExpert.com
> Toll Free: 877-224-8987
> Direct: 775-745-6404 (Outside the US and Canada)
>
> ________________________________
>
> From: Scott Morris [mailto:swm@emanon.com]
> Sent: Sat 6/17/2006 1:22 PM
> To: Brian Dennis; Petr Lapukhov; 'Ken'
> Cc: 'Cisco certification'
> Subject: RE: What does FECN do?
>
>
> However, unless specifically configured on Cisco devices, received BECN's
or
> FECNs have been routinely ignored regardless of the upper layer protocol
> support. Cisco is not alone in this long-standing idea though.
>
> Just because you CAN do it, doesn't mean you will. ;)
>
> scott
>
> ________________________________
>
> From: Brian Dennis [mailto:bdennis@internetworkexpert.com]
> Sent: Saturday, June 17, 2006 12:37 PM
> To: Scott Morris; Petr Lapukhov; Ken
> Cc: Cisco certification
> Subject: RE: What does FECN do?
>
>
> It really depends on the upper layer protocols in regards to Cisco's
support
> and there has been support for FECN and BECN for protocols that understood
> the concept of an ECN (Explicit Congestion Notification).
> The IOS has supported DECnet and OSI for a very long time. Also SNA using
> direct encapsulation LLC2 encapsulation supports BECN.
>
> Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)
> bdennis@internetworkexpert.com
>
> Internetwork Expert, Inc.
> http://www.InternetworkExpert.com
> Toll Free: 877-224-8987
> Direct: 775-745-6404 (Outside the US and Canada)
>
>
>
>
> ________________________________
>
> From: nobody@groupstudy.com on behalf of Scott Morris
> Sent: Sat 6/17/2006 9:27 AM
> To: Petr Lapukhov; 'Ken'
> Cc: 'Cisco certification'
> Subject: RE: What does FECN do?
>
>
>
> While very true, this gives an example of us being concerned with our
> endpoints only. (Which very well may be the design of the network these
> days!)
>
> The history of FECN and BECN was revolving around a true end-to-end
> frame-relay network, and a Frame Switch in the middle would actually
> generate both types of ECNs (each a separate bit within the frame relay
> frame format).
>
> The FECN would follow with the traffic telling receiving stations (upper
> layer protocols, if informed) to expect some delays in incoming traffic
due
> to congestion. The BECN would go on the back path telling the receiver to
> slow down in transmission. If, of course, it were paying attention to
> those! Cisco's default behavior is to ignore these notifications. Go
> figure.
>
> In today's frame-relay networks though, where SPs often re-encapsulate the
> frames into IP-IP tunnels, or MPLS clouds or whatever their choice is, the
> functionality is a bit warped.
>
> http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/frame.htm#wp102
> 0620
>
> There are capabilities for ECN marking within MPLS clouds (MPLS-VPN), but
I
> don't have any data suggesting which service providers do or do not
actually
> support this.... Bottom line, in real life you should know your network's
> capabilities. In the lab, you should do whatever the lab asks for!
>
> Ahhhhh..... Evolution. ;)
>
>
> Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, JNCIE
> #153, CISSP, et al.
> CCSI/JNCI
> IPExpert CCIE Program Manager
> IPExpert Sr. Technical Instructor
> smorris@ipexpert.com
> http://www.ipexpert.com
>
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Petr
> Lapukhov
> Sent: Saturday, June 17, 2006 8:27 AM
> To: Ken
> Cc: Cisco certification
> Subject: Re: What does FECN do?
>
> Ken,
>
> Most of the time FECN is an informative bit, that may be used simply for
> statistical purposes.
>
> On the over hand, BECN frames actually signal source to slow down, but
that
> would work okay only if data exchange is bidirectional.
>
> Now, for a good example of FECN usefulness consider "frame-relay
> fecn-adapt" command wihin map-class.
> (Or it's equivalent "shape fecn-adapt" with MQC).
>
> Imagine that you have unidirectional stream of packets (e.g. video feed)
> that overloads your FR network. You will have a lot of FECN bit set
packets
> in direction from sender to receivers, but not a single packet backwards,
so
> no BECN frames will arrive to sender.
>
> Here you may use fecn-adapt, that enables reflection of FECN bit in
special
> FR frames back to sender with BECN bit set. In this way, a FECN signalling
> is converted to BECNs, that actually signal sender to slow down sending
> rate.
>
> http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/
> fqos
> _r/qrfcmd9.htm#wp1103558
>
> HTH
>
> --
> Petr Lapukhov, CCIE #16379
> petr@internetworkexpert.com
>
> Internetwork Expert, Inc.
> http://www.InternetworkExpert.com
> Toll Free: 877-224-8987
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